Emplacement temperature estimation of the 2015 dome collapse of Volcán de Colima as key proxy for flow dynamics of confined and unconfined pyroclastic density currents

Accepted Manuscript Emplacement temperature estimation of the 2015 dome collapse of Volcán de Colima as key proxy for flow dynamics of confined and unconfined pyroclastic density currents

A. Pensa, L. Capra, G. Giordano, S. Corrado PII: DOI: Reference:

S0377-0273(17)30741-2 doi:10.1016/j.jvolgeores.2018.05.010 VOLGEO 6384

To appear in:

Journal of Volcanology and Geothermal Research

Received date: Revised date: Accepted date:

19 December 2017 3 May 2018 9 May 2018

Please cite this article as: A. Pensa, L. Capra, G. Giordano, S. Corrado , Emplacement temperature estimation of the 2015 dome collapse of Volcán de Colima as key proxy for flow dynamics of confined and unconfined pyroclastic density currents. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Volgeo(2017), doi:10.1016/j.jvolgeores.2018.05.010

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ACCEPTED MANUSCRIPT Emplacement temperature estimation of the 2015 dome collapse of Volcán de Colima as key proxy for flow dynamics of confined and unconfined pyroclastic density currents. 1

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Pensa1, A., Capra1, L., Giordano2 G., Corrado2, S. Centro de Geociencias, Universidad Autónoma de México (UNAM), Mexico

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Geology Department, Roma Tre University, Italy

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Corresponding author: [email protected]

Keywords

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Emplacement temperature, reflectance analysis, topography confinement, block-and-ash flow

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dynamics

Abstract

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The recent 10th -11th of July 2015 Volcán de Colima eruption involved the collapse of the summit dome that breached to the south generating pyroclastic density currents (PDCs) along the Montegrande ravine on the southern flank of the volcano. Trees within the valley were

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buried, uprooted and variably transported by the PDCs, while the trees on the edges of the

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valley and on the overbanks, were mainly burned and folded. The emplacement temperature of valley confined and overbank PDC deposits were reconstructed using Partial Thermal Remanent Magnetization (pTRM) analysis of lithic clasts and Charcoal Reflectance analysis (Ro %) applied to the charred wood. A total of 13 sites were sampled for the pTRM study and 39 charcoaled wood fragments were collected for the charcoal optical analysis along the entire deposit length in order to detect temperature variation from proximal to distal zone. The result overlap from both data sets display a T max from ≃ 345 -385°C in valley-confined area (from 3.5 to 8.5 km from the vent) and ≃170-220°C (from 8.0 to 10.5 km from the vent)

ACCEPTED MANUSCRIPT in unconfined distal area. The emplacement temperature pattern along the 10.5 km long deposit appear related to the degree of topography confinement:

valley confined and

unconfined. In particular the valley confined setting is very conservative in terms of temperature, while the major drop occurs in a very narrow space where the PDC expanded over unconfined flat topography just at the exit of the main valley. This study represents the

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first attempt in determining the relationship between PDCs flow dynamics variation and

Introduction

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topographic confining using deposit emplacement temperature as key proxy.

Block-and-ash-flows (BAFs) are considered one of the most destructive and complex

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phenomena among pyroclastic density currents (PDCs). The 1902 eruption of Mt. Pelée (Bourdier et al., 1989; Fisher et al., 1980; Lajoie et al., 1990), the 1991-1995 eruption Mt.

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Unzen Volcano, the 1995 eruption (Miyabuchi, 1999; Nakada et al., 1999; Uehara et al.,

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2015); the 1995-1998 eruption of Soufrière Hills volcano (Sparks and Young, 2002; Druitt and Kokelaar, 2002; Robertson et al., 2000; Young et al., 1998), the 2006 and 2010 eruptions

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of Merapi volcano (Charbonnier and Gertisser, 2008; Komorowski et al., 2013; Lube et al., 2011), 1999 and 2015 eruptions of Volcàn de Colima (Capra et al., 2016, 2015; Reyes-

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Dávila et al., 2016; Sarocchi et al., 2011; Saucedo et al., 2004) are only few of the most recent events where BAFs display their destructive power. BAFs form during dome collapse events, either gravity-driven or triggered by explosions (Sulpizio et al., 2014). They consist of dense, granular flows strongly controlled by the topography, dominated by particle–particle collisions, which emplace massive, m-thick deposits along valleys. They generate also overriding dilute portions of the flows, where traction processes supported by fluid turbulence dominate the particle motion. Their propagation is only partially controlled by

ACCEPTED MANUSCRIPT topography, generating centimetric massive-to-stratified ash layers on interfluves and topographic heights. Based on flow regime, flanks slope profile and channels depth, BAFs can affect differently the involved area in terms of deposit runout and damages to human settlings. Similarly to the 1975 Ngauruhoe eruption (New Zealand, Lube et al., 2007) and the 2006

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eruption Tungurahua volcano (Ecuador, Douillet et al., 2013; Kelfoun et al., 2009), the

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emplacement of the 2015 BAFs triggered by Volcán de Colima dome collapse were

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controlled by the topography, reaching the proximity of several small towns. Due to the high frequencies of gravity-driven flows along the south flank of Volcán de Colima and the

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increasing number of people living on its slopes, it is extremely necessary to improve our understanding on what factors control and determine different flow regimes and depositional

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dynamics.

Several numerical (Charbonnier and Gertisser, 2008; Kelfoun, 2017, 2011; Kelfoun et al.,

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2000; Sulpizio et al., 2010) and analogue models (Andrews, 2014; Breard and Lube, 2017;

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Lube et al., 2007) have been carried on in order to better constrain the relationship between PDCs deposits distribution and their internal structure with the mechanisms of transport and

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emplacement in different morphological conditions. Despite the recent important advancements in laboratory experiments, our knowledge about gravity-driven flows is still

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not well understood, and especially on how and where the thermal energy is transported (e.g Doronzo et al., 2016; Giordano and Doronzo, 2017). External conditions such as topography confinement can affect noticeably the flow dynamic and the depositional process (Doronzo 2012). The ability of a pyroclastic flow to maintain an high dynamic pressure, also along low angle slopes, and to reach great run out distances are strictly connected to its thermal state (Lube et al., 2007, Andrews, 2014). In turn the capacity to maintain high temperature within

ACCEPTED MANUSCRIPT the flow is extremely dependant on the valley morphology that can enhance or inhibit the ingestion of cold air at the front and expecially along the lateral margins (Andrews 2014). In this study we reconstructed the variation of 2015 Volcán de Colima BAF emplacement temperature in order to investigate the role of topography in confining flow propagation and sedimentation. The evaluation of emplacement temperature variation was determined by

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using two independent proxies: the partial thermal remanent magnetization of lithic clasts and

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the charcoal reflectance analysis of charred wood fragments. The very good overlap and

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accuracy of temperature values obtained by the two methods, revealed important thermal

Volcanological setting

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1.3

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variation within the deposit in correspondence of different topographic conditions.

The Colima Volcanic Complex is located in the wester sector of the Trans-Mexican Volcanic Belt (TMVB, Fig. 1) and it is composed by three main volcanic edifices, from north to south:

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Cantaro, Nevado de Colima, and Volcán de Colima. Volcán de Colima (3850 m a.s.l.) is considered one of the most active volcanos in Mexico which major volcanic activity range from Plinian eruptions events (i.e.) the 1576, the 1818 and the 1913 eruptions, classified VEI

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4 (Luhr et al., 2006; Saucedo et al., 2010), vulcanian explosive events to episodes of growth

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and dome collapses (i.e.1991, 2000-2005 and 2015 events; Capra et al., 2016; Macías et al., 2006; Saucedo et al., 2005, 2004; Sulpizio et al., 2010).

1.3.1 The Montegrande ravine morphology The Montegrande ravine originates at the intersection of two main gullies at the main break in the slope of the volcano edifice which slope ranges between 45-15 degrees (Macorps et al., 2017). The total length of Montegrande ravine is 6.5 km which slope decreases from 15°-10° to 5°-2° up to the distal fan (10.5 km from the vent) (Fig. 2). The Montegrande ravine before

ACCEPTED MANUSCRIPT the 2015 eruption was characterised by a sinuous path with strong tight turns of around 60°– 20° alternated by straight areas (Vázquez et al., 2016). The ravine consists of lateral walls up to 20-25m-high made by late Pleistocene debris avalanche deposits and pyroclastic flow deposits from the 1818 and 1913 Plinian eruption (Capra et al., 2016); the main channel is characterized by numerous m-thick lahars terraces strongly affecting its width (from 3 m to

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20 m).

1.3.2 The 2015 eruption

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The 10th -11th of July 2015 dome collapse was anticipated in 2013 and 2014 by numerous

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explosions with rock falls and lava flows emissions. The 2015 dome collapse consisted in two main events that generated PDCs along Montegrande and San Antonio ravines Fig. 1d,

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(Capra et al., 2016; Capra et al., 2018; Reyes-Dávila et al., 2016). On the 10th of July part of the summit dome collapsed. This generated the first series of

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pulsing block-and-ash flows that channelled mainly within the Montegrande ravine, without

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reaching the end of the valley (stopped at ~8.5-9 km from the vent) (Macorps et al., 2017; Capra et al., 2018). This event lasted for 52 minutes (Reyes-Dávila et al., 2016); the

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associated ash plume rose up to 4 km and drifted toward W by strong winds. On the 11th of July the second dome collapse event occurred, involving also part of the southern crater rim.

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This second event continued for 1 h and 47 minutes (Reyes-Dávila et al., 2016). A new ash cloud rose up and a second series of block-and-ash flows overspilled completely the Montegrande ravine and secondarily, along the San Antonio ravine up to a 6.1 km from the crater (Macorps et al., 2017) (Fig. 1). PDC emplaced on 11 July had a maximum runout of 10.5 km along the Montegrande ravine with a maximum thickness of 20 m (Capra et al., 2016). Once reached the end of the valley the flow spread on the distal fan. The Montegrande ravine morphology was completely modified; during the BAF emplacement on the 10th of

ACCEPTED MANUSCRIPT July pine trees within the valley were buried, folded and tree canopy covered by ash. On the second day pine trees, were not only buried, folded and uprooted but also burned (Fig. 1b). Nowadays, still standing survived pine trees along the overbanks display one side (facing the volcano) totally burned (albeit only superficially), barked by the passage of the flow with blocks impact on their trunks. Tree canopy are half burned half green.

