An overview of the 2009 eruption of Redoubt Volcano, Alaska

Journal of Volcanology and Geothermal Research 259 (2013) 2–15

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An overview of the 2009 eruption of Redoubt Volcano, Alaska Katharine F. Bull a,⁎, Helena Buurman b a b

Alaska Volcano Observatory/Alaska Division of Geological and Geophysical Surveys, 3354 College Rd., Fairbanks, AK 99709, USA Alaska Volcano Observatory/Geophysical Institute, University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775-7320, USA

a r t i c l e

i n f o

Article history: Received 1 June 2011 Accepted 21 June 2012 Available online 1 July 2012 Keywords: Redoubt Volcano Eruption Seismicity Effusion Volcano monitoring Lava dome

a b s t r a c t In March 2009, Redoubt Volcano, Alaska erupted for the first time since 1990. Explosions ejected plumes that disrupted international and domestic airspace, sent lahars more than 35 km down the Drift River to the coast, and resulted in tephra fall on communities over 100 km away. Geodetic data suggest that magma began to ascend slowly from deep in the crust and reached mid- to shallow-crustal levels as early as May, 2008. Heat flux at the volcano during the precursory phase melted ~4% of the Drift glacier atop Redoubt's summit. Petrologic data indicate the deeply sourced magma, low-silica andesite, temporarily arrested at 9–11 km and/or at 4–6 km depth, where it encountered and mixed with segregated stored high-silica andesite bodies. The two magma compositions mixed to form intermediate-silica andesite, and all three magma types erupted during the earliest 2009 events. Only intermediate- and high-silica andesites were produced throughout the explosive and effusive phases of the eruption. The explosive phase began with a phreatic explosion followed by a seismic swarm, which signaled the start of lava effusion on March 22, shortly prior to the first magmatic explosion early on March 23, 2009 (UTC). More than 19 explosions (or “Events”) were produced over 13 days from a single vent immediately south of the 1989–90 lava domes. During that period multiple small pyroclastic density currents flowed primarily to the north and into glacial ravines, three major lahars flooded the Drift River Terminal over 35 km down-river on the coast, tephra fall deposited on all aspects of the edifice and on several communities north and east of the volcano, and at least two, and possibly three lava domes were emplaced. Lightning accompanied almost all the explosions. A shift in the eruptive character took place following Event 9 on March 27 in terms of infrasound signal onsets, the character of repeating earthquakes, and the nature of tephra ejecta. More than nine additional explosions occurred in the next two days, followed by a hiatus in explosive activity between March 29 and April 4. During this hiatus effusion of a lava dome occurred, whose growth slowed on or around April 2. The final explosion pulverized the very poorly vesicular dome on April 4, and was immediately followed by the extrusion of the final dome that ceased growing by July 1, 2009, and reached 72 M m3 in bulk volume. The dome remains as of this writing. Effusion of the final dome in the first month produced blocky intermediate- to high-silica andesite lava, which then expanded by means of lava injection beneath a fracturing and annealing, cooling surface crust. In the first week of May, a seismic swarm accompanied extrusion of an intermediate- to high-silica andesite from the apex of the dome that was highly vesicular and characterized by lower P2O5 content. The dome remained stable throughout its growth period likely due to combined factors that include an emptied conduit system, steady degassing through coalesced vesicles in the effusing lava, and a large crater-pit created by the previous explosions. We estimate the total volume of erupted material from the 2009 eruption to be between ~80 M and 120 M m3 dense-rock equivalent (DRE). The aim of this report is to synthesize the results from various datasets gathered both during the eruption and retrospectively, and which are represented by the papers in this publication. We therefore provide an overall view of the 2009 eruption and an introduction to this special issue publication. © 2012 Elsevier B.V. All rights reserved.

1. Introduction As signs of unrest at Redoubt Volcano began in the fall of 2008, memories returned to 1989–90 when the volcano's previous eruption ⁎ Corresponding author at: Exploration Unlimited, PO Box 81418, Fairbanks, AK 99708, USA. Tel.: +1 907 455 6879. E-mail address: [email protected] (K.F. Bull). 0377-0273/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2012.06.024

resulted in the near-loss of a commercial jet, ash fall that deposited on communities in south-central Alaska, and floods that inundated nearby oil-storage infrastructure (Brantley, 1990; Miller and Chouet, 1994). As the unrest progressed in late 2008, the Alaska Volcano Observatory (AVO) utilized additional monitoring tools and increased information dissemination through frequent and timely use of the AVO website and Volcano Activity Notifications (VANs). In March 2009 the eruption began, and although the potential hazards had

K.F. Bull, H. Buurman / Journal of Volcanology and Geothermal Research 259 (2013) 2–15

2. Background

changed little from 1990, improved communication and monitoring tools allowed for successful hazard assessment. Disruption to air traffic caused the Ted Stevens International Airport in Anchorage to shut down for 20 h and resulted in over 300 canceled, rerouted or delayed flights, but aviation encounters with ash were avoided (Schaefer, 2012). Flooding of the Drift River Marine Terminal (formerly Drift River Oil Terminal; DRT) oil-storage facility from lahars forced the removal of 6 M gallons of crude oil and the evacuation of personnel from the terminal. An incident command was established during the eruption that improved interagency cooperation and aided communication with the public. As a result of the extensive monitoring and research that took place in 2008 and 2009, the eruption produced a large number of datasets. One of the challenges facing modern volcano observatories lies with consolidating the plethora of data streams and extracting interpretations that fit all the observations. Prior to the 2009 eruption, Redoubt Volcano was routinely monitored by the Alaska Volcano Observatory (AVO) using visual and thermal satellite observations and real-time seismic monitoring, in addition to sporadic campaign-style geodetic surveys and airborne gas measurements. When unrest began in late 2008, scientists immediately began to augment the regular geophysical monitoring data with additional monitoring techniques. Among these techniques were: time-lapse photography; campaign-style broadband seismometers; a lightning mapping array; radar (NEXRAD and, eventually, USGS C-Band Doppler); and airborne- and satellite-derived gas measurements. When the volcano finally erupted in March 2009, it produced a collection of rich and varied real-time datasets that were further augmented by field-based data collection such as: oblique-photo photogrammetry; sample collection of water, tephra-fall, lahar and pyroclastic density current deposits; and Forward-looking Infrared (FLIR) images. Each separate dataset has produced one (or more) of the articles contained in this issue. The purpose of this paper is to synthesize the results of the various datasets and thereby provide an overall view of the 2009 eruption. Schaefer (2012) has presented a detailed chronology of the eruption, an overview of monitoring methods, and a discussion of impacts. The publication also provides a brief explanation of the various ways AVO interfaces with the public with respect to color-code warnings, alert levels and interagency protocol. Rather than duplicate this material, our intent is to complement that work. We consider additional data and summarize the significant results provided by authors of other articles in this issue.

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2.1. Geographic and geologic setting Redoubt Volcano is located 170 km southwest of Anchorage on the west side of Cook Inlet and is one of four historically active volcanoes that lie proximal to Alaska's largest population center (Fig. 1). The volcano lies toward the northeast end of the Aleutian volcanic arc, which comprises over 100 primarily andesitic volcanoes. The summit of the volcano reaches 3110 m above sea level (asl), and the majority of the volcano is ice-covered. The crater just northwest of the true summit is lined with ice and snow and its northern rim is dissected by the Drift glacier. The glacier flows north from a narrow canyon and broadens into a wide terminus on the Drift River valley floor. Redoubt lies near the headwaters of the Drift River, which flows over 35 km east from the glacier to meet Cook Inlet. The inlet hosts active petroleum platforms, and the production is stored at DRT, which sits at the mouth of the Drift River. The edifice of Redoubt Volcano comprises a ~1500-m-thick sequence of mid-Pleistocene to Holocene dacitic to basaltic pyroclasticdensity-current (PDC) deposits, block-and-ash-flow deposits and lava flows built on Jurassic tonalite (Till et al., 1994). Plutonic xenoliths sampled from clasts in PDC deposits Pleistocene or younger in age contain Proterozoic zircon, suggesting that cryptic Proterozoic basement underlies the edifice at depth (Bacon et al., 2012). Deposits of dacitic PDCs likely sourced near the present vent directly overlie tonalite basement on the north flank. Glacially dissected outcrops of an altered dacite dome exposed on the south flank indicate early effusive activity. The dacitic deposits are overlain by thick sequences of andesitic to basaltic lava flows and block-and-ash-flow deposits. At least three largevolume, clay-rich lahar deposits crop out in valleys on the south, east and north sides of the edifice, attesting to multiple flank-collapse events in the volcano's history (Riehle et al., 1981; Beget and Nye, 1994). The most recent flank-collapse occurred on the north side of the edifice ~900 years ago, removing a large portion of the upper peak (Beget et al., 2009). 2.2. Recent eruptive history prior to 2009 The two most recent eruptions at Redoubt Volcano occurred during 1965–8 and 1989–90 (Brantley, 1990; Miller and Chouet, 1994).

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Fig. 1. Location of Redoubt Volcano, in south-central Alaska. A. Regional map of Cook Inlet region showing Redoubt Volcano, Drift River Marine Terminal (DRT), and other nearby volcanoes. Regional scale location map (left). B. Shaded-relief map of the greater Redoubt Volcano area, showing location of lava domes emplaced during eruptions in 1966–68, 1989–90, and 2009. The relief between the summit of the volcano and the terminus of the Drift glacier is roughly 2800 m.