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The overriding ash clouds deposits were dispersed towards the SW (Fig. 1c), affecting the

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villages of La Yerbabuena, La Becerrera, San Antonio, Carizzalillo, El Naranjal, Nuevo

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Naranjal and Suchitlan, Comala (5 cm deposited, Capra et al., 2015); a total of 70 persons were evacuated. Following the emplacement of the BAF deposits the eruption continued

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with lava flow emission that reached three km from the vent. During the subsequent rainy season, that also included the Hurricane Patricia (October 2015), the BAF deposits were

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eroded and remobilized by multiple lahars and stream flows. The post eruption plane

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1.3.3 The BAF deposits

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morphology of the Montegrande ravine was rapidly modified and cut by deep gullies.

The total amount of material emplaced during the 2015 eruption was estimated from a

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minimum value of 4.5 ×106 m3 (Capra et al., 2016) up to 7.7 x 106 m3 (Macorps et al., 2017). The deposit is mainly constituted by three main sedimentary facies, a massive valley-

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confined facies, massive and stratified veneer facies. The total area involved during the eruption is ~5 km2. 

The valley-confined facies is massive, matrix-rich, dark to light-grey in colour and with abundant angular to sub-angular andesitic blocks up to 2 m in diameter, embedded in a lapilli-ash matrix (Capra et al., 2016; Macorps et al., 2017; Fig. 2). According to Macorps et al., (2017) at least three flow units (VC1, VC2 and VC3) were identified, with total maximum thickness from 15-20 m (i.e. sites COL- 10,

ACCEPTED MANUSCRIPT COL-42, COL-49; Fig 2 a, b, c) to 6 - 8 m (COL-01; Fig. 2d). In general, several flow units can be recognized and separated by block-enriched horizons. Only in few outcrops we were able to distinguish between the 10 and the 11 July eruptive sequence (i.e. COL-42, Fig. 2d), based on stratigraphic correlation of a cm-thick white BAF left by the 10 July PDC on top of lateral terraces, covered by thicker BAF

The massive veneer facies mainly constituting the overbank deposits is generally

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

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units enriched on vesciculated fragments, distinctive characteristic of the 11 July units.

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characterized by better sorted and finer-grained than the respective stratigraphically correlated valley-confined facies. The maximum thickness reached by overbank

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deposits range from 6 to 8 m. Three overbank units OB1, OB2 and OB3 were identified by Macorps et al., (2017) correlating with the three-main flow massive

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units.

On top of the massive valley confined facies and massive veneer facies, lies the surge

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facies composed by fine-grained stratified coarse-ash to lapilli (20 to 30-cm-thick).

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These very fine deposits display diffuse cross-stratifications of lapilli and coarse-ash

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layers with imbricated angular lithic clasts.

1.3.4 Facies distribution along the Montegrande ravine

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The deposit distribution along the Montegrande ravine can be subdivided mainly into two areas: the confined zone (from 3.5 km, at the beginning of the Montegrande ravine and up to 8.5-9 km) and the unconfined distal fan (from 9 to 10.5 km) (Fig. 3). The closest area to the vent is characterised by steep topography, from 45°up to 15° (Fig. 3), displaying numerous small gullies that testify the beginning of the Montegrande and San Antonio ravines. The presence of several small valleys allowed a wider distribution and channelling of multiple lobes along different interfluves. According to Macorps et al., (2017),

ACCEPTED MANUSCRIPT the dominant facies is the valley confined massive facies (Fig. 2 a,b,c,d). Downwards the Montegrande and the San Antonio ravines morphology becomes more engraved and dominant. The strong topography confinement inhibited the lateral spreading deposit especially during the 10th of July phase. Along the main Montegrande channel the valleyconfined massive facies is predominant; different lobes are distinguishable from high

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concentration of lithic blocks at their fronts. The massive veneer facies is also present along

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the overbanks of the Montegrande ravine and within the San Antonio valley, indicating the

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lateral passive overspill of the central flow. Surge facies is also observed in this area on top of the overbanks and in the forested areas (Figs. 1d and 2). The second depositional area is the

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distal fan where the deposit, not more topographically confined, spread radially and stopped its run. This area is principally composed by the facies organised in at least two lobes

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carrying blocks up to 3 m. Along the margins of the distal fan deposits the surge facies is recognisable. Sporadically “ash pools” (2–3 m wide and ~0.6 m deep) are also present

1.4

Methods

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(Capra et al., 2016).

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The emplacement temperature estimation of the BAF deposits was performed using two

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independent proxies: the Partial Thermal Remanent Magnetization (pTRM) on lithic clasts and the Reflectance optical analysis on charred wood fragments. The calibration of these two methods for the evaluation of PDCs emplacement temperature has been recently validated in Pensa et al., (2015a). Below a brief description of both methods is provided and higher details are available in previous papers: Caricchi et al., (2014); Pensa et al., (2015b); Scott and Glasspool, (2005, 2007), Ascough et al., (2010) for Reflectance analysis and Bardot, (2000); Bardot and McClelland,(2000); Cioni et al., (2004); Ort et al., (2015); Paterson et

ACCEPTED MANUSCRIPT al., (2010); Pensa et al., (2015a); Trolese et al., (2017); Zanella et al., (2008) for the pTRM analysis.

1.4.1 Reflectance analysis (Ro%) 1.4.1.1 Generalities and correlation against T°C

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The use of Charcoal Reflectance analysis for the determination of emplacement temperature

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estimation of PDC has been recognised and validated as a valuable proxy only in recent

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studies (Caricchi et al., 2014; Hudspith et al., 2010; Pensa et al., 2015a; Scott et al., 2008). Usually applied as a temperature proxy for kerogen carbonification process

(Aldega et al.,

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2007; Caricchi et al., 2015; Corrado et al., 2005; Schito et al., 2017), reflectance analysis has undergone a strong development in volcanological and archaeological studies and paleo-

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wildfire reconstruction on charcoal instead of kerogen. The high presence of remaining charcoal fragments after volcanic eruptions and wildfires has prompted researchers to find a

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relationship between rank of charcoalification of wood fragments, heat exposition duration,

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burning/burial mode and deposit charring temperature. In the last 10-15 years several laboratory experiments on pyrolysis process were performed using different type of not-

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burned organic matter (Ascough et al., 2010; Hudspith et al., 2010; Mcparland et al., 2007, 2009; Scott and Glasspool, 2005, 2007). Based on Correia and Maury, (1974) studies, Scott

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and Glasspool (2005) were the first to carry on experiments on reflectance analysis of wood charred by pyroclastic flows. The detailed description of Scott and Glasspool (2005) experiment is reported in Pensa et al., (2015a). As displayed in Fig. 4, increasing temperature is directly related with an intensification of charcoal rank and reflectance percentage. On the basis of Scott & Glasspool (2005) and Scott et al., (2008) procedure, other researchers carried on pyrolysis experiments on different wood species: Matteucia struthiopteris, Osmunda regalis, Pteridium aquilinum, (commonly known as ferns Mcparland et al., 2007;

ACCEPTED MANUSCRIPT McParland et al., 2009); Quercus (oak tree McParland et al., 2007); Pinus sylvestris, Rhizophora apiculata (pine tree and mangrove respectively, see Ascough et al., 2010a); Betula nana, Betula papyrifera, Picea mariana, Picea glauca, Populus tremuloides (paper and dwarf birch, black and white spruce and trembling aspen respectively, see Hudspith et al., 2010b). As for the Scott and Glasspool’s (2005, 2007) experiments the different calibration

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curves display direct relationship between increasing burning temperature and charcoal

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reflectance degree, indicating no influence due to different tree species. In Fig. 5a the

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different curves are reported. It should be highlighted that the trend line equations by Scott and Glasspool (2005, 2007) and Mcparland et al. (2009) have been extrapolated by the

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authors from published data. Based on the fact that the majority of charcoal fragments collected belong to the species Pinus harwegii (http://www.conifers.org/topics/mex/j11.htm),

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we decide to choose among the five pyrolysis curves, the experimental equation by Ascough et al. (2010) because is referred to the same tree genus (e.g., Pinus sylvestris). The

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temperature estimations obtained adopting the correlations proposed by Hudspith et al.

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(2014); Mcparland et al. (2009); Scott and Glasspool (2005, 2007), are also reported in Table 1 and plotted (grey area) in the graph (Fig. 5b) to better constrain the temperature error

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margins.

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1.4.1.2 Sampling strategy and laboratory procedures The sampling strategy consisted of selecting charcoal fragments from the base of still standing trees trunks in situ (at the same high where possible: from 0 to 50 cm), exactly at the contact with the BAF deposit, in order to detect lateral possible differences in emplacement temperature. The consistency of this sampling method was easy to apply along the valley sides where most of the trees are still standing or bended, rather than in the middle of the valley where trees are mostly buried or uprooted. Due to the absence of still standing trees

ACCEPTED MANUSCRIPT along the edge of the distal fan area, we sampled charcoal wood fragments from an uprooted tree transported within the flow (COL-01) . In order to investigate possible differences in reflectance values within the deposit a total of 78 samples were collected along the 10.5 km long BAF deposit, 39 of which were selected

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for the emplacement temperature evaluation in this study (Table 1). Almost the totality of the wood fragments collected belonged to pine trees (e.g., Pinus harwegii) and only a few to trees

(e.g.,

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guatemalensis

and

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Jaliscana)

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spruce

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(http://www.conifers.org/topics/mex/j11.htm). Woody fragments from the edge of the BAF deposit and from the overbanks are mainly constituted by cortex portions: here trees were

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burned only at surface, and the huge lithic blocks did not scuff the external portion. On the contrary, wood fragments from the centre of the deposit consist of burned scraps of the inner

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portion of trunks or branches scuffed from lithic clasts collision. Despite the central position within the BAF deposit and the absence of cortex protection the trunks burned degree was

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superficial (few millimetres from the border). For this reason, it was not necessary to sample the inner portion of the trunk to evaluate variation in Reflectance values from the edge to the centre of the tree. This suggests that flames did not develop, and the burning degree was a

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consequence of instantaneous heat transfer from the deposit to the trees. This is also

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corroborated by the fact that all the trees (especially those along the edge of the valley) displayed only one burned side (facing the direction of the BAF). Detailed procedure about sample preparation is described in Pensa et al. (2015a). For good statistical representation 20 to 30 reflectance measurements were performed on each charcoal specimen, using only fragments whose surface was unaltered.

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reflectance values and standard deviations were calculated from these measurements. Figure 6 displays representative charcoal fragments and their reflectance measurements collected within the BAF deposit (See details in Table 1).

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1.4.2 pTRM- partial Thermal Remanent Magnetization analysis The use of pTRM for the determination of PDC paleo -temperature estimations is a very well-established tool that has been validate by several studies during the last three decades

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(See Paterson et al., 2010 and references therein). The pTRM analysis is based on the capacity of lithic clasts to acquire the direction of magnetic field orientation when subject to

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heating, and subsequently cooling, during volcanic eruptions. According to Aramaki and

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Akimoto, (1957) studies the cooling of a high temperature deposit starts at the moment of its deposition and needs to be uniformed to allow the acquisition of magnetic component

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directions by lithic clasts incorporated within the PDC. The direction of the magnetic

eruption/heating. Therefore, if

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component will result parallel to the Earth magnetic field at the moment of the the emplacement temperature is higher than the Curie

temperature of the clasts (T>580°C), the lithic clasts will show one single high temperature

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component of magnetization parallel to the geomagnetic field present at the moment of the eruption (Fig. 7a). On the contrary at temperatures lower than the Curie temperature, the clasts will display multiple (usually two/three) magnetic components: one low temperature

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(LT) magnetic component, acquired during the last heating event (eruption) and therefore

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parallel to the HT component of single component lithic clasts, and other magnetic components at high temperature (HT) randomly oriented acquired during previous thermal events (Fig. 7b).

The number of magnetic components of a lithic clast is determined during a progressive thermal demagnetization (PDT) process that emulates backwards (thermal steps from ambient temperature to Curie temperature) the natural processes. As explained in details in (Bardot and McClelland, 2000; Cioni et al., 2004; Marti, 1991; Zanella et al., 2014, 2008), during the PDT one, two or multiple components of magnetization may be distinguished. According

ACCEPTED MANUSCRIPT to this method, in case of lithic clasts with double magnetic component, the intersection temperature of the two components is the evaluation of the emplacement temperature (with associated error equivalent to temperature difference between the previous and subsequent demagnetization thermal step). In case of lithic clasts with single magnetic component the highest temperature, at which the magnetization is stable, constitutes the minimum

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emplacement temperature estimation (Lesti et al., 2011).

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The total or partial magnetization of a lithic clast depends therefore on the temperature reached by the deposit at the time of emplacement (higher or lower than Curie temperature)

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but also by the origin of the lithic clasts (accessory or accidental) and by the blocking temperature of the magnetic minerals composing the lithic clasts. Accessory and accidental

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lithic clasts present within the deposit experience different thermal history; ones are from wall conduit (incorporated into the PDC at very high temperatures) and the others are picked

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up from vent flanks (incorporated cold into the PDC and subsequently heated). This could

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result in different pTRM result as the accessory lithic clasts will display one single component due to the very high temperature experienced, while the accidental lithic clasts

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could show single or multiple components depending on the deposit emplacement temperature (Cioni et al., 2004; Marti, 1991; Pensa et al., 2015a; Zanella et al., 2014, 2008)

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The adopted laboratory procedure is detailed in Bardot and McClelland (2000).

1.4.2.1 pTRM sampling strategy and laboratory procedures The main strategy adopted during the collection of lithic clasts was to sample lithic clasts from different localities along the BAF deposit in order to detect emplacement temperature variation along the valley confined area and in the distal fan area (Table 2). Also, lithic clasts from valley edges and overbanks localities were sampled to investigate lateral temperature

ACCEPTED MANUSCRIPT difference. The other principal aspect during sampling was to collect, where possible, the lithic clasts in proximity of charcoal fragments to be able to compare the pTRM and Ro% data sets (Pensa et al., 2015b). Finally, during sampling, the distinction between the original deposit and the lahars deposits emplaced soon after the dome collapse (Capra et al., 2016) was some times uncertain, but based on matrix percentage and its grainsize, clasts sorting and

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sedimentary feautres such as layering, we could distinguish the two deposits.

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In order to have a representative data set 13 sites (for a total of 100 lithic clasts) distributed

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along the BAF deposit were selected because of their proximity to charred wood and analysed in this study. Twelve sites (Table 2) were selected along the confined deposit while

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one on the distal fan (COL-01-03) (Fig. 1d, Table 2). Only in one locality COL-42 was possible to sample lithic clasts from both deposits of the 10th and 11th of July deposits (Fig.

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2b). All the other lithic clasts were possibly collected within the 11th of July deposit. In fact, due to the intense lahar activity and constant changing morphology it was not possible to

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investigate variation in temperature from the base to the top of the BAF deposit.

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The lithology of the fragments collected is constituted by fresh andesitic lava, once constituting the dome; altered lithic clasts were discarded. According to Marti, (1991) study

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the size of the lithic fragments collected ranged from 1 to 10 cm in diameter. In the field, all the selected clasts were oriented by a magnetic compass, marking the dip and the strike in

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situ on the flattest exposed surface. Samples were treated as described in Cioni et al., (2004). The pTRM analysis was undertaken at Paleomagnetic Laboratory at Centro de Geociencias, UNAM using a JR-6A Spinner Magnetometer and REMASOFT software by Agico was used to process data according to Chadima, M., Hrouda, (2006) and paleomagnetic mean directions for each site are calculated applying Fisher, (1953) statistics. As applied in Pensa et al 2015a, thirteen thermal steps at increasing temperature (40°C to 50°C) were chosen to complete the demagnetization process (at 580°C -620°C).

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1.5 Results 1.5.1 Charcoal reflectance results From optical analysis charcoal fragments resulted well distinguishable, displaying

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microscopic characteristics referable to the inertinite maceral group (Scott and Glasspool, 2007). Cell walls of wood fragments from the trunk inner part are mostly intact, thick (20-40

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μm) and cells shape varies from round to elongate (Fig. 6b). On the contrary samples

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belonging to tree cortex display cell walls deformed and wavy, variable thickness with traces of resins (COL-17-01). Generally, reflectance analysis results indicate unimodal trends,

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which mean values range from a minimum of ≃0.197% to a maximum of ≃0.960%. Other

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samples instead contain contemporaneously high and low reflective fragments, with substantial differences in cell wall features. The presence of different reflecting families is

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highlighted by histograms with bimodal trends or sometimes with broader data distribution

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(Fig. 6c). We interpreted this result as a non-uniform wood charring. This hypothesis is corroborated by traces of resin and fragments with different reflectance degree, mixed with not burned portions in the same thin section. Since our purpose was to estimate the effective

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charring temperature experienced by the involved tree, in case of bimodal trends we decide to

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consider only the higher reflectance percentage values. The principal feature highlighted by reflectance data is a slight decrease towards the distal fan area in charcoal rank (Table 1). Nevertheless, charcoal reflectance analysis of the entire BAF deposit do not display significant difference in temperature between valley confined and overbank deposits.

1.5.1.1 Reflectance results in Valley-confined zone (from 3.0 to 8.5-9 km)

ACCEPTED MANUSCRIPT Reflectance data from samples collected in proximity of the vent at the entrance of Montegrande ravine (COL-10-03, COL-10-05,) and on the overbanks (COL-11-03, COL-1202, COL-12-03, COL-27-01) indicate reflectance values ranging from 0.282% to 0.863% (Table 1). Plotting these values on the Ascough et al., (2010) curve (Fig. 5b), temperature experienced by trees in the semi-confined area varies from 317°C ±2°C to 376°C ±5°C. In

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particular burned trees located within the valley display temperatures that vary from

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345°C±3°C to 369°C±3°C, whereas trees on the overbanks display temperature range from

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317±2°C to 376±5°C (Table 1). Reflectance data of samples collected along the Montegrande ravine, within the main channel (Table 1) show reflectance values ranging from 0.197% to

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0.960% corresponding to temperatures ranging from 316°C ±3°C to 385°C±4°C. Reflectance results of samples from overbanks (Table 1) display reflectance values from 308°C ±2°C to

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362°C±5°C corresponding to similar temperature range (from 317°C ±3°C to 385°C±4°C)

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(Table 1) of the central valley samples.

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1.5.1.2 Reflectance results in unconfined distal fan (from 8.5 to 10.5 km from the vent). Reflectance data from woody fragments collected along the distal fan (Table 1) indicate

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reflectance values that span from 0.367% to 0.671%, that indicate a range of temperature

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between 325°C ±3°C -357°C±3°C according to Ascough et al.(2010).

1.5.2 Partial remanent magnetization (pTRM) results The pTRM analysis shows that within the BAF deposit are present both accessory and accidental lithic clasts. 27 lithic clasts out of 100 display single magnetic component, while 48 sample have double HT and LT components. A total of 25 samples were discarded because displaying unstable behaviour or because the crashed during the demagnetization process.

ACCEPTED MANUSCRIPT According to Cioni et al.(2004); Pensa et al.(2015a); Zanella et al. (2008) the lithic clasts were classified in different families based on their paleomagnetic behaviours (Table 2). Compared to the mentioned previous studies the Colima BAF lithic clasts displays two different paleomagnetic behaviours (Type B1,2 and Type C lithic clasts). which

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Type B is characterised by lithic clasts with one single magnetic component

orientation (Declination and Inclination) is parallel to the actual Mexican GAD, that

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correspond to: Declination = 6.5835° ± 0.31° (changing by 0.10° W per year) Inclination =

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46.3575°±0.22° (from www.ngdc.noaa.gov). Among Type B lithic clasts we distinguished two groups of fragments based on the pattern of their demagnetization curve and intensity of

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magnetization decay (See Pensa et al., 2015b). Type B1 type are lithic clasts with typical decrease in intensity with increasing temperatures and a fixed orientation (Fig. 8b); while in

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B2 group are lithic clasts where the intensity of magnetization decreases to less than 20% at lower temperature than the Curie temperature (580°C for magnetite), showing therefore large

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scatter in orientation at higher temperature steps (Fig. 8c). Among the 27 lithic clasts displaying single magnetic component 7 fragments (Type B1+B2) display parallel orientation to the actual Mexican GAD; while 20 fragments (dots in red in Fig. 8a) show an orientation

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shifted between ≃ 45° to 160° W respect with the Mexican GAD.