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Table 1 Chronology compilation: explosive events (shaded dark grey, with reanalysis events shaded medium grey), seismic swarms (light grey), lahar signals based on seismic data (white) and image observations (medium grey). Data from: Buurman et al., 2013; Schaefer, 2012; unpublished AVO data; this study.

Event / feature Swarm

Date, 2009 (month /day) (UTC)

Time* (UTC)

Maximum plume height (km asl)

2/26

6:00

3/15

21:05

Swarm

3/20

12:00

Event 1

3/23

6:38

5.5

Event 2

3/23

7:02

13.4

Event 3

3/23

8:14

14.6

Lahar

3/23

Event 4

3/23

9:39

13.1

Reanalysis

3/23

9:48

13.7

Event 0

Swarm end-time (UTC)

DFR starttime (UTC)

DFR endtime (UTC)

RDE starttime (UTC)

RDE endtime (UTC)

Image type**

13:00 (2/27)

Observations*** 31−h duration

4.6

Phreatic explosion. Vent S of 1990 dome. No juvenile material confirmed in ash deposit (Wallace et al., 2013)

Lahar

6:34 (3/23)

SPU duration = 20 min; RDT duration = 14 min

undet.

Event 5

3/23

12:31

18.3

Lahar

3/23 12:58

undet.

3/23

Lahar

8:40

9:11

11:49

10:00

11:50

RDT duration = 7 min 13:27

12:38

13:23

0:21

Event 6

3/24

3:41

PDC & Lahar

3/24

3:46

Lahar (and PDC?)

3/24

Lahar

3/24

3:56

Reanalysis

3/24

13:12

4.6

Event 7

3/26

16:34

8.2

Lahar

3/26

Event 8

3/26

Lahar & PDC 3/26

Lahar

3/26

4:45

3:54

0:00 7:47

Lahar

3/27

Event 10

3/27

Lahar

3/27

8:29

Reanalysis

3/27

8:43

Tephra

3/27

14:42

Event 11

3/27

16:39

PDC

3/27

16:41

Lahar

3/27

Lahar

3/27

Dome

3/27

Event 12

3/28

Lahar

3/28

Tephra

3/28

17:23

--

--

Lh reached DRT SPU duration = 11 min; RDT duration = 14 min

18:31

17:35

Hutcam

Lahar in hutcam images 09:30-09:36. Probable PDCs on upper piedmont and W shoulder of Drift glacier gorge (steaming in Dumbbell Hills cam on W shoulder).

DH

Evidence of small lahar

18:35

Note long duration. Lh reached DRT

8:28

8−h duration

12.5

SPU duration = < 1 min; RDT duration = 21 8:03

8:29

8:03

8:29

8:36

9:07

8:33

9:28

Same start time at each station. Ends with onset of Event 10 explosion (all cameras dark].

14.9

SPU duration = 5 min; RDT duration = 9 min

undet.

RDT duration = 7 min DH

15.6

Dumbbell Hills image shows significant tephra fall deposit in upper Drift R. valley SPU duration = 8 min; RDT duration = 10 min

DH 17:35

16:47

Spectacular image of PDC descending Drift gorge.

17:35

16:56

DH

Small lahar visible in valley.

Satellite

Possibly a remnant of 1990 dome on north lip of crater, but bulk of 1990 dome is gone

14.6

SPU duration = 2 min; RDT duration = 9 min 1:43

1:41

Lahar is visible in Dumbbell Hills camera at 19:56. Can also see steam cloud from flow as seen in hutcam (above entry).

18.9

16:45

1:34

DH

SPU duration = <1 min; RDT duration = 1 min

17:33

3/27

Steaming lahar/rock avalanches (and small PDC?) in images; column at 19:46. Cloud flowed down Drift glacier into drainage. Present in image at 19:46, but not at 19:33. Two arms of flow, one on E shoulder, other in main drainage. Can see active mudflows and steam clouds in drainage. Ends by 20:01. At 20:01 see deposits on E flank.

4:51

21:41

3/27

Hutcam

RDT duration = < 1 16:45

Event 9

Image at 06:42. Lahar took place prior to image. Lahar track is visible across the piedmont lobe of Drift glacier. No hutcam images exist between this image and the one on Mar 22 at 20:37. SPU duration = 15 min; RDT duration = 17

17:30

Lahar

DH Hutcam

18.3

3:51

17:24

Lahar reached DRT RDT duration = 2 min

<14:57 3/24

Note long duration. Lahar reached DRT SPU duration = 20 min; RDT duration = 22 min

12:39

Lahar

Lahar reached DRT RDT duration = 30+ min

09:58 10:52

09:04

SPU duration = 22 min; RDT duration = 9 min

3/23 3/23

Swarm

SPU duration = 2 min; RDT duration = n/a SPU duration = 5 min; RDT duration = 8 min 08:33

Reanalysis

Reanalysis

66−h duration

2:14

1:50

2:22 DH

Active tephra fall from an explosion.

K.F. Bull, H. Buurman / Journal of Volcanology and Geothermal Research 259 (2013) 2–15 Table 1 (continued)

Event / feature Event 13

Time* (UTC)

3/28

3:25

Lahar (&PDC?)

3/28

Tephra

3/28

3:56

Event 14

3/28

7:20

PDC(?)

3/28

Lightning

3/28

7:27

Event 15

3/28

9:20

PDC(?)

3/28

PDC

3/28

9:27

3/28

10:00

Reanalysis

Maximum plume Swarm height (km end-time asl) (UTC)

DFR starttime (UTC)

DFR endtime (UTC)

RDE starttime (UTC)

RDE endtime (UTC)

3:36

4:03

3:28

3:41

Image type**

15.2

Observations*** SPU duration = 4 min; RDT duration = 4 min

DH 14.6

Heavy tephra fall; no change in Drift River discharge. SPU duration = 2 min; RDT duration = 2 min

--

--

7:24

7:41 DH

14.6

Lightning in image. SPU duration = 2 min; RDT duration = 2 min

--

--

9:23

9:31 DH

undet.

Lightning in image. Dilute PDC cloud down gorge; thin deposit across valley. RDT duration = 6 min

Lahar

3/28

10:07

11:10

10:12

10:36

Lahar

3/28

16:37

17:00

16:51

17:08

Event 16

3/28

21:40

Lahar

3/28

21:41

DH

Small lahar.

Lahar

3/28

21:56

DH

Small lahar.

Lahar

3/28

23:26

DH

Small lahar.

Lahar

3/28

Lahar

3/28

23:41

DH

Small lahar.

Event 17

3/28

23:29

Lahar

3/29

0:11

DH

Small, steaming lahar.

Event 18

3/29

3:23

PDC?, tephra

3/29

3:26

DH

Dilute tephra cloud to N (possible diute PDC?). No obvious flow visible.

Lahar

3/29

Lahar

3/29

3:41

DH

White steam in drainage at base of gorge; small, steaming lahar.

Lahar

3/29

3:56

DH

White steam in drainage and steamy, fresh material along small-drainange banks. Fresh material deposited too late for PDC; lahar deposit.

7:50

Swarm

3/29

Lahar

3/29

Note long duration at DFR,
5.2

SPU duration = 6 min; RDT duration = 12 min

23:40

0:37

23:33

0:47

Note long duration.

12.5

SPU duration = 9 min; RDT duration = 37+ min

14.6

SPU duration = 10 min; RDT duration = 44 min

3:35

4:45

3:45

4:58

Note long duration.

9:00

Lahar?

3/30

Reanalysis

3/30

17:44

undet.

Reanalysis

3/30

18:50

6.1

Lahar?

3/30

20:26

Reanalysis

4/1

0:07

(misc.)

4/1

Swarm

4/2

19:00

Event 19

4/4

13:58

Lahar

4/4

14:12

Reanalysis

a

Date, 2009 (month /day) (UTC)

1−h duration 20:52

21:30

21:18

21:47

--

--

8:31

8:42 RDT duration = < 1 min RDT duration = n/a DH

4.6

RDT duration = < 1 min DFR

4/4

14:16

Lahar

4/4

14:26

Lahar

4/4

Lahar

4/4

PDC, Tephra

4/4

Reanalysis

4/5

18:36

Swarm

5/2

21:00

Increase in Drift River discharge volume; likely from small lahar.

13:58 (4/4)

1st DFR webcam images (camera installed Mar 28) 43−h duration

15.2

SPU duration = 31 min; RDT duration = 75 min DH

Large lahar coincident with large eruption column in image.

DH

Dark streak in image; passing of the valley-filling lahar-? Strongest flow of eruption; almost reached the camera.

15.2

RDT duration = n/a

14:28 15:05

undet.

15:46

14:30

16:19

Note long duration. Lahar reached DRT. DFR

A PDC or lahar. Can be seen in lower right corner of DFR images. 7:05:15 start of flow is visible; at 7:06:16 steam plumes cover piedmont lobe fan. By 7:33 the steam had dissipated.