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Type C represents all the lithic clasts with two magnetic components (HT and LT) (Fig. 8d,e). A total of 48 lithic clasts display double magnetic component. The Type C lithic clasts display a LT component that is close to the Mexican GAD at the time of the eruption and a HT component completely ramdom. As displayed in Fig. 8d, 13 lithic clasts (black dots) out of 48 show LT compoment orientation close to the actual Mexican GAD; while for the remaining 35 fragments (red dots, Fig. 8d) the LT component direction result shifted between ≃ 30° to 160° W respect with the actual Mexican GAD.

ACCEPTED MANUSCRIPT In Table 2 is summarised the result of the pTRM analysis on the 100 lithic clasts selected. The close orientation to the Mexican GAD displayed by the single component of the 7 lithic clasts belonging to the Type B (B1+ B2 groups), and by the LT component of the 13 fragments of Type C indicate that they were heated during the same eruption event despite suggesting different origin and thermal history. The meaning of presence of numerous

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fragments among both Type B and C groups with shifted orientation respect with the

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Mexican GAD (between ≃30° to 160° W) will be explained in the discussion section.

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In order to better evaluate and display the emplacement temperature variation throw-out the BAF deposit extension the paleomagnetic result will be presented separately for different

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areas.

1.5.2.1 pTRM results in Valley-confined zone (from 3 to 8.5 km)

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In the three sites closest to the vent (23 lithic clasts sampled) for pTRM analysis purposes we

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found lithic clasts belonging to both Types B and C. Sites COL-35-01 and COL-36-01 lie in the centre of paleo-gullies forming the upper part of Montgrande ravine, while site COL-12-

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01 is located on the overbank (Table 2). A total of 6 lithic clasts display single magnetic component belonging to Type B2; three of

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which show shifted orientation respect with the Mexican GAD (between 45° to 160° W, Fig. 8a), while the other three samples are characterised by single magnetic component orientation close to the expected GAD (Dec. 320.1° Inc 48.8°). All the samples belonging to type B2 display magnetization stable from 440°C to 580 °C. Ten fragments show double magnetic component (HT and LT). Three samples are characterised by LT component oriented parallel to the GAD (Dec. 344.2°, Inc. 37.6°), the remaining seven fragments with double magnetic component show an LT component moved (between 30° to 160° W, Fig. 8d ) from the Mexican GAD. Despite the different orientation, the LT component of all the samples shows

ACCEPTED MANUSCRIPT stable magnetization for temperature from 300°C and 400°C.

Site COL-12-01 on the

overbank shows only one lithic clast with stable behaviour belonging to Type C fragments with stable magnetization at 260°C. A total of seven fragments were discarded because displaying unstable behaviour or they

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broke during the processing.

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Nine sites (Table 2) were selected along the main channel of Montegrande ravine, while the COL-16-01 site was chosen from the overbank. All sites are from the 11th of July deposit

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except the site COL-42-02 which is from the previous deposit emplaced on the 10th of July.

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The 71 collected fragments were classified among type B and C. Twenty lithic clasts show single magnetic component; twelve belonging to B1 group and 8 of B2. Eleven lithic clasts

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show single component orientation parallel to the GAD (Dec. 338.4°, Inc. 43.0°), while nine with shifted orientation (between 45° and 160° W, Fig. 8a) respect with the Mexican GAD.

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temperatures >350-580°C.

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All the samples belonging to type B1 and B2 display magnetization stable for

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A total of thirty-three fragments were identified as type C showing double magnetic component (HT and LT). Nine lithic clasts out of 33 are characterised by LT component

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parallel to the GAD (Dec.344.7°, Inc. 45.3°), while the twenty-four fragments left display the LT component with moved orientation (between 30° to 160° W, Fig.8 d) respect with the Mexican GAD. The LT component of type C samples collected within the 11th of July deposit (valley confined) display stable magnetization for temperatures from 300° to 480 °C, while the only one sample from the 10th of July deposit suggests a magnetization stable for temperature from 300 to 400°C. It has to be noted that notwithstanding the shifted LT component orientation of

ACCEPTED MANUSCRIPT the 24 fragments, the magnetization temperature inferred by these lithic clasts is comparable with the ones displaying parallel orientation with the actual Mexican GAD. Site COL-16-01 on the overbanks is characterised only by two lithic clasts with stable behaviour belonging to Type C clasts, with magnetization stable (Dec. 290.4°, Inc. 42.8°) for temperature of 220°C.

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A total of eighteen lithic clasts were discarded because displaying unstable behaviour or they

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broke during the processing.

1.5.2.2 pTRM results in Unconfined distal fan (from 8.5 to 10.5 km from the vent).

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Site COL-01-01 collected on the front of distal fan deposit, displays five lithic clasts belonging to type C and one to type B2. The LT component of the five fragments of Type C,

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shows magnetic stable behaviour (Dec. 282.0°, Inc. 60.2°) for temperature from 170°C to 220°C.

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1.6 Discussions

1.6.1 Interpretation of paleomagnetic and reflectance data

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Paleomagnetic data of the 13 selected sites along the Montegrande ravine revealed substantial differences in emplacement temperature

between valley confined area and distal fan

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unconfined area. The general trend shows a low decrease in emplacement temperature along the entire confined length of the valley and a sharp drop in temperature in distal areas. The most proximal semi-confined sites located within the valley (Table 2) display emplacement temperature variation between 300° and 400°C (±50°C). The two sites located along the overbanks in proximity area suggest comparable emplacement temperatures ranging from 220° to 260°C(±40°C). Similar to higher emplacement temperature are inferred from valley confined sites located along the Montegrande ravine (Table 2). Here, emplacement

ACCEPTED MANUSCRIPT temperatures range from 350° to 480°C (±50°C) for the 11th of July deposit and from 300 to 400°C(±50°C) for the 10th of July deposit. Once reached the end of the valley, the emplacement temperature dropped noticeably ranging from 170° to 220°C (±40°C). Parallely to paleomagnetic data, the analysis of the charcoal reflectance data indicate a decrease in temperature from proximal to distal area, with emplacement temperature

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remaining quite high till the end of the ravine and dropping subsequently along the distal fan.

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In proximal area Ro% suggests temperatures varing from 345°C±3°C to 369°C±3°C within

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the valley and from 317±2°C to 376±5°C on the overbanks (Table, Fig. 10a). As for the paleomagnetic data, also the Ro% data suggest a slight increase in temperature within the

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main channel with temperature varying from 317°C ±3°C to 385°C±4°C and from 308°C ±2°C to 362°C±5°C on the overbanks (Table, Fig. 10a). Along the distal fan, also charcoal

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reflectance analysis revealed a decrease in temperature respect the valley confined area with

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estimation (Table, Fig. 10a,b).

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values from 325°C ±3°C -357°C±3°C, slightly higher respect the paleomagnetic temperature

Emplacement temperature estimations obtained from the two proxies indicate a very good

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overlap between the two data sets. The calibration of these two independent proxies have been corroborated by Pensa et al., (2015a) for what concern ignimbrites emplacement

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temperature assessment and for the first time, applied in this study to BAF deposit. Despite the substantial differences in componentry, transport and emplacement dynamics between ignimbrites and BAFs, our result corroborated the validity and applicability of the Reflectance method to different volcanic deposits. The identification of lithic clast families (Tybe B and C) with dissimilar magnetic behaviours within the BAF deposit suggest that during the collapse were involved parts of the dome at different temperatures (Fig. 9). Endogenous domes, as that one formed on Volcán de Colima

ACCEPTED MANUSCRIPT summit, display a cold shield that protects the inner growing hot core (Tanaka et al., 2004). While the inner core at very high temperature increases, the cooling dome shield acquires its pTRM (Fig. 9a). At this stage, if the collapse occurs, lithic clasts from the outer margin will be incorporated at ambient temperature (cold) while fragments from the dome core will be embedded at very high temperature into the BAF (Fig. 9b). This will result in the presence of

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lithic clasts showing a different number of magnetic components within the same deposit.

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Fragments incorporated in the BAF at very high temperature (>=Curie T), if prevented from

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cooling during flow (e.g. large clasts) once settled in the deposit, will display single magnetic component, oriented parallel to the Earth magnetic field (type B1 and B2).

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Fragments from dome shield embedded cold can display single magnetic component random oriented if their blocking temperature Tb is not exceeded (either because the flow was cold or

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because the magnetic minerals were too coercitive to be affected by the thermal event) once incorporated within the flow or be characterised by double magnetic components (type C) if

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re-heated by the surrounding gas-particles mixture during the deposit emplacement. The

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double magnetic components refer to one high temperature component, acquired previously the collapse (dome shield cooled) (HT), randomly oriented in the flow, and to one low

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magnetic component recorded after the deposition relative to the re-heating event (LT), oriented parallel to the Earth magnetic field (EMF). Among the type C group can be also

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present accidental lithic clasts (with same lithology of the dome), incorporated cold from the crater wall or during the flow along the flanks. They will be characterised by HT magnetic component recorded during previous thermal events, and a LT magnetic component acquired once embedded in the new hot flow deposit, which direction oriented parallel to the EMF. In the specific case of Volcán de Colima BAF deposit we identified type C lithic clasts characterised by LT component parallel to EMF and also fragments with the LT magnetic component orientation shifted between 45° to 160° W respect with the actual Mexican GAD.

ACCEPTED MANUSCRIPT Due to the perfect overlap in magnetization temperature we attributed such discrepancy in orientation d to post deposition compaction that involved some lithic fragments. Due to the same andesitic composition was not possible to distinguish type C lithic clasts from the chill dome margin and those incorporated from the destructed crater wall or picked up along the flanks. Similar explanation can be addressed for the numerous fragmens belonging to Tybe B

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clasts showing single component with different orientation respect with the Mexican GAD.

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The temperature ranges obtained with reflectance analysis of charred woods presented in this

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paper are based the experimental curve of Ascough et al., (2010) on Pinus sylvestris. Our decision is based on the fact that the majority of our analysed fragments belong to the same

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tree species Pinus harwegii. This assumption is also founded on the close similarity with the other curves of Scott and Glasspool, (2005, 2007); Hudspith et al., (2010); McParland et al.,

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(2009) extrapolated from pyrolysis of different tree types. For this reason, we expected that Pinus harwegii pyrolysis curve would produce a Reflectance vs Temperature trend very

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similar or identical to that of Pinus sylvestris. Consequently, using Ascough et al., (2010)

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curve equation we converted our Reflectance values into temperatures. Reflectance estimations presented in this work display very low standard deviations (Table 1)

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this indicate that the Reflectance analysis provide accurate and clustered values about charcoalification degree; also suggesting the absence of weathering alteration post burning.

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Field evidences suggest that trees were buried rapidly. According to Reyes-Dávila et al., (2016) the event of the 10th of July lasted for 52 minutes, while the 11th of July event continued for 1 h and 47 minutes. Based on monitoring station images of the day of the collapse Capra et. al 2018 calculate an approximal velocity between 7 to 10 m/s of the BAF within the Montegrande channel. Indications of superficial charring involving the first few centimetres of trunks indicate that the time during flow emplacement was not sufficient to burned completely the large trees, so they were entombed in the deposit before an effective

ACCEPTED MANUSCRIPT heating took place. According to Caricchi et al., (2014) this is correlated to the wood-coal low thermal diffusivity (of the order of 10−8 m2/s and 10−7 m2/s, respectively; Stanger et al., 2014) that indicates a thermal equilibration time of 10 s for fragments of 0.1 cm, 4000 s for clasts of 2 cm and 100.000 s for samples larger than 10 cm. At equal fragment dimensions the thermal equilibration time of lithic clasts is more rapid

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respect with wood fragments. As stated by Bardot, (2000); Cioni et al., (2004); Marti, (1991)

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rocks thermal diffusivity values are of the order of 10−6 m2/s. This implies that lithic

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fragments of radius a = 0.1 cm are almost instantaneously equilibrated with the deposit once emplaced, while lithic clasts of 2 cm and 10 cm size need a longer time of 200 s and 6000 s

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respectively (See Cioni et al., 2004; Martí, 1991 for details).

Therefore, we can assume that both Reflectance and pTRM temperature data sets of this

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study indicate the maximum emplacement temperature of the deposit. This result highlights the importance to consider valid all the temperature estimations from

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paleomagnetic analysis of lithic clasts displaying double magnetic components (Type C). As

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pointed out by several authors (Bardot, 2000; Cioni et al., 2004; McClelland et al., 2004; Pensa et al., 2015b; Porreca et al., 2008) the LT magnetic component of clast population

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embedded cold (or ambient temperature) within the pyroclastic flow and re-heated provides the best estimation of deposit temperature after emplacement.

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This assumption finds its validity in the fact that temperature valuations obtained with Ro% analysis show a very good overlap with the paleomagnetic temperature estimations inferred by type C lithic clasts (Fig. 10a,b). This data agreement is displayed in Tables 3a, b, c, d, e, where Ro% and pTRM are compared in four representative points chosen along the BAF deposit (Fig. 1d and Fig. 2a, b, c, d).

1.6.2 BAF dynamics and implications for temperature variation

ACCEPTED MANUSCRIPT The combination of the Ro% and pTRM analyses allowed the determination of more restricted and accurate ranges of temperature that highlight the presence of two main “morphological areas” related to different topographic confining conditions: valley confined and unconfined morphologies relative to Montegrande ravine length and the distal fan respectively.

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The most proximal area (<3.5 km from the vent) is characterised by very high slope (45° to

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35°) that did not allow deposition, and by medium slope (30°-15°) where the most proximal

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BAF deposit lies. According to Lube et al., (2007) unconfined (or semi-confined) currents are restricted around the repose angle (25° to 30°), showing increasing thickness downwards

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and characterised by quasi-steady flow regime, where gravitational and frictional forces are equalized.

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The vent closest deposit that we could analysed, lies at medium slope (Sites COL-35, COL36 pTRM, and COL-10 for Ro%) where the Montegrande ravine start to be well defined, and

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displays emplacement temperature between 300°-400°C (pTRM) and 345°-376°C (Ro%) (Fig.

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10 a,b) within the gullies and 260°C on the overbanks (Tables 1 and 2, Fig 10a,b). According to Devine et al., (1998), andesitic magma has a temperature of ~880°C which indicates a

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strong drop in temperature of ~400-480°C in a very short space and time. Due to the absence of convective column and associated ingestion of air, such loss of heat can be imputed mainly

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to dome disruption along the flank and to deposit spreading up to the main break in slope. As mentioned before in this area the deposit is not confined in one single valley as downwards along the Montegrande ravine, but it is wider canalised into different gullies and also spread on the overbanks (Macorps et al., 2017). As pointed out by Yuan and Horner-Devine, (2013) lateral spreading increases the interfacial surface between air and deposit that contributes to heat loss. Air entrainment through the upper margins has been highlighted in analogue experiments by Andrews, (2014). Eddies developed behind the flow head can penetrate into

ACCEPTED MANUSCRIPT the body causing air mixing. Usually the air entrainment from the upper margins is not as efficient to affect current dynamics as the air ingested in the front part, but if the mixing penetrates to the base of the current it can cause the separation of the front head in multiple pulses, with the resulting formation of different lobes. The semi-confined condition of this area also allows the formation of vortexes along the lateral margins (Andrews, 2014); in fact,

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although horizontal average velocities are directed away from the vent, velocities along the

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lateral margins are inward-directed enhancing the efficiency of air cooling.

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The valley confined morphological area comprises the entire extent of the Montegrande ravine. Here the deposit is well channelled within the ravine. Ro% and pTRM estimations

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indicate temperature ranges within the valley from 316-385°C and 350-480°C respectively (representative sites COL-42, Fig. 10a,b). Temperature emplacement on the overbank was

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estimate ~220 °C similarly to the previous area.

Comparing emplacement temperature values of this area with the proximal area estimations it

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is evident that there was not a substantial decrease in temperature with distance from the vent.

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In particular lithic clasts collected at sites COL-23 and COL-42 show for the event of the 11th of July higher temperature (400-480°C) respect to the proximal zone (Fig. 10a,b). These

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anomalous higher temperature values, together with the general conservation of such high temperature through almost the entire length of Montegrande valley, could be due to two

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principal factors. The 11th of July BAF deposit was emplaced above the previous BAF deposit that already partially filled the Montegrande ravine insulating the second event from the paleosoil and partially from the pre-existing forest. This has certainly contributed to the decrease in heat loss from the base, also considering that the emplacement temperature of the 10th of July deposit was estimated between 300-350°C (pTRM) and 322°C (Ro%) (Site COL42, Fig. 10a,b). The second factor that has strongly inhibited heat dispersion is the topography confinement. The 20 m high paleo-valley walls of the Montegrande ravine well

ACCEPTED MANUSCRIPT channelled the flow that passively overspilled mainly where the valley is meandering with strong angles. This strong lateral confinement did not allow any air mixing from the flow margins, inhibiting any kind of cooling. Furthermore, the variation in width and depth of the main channel due to the presence of pre-existing lahars terraces led to increase in deposit

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thickness and the decrease of air/deposit interfacial area.

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According to Lube et al., (2007) the channelling of pyroclastic density currents exerts a

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strong influence on flow dynamics. For example, the 1975 Ngauruhoe eruption (New Zealand), the confined PDCs were able to travel up to 50% farther respect to unconfined

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currents over slope below the static angle of repose (below 30°). This can be attributed to the combination between initial mass flux, inclination of the slope, inertial forces and frictional

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forces (Félix and Thomas, 2004; Lube et al., 2007). In the case of Volcàn de Colima, the BAF was able to travel for ~6.5 km over a plane between 15° and 5° in slope. This indicates

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that, despite the distance from the vent, the initial energy was not dissipated and that the

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dynamic pressure allowed the inertial forces to overcome the frictional forces. The high walls and also the sinuosity of the valley channel contributed to maintain the flow unsteady, with

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stages of different acceleration and deceleration.

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Such pulsing behaviour, together with variation in topography confinement conditions, produced local differencies in depositional modality. Depending on slope, granulometry, flow velocity, channel depth and width, the sediment flux can vary greatly along valleys. According to Doronzo, (2012) (and reference therein), low flow velocity (low slope angle) and confined topographic conditions triggers high deposition rate; while high flow velocity (steep slopes) and wider valley flanks enhance particles transport rather than sedimentation. High deposition rate (deposit thickness), coupled with narrow and deep channel

ACCEPTED MANUSCRIPT characteristics, favours significantly local temperature retaining (Doronzo et al., 2016, Giordano and Doronzo, 2017). In the case of Volcan de Colima 2015 eruption, the Montegrande valley displays subsequent flanks narrowings (in correspondance of bends) and enlargements inducing local enhances in sedimentation and flow transport respectively. Despite the morphological complexity of the Montegrande ravine, that could have led to local

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variations in deposit thickness and therefore temperature retainment, pTRM and charcoal

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reflectance results show a rather homogeneous temperature in valley confined environment

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(Fig. 10). This suggests, for the case of Volcan de Colima eruption, the coexistence of high trasport and high deposition rate along the entire valley length, maintaining high

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emplacement temperatures. This scenario can be due to the overcome of the inertial forces on the frictional forces that produced the formation of a flow able to float along a twisting valley,

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but strongly slowed at the base for interaction with the topography Doronzo, (2012).

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With the widening of the valley channel approaching the end of the main valley, the Ro%

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and pTRM analysis indicate a temperature decrease to 338°C and 300-350°C respectively (Site COL-49, Fig 10a,b). This result can be attributed to the larger area where the BAF could

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expand and to the decrease in thickness deposit. Furthermore, since the 10th of July BAF did not reach the end of the Montegrande ravine, the 11th of July BAF deposit was no longer

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insulated at the base, lying directly on the paleosoil. The final morphological area is represented by the distal fan. Once reached the end of the valley the deposit spread radially on the distal plain. Emplacement temperature estimation (pTRM) from the margin of the deposit indicates a strong drop in temperature to 170-220°C (COL-01-01, Table 2, Fig. 10b), while Ro% analysis indicates 326°C (COL-01-02 Table 1, Fig. 10a). This discrepancy between the two methods could be due to fact that the sampled charred wood was not standing, but embedded within the flow, and probably transported

ACCEPTED MANUSCRIPT from a zone at higher temperature (note that the Ro signal can only record the maximum temperature and cannot be overwritten by lower T). Despite this result, Ro% charcoal value indicates a decrease in temperature, thus it should not have been transported from far distances. The abrupt decrease in temperature highlighted by pTRM analysis, is mainly due to the new unconfined setting that stopped the deposit flow. Here the dynamic pressure

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dropped immediately and in such low slope angle (~5°-2°, Fig. 3) frictional forces overcome

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the inertial ones, favouring on the one side deposition and on the other side air ingestion and

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consequently heat dissipation. The minor deposit thickness (6-8 m) coupled with the distribution on a wider surface and direct contact with paleosoil quickly enhanced the heat

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dissipation.