Satellite

Images after explosion show at least two PDC events; one dilute deposit as ring on edifice, second a blast to the north with dome material. Tephra-fall overlies both. SPU duration = 3 min.; RDT duration = 1.5 min

1:00 (5/8)

123−h duration

Time: of event = at seismic station SPU; of swarm = start time; and of image = time stamp on image. Image type: DH = Dumbbell Hill time-lapse; DFR = DFR station webcam; and Hutcam = Juergen's Hut webcam. c Observation abbreviations: DH = Dumbbell Hill; PDC = pyroclastic density current; DRT = Drift River Terminal; and DFR and RDE are seismic stations. b

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Explosions during the 1965–8 eruption produced pyroclastic density currents and removed almost 60 M m 3 of ice from the upper Drift glacier, which had a total glacier volume estimated to be about 1000 M m 3 (Sturm et al., 1986). Rapid melting and explosive destruction of the glacier generated lahars that inundated the Drift River valley and ran the length of the river to the coast — at times causing evacuation of survey crews preparing the site for the DRT (Brantley, 1990). Effusive activity from this eruption produced at least one lava dome that formed a prominent ridge within the crater, west of the sites of the 1989–90 and 2009 lava domes. The 1989–90 eruption began in mid-December 1989 and included 25 explosions that sent ash plumes to between 8 and 12 km asl, removed a large portion of the Drift glacier, deposited ash on surrounding communities, generated PDCs from both column-collapse and dome-collapse events, and produced lahars that in some cases flooded parts of DRT (Brantley, 1990; Dorava and Meyer, 1994; Gardner et al., 1994; Miller, 1994; Scott and McGimsey, 1994; Trabant et al., 1994). The eruption lasted four months and a total of 14 lava domes were produced, the last of which remained on the north rim of the volcano's crater (Brantley, 1990; Miller and Chouet, 1994). The final 1990 lava dome had a volume estimated to be 10 M m 3 (Miller, 1994).

signifying crustal response at those depths to magma movement, likely already ascending (Power et al., 2013). Coarse-grained clinopyroxenerich rims on low-silica andesite amphiboles erupted during early explosions are consistent with slow ascent or shallow storage of magma, or both (Coombs et al., 2013). In late January 2009, a short-lived burst of tremor was followed two days later by more sustained and energetic episodes of tremor. Together with an increase in earthquake activity below the summit, this seismicity was reflecting active magma at shallow depths (Buurman et al., 2013). In addition, major surface changes on Drift glacier indicated sufficient increase in heat flux from the volcano to cause glacial melting at a rate of 0.2 m 3 s −1 (Bleick et al., 2013). Water-rich flows began to emerge from the margins of the Drift glacier, crevasses opened and began to change shape, and melt-holes enlarged. A further increase in precursory activity occurred in late February following 20 days of sustained, low-amplitude tremor. A few hours after tremor ceased, a swarm of volcano-tectonic earthquakes began and lasted for 31 h (Table 1). During this time, the heat flux was causing glacial melting at a rate of 2.2 m3 s−1 (Bleick et al., 2013). Airborne CO2 and SO2 levels reflected high carbon-to-sulfur (C/S) values, and glacial-melt water samples, combined with the lack of H2S in the plume, indicated that scrubbing was not a large factor in removing SO2 by surface or deep-hydrothermal waters (Werner et al., 2012).

3. Chronology of the 2009 eruption 3.2. Explosive phase — March 15–April 4, 2009 In order to describe the 2009 eruption of Redoubt Volcano (hereafter referred to as “Redoubt”), we have chosen to present data that best capture Redoubt's eruptive activity in chronological order. The eruption has been divided into three “phases” of activity as outlined by Schaefer (2012): the “precursory”, “explosive” and “effusive” phases. An overview of each phase follows. Table 1 shows in chronological order the explosive events, seismic swarms, lahar signals detected at seismic stations, and observations from time-lapse images. All dates and times are Universal Coordinated Time (UTC). To convert from UTC to Alaska Standard Time, before March 8, 2009, subtract 9 h; to convert to Alaska Daylight Time, after March 8, 2009, subtract 8 h. 3.1. Precursory phase — July 2008–15 March 2009 The onset of unrest at Redoubt was gradual. Grapenthin et al. (2013) cite retrospective analysis of geodetic data that show an inflationary signal at 9–11 km in May, 2008 below the edifice, implying that ascent of magma from deep in the crust occurred prior to that time. AVO was alerted to the first indication of unrest at Redoubt in late July–early August 2008, when field geologists working on the edifice noted an H2S odor emanating from a fumarole near the ice-covered 1990 lava dome. This odor was also detected and reported in mid-September by an aircraft pilot (Schaefer, 2012). At that time AVO seismologists detected no anomalous seismicity. On September 23, local part-time residents reported explosion-like noises near the volcano that coincided with a volcanic tremor-like signal recorded on several seismic stations (Buurman et al., 2013; Power et al., 2013). As a result, AVO launched overflights to collect airborne gas emissions, make direct observations and capture photographs for time-series comparisons. Anomalous levels of H2S, SO2 and CO2 were detected (Werner et al., 2013), while observers noted an increase in the area of rock exposed around fumaroles and a 50-m-wide collapse pit that had formed in the upper Drift glacier (Bleick et al., 2013). Indications of magma moving at depth soon increased. During October and November, airborne gas measurements indicated that H2S, SO2, and CO2 remained above background levels downwind of the volcano, and observations revealed an approximate 10% increase in areas of exposed rock around fumaroles since September (Werner et al., 2013; Schaefer, 2012). In mid-December AVO recorded deep (25–35 km) long-period (DLP) earthquakes beneath the edifice,

The eruptive activity at Redoubt between March 15 and April 4, 2009 was characterized by explosions and lava-dome effusion (Fig. 2). For simplicity, this period is referred to as the “explosive phase” (Schaefer, 2012). An explosion is defined as an “Event”, and assigned a sequential number if AVO released a Volcano Activity Notification (VAN) and Volcano Observatory Notice for Aviation (VONA) in response. In most cases seismicity associated with numbered events were detected on seismic station SPU (located on Mount Spurr, ~80 km to the north). Events were defined similarly during the 1989–90 eruption of Redoubt (Power et al., 1994). Retrospective analysis by McNutt et al. (2013) identified additional events after the eruption ended, and these events (labeled as “reanalysis”) are defined using a different set of criteria (Table 1). 3.2.1. March 15–22: Event 0, phreatic explosion and extrusion of the first lava dome On March 15 an explosion at 21:05 surprised AVO scientists refueling their aircraft at DRT following a gas-measurement flight (Schaefer, 2012). They flew back to Redoubt and observed a gray plume, a hole in the glacier, and ash deposited southward from the hole for 1.5 km. The glacial hole was at the approximate location of a February melt-pit, immediately south of the 1990 lava dome (Bleick et al., 2013). The ash consisted of orange-red and oxidized particles and did not contain freshly broken pumice or scoria, indicating that the particles were non-juvenile and the ash eruption was likely initiated by a phreatic explosion (Wallace et al., 2013). Interestingly, the explosion at 21:05 did not create a signal that registered on infrasound detectors and was therefore unlikely large enough to be an ash-producing or vent-clearing event (Fee et al., 2013; McNutt et al., 2013). However, tremor followed the explosion at 21:22. The energy of the small explosion may have led to the removal of the overlying fractured ice, and the tremor reflected activity that produced the ash. AVO responded to the March 15 explosion by changing the volcano alert level from ADVISORY to WATCH and the aviation color code from YELLOW to ORANGE and increased its level of surveillance of the volcano. Gas measurements on March 20 reflect low C/S values (~ 2–3), which suggests that fresh magma was at shallow depths in the edifice (Werner et al., 2013). A seismic swarm also began on March 20 that lasted 66 h and culminated in the first large magmatic explosion of the eruptive sequence (Buurman et al., 2013). Satellite

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7

Fig. 2. Synthesis figure. Data predominantly from the explosive phase plotted as a function of time. Data from each dataset are normalized to 100% to avoid multiple values on the vertical axis. Explosive events are plotted as asterisks; the height of the event is a function of plume height (see Table 1). Line-lengths of lahar, swarm and tremor data are plotted as a function of signal duration (see Table 1). Length of dome-growth lines (blue) are plotted as a function of duration of growth from observation. Second dome is inferred.

images show that lava started effusing into the March 15 glacier hole during the final hours of the seismic swarm on March 23 (Schaefer, 2012). Prior to the first explosion, shallowly emplaced magma manifested at the surface by increased heat flux, visible as heightened glacial melting and expanded areas of exposed rock. Analysis of satellite imagery shows that by early March the melt rate had increased to 22 m 3 s − 1, and the estimated amount of ice loss between July 2008 and the first magmatic explosion on March 23, 2009, was about 35 M m 3, or 4% of the volume of the Drift glacier (Bleick et al., 2013). 3.2.2. March 23–24: Events 1–6 The first two days of activity starting on March 23 involved 9 explosions that produced tephra fall, small PDCs and multiple lahars, 2 of which reached the coast (Fig. 2; Table 1). The ash plume produced by Event 1 reached 5.5 km asl, whereas plumes reached between 13 and 18 km asl for most of the explosions up to and including Event 6 (Ekstrand et al., 2013; Schneider and Hoblitt, 2013; Wallace et al., 2013). In addition, SO2 levels detected by the Ozone Monitoring Instrument (OMI) were high (>50,000 t day−1) during this period (Fig. 2) (Lopez et al., 2013). Airborne SO2 and CO2 levels (and C/S ratios) on March 24 following Event 6 were still anomalously high (Werner, et al., 2013), and infrasound signals produced during Events 1–8 had durations >10 min and emergent onsets (Fee et al., 2013). Events 5 and 6 stand out in a number of ways. Event 5 produced the highest relative acoustic energy detected during the eruption (Fee et al., 2013) and the highest overall acoustic amplitude (McNutt et al., 2013). High-amplitude tremor occurred after both explosions (Buurman et al., 2013), and the events also produced an ice-rich lahar that filled the Drift River valley and flooded DRT near the coast (Table 1) (Alaska Department of Environmental Conservation, 2009; Schaefer, 2012; Waythomas et al., 2013). These explosions ejected the largest and most vesicular pyroclasts of the eruption — coarse, highly vesicular scoria, as well as some dense clasts — and the highest mass of any