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1.7 Conclusions

In this paper we present the detailed reconstruction of emplacement temperature estimation of the 2015 Volcán de Colima BAF through the simultaneous application of charcoal reflectance

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(Ro%) and partial thermal remanent magnetization (pTRM) analyses. The very good overlap

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between the Ro% and pTRM estimations highlights the validity of these two independent proxies for emplacement temperature estimation applied for the first time to BAF deposit in this study.

The accurate study of paleomagnetic lithic clasts behaviour allowed the identification of lithic fragments origin: dome core (fragments type B1, B2), crater walls and/or dome shield (fragments type C). The temperature variation displayed by the BAF deposit allowed the identification of two main areas: the valley confined zone that includes the total length of Montegrande ravine and the unconfined zone represented by the distal fan. Both Ro% and

ACCEPTED MANUSCRIPT pTRM data sets indicate a strong difference in emplacement temperature between valley confined and unconfined deposits. The values overlap suggests a temperature range from 345° to 385 °C for the deposit confined within the Montegrande ravine and 170°-220°C along the distal fan. According to our results, the principal factors contributing to maintain of high temperatures

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till the end of the Montegrande ravine are the strong morphological confinement, the

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preservation of high initial energy and dynamic pressure that allow a greater runout of the

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flow, despite the low slope angle; the thickness and the lateral and basal isolation of the

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deposit that inhibited the heat dispersion.

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1.8 Acknowledgements

This research was funded by DGAPA-IN105116, UNAM. The authors gratefully

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acknowledge the Academic Laboratory of Basin Analysis (ALBA) at Roma Tre University

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for the use of the equipment for the Reflectance analysis. We would like to thank also the Editor Juan Martí and the Reviewers Domenico Doronzo and Massimiliano Porreca for

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contributing to the improvement of this research.

1.9 Captions

Figure 1 a) Sketch map of the Trans Mexican Volcanic Belt (TMVB) and location of Volcán de Colima and nearest comunities. b) BAF deposit along the Montegrande ravine soon after the dome collapse (photo by Raul Arámbula) and c) photo of the Montegrande ravine today and view of BAF deposit total length. d) Map of valley confined facies (blue) and overbank facies (orange) based and modified after Macorps et al. (2017) and total area involved in the eruption (yellow). Triangles and dots represent respectively sampled lithic clasts and charcoal fragments. Dashed lines separate valley confined morphology (representative sites COL-10, COL-42, COL-49) to unconfined morphology (representative site COL-01). Figure 2 Valley confined deposit profiles, deposit images and stratigraphic logs of five representative points of the Montegrande ravine. In the selected sites charred fragments and

ACCEPTED MANUSCRIPT lithic clasts were collected in the same area: a) site COL-10 proximal area of the valley (COL-10-05 charcoal sample, COL-36-01 lithic clasts); b) site COL-42 central area. Here both the BAFs of the 10th and the 11th of July where recognised. COL-42-01 and COL-42-02 represent respectively, charcoal fragments and lithic clasts collected within the 10th of July BAF. COL-42-03 and COL-42-04 constitute respectively, lithic fragments and charred wood of the 11th of July BAF; c) site COL-49 central area, COL-49-01 lithic clasts and COL-49-02 charred samples; d) COL-01 distal fan, COL-01-01 lithic clasts and COL-01-02 charcoal fragments.

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Figure 3 Montegrande ravine slope profile, modified after Vázquez et al., 2016 and Macorps et al., 2017 and images of the valley after the 2015 Colima eruption

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Figure 4 Experimental charcoalification of S. sempervirens wood from Scott et al., (2007). a) Graph displaying the variation in mean reflectance under oil immersion of four different samples of S. sempervirens burnt at different temperatures (300 °C - line with white circles, 400 °C - line with black squares, 500 °C – line with black circles, and 600 °C - line with black triangles), and at different lengths of time (20, 40, 60 min, 2, 4, 24, 96, and 168 h). b) Graph showing random reflectance variation versus temperature of Sequoia sempervirens charred for one hour (black line with black squares). The black line with empty dots refers to the Gandoderma fungus charcoalification experiment (from Scott and Glasspool 2007).

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Figura 5 Conversion of reflectance measurements (Ro%) into paleo-temperatures. a) Representation of the five pyrolysis curves of Scott and Glaspool 2005 (dashed blue line with triangles), Scott et al., 2007 (dashed green line with squared), Hudspith et al., 2014 (dashed yellow line with diamonds); Ascough et al., 2010 (red solid line with circles) and McParland et al., 2009 (dashed black line with rectangles). Trend lines equations, based on published data, are reported for each curve. b) Reflectance measurements are converted into temperature values using the experimental curves of Ascough et al., 2010 for Pinus sylvestris (red circles). The range of temperature defined by the Ascough et al., 2010 curve for given Ro% values (black solid lines) is considered an estimation of the BAF emplacement temperature. The grey coloured zone corresponding to the area enclosed by the five pyrolysis curves, defines the BAF emplacement temperature range. Error bars (Tab. 1) are calculated taking into account the standard deviations of Ro% data during the conversion.

Figure 6 Selected charred wood samples for Reflectance analysis. Column a macroscopic images of wood samples in the field; column b microphotographs of wood fragments under reflected light from polished blocks under oil microscope; c results of optical analyses reported in terms of reflectance distribution. Generally, the histograms show Gaussian distribution, with bimodal trends and wider distribution in some cases (Col-10-05, COL-1604, COL-17-01 and COL-01-01). Values of mean Ro%, standard deviation and number of analyses per each sample are reported. Figure 7 Schematic representation of magnetization processes of lithic clasts. a) Deposition of ignimbrite with emplacement temperature (Te) higher than the Curie temperature (Te>Tc) of the magnetic minerals of the lithic clast. Clasts will carry a single component

ACCEPTED MANUSCRIPT magnetization vector oriented parallel to the Earth magnetic field (EMF) recorded during cooling; b) remobilization and reheating of the clasts after cooling by a new eruptive event at lower temperature than the Curie temperature (Te
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Figura 8 Thermal demagnetization data representative of different paleomagnetic behaviours of lithic clasts collected within the BAF deposit. a) Equal area stereonet of mean remanence direction of Single magnetic component of Types B1 and B2 lithic clasts displaying single component which direction is parallel to the Mexican GAD (black dots) and orientation shifted between 45° to 160° W (red dots in grey area) respect to the Mexican GAD; b) orthogonal plots and demagnetization curve (solid dots, lower hemisphere; open dots, upper hemisphere) of representative samples (COL-04-02, COL-26-06) of single magnetic component lithic clasts belonging to Type B1 and c) Type B2 d) Equal area stereonet of mean remanence direction of LT component of Type C lithic clasts characterised by double components which LT component direction is parallel to the Mexican GAD (black dots) and also shifted between 30° to 160° W respect with the Mexican GAD (red dots in grey area); e) orthogonal plots and demagnetization curve (solid dots, lower hemisphere; open dots, upper hemisphere) of representative sample (COL-36-04) of double magnetic component lithic clast

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Figura 9 Schematic model of pTRM acquisition of lithic clasts during a) endogenous dome formation and b) after dome collapse and BAF emplacement.

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Figura 10 SPOT image (2.5m in resolution, 1, 2, 3, and 4 bands in RGB combination). The two images display the BAF emplacement temperature variation obtained with a) Reflectance analysis of charred wood and b) pTRM analysis of lithic clasts. Red circles refer to valley confined samples, white circles represent overbank samples and yellow circles fragments collected along the distal fan. The different size of the circles refers to variation in temperature value, see the legend.

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Table 1 Summary table of the localities sampled for Reflectance analysis purpose. Tree type, position within the BAF deposit, distance from the vent, Lat (latitude), Long (longitude), day of the event, Ro% mean and standard deviation are reported. Reflectance data conversion into emplacement temperature values (and relative errors based on standard deviation) are listed according the five pyrolysis curves published in literature (Scott and Glasspool 2005, 2007; Hudpith et al., 2014, Ascough et al., 2010 and McParland et al., 2009). Highlighted in yellow are the temperature values obtained using the equation of Ascough et al., 2010 for pine tree, used in this study. Table 2 Summary table of the paleomagnetic localities sampled, number of lithic clasts collected in each locality, analysis of magnetic components and emplacement temperatures of each paleomagnetic site. Dec and Inc refer to the Low Temperature component (LT) when referred to samples with double magnetic component, and to High Temperature component (HT) when referred to samples with single magnetic component. Lat (latitude), Long (longitude), Dist km (distance in km from the vent), N. Samp (number of samples), Comp

ACCEPTED MANUSCRIPT magnetic components, Samp Disc (number of samples discarded), Dec (declination), Inc (inclination), a95 (ellipse of confidence in degrees).

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Table 3a Summary table of the emplacement temperature estimations obtained with pTRM analysis of nine lithic clasts, collected at the paleomagnetic site COL-36-01, and Ro% analysis of COL-10-05 charcoal fragment both collected in the same locality (proximal area within the 11th od July BAF) within the Montegrande valley. (Type= lithic clast lithology; Dim. cm= dimension in centimetre; Dec.= declination in degrees; Inc.= inclination in degrees; α95= ellipse of confidence in degrees, LT= low-temperaturecomponent; HT= hightemperature component; Ro%= charcoal reflectance, St Dev standard deviation)

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Table 3b Summary table of the emplacement temperature estimations obtained with pTRM analysis of eight lithic clasts, collected at the paleomagnetic site COL-42-02, and Ro% analysis of COL-42-01 charcoal fragment both collected in the same locality (central area within the 10th of July BAF) within the Montegrande valley. (Type= lithic clast lithology; Dim. cm= dimension in centimetre; Dec.= declination in degrees; Inc.= inclination in degrees; α95= ellipse of confidence in degrees, LT= low-temperaturecomponent; HT= hightemperature component; Ro%= charcoal reflectance, St Dev standard deviation)

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Table 3c Summary table of the emplacement temperature estimations obtained with pTRM analysis of eight lithic clasts, collected at the paleomagnetic site COL-42-03, and Ro% analysis of COL-42-04 charcoal fragment both collected in the same locality (central area within the 11th of July BAF) within the Montegrande valley. (Type= lithic clast lithology; Dim. cm= dimension in centimetre; Dec.= declination in degrees; Inc.= inclination in degrees; α95= ellipse of confidence in degrees, LT= low-temperaturecomponent; HT= hightemperature component; Ro%= charcoal reflectance, St Dev standard deviation)

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Table 3d Summary table of the emplacement temperature estimations obtained with pTRM analysis of eight lithic clasts, collected at the paleomagnetic site COL-49-01, and Ro% analysis of COL-49-02 charcoal fragment both collected in the same locality (central/distal area within the 11th od July BAF) within the Montegrande valley. (Type= lithic clast lithology; Dim. cm= dimension in centimetre; Dec.= declination in degrees; Inc.= inclination in degrees; α95= ellipse of confidence in degrees, LT= low-temperaturecomponent; HT= high-temperature component; Ro%= charcoal reflectance, St Dev standard deviation)

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Table 3e Summary table of the emplacement temperature estimations obtained with pTRM analysis of six lithic clasts, collected at the paleomagnetic site COL-01-01, and Ro% analysis of COL-01-02 charcoal fragment both collected in the same locality (distal fan area within the 11th od July BAF) within the Montegrande valley. (Type= lithic clast lithology; Dim. cm= dimension in centimetre; Dec.= declination in degrees; Inc.= inclination in degrees; α95= ellipse of confidence in degrees, LT= low-temperaturecomponent; HT= high-temperature component; Ro%= charcoal reflectance, St Dev standard deviation)

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ACCEPTED MANUSCRIPT Geothermal Research 193, 49–66. doi:10.1016/j.jvolgeores.2010.03.007 Sulpizio, R., Dellino, P., Doronzo, D.M., Sarocchi, D., 2014. Pyroclastic density currents: State of the art and perspectives. Journal of Volcanology and Geothermal Research 283, 36–65. doi:10.1016/j.jvolgeores.2014.06.014 Tanaka, H., Hoshizumi, H., Iwasaki, Y., Shibuya, H., 2004. Applications of paleomagnetism

PT

in the volcanic field: A case study of the Unzen Volcano, Japan. Earth, Planets and

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Space 56, 635–647.

SC

Trolese, M., Giordano, G., Cifelli, F., Winkler, A., Mattei, M., 2017. Forced transport of thermal energy in magmatic and phreatomagmatic large volume ignimbrites:

NU

Paleomagnetic evidence from the Colli Albani volcano, Italy. Earth and Planetary Science Letters 478, 179–191. doi:10.1016/j.epsl.2017.09.004

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Uehara, D., Cas, R.A.F., Folkes, C., Takarada, S., Oda, H., Porreca, M., 2015. Using thermal remanent magnetisation (TRM) to distinguish block and ash flow and debris flow

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deposits, and to estimate their emplacement temperature: 1991-1995 lava dome eruption

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at Mt. Unzen Volcano, Japan. Journal of Volcanology and Geothermal Research 303, 92–111. doi:10.1016/j.jvolgeores.2015.07.019

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Vázquez, R., Capra, L., Coviello, V., 2016. Factors controlling erosion/deposition phenomena related to lahars at Volcán de Colima, Mexico. Natural Hazards and Earth

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System Sciences 16, 1881–1895. doi:10.5194/nhess-16-1881-2016 Www.ngdc.noaa.gov, n.d. No Title [WWW Document]. Young, S.R., Steven, R., Sparks, J., Aspinall, W.P., Lynch, L.L., Miller, A.D., Robertson, R.E. a, Shepherd, J.B., 1998. Overview of the eruption of Soufriere Hills Volcano, Montserrat, July 18, 1995, to December 1997. Geophys. Res. Lett. 25, 3389–3392. doi:10.1029/98GL01405 Yuan, Y., Horner-Devine, A.R., 2013. Laboratory Investigation of the Impact of Lateral

ACCEPTED MANUSCRIPT Spreading on Buoyancy Flux in a River Plume. Journal of Physical Oceanography 43, 2588–2610. doi:10.1175/JPO-D-12-0117.1 Zanella, E., Gurioli, L., Lanza, R., Sulpizio, R., Bontempi, M., 2008. Deposition temperature of the AD 472 Pollena pyroclastic density current deposits, Somma-Vesuvius, Italy. Bulletin of Volcanology 70, 1237–1248. doi:10.1007/s00445-008-0199-9

PT

Zanella, E., Sulpizio, R., Gurioli, L., Lanza, R., 2014. Temperatures of the pyroclastic density

RI

currents deposits emplaced in the last 22 kyr at Somma-Vesuvius (Italy). Geological

AC

CE

PT E

D

MA

NU

SC

Society, London, Special Publications 13–33. doi:10.1144/SP396.4

ACCEPTED MANUSCRIPT

Valley confined zone

Table 1 Sample

Tree type

Position

Distance vent km

Lat

Long

Event

Ro% mean

SD

COL-10-03

Spruce tree

3.45

644410

2154898

Pine tree

3.45

644414

2154885

COL-11-03

Pine tree

3.65

644445

2154691

COL-12-02

Pine tree

overbank

3.8

644435

2154528

COL-12-03

Pine tree

overbank

3.85

644415

2154502

COL-27-01

Spruce tree

overbank

3.87

644409

2154489

COL-13-01

Pine tree

overbank

4.27

644129

2154139

COL-14-01

Spruce tree

overbank

4.4

644139

2153987

COL-15-01

Pine tree

4.42

644190

2153974

COL-39-02

Pine tree

4.53

644316

2153829

COL-16-04

Pine tree

valleyconfined valleyconfined overbank

4.66

644339

2153689

COL-42-01

Pine tree

5.11

644643

2153205

COL-42-04

Pine tree

5.11

644643

2153205

COL-18-01 A

Pine tree

valleyconfined valleyconfined overbank

5.43

644878

2152872

COL-18-01 B

Pine tree

overbank

5.43

644878

2152872

COL-19-01

Pine tree

5.45

644740

2152849

COL-17-01

Pine tree

valleyconfined overbank

5.52

644773

2152779

COL-24-02

Pine tree

overbank

6.02

644816

2152259

COL-22-02

Pine tree

overbank

6.03

644821

2152258

COL-23-01

Pine tree

6.04

644821

2152260

COL-50-01

Pine tree

valleyconfined overbank

6.72

644697

2151575

COL-46-01

Spruce tree

overbank

6.78

644513

2151513

COL-47-01

Pine tree

overbank

7.31

645320

2150973

COL-48-01

Spruce tree

valleyconfined

7.4

645315

2250961

11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 10th of July 11th of July 11th of July 11th of July 10th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July