tephra deposits of the eruption (15.1 × 109 kg, Event 6) (Wallace et al., 2013). The majority of the vesicular clasts erupted during Events 5 and 6 are crystal-rich low-silica andesites that have the most mafic compositions erupted during 2009 (~ 57.5 wt.% SiO2) (Coombs et al., 2013). Crystal-rich intermediate- and high-silica andesites (59–62.5 wt.% SiO2) were ejected early as well, but later events only produced intermediate- and high-silica andesites (Coombs et al., 2013). Major- and trace-element chemistry presented by Coombs et al. (2013) indicates that the low- and high-silica andesites are not related by fractional crystallization, but rather that the high-silica andesite formed through in-situ differentiation of earlier Redoubt intrusions. Intermediate-silica andesite samples exhibit mixed phenocryst populations and banding textures that are consistent with formation by the mixing of low-and high-silica andesites, and some variations in whole-rock trace element versus silica trends suggest multiple high-silica andesite magma sources. Results from plagioclase melt hygrometry analyses indicate all magma types were stored between 100 and 150 MPa, or 4–6 km depth (2–4.5 km below sea level) (Coombs et al., 2013). These depths roughly correspond to the shallow-end of the model presented by Grapenthin et al. (2013), which suggests evacuation of magma from a prolate spheroid body between approximately 11 and 6 km depth. Geologists were unable to sample the PDC deposits due to high risk and inaccessibility. Most PDCs flowed within a limited range (≤2 km from the vent) onto the steep upper edifice and/or into ravines carved into the upper Drift glacier. 3.2.3. March 24–26: Events 7, 8 Following a pause of roughly 60 h, Event 7 on March 26 was less energetic than earlier ones; its seismic signal lasted b1 min at station SPU and 1 min at DFR (Fig. 3), and the explosion produced a relatively low plume (6.7 km asl), very little acoustic energy, and a small lightning signal (Table 1) (Behnke et al., 2013; Fee et al., 2013). Less than 1 h later, Event 8 was significantly larger. The relative acoustic energy

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The explosions themselves were also notable during this part of the eruption. The infrasound signals from Events 10–15 had similar characteristics, including impulsive onsets, relatively short durations, and frequency content. This implies that these events had similar pressure releases, or degassing histories, and thus were likely produced by similar explosive sources (Fee et al., 2013). These explosions also produced very long period (VLP) seismic signals. Haney et al. (2013) inverted the full waveforms of VLP signals of Event 12 in the 10–33 s period band for the location and precise seismic source mechanism of this explosion. Their preferred model for Event 12 is a volumetric source acting to the southeast of the crater at an elevation of 0.4 km asl (1.9 km below the crater floor). In their model, the imaged volumetric source consists of a sill feeding into a dike. Overall during this period gas levels remained high. OMI-SO2 levels were > 13,000 t day −1 between Events 7 and 15, but dropped to 200 t SO2 per day on March 29, after Event 18 (Lopez et al., 2013). The exact timing of the drop is not known. The mass of tephra for the combined (and inseparable) deposits of Events 9–18 was ~ 13 × 10 9 kg (Wallace et al., 2013). In addition, the deposits were uniformly very fine-grained, making componentry analysis difficult and whole-rock chemical analysis inappropriate. Fig. 3. Location of instrument stations on Redoubt Volcano as of May 2009.

from Event 8 was close to 70 Pa 2 s, and the explosion resulted in a voluminous lahar that reached DRT, as well as at least one PDC (Schaefer, 2012; Buurman et al., 2013; Fee et al., 2013). The plume reached 19 km asl, the highest of the eruption. Fall deposits from Event 8 contain ~ 60 wt.% dense clasts, suggesting that a dome or conduit plug may have been destroyed during this explosion (Wallace et al., 2013). These samples, the views of lava effusion prior to Event 1 (indicating active effusion had begun early in the eruption), and the pause between Events 6 and 7 suggest that lava may have produced a second, small dome that was destroyed by Events 7 and 8. No satellite views were available during this time to confirm the dome's presence. 3.2.4. March 27–29: Events 9–18 Redoubt was quiet for just over half a day before it produced more than 10 explosions separated by b1–11 h, and numerous PDCs and lahars within a 43-hour period (Fig. 2, Table 1). A vigorous seismic swarm of repeating earthquakes preceded the first of these explosions (Event 9), lasting 8 h and representing the most energetic swarm of the eruption sequence. The earthquakes were dominated by one event family that displayed clear P- and S-wave arrivals, characteristic of volcano-tectonic (VT) earthquakes (Buurman et al., 2013). Seismicity displayed some uncommon characteristics during this part of the eruption. During the energetic seismic swarm of repeating earthquakes that preceded Event 9 the earthquakes became progressively more closely spaced in time until they merged into tremor that, in the final minutes before Event 9, glided upward in frequency (Buurman et al., 2013; Hotovec et al., 2013). This was the first of several instances of gliding tremor that occurred prior to explosions from Events 9 through 18. Hotovec et al. (2013) discuss many notable characteristics of the seismicity during this period: 1) the dominant frequency of the gliding tremor was high (up to 30 Hz; 1–5 Hz is normal); 2) the dominant frequency of the tremor shifted upward in a repeatable way for Events 12–15, indicating that whatever the source of the seismicity, it was not destroyed between explosions; and 3) there was a repeated lack of seismicity over some seconds (ranging from 15 to 240 s) immediately before the onset of most explosions between Events 9 and 18. The cause of these earthquakes is thus not yet entirely known, but is likely a shear source proximal to the conduit at a depth that could withstand and endure explosions (Hotovec et al., 2013).

3.2.5. March 29–April 4: between Events 18 and 19 Although there were no major ash-producing explosive events between March 29 and April 4, Redoubt remained active. About 4.5 h after Event 18, a 1-hour swarm of low frequency earthquakes preceded an episode of sustained, high amplitude tremor that lasted for 20 h before dropping in amplitude and continuing at low levels until the onset of the Event 19 explosion (Fig. 1, Table 1) (Buurman et al., 2013). A little over an hour after the swarm onset, fresh lava was seen in satellite images — a dome already over close to 200 m in length. By March 31 the dome had almost doubled in size, although a continuous plume during this time period made views difficult. Two days prior to Event 19, activity suddenly quieted down. On April 2, OMI detected approximately no SO2 (Lopez et al., 2013), and the lava dome grew little between April 2 and 4. The fourth seismic swarm of the eruption also began on April 2. Over 1900 lowfrequency, repeating earthquakes were recorded during the swarm, which lasted a total of 43 h and culminated in Event 19. Toward the end of the swarm, repeating high-frequency or VT-type earthquakes also began to occur. These earthquakes were located in clusters between 3 and 6 km depth, and persisted through April and May. Buurman et al. (2013) interpret these events as being related to stress adjustments around the magma storage area following magma release, and note the relatively late occurrence of this type of seismicity during the 2009 eruption compared with that during the 1989–90 eruption, where the earthquakes occurred much sooner after the onset of eruptive activity. 3.2.6. April 4: Event 19 The five-day hiatus in explosive activity between Events 18 and 19 ended with two pulses of explosions that occurred 18 min apart on April 4. A much smaller explosion on April 5th proved to be the last of the eruption (Fig. 2, Table 1). Satellite images reveal that the April 4 explosions blasted a deep, wide crater around the vent. Plumes from both pulses reached ~15 km asl (Table 1). These two pulses are also reflected in the deposits as seen by satellite imagery (Fig. 4). The earliest deposit appears to be a dilute ring of tephra around the edifice, suggesting a column-collapse or dilute PDC (“surge”) deposit. Overlying the dilute deposit is a b1–3-m-thick deposit that was emplaced on the north flank of the volcano, east and west of the upper Drift glacier. Tephrafall deposits overlie the north-directed PDC deposits, and the east and southeast flanks of the edifice as well (Fig. 4). Lahars were seen in the Dumbbell Hill time-lapse camera following each explosive pulse, the second of which was recorded on stations DFR and RDE for over an

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9

152°52'0"W 60°41'30"N

DRT LAHAR DEPOSITS

R

FT

DRI

E RIV

PDC 2 COOK

PDC 1

INLET REDOUBT VOLCANO

TEPHRA DEPOSITS

COOK INLET

0

2

4

6

8

10 Kilometers

60°13'30 "N 152°2'30"W Fig. 4. Event 19 deposits mapped onto Worldview satellite images. Green are PDC deposits (1 and 2), yellow tephra-fall deposits and purples are lahar deposits. Colors are transparent, so shades change depending on underlying image or deposits.

hour (Table 1). The combined water-rich flowage was more extensive than the previous lahars and inundated an area of approximately 105 km2, reaching the coast and flooding part of the DRT (Alaska Department of Environmental Conservation, 2009; Schaefer, 2012; Waythomas et al., 2013). The infrasound signals associated with the two pulses of Event 19 had the longest duration of any event during the eruption and, like the earliest explosions, both pulses had emergent onsets (Fee et al., 2013; McNutt et al., 2013). The second explosion pulse produced much lower frequency energy than the first pulse. Increases in airborne emissions of SO2, CO2, and also Cl were recorded (Lopez et al., 2013; Pfeffer et al., 2013; Werner et al., 2013). A number of the observations made during the explosions of Event 19 suggest that dome failure played a part in the onset of explosive activity. First, satellite images show the presence of a large dome in the crater prior to the Event 19 explosion. Second, the emergent onsets of the explosive pulses in the infrasound record suggest that the pulses began relatively slowly. The lower-frequency energy from the second pulse can be attributed to large plume oscillations that sometimes follow dome collapses (Ripepe et al., 2010; Fee et al., 2013). However, high plume heights (~ 15 km asl; Fig. 2, Table 1) and the increase in emitted airborne gas suggest that some conduit overpressure may have been involved as well. The clasts from Event 19 fall deposits and the second, northerly emplaced PDC deposit are predominantly dense andesite, reflecting degassed lava (Wallace et al., 2013). It is possible that the dense material extruded as such and formed a plug over (and/or within?) the conduit, causing a build-up of over-pressure. Any fracturing or weakness of the dome would have resulted in a vulcanian-type

explosion similar to other witnessed explosions, with plume heights at or above 15 km. 3.2.7. Explosive phase — general observations and summary 3.2.7.1. General observations. Many of the events in the explosive phase had emergent seismic and infrasound onsets, which are unusual for short-duration explosions, although similar to some Augustine 2006 events (McNutt et al., 2010; Fee et al., 2013; McNutt et al., 2013). The explosive phase produced predominantly short-duration, very high-amplitude infrasound signals recorded 4500 km away (Fee et al., 2013; McNutt et al., 2013). The local (12 km) and the distant (547 km) infrasound stations recorded similar signals and showed little loss of acoustic source features at great distances (>500 km) (Fee et al., 2013). The acoustic energy output during the explosive phase also shows a good correlation with SO2 gas emissions as measured by the OMI, a correlation that has not been previously recorded (Fee et al., 2013; Lopez et al., 2013). The 2009 Redoubt explosions also produced some of the richest volcanic lightning data ever recorded. Behnke et al. (2013) measured the sources of VHF radiation produced by lightning with a lightning mapping array. During the largest of the explosive events large volcanic lightning storms occurred akin to those associated with severe thunderstorms (Table 1). The large lightning storms took place in two separate temporal–spatial zones: at the explosion-source (i.e. the vent) and in the plumes, when the peak plume height was greater than 10 km (Behnke et al., 2013). 3.2.7.2. Summary. The explosive phase of the eruption lasted 13 days and comprised more than 19 explosive events and intermittent, if

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not continuous, lava effusion that produced two, and possibly three lava domes. The phase commenced on March 15 with a phreatic explosion followed by extrusion from upper crustal levels of crystalrich, low-, intermediate- and high-silica andesite lavas that had been stored and equilibrated at depths of 4–6 km. Low-silica andesite was only produced early in the eruption. Early events were also marked by seismic and infrasound signals that had emergent onsets. Events 9–18 displayed signals with impulsive onsets and produced tephra that was extremely fine-grained, indicating a change in the magma properties perhaps as an increase in viscosity. Lightning was associated with the majority of explosions and plumes. The explosive phase culminated in a two-pulse explosion (Event 19) that was marked by slow onset, suggesting that dome failure may have been a factor in triggering the explosion. Plumes associated with both pulses reached heights close to 15 km asl and airborne gas emissions increased, suggesting that conduit overpressure may have also contributed to the explosion. Event 19 destroyed a moderately large (~40 M m 3; Section 4.1, below), dense lava dome. 3.3. Effusive phase — April 4–July 1, 2009 Following the explosions of April 4 and 5, eruptive activity was limited to lava effusion that built the final lava dome. Satellite images revealed lava in the newly cleared vent shortly after the April 4 explosions, which was confirmed by Forward-Looking Infrared (FLIR) thermal imaging (Bull et al., 2013; Wessels et al., 2013). The small explosion of April 5 apparently had little effect on the growing dome. AVO geologists observed and monitored growth of the lava dome in near real-time by several means. Telemetered images from a fixed site recorded changes in size, location, modes of growth and surface textures of the dome (Bull et al., 2013). Dome-surface textures and thermal activity were also recorded regularly utilizing a handheld FLIR camera (Wessels et al., 2013). Diefenbach et al. (2013) utilized photogrammetry techniques on oblique aerial photographs to create digital elevation models (DEMs) and calculate dome volumes and effusion rates. Dome growth in the first month varied. In the first 12 days the dome expanded rapidly at first (35 m 3 s −1), extruding blocky lava into the newly enlarged crater (Bull et al., 2013; Diefenbach et al., 2013). Between April 16 and May 4 the extrusion rate slowed to an average of 4 m 3 s−1 (Diefenbach et al., 2013), and expansion was by means of lava intrusion into the dome interior. As the dome grew, the expansion caused the confining surface-crust to crack, and the cracks subsequently became annealed by the newly intruded magma, thereby enlarging the dome (Bull et al., 2013). Starting in the first few days of May, several changes occurred at the dome. A swarm of repeating, low frequency earthquakes occurred on May 2–8, lasting 123 h (Buurman et al., 2013). This swarm was the longest-lived of all the seismic swarms recorded during the 2009 eruption, and it also exhibited the highest rate of hourly events. Unlike previous swarms, this swarm did not precede an explosion. Ketner and Power (2013) note a change in seismicity (earthquake rates and characteristics) beginning on May 6 immediately following a series of rockfall signals originating from the dome. The earthquakes transition from a slower and more regular rate to a higher and irregular rate following the rock fall. Airborne and satellite-detected gas emissions in early May continued to be high, and included chlorine gas (Lopez et al., 2013; Pfeffer et al., 2013; Werner, et al. 2013). On May 4, the webcam at Juergen's Hut, 11 km north of the volcano (commonly referred to as the “hutcam”; Fig. 3), relayed the first good views of the entire dome since April 30. These views revealed a change in lava texture on the top of the dome, from blocky lava facies to more rubbley (“upper”) lava facies comprising smaller blocks (Bull et al., 2013). By June 9 the surface area of the newer, upper lava facies higher on the dome had increased to 36% of the

total dome-surface area (Bull et al., 2013; Diefenbach et al., 2013). FLIR images from that time show elevated heat at the dome apex, hot, radial fractures, and encroachment of cooler material over the surface of the dome (Wessels et al., 2013). The dome was therefore enlarging by means of exogenous (extrusive) growth synchronous with expansion by lava injection beneath the fracturing and annealing surface crust (Bull et al., 2013). Lava samples collected from the dome in August 2010 indicate that the upper facies lava was more vesicular (55–66%) than the blocky facies (32–44%) compositionally distinct from the earlier, blocky lava (lower P2O5, lower light rare earth elements), and that the vesicles had coalesced, likely enabling easy passage of gases through the effusing lava (Bull et al., 2013; Coombs et al., 2013). The end of the eruption was defined based on dome volume changes and geophysical monitoring parameters. Calculations of the dome volume made by Diefenbach et al. (2013) suggest that growth of the dome, and therefore lava effusion, had ceased by July 1. The dome deflated a small amount by August 20, but continued to show warmer areas in thermal and nighttime images in the months following the cessation of growth (Diefenbach et al., 2013; Wessels et al., 2013). The seismicity had approached background levels in July, so the eruption was considered to have ended on July 1. 4. Erupted volumes Erupted volume estimates are useful for comparison between eruptions and for use in calculations such as estimates of magma storage volumes (e.g. erupted versus unerupted magma) and amounts or proportions of exsolved gases. Ideally, numerous and evenly distributed samples from each flow and fall deposit produced from each event would provide us an estimate of the total volume of juvenile magma erupted. That value should roughly equal the total of dome plus fall deposit volumes (i.e., extruded plus conduit-sourced material). However, thorough sampling was prevented by a number of factors, such as inaccessible terrain (steep and crevassed edifice and/or deposition into the upper Drift glacier ravines carved by hot PDCs and lahars), hazardous conditions such as explosions and ash fall near the volcano, poor weather, and in some cases the inability to differentiate the various explosive events in the deposits. Nonetheless, we have data from extensive sampling of tephra-fall deposits and two methods used to estimate the volumes of the early domes (the final-dome volume is from Diefenbach et al., 2013). In combination, these likely represent the bulk of the erupted volume and provide the most accurate minimum and maximum eruptive volumes. All estimates are presented in Tables 2–5. 4.1. Dome volumes (Table 2) We present the volumes of the early domes using two methods (Table 2). In method 1 we compare the areal dimensions of the two observed early domes (the dome that grew on March 22 and the one that began growing on March 28; areal dimensions of the possible March 24 dome are unknown) to the volume of the final April 4 dome when it had roughly the same areal dimensions. The final-dome volume was derived from photogrammetry techniques (Diefenbach et al., 2013). In method 1 we assume that domes of similar areal dimensions have similar heights. We derive a proportion factor for the known dimensions of the March 22 dome and the March 28 dome and apply that to the volume of the final (April 4) dome derived from photogrammetry (Diefenbach et al., 2013). The March 22 dome was roughly 0.18 of the volume of the final dome on April 16, and the March 28 dome was 0.84 of the volume of the final dome on May 8 (Table 2). Method 2, from Diefenbach et al. (2013), utilizes the best-known duration of effusion of each dome and multiplies that by the average extrusion rate of the April 4 dome over the 88 days of its growth (9.5 m3 s −1). The volumes using these two methods result in approximately one order of magnitude larger volume using method 1. The difference is a result of

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Table 2 Dome volumes. Domes

Method 1 (this study)

Method 2 (from Diefenbach et al., 2013)

Start date, 2009 (UTC)

End date, 2009 (UTC)

Feature name

Areal dimensions

Fraction of final dome

Inflated dome volume (m3)

Erupted volume Duration Effusion Inflated eruptive (DRE) (m3) (s) rate (m3/s) volume (m3)

Erupted volume (DRE) (m3)

Mar 22

Mar 22

115 m × 75 m

0.18

6.5E ^ 06

4.9E ^ 06

5.2E ^04

9.5

4.9E ^05

3.7E ^ 05

Mar 28

Apr 4

700 m × 330 m

0.84

3.9E ^ 07

3.6E ^ 07

5.2E ^05

9.5

4.9E ^06

4.4E ^ 06

Apr 4

Jul 7

Mar 22 dome Mar 28 dome Apr 4 dome

(n/a)

5.4E ^ 07 9.4E ^ 07

n/a 9.5

7.2E ^07 7.7E ^07

5.4E ^ 07 5.9E ^ 07

Mar 24 dome

(Estimated from final dome; see text)

7.2E ^ 07 Total vol. 3 domes Total vol. 4 domes

1.5E ^ 06 9.6E ^ 07

2.2E ^05

9.5

2.1E ^06

1.5E ^ 06 6.0E ^ 07

Mar 24

Mar 26

Table 3 Pyroclastic density current deposit volumes. Date, 2009 (UTC)

Feature and/or event (E)

Deposit area (m2)

Deposit thickness estimate (m)

Inflated eruptive volume (m3)

Erupted volume (DRE; m3)

Apr 4 Apr 4

E19 PDC 1 E19 PDC 2

3.5E ^07 2.4E ^07

1.0E ^ 02 5.0E ^ 01 Total

3.5E ^ 05 1.2E ^ 07 1.2E ^ 07

2.4E ^ 05 8.3E ^ 06 8.3E ^ 06

the high extrusion rate between April 4 and 16 for the final dome. Our first view of that dome was on April 16, by which time the volume was 36 M m 3 (and the areal dimensions were 600 m × 420 m), which indicates an extrusion rate over those 12 days of 35 m 3 s−1, a considerably faster extrusion rate than the overall average of 9.5 m3 s−1 (Diefenbach et al., 2013). In order to convert bulk volume to dense-rock equivalent (DRE), we used a conversion factor of 0.75 for all domes except the March 28 dome, for which we used 0.90 (Table 2). Vesicularity was high to extremely high (32–66%) for carapace samples from the final dome (see Bull et al., 2013), but interior-dome vesicularities are likely lower. Average vesicularities for other similar domes range from 20 to 30% (e.g. Soufriere Hills — Calder et al., 2002), so using an average value of 25% (or 0.75 conversion factor) is reasonable. Data show that the March 28 dome destroyed in Event 19, however, was likely more dense. For example, virtually all juvenile clasts from Event 19 deposits, tephra fall, PDC and lahar, were dense (≤10% vesicularity) and less than ~ 5% of the clasts were scoria (Coombs et al., 2013; Wallace et al., 2013). As a result, for the March 28 dome we used 0.90 as the conversion factor from bulk volume to DRE volume (Table 2). 4.2. PDC volumes (Table 3) In contrast to the 1989–90 eruption, PDCs produced during the 2009 eruption were generally small and inaccessible for sampling. Other potentially more accessible PDC deposits may have been quickly covered by tephra fall or snow. The exceptions were the two PDC deposits produced during Event 19 on April 4, which we were able to sample (see

Coombs et al., 2013; Wallace et al., 2013) and map (Fig. 4). The bulk volume of the two PDC deposits were calculated by multiplying the area, derived from GIS-mapping, by the estimated average thickness derived from sampling and field-observations (Table 3). In order to convert bulk to DRE PDC-volumes we used the density conversion factor of 0.70 used by Gardner et al. (1994) for 1989–90 deposits. That value is appropriate to use for the 2009 PDC deposits given the similar composition of the lavas and the large proportion of block-and-ash flow deposits composed of relatively dense dome material in the PDC deposits from the 1989–90 eruption. Despite the high density (≤ 10% vesicularity) of the vast majority of the clasts in the 2009 deposits, the high percentage of fines increases the proportion of void space between grains, and thus we assume would decrease the density conversion factor from 0.90 to approximately 0.70. 4.3. Fall deposits (Table 4) Wallace et al. (2013) calculated the mass of tephra-fall deposits using the root-area method of Pyle (1989), modified by Fierstein and Nathenson (1992). Their bulk volume calculations are based on an assumed bulk density of ash =1000 kg m −3, and the DRE volume is based on a density of 2653 kg m −3, the average of calculated densities of 2009 lithologies (Coombs et al., 2013). 4.4. Lahar deposits The difficulty in estimating the volumes of the flows, the fraction of solids in the flows and the fraction of those solids that are juvenile Table 5 Total erupted volumes — summary (see text).

Table 4 Fall deposit volumes. Data from Wallace et al. (2013). Event start date, 2009 (UTC)

Event end date, 2009 (UTC)

Event (E)

Inflated eruptive volume (m3)

Erupted volume (DRE) (m3)

Mar 23 Mar 23 Mar 24 Mar 26 Mar 27 Apr 4

Mar 23 Mar 23 Mar 24 Mar 26 Mar 29 Apr 4

E2–4 E5 E6 E7–8 E9–18 E19 Total

9.6E ^ 06 4.4E ^ 06 1.5E ^ 07 4.6E ^ 06 1.3E ^ 07 7.8E ^ 06 5.5E ^ 07

3.6E ^ 06 1.7E ^ 06 5.7E ^ 06 1.7E ^ 06 5.0E ^ 06 3.0E ^ 06 2.1E ^ 07

To establish if Event 19 PDC + fall deposits volumes = destroyed dome volume (see text for discussion)

Minimum Maximum estimate estimate (m3) (m3)

Event 19 (Apr 4) fall + PDC deposits (i.e. March 28 dome + any conduit material) March 28 dome vol. (destroyed in Event 19)

2.0E ^07

Resulting final volume estimates Total erupted DRE vol. est. (Mar 22, Mar 28 and Apr 4 domes + fall deposits) Total erupted DRE vol. est. (Mar 22, Mar 24, Mar 28 and Apr 4 domes + fall deposits):

4.4E ^06

3.6E ^ 07

7.9E ^07

1.2E ^ 08

8.1E ^07

1.2E ^ 08

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material from the available data, resulted in too large a range of possible values for inclusion in volume calculations. 4.5. Total eruptive volume (Table 5) Ideally the total erupted volume equals the lava effused plus the juvenile lava ejected explosively from the conduit. PDC and lahar deposits are likely included in those values. The large uncertainty in the estimated juvenile-rock component of the lahar volume, and the lack of available data make this a difficult factor to utilize in total volume calculations. In fact, we can reasonably assume that the majority of erupted juvenile components may be accounted for in dome, fall and PDC volumes. If we assume that the March 28 dome destroyed in Event 19 was deposited in the PDCs on April 4, and there was minimal contribution of conduit-sourced magma, then the fall plus the PDC deposit should roughly equal the dome volume. From the above calculations, the minimum dome-volume estimate is about one third of the PDC + fall volume, but the maximum dome volume is about twice the PDC + fall volume. Overall, this range in values suggests that the volume of the combined PDC and fall deposits are roughly equal to the dome volume. The difference between the two estimates suggests that either method 2 for calculating the (minimum) dome volume (Table 2) underestimated the average effusion rate for growth of that dome, or that method 1 either over-estimated the size of the dome in comparison to the final dome, and/or a somewhat significant fraction of the dome material was incorporated into the April 4 lahar and is thus unaccounted for (Table 2). In sum, considering minimum and maximum values for both three and four domes, the total DRE eruptive volume ranges from 79 to 120 M m 3 (0.08–0.12 km3) for three domes and 81–120 M m 3 (0.08–0.12 km3) for four domes (Table 5). The estimate for the 1989–90 total eruptive volume was 150–250 M m 3 (0.15–0.25 km3) (Gardner et al., 1994). 5. Comparison of 2009 and 1989–90 eruptions of Redoubt Volcano Monitoring a volcanic eruption and preparing the public for impending hazards are greatly facilitated when the activity mimics a prior eruption. AVO thus looks for any patterns of repeated behavior during and between eruptions of a volcano. The similarities and differences between the 2009 and 1989–90 eruptions of Redoubt Volcano are discussed in several papers in this issue. For example, a comparison of the two eruptions in terms of seismic observations is presented in detail by Power et al. (2013), petrologic comparisons are made by Coombs et al. (2013), and comparisons with respect to dome growth are made by Diefenbach et al. (2013). Table 3 is a summary comparison of numerous aspects of the two eruptions. Similarities are striking in a number of ways: the large extent, high ice content and destructive force of the lahars; the eruption style of cyclical effusion and destruction of multiple lava domes throughout the eruption; the occurrence of seismic swarms prior to explosions; and the fine-grained nature of many of the tephra-fall deposits likely caused by magma interaction with glacial meltwater (Wallace et al., 2013). In addition, comparable petrologic characteristics include whole-rock compositions (with the exception of the more mafic 2009 low-silica andesite), phase assemblages, phase compositions, the phenocryst-rich nature of the lavas, and the production of lower silica andesite lavas early in each eruption unrelated to the higher silica andesite through fractional crystallization (Coombs et al., 2013). The two eruptions also shared high production of SO2 and similar rates of SO2 decay (Werner et al., 2012, 2013). Analogous eruption mechanisms have been suggested for the 1989 and 2009 Redoubt eruptions as well. Injection of a relatively mafic magma into a more evolved body stored at shallow levels as an eruption-trigger were evoked for Redoubt in 2009 (see above) and 1989, and similarly for nearby Augustine Volcano in 1986

(Wolf and Eichelberger, 1997; Browne and Gardner, 2006; Larsen et al., 2010; Coombs et al., 2013). In addition, seismic models from both Redoubt eruptions suggest shallow magma storage ~ 3–6 km below the volcano (~ 1–3 km bsl) and movement to even higher levels immediately prior to eruption (DeShon et al., 2007; Haney et al., 2013; Power et al., 2013; Coombs et al., 2013). The differences between the 1989–90 and 2009 eruptions are perhaps more pronounced than their similarities, especially when considering the hope or expectation that the volcano will repeat a similar pattern of activity. The precursory phase was particularly different in 2009, both seismically and in terms of the disruption of the Drift glacier. The increase in detected seismicity is partially explained by improved technology, but Power et al. (2013) provide evidence that deep LP events and shallow volcanic tremor months prior to the first explosion marked the lead up to the 2009 eruption in contrast to 23 h of precursory seismicity in 1989. In 1989 no depressions or surface-change in the Drift glacier were observed prior to the eruption, whereas increased meltwater runoff and the expansion and initiation of crevasses for months leading up to the 2009 eruption were observed in over-flights and satellite imagery (Bleick et al., 2013). Explosions during the 1989–90 eruption did not destroy the entire crater-portion of the Drift glacier, but did completely remove the upper glacier from below the crater (Brantley, 1990). In contrast, in 2009 explosions pulverized most of the crater-glacier, but left portions of ice intact between the crater and piedmont lobe. In 1989–90, the slightly more northerly vent placement and the remaining crater ice forced a larger portion of the lava to extrude onto the steep north slope, possibly facilitating the higher number of dome failures during the 1989–90 eruption. Stability of the final dome in 2009 may be due to the complete emptying (and fracturing?) of the conduit complex by means of the powerful explosions during the explosive phase, aided by the high percentage and coalesced texture of the vesicles in the lava that allowed gases to pass through the effusing dome, and by the large crater (~ 700 m diameter) formed by the prior explosions (Bull et al., 2013). In terms of overall eruption volumes, the 2009 eruption produced approximately half the volume of the 1989–90 eruption in slightly more than half the time. Perhaps the most important contrast in the 20 years between Redoubt's most recent active episodes is the improvement in monitoring and the number of data streams that have increased our ability to monitor the activity in myriad ways. Broadband seismometers are sensitive to a much wider range of frequencies in addition to having a much larger dynamic range, which allows the seismicity to be recorded on scale. Improvements in satellite imagery quality and frequency have substantially increased remote observation and monitoring capabilities. Additional datasets utilized during 2009 include infrasound detection, lightning detection, webcam imagery, FLIR imagery, nighttime (low-light) imagery, geodetic data, plume halogen chemistry and satellite-detected SO2 gas emissions (OMI). 6. Summary and conclusions The richness of data including seismic, geodetic, gas, satellite, FLIR, geochemical, visual, deposit-mapping and physical samples of erupted products obtained during the 2009 eruption of Redoubt combines to provide a comprehensive view of the geologic processes involved in the eruption. Inaccessibility of the most proximal areas around the volcano resulted in some limitations in our ability to collect and describe all PDC and tephra fall deposits. Nonetheless, we can summarize the data presented above and draw several conclusions. The eruption was likely driven by intrusion and ascent of low-silica andesite at or near the base of the crust, beginning as early as May 2008. In mid-December the lower crust (~25 km) was adjusting to the departure of the magma, which had ascended slowly and aseismically into the upper crust (9–11 km) and encountered and mixed with bodies of

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stalled, differentiating older intrusions in the form of high-silica andesite. In late January, magma was active high in the crust (~4–6 km) producing a sudden onslaught of tremor and VT earthquakes. The rising magma, in the form of propagating dikes or stocks, soon reached higher levels (~1–3 km). Low- and high-silica andesites, along with their mixed products of intermediate-silica andesites, reached the surface and began to effuse less than a day before the first magmatic explosion on March 23. High heat flux during the precursory phase caused a noticeable fraction of the Drift glacier to melt. The explosive phase began on March 23 and lasted for 13 days. This phase was characterized by more than 19 explosions, several seismic swarms and intermittent to continuous lava effusion. The effusion produced at least two and possibly three lava domes, all of which were destroyed in explosions. All explosions were likely triggered by conduit over-pressures rather than dome failures, although Event 19 may have been an exception. Early Events (5 and 6) produced low-silica andesite in addition to intermediate- to high-silica andesite. Intermediateto high-silica andesite was exclusively erupted after Event 8. The character of eruptive activity changed after Event 9. Examples include the repeatable episodes of gliding tremor which preceded many of the explosions, the nature of infrasound signals (impulsive rather than emergent onsets), and the shorter durations of the explosions. The OMI-SO2 levels were also quite high after Event 9, COSPEC-SO2 values were high, and the tephra mass was not only high, but the deposits were remarkably fine-grained. Such factors are suggestive of a change in the character of the erupting magma or magmatic conditions (i.e. a viscosity increase), and perhaps reflect an increase in the gas overpressure caused by a higher influx of magma into the storage area. The period between Events 18 and 19 was a hiatus in explosive activity, but active lava effusion was taking place and two seismic swarms were recorded during this time. The effusion produced the last of the lava domes emplaced during the explosive phase of the eruption, and this dome consisted almost exclusively of dense, degassed magma. High gas emission values, the plume heights of both explosion pulses of Event 19, and volume estimates suggest that dome failure triggered the event, but that conduit overpressure below a dense dome (and conduit obstruction?) contributed to the magnitude of the explosion. The effusive phase commenced shortly after Event 19 on April 4, when lava effusion initiated growth of the final lava dome. Effusion was continuous through June, ceasing by July 1, 2009. A month after the dome-growth started, data indicate a change in the eruptive behavior, characterized by extrusion from the dome's apex of a more highly vesicular lava and one characterized by less P2O5, and a long-lasting swarm of repeating earthquakes. An influx of a separate, also evolved (intermediate- to high-silica andesite) magma into the effusing system could account for the changes. The final lava dome proved to be very

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stable and grew to a volume of 72 M m 3, almost ten times that of the last 1990 dome. Stability of the dome is likely due to the complete evacuation of the conduit complex, high vesicularity and high permeability in the lava, and the large crater (~700 m diameter) formed by the prior explosions. We estimate the total DRE volume of eruptive products at Redoubt in 2009 to be ~79–120 M m3. The magmatic eruption lasted from March 22 to approximately July 1, or roughly 3.5 months. The 1989–90 eruption lasted 5 months and produced an estimated DRE volume of 150–250 Mm 3. In sum, the 2009 eruption of Redoubt Volcano disrupted air traffic and petroleum production in Cook Inlet which proved costly to the state and private industries, and ashfall caused damage and inconvenienced communities. However, updated and innovative monitoring techniques and improved interagency communication prevented human tragedy and minimized damage to infrastructure. A multiplicity of new and/or improved methods to monitor and examine the volcano in real-time, near real-time and using retrospective analysis have also provided invaluable information about the mechanisms of arc eruptions. Papers in this special issue suggest that the activation of the 2009 and the 1989–90 eruptions occurred due to a low-silica andesite magma rising aseismically from close to the lower crust, and that the rising magma encountered and mixed with differentiating andesite bodies that had been stored for months to years at shallow crustal levels. Such revelations contribute significantly to our understanding of the complex underpinnings of arc volcanoes and their eruption triggers. Additional research presented herein has also opened up new avenues of research with respect to the quantity and timing of energy released during eruptions, as well as infrasound, lightning, geodesy and plume dynamics. The recently developed technique of detecting SO2 gas via satellite technology, and the novel research tracing rapid halogen-mediated chemical evolution of volcanic emissions (Kelly et al., 2013) reveal new perspectives on magmatic activity via plume chemistry. With increasing research, more of these data may prove to be real-time eruption predictors, and thus increasingly beneficial to the public at large.

Acknowledgments This work represents the combined efforts of AVO staff, in addition to contributors from other observatories and institutions. In particular we offer thanks to T. Lopez, D. Fee, J. Power, and J. Larsen at AVO for helpful and insightful discussions. Reviews of early drafts by J. Schaefer and W. Scott greatly improved the paper. We thank C. Bacon and B. Chouet for careful and constructive reviews of the manuscript.

Appendix 1. Comparison of 1989–90 and 2009 eruptions of Redoubt Volcano (modified after McGimsey et al., 2009)

Feature

1989–90

Precursory Few direct observations made in months leading to the eruption (no field work activity and few pilot observations), no gas measurements were taken; GPS instrumentation and telemetry was not yet available; b1 month prior (Nov): increased fumarolic activity; b1 day prior (Dec): 23-hour swarm of repetitive, shallow long-period seismic events centered 1.4 km below the vent; no depressions or changes in Drift glacier observed prior to eruption.

Eruption style

Deposits

At least 20 explosive events over 5 months; initial gas-rich, vent‐clearing explosions followed by cyclical lava dome effusion and explosions; produced 14 domes, 13 of which were destroyed; approximately 9 of the explosions were initiated by dome failure; total eruption = 6 months. Initial gas-rich explosions produced ice-and snow-rich PDC and lahar deposits; later explosions resulted from dome‐failure and produced PDC deposits rich in dense dome clasts.

2009 8–9 months prior (May, Jun): inflation commenced >25 km depth; increased fumarolic activity; Drift glacier ice-melt rate 0.2 m3/s; 5 months prior (Oct): increased fumarolic activity; elevated CO2, SO2 gas; 3 months prior (Dec): deep, long-period seismic events 25–38 km depth bsl; 2 months prior (Jan): shallow volcanic tremor (DRS 3 cm2) episodes lasting up to 36 h; changes observed in Drift glacier surface; 1 month prior (Feb): sustained, low-amplitude seismic tremor; 66-h seismic swarm immediately prior to 1st explosion; Drift glacier melt rate 2.2 m3/s, to 4 m3/s immediately prior to first explosion; high C/S gas values. More than 23 (19 labeled) explosive events over 2 months; at least 3 and possibly 4 domes emplaced during the eruption; all but the final dome were destroyed in explosions; final explosion (Event 19) possibly initiated by dome failure; total eruption = 3.5 months. Initial gas-rich explosions produced widespread tephra-fall, but minor PDC deposits; final explosion produced largest PCD rich in dense dome clasts. (continued on next page)

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Appendix 1 (continued) Feature

1989–90

2009

Multiple lahars into upper Drift River valley; 3 major lahars flowed the length of the Drift River from the edifice to coast; flows caused channel-changes in the Drift River, which contributed to flooding of the DRT; source both precursory meltwater and pulverized (+/–melted) glacier ice. Drift Disruption and melting of 35 M m3 of glacier during precursory phase observed; glacier eventual removal of nearly entire crater-ice via melting and explosions (vent slightly south of 1989–90 vent); partial removal of Drift glacier between the crater and the piedmont lobe. Low-silica (b58 wt.% SiO2) andesite (LSA) produced early in eruption, unrelated Petrology to intermediate-or high‐silica (59–62.5 wt.% SiO2) andesite (ISA, HSA); ISA, HSA erupted throughout eruption; andesites crystal-rich; variable degrees of heating by an unerupted magma; late lava in final dome (May 1–July 1) low in P2O5, likely different, cooler magma; magma storage of all andesites at 100–150 MPa (6–9 km depth below the vent); ISA likely hybrid of HSA and either 2009 or similar LSA. Seismic network comprised 7 short-period and 6 broad band instruments at Seismicity Seismic network comprised 5 short-period instruments at eruption onset; shallow VT and hybrid earthquakes separated early episodes of dome growth; eruption onset; 6 seismic swarms identified during the unrest, 5/6 swarms were 13 swarms of LP events at shallow depths preceded many explosions; a persis- dominated by repeating earthquakes; 3 explosions were preceded by seismic swarms; hypocenters scattered between 0–8 km depth; gliding tremor tent cluster of VT earthquakes at 6–9 km depth. observed. Gas Incomplete record for early eruption; total SO2 released 0.9 M t, ~20% of which High C/S during precursory phase; high CO2 gas levels b1 month prior to 1st was released during explosion on 12/15/'89; gradual decay in SO2 through and explosion (>9000 t/d); total SO2 released ~1.3 M t; max SO2 > 14,000 t/d post eruption. during final dome growth; overall gradual decay in SO2 similar to 1989–90 curve. Early explosions (Events 5 and 6) produced large scoria, otherwise predominantly Tephra fall Early phreatomagmatic explosions produced large volumes of fine-grained fine-grained; abundant accretionary lapilli; distribution primarily N, E, SE. scoria; later events related to dome failure predominantly fine-grained PDC elutriate; abundant accretionary lapilli; deposit distribution primarily N, NE, E. Lava 14 lava domes produced over 6 months (December–April), final dome remained 3 (4?) lava domes (possible dome of March 24 was not observed) over domes until 2009 eruption; predominantly blocky facies; confined by ice and bedrock 3.5 months; final dome still in place; blocky lava changed 1 month into final on 3 sides; effusion rate progressively slowed, ranging 26–2.1 m3/s, ave rate dome growth to finer, >vesicular facies; vesicularity estimate b30% for blocky facies, 50–65% for vesicular facies; effusion rate for final dome 2–35 m3/s, 5.8 m3/s; final dome bulk (inflated) volume 10 M m3; total erupted bulk volume of all domes 88 M m3. average 9.5 m3/s; final dome bulk volume 72 M m3; total est. bulk (inflated) volume for 3 domes 77–118 M m3, for 4 domes 79–96 M m3. Volumes Est. total DRE volume for the eruption: 150–250 M m3 Est. total DRE volume for the eruption: 79–120 M m3 Lahars

Multiple lahars into upper Drift River valley; 3 largest flows reached the coast; flows caused channel-changes in the Drift River, which contributed to flooding of the DRT; source pulverized (+/–melted) glacier ice and not precursory meltwater. No disruption of glacier during precursory phase observed; 113–121 M m3 ice and snow mechanically entrained in avalanches, lahars and PDCs; partial removal of crater-ice during eruption; entire Drift glacier between crater and piedmont lobe was removed. Eruption produced crystal-rich andesite and dacite (58.2–63.4 wt.% SiO2); earliest scoria comprised lowest silica andesite (b59 wt.% SiO2); earliest lava domes comprised highest silica andesite (>63 wt.% SiO2); early low-silica andesite not related to higher-silica andesites by fractional crystallization; abundant evidence for magma mixing; seismic data suggest magma storage 6–10 km below the vent.

Data sources: Bleick et al. (2013), Bull et al. (2013), Buurman et al. (2013), Coombs et al. (2013), Diefenbach et al. (2013), Dorava and Meyer (1994), Gardner et al. (1994), Hotovec et al. (2013), Miller (1994), Miller and Chouet (1994), Nye et al. (1994), Power et al. (1994), Power et al. (2013), Scott and McGimsey (1994), Swanson et al. (1994), Trabant et al. (1994), Werner et al. (in review), Werner et al. (2013).

References Alaska Department of Environmental Conservation, 2009. Unified command: Drift River Terminal Coordination Situation Reports. http://www.dec.state.ak.us/spar/ perp/response/sum_fy09/090324201/090324201_index.htm. Bacon, C.R., Vazquez, J.A., Wooden, J.L., 2012. Paleozoic and Paleoproterozoic zircon in plutonic xenoliths assimilated at Redoubt Volcano, Alaska. Geological Society of America Bulletin 124 (1–2), 24–34, http://dx.doi.org/10.1130/B30439.1. Beget, J.E., Montanaro, C., Trainor, T., Bull, K., 2009. Large scale edifice collapse at Redoubt Volcano, Alaska. EOS. Transactions of the American Geophysical Union 90 (52) (Fall Meet. Suppl., Abstract V43A-2223). Beget, J.E., Nye, C.J., 1994. Postglacial eruption history of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 62, 31–54. Behnke, S.A., Thomas, R.J., McNutt, S.R., Schneider, D.J., Krehbiel, P.R., Rison, W., Edens, H.E., 2013. Observations of volcanic lightning during the 2009 eruption of Redoubt Volcano. Journal of Volcanology and Geothermal Research 259, 214–234. Bleick, H.A., Coombs, M.L., Cervelli, P.F., Bull, K.F., Wessels, R.L., 2013. Volcano–ice interactions precursory to the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 373–388. The eruption of Redoubt Volcano, Alaska, December 14, 1989–August 31, 1990. In: Brantley, S.R. (Ed.), U.S. Geol. Surv. Circ., 1061. 33 pp. Browne, B.L., Gardner, J.E., 2006. The influence of magma ascent path on the texture, mineralogy, and formation of hornblende reaction rims. Earth and Planetary Science Letters 246, 161–176. Bull, K.F., Anderson, S.W., Diefenbach, A.K., Wessels, R.L., Henton, S.M., 2013. Emplacement of the final lava dome of the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 334–348. Buurman, H., West, M.E., Thompson, G., 2013. The Seismicity of the 2009 Redoubt eruption. Journal of Volcanology and Geothermal Research 259, 16–30. Calder, E.S., Luckett, R., Sparks, R.S.J., Voight, B., 2002. Mechanisms of lava dome stability and generation of rockfalls and pyroclastic flows at Soufrière Hills Volcano, Montserrat. In: Druitt, T.H., Kokelaar, B.P. (Eds.), The Eruption of Soufrière Hills Volcano, Montserrat, from 1995 to 1999: Geological Society Memoir, 21, pp. 173–190. Coombs, M.L., Sisson, T.W., Bleick, H.A., Henton, S.M., Nye, C.J., Payne, A.L., Cameron, C.E., Larsen, J.F., Wallace, K.L., Bull, K.F., 2013. Andesites of the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 349–372. DeShon, H.R., Thurber, C.H., Rowe, C., 2007. High-precision earthquake location and three-dimensional P wave velocity determination at Redoubt