0.554

COL-10-05

valleyconfined valleyconfined overbank

± °C

HUDSPITH et al. 2014

± °C

ASCOUGH et al. 2010

± °C

MCPARLAND et al. 2009

± °C

4

SCOTT et al. 2007 311

4

369

5

345

3

377

4

0.798

0.035

326

4

346

5

408

5

369

3

413

5

0.429

0.024

279

3

292

4

348

4

332

2

359

4

0.282

0.023

259

3

269

4

321

4

317

2

337

3

0.684

0.038

312

5

330

5

390

6

358

4

396

5

0.863

0.054

334

6

355

7

417

7

376

5

422

7

0.369

0.024

271

3

283

4

337

4

326

3

350

4

0.575

0.038

299

5

314

6

I R

373

6

347

4

381

6

0.503

0.025

289

3

303

4

361

4

340

3

370

4

0.960

0.043

345

5

368

6

430

6

385

4

435

6

0.632

0.051

306

6

322

7

382

8

353

5

389

7

0.329

0.026

265

4

276

4

329

5

322

3

344

4

0.881

0.043

336

5

357

6

419

6

377

4

424

6

0.197

0.019

246

3

255

3

304

4

308

2

324

3

0.242

0.063

253

9

262

10

313

12

313

7

330

10

0.368

0.022

271

3

282

3

337

4

326

2

350

3

0.514

0.030

291

4

305

5

363

5

341

3

372

4

0.408

0.022

276

3

289

3

344

4

330

2

356

3

0.371

0.028

271

4

283

4

337

5

326

3

350

4

0.571

0.035

298

5

313

5

372

6

347

4

380

5

0.671

0.005

311

6

328

7

388

8

357

5

402

0

0.380

0.026

272

4

284

4

339

5

327

3

352

4

0.721

0.052

317

6

335

7

396

8

362

5

402

7

0.429

0.023

279

3

292

4

348

4

332

2

359

3

D E

T P

E C

C A

0.028

SCOTT et al. 2005 296

± °C

C S

U N

A M

T P

Distal fan unconfined zone

ACCEPTED MANUSCRIPT COL-04-04

Pine tree

overbank

7.47

645441

2150807

COL-04-03

Pine tree

7.48

645441

2150807

COL-04-02

Pine tree

7.48

645441

2150807

COL-05-01

Pine tree

valleyconfined valleyconfined overbank

7.52

645461

2150776

COL-05-02

Pine tree

overbank

7.52

645460

2150773

COL-07-01

Pine tree

7.93

645417

2150315

COL-06-01

Pine tree

7.93

645371

2150357

COL-49-02

Pine tree

valleyconfined valleyconfined overbank

7.98

645386

2150302

COL-59-01 A

Pine tree

8.2

645445

2150097

COL-08-01

Pine tree

8.2

645415

2150085

COL-09-02

Pine tree

valleyconfined valleyconfined overbank

8.44

645434

2149839

COL-78-01

Pine tree

distal fan

8.82

645888

2149505

COL-80-01 A

Pine tree

distal fan

9.42

645647

2148871

COL-01-01

Pine tree

distal fan

9.43

645810

2148886

COL-01-02

Pine tree

distal fan

9.45

645810

2148886

11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July 11th of July

0.269

0.024

257

3

267

4

318

5

315

3

335

4

0.278

0.018

258

3

268

3

320

3

316

2

336

3

0.416

0.024

277

3

290

4

346

4

331

2

357

4

0.408

0.031

276

4

289

5

344

6

330

3

356

5

0.463

0.031

284

4

297

5

354

5

336

3

364

5

0.364

0.027

270

4

282

4

336

5

325

3

349

4

0.420

0.031

278

4

290

5

346

5

331

3

358

5

0.483

0.026

286

3

300

4

357

338

3

367

4

0.280

0.018

258

3

269

3

320

3

317

2

336

3

0.454

0.026

283

3

296

4

I R

4

352

4

335

3

363

4

0.486

0.029

287

4

301

358

5

338

3

367

4

0.671

0.029

311

4

328

4

388

4

357

3

394

4

0.488

0.026

287

U N

4

3

301

4

358

4

338

3

368

4

0.612

0.038

303

5

319

5

379

6

351

4

386

5

271

4

282

5

336

6

326

3

340

5

D E

0.367

T P

C A

E C

0.031

A M

C S

T P

ACCEPTED MANUSCRIPT Table 2 Site

Area

Lat

Dist km from vent

Long

N. N. Sample Sample Disc.

11th of July

COL-35-01

Valley confined

644357 2154837

3.4

8

2

11th of July

COL-36-01

Valley confined

644385 2154991

3.6

9

/

11th of July

COL-12-01

Overbank 644435 2154528

3.75

6

5

11th of July

COL-29-01

Valley confined

644235 2154252

4.11

8

3

11th of July

COL-16-01

Overbank 644339 2153689

4.6

6

1

10th of July

COL-42-02

5.1

8

5.1

8

11th of July 11th of July

COL-42-03 COL-26-01

11th of July

COL-23-01

11th of July

COL-45-01

11th of July

COL-04-05

11th of July

COL-49-01

Distal fan unconfined zone

Valley confined zone

Event

11th of July

COL-01-03

Valley confined Valley confined

644643 2153205

Valley confined

644822 2152458

Valley confined Valley confined Valley confined Valley confined Distal fan

D E

T P

5.8

10

1 4

E C

6

9

2

644631 2151802

6.45

8

1

645441 2150807

7.5

6

1

645386 2150302

8

8

2

645810 2148886

9.4

6

/

644821 2152260

C A

Andesite Lithic clasts Andesite Lithic clasts Andesite Pumice clasts Andesite Lithic clasts Andesite Lithic clasts Andesite Lithic clasts Andesite Lithic clasts Andesite Lithic clasts Andesite Lithic clasts Andesite Lithic clasts Andesite Lithic clasts Andesite Lithic clasts Andesite Lithic clasts

Double Single Double Single Double

Paleomag Behaviours

Single

Double Single Double Single Double Single Double Single Double Single Double Single Double Single Double Single Double Single Double Single

Dec

Inc

α95

Temperat ure

349.4 332.7 353.7 / 295.7

29.3 21.7 39.4 / 11.2

0 0 90 / 7

350°C >480°C 300-400°C / 260°C

/

B1 / / / / /

B2 / 1 / 5 /

C 5 / 4 / 1

/ / / / 3 / / / / /

/ / 1 / / / 2 / / /

/ 4 / 2 / 3 / 7 / 2

/ 340.1 334.7 290.4

/ 42.2 48.6 42.8

99.3 0

4.2 336.7 330.1 / 347.1

27.9 37.6 51.4 / 63.1

0 0 32 / 0

2 / 2 / 2 / 3 / / /

2 / / / / / / / 3 /

/ 5 / 5 / 2 / 3 / 5

339.6 335.8 / 248 / 336 358.6 261.8 / 282

44.1 44.6 / 24.9 / 52.2 48.7 10.5 / 60.2

44.2 50.3 / 36.6 / 37 0 18.5 / 90.5

300-350°C >350°C 400-440°C / 400-440°C >350400°C 440-480°C / 400-440°C / 350-400°C >580°C 300-350°C / 170-220°C

/

1

/

/

/

/

/

T P

I R

C S

U N

A M 3

Mag. Comp.

Clasts type

/ 400°C >350°C 220°C

ACCEPTED MANUSCRIPT Table 3a valley confined zone N. Samples: 9

11th of July event

GPS

pTRM

Ro%

644385E 2154991N Sample

COL-36-01

COL-10-05

Type

Dim cm

Dec

Inc

α95

Paleomag behaviours

Double comp. (LT)

COL-36-01-01

Andesite lava

6

268.6

26.2

7.9

C

400°C±50°C

COL-36-01-02

Andesite lava

5.5

240.8

15

10

B2

COL-36-01-03

Andesite lava

4.5

184.5

83.3

7.7

B2

COL-36-01-04

Andesite lava

3

4.9

49

9.8

A M

300°C±50°C

COL-36-01-05

Andesite lava

5.5

339

25.4

6.5

C

350°C±50°C

COL-36-01-06

Andesite lava

4.5

302.7

5.2

C

300°C±50°C

COL-36-01-07

Andesite lava

COL-36-01-08 COL-36-01-09

D E

T P 28

C

Single comp.

Ro%

I R

0.798

T P

C S

>480°C

U N

>440°C

3

E C

230.1

47.6

4.5

B2

>480°C

Andesite lava

4

315.1

76.3

7.9

B2

>480°C

Andesite lava

4

296.3

49.9

9.3

B2

>480°C

C A

St Dev 0.035

Temperature (Ascough et al 2010) 369°C± 3°C

ACCEPTED MANUSCRIPT Table 3b valley confined zone N. Samples: 8

10th of July event

GPS

pTRM

Ro%

644643E 2153205N Sample

COL-42-02

COL-42-01

Type

Dim cm

Dec

Inc

α95

Paleomag behaviours

Double comp. (LT)

COL-42-0201

Andesite lava

11

8.6

6.2

8.1

C

350°C±50°C

COL-42-0202

Andesite lava

3.5

319.4

4.5

6.2

B2

COL-42-0203

Andesite lava

3.5

305.6

-35.3

-7

C

COL-42-0204

Andesite lava

4.5

336.7

37.6

9.6

A M

COL-42-0205 COL-42-0206

Andesite lava Andesite lava

4.5

4.2

27.9

4.5

1.4

COL-42-0207 COL-42-0208

C A

E C

T P

D E

85.4

B2

I R

0.329

T P

C S

U N

440°C±50°C discarded

C

350°C±50°C

4.4

C

300°C±50°C

unstable behaviour

Ro%

>350°C

5.4

broken during processing

Single comp.

>350°C

St Dev

0.026

Temperature (Ascough et al 2010) 322°C± 3°C

ACCEPTED MANUSCRIPT Table 3c valley confined zone N. Samples: 8 GPS

11th of July event pTRM

Ro%

COL-42-03

COL-42-04

644643E 2153205N Sample

Type

Dim cm

Dec

Inc

α95

Paleomag behaviours

Double comp. (LT)

COL-42-0301

Andesite lava

3.5

308

53.7

7.4

C

400°C±50°C

COL-42-0302

Andesite lava

4

297.9

36.9

17.5

C

350°C±50°C

COL-42-0303

Andesite lava

5.5

294.5

49.7

3.4

C

COL-42-0304

Andesite lava

3

314.7

53.3

4.8

COL-42-0305 COL-42-0306

Andesite lava

4.5

335.2

58

COL-42-0307

Andesite lava

COL-42-0308

Andesite lava

T P

D E 4.1

U N

A M C

440°C±50°C 440°C±50°C

C

440°C±50°C

unstable behaviour

E C

22.9

6.8

C

400°C±50°C

302.3

41

3.7

C

440°C±50°C

3

C A 4.5

328.6

Ro%

I R

0.881

C S

Single comp.

T P

St Dev

0.043

Temperature (Ascough et al 2010) 377°C± 4°C

ACCEPTED MANUSCRIPT Table 3d valley confined zone N. Samples: 8

11th of July event

GPS

pTRM

Ro%

645386E 2150302N Sample

COL-49-01

COL-49-02

Dim cm

COL-49-0101

Andesite lava

6

COL-49-0102

Andesite lava

3

227.9

15.3

5.7

C

COL-49-0103

Andesite lava

2

215

-1.6

15.8

B2

COL-49-0104

Andesite lava

4

COL-49-0105 COL-49-0106

Andesite lava

3

253.4

Andesite lava

4.5

274.4

COL-49-0107

Andesite lava

2.5

E C

COL-49-0108

Andesite lava

C A 3

Dec

266.3 257.5

Inc

α95

Type

Paleomag behaviour s

D E

16.2

Double comp. (LT)

Single comp.

C S

350°C±50° C

U N

>440°C

A M

17.4

C

13.3

B2

>400°C

24.6

7.5

B2

>400°C

7.8

11.3

C

T P 7.2

350°C±50° C

300°C±50° C

St Dev

T P

0.026

I R

Ro%

0.483

Temperature (Ascough et al 2010) 338°C± 3°C

ACCEPTED MANUSCRIPT Table 3e unconfined zone N. Samples: 6

11th of July event

GPS

pTRM

Ro%

645810E 2148886N Sample

COL-01-01

COL-01-02

Type

Dim cm

Dec

Inc

α95

Paleomag behaviours

Double comp. (LT)

COL-01-0101

Andesite lava

2

47.6

40.6

7.8

C

220°C±40°C

COL-01-0102

Andesite lava

1

215.8

10.9

3.9

C

170°C±40°C

COL-01-0103

Andesite lava

3

313

14.9

10.1

C

170°C±40°C

COL-01-0104

Andesite lava

3

273.8

30.5

4.2

C

COL-01-0105 COL-01-0106

Andesite lava Andesite lava

3

18.4

32.1

5.4

B2

3

171.5

D E

C A

E C

T P -3.3

7

Single comp.

I R

C S

U N

220°C±40°C >380°C 220°C±40°C

St Dev

T P

0.305

A M

C

Ro%

0.031

Temperature (Ascough et al 2010) 326°C± 3°C

ACCEPTED MANUSCRIPT Highlights

PT RI SC NU MA D PT E CE

  

We determined the emplacement temperature of the 2015 Volcàn de Colima BAF deposit Proxies used for T° estimation: paleomagnetism and charcoal reflectance analyses Deposit T° strongly correlated to topography confinement and sedimentation process Noticeable T° differences between valley confined and distal fan areas

AC



Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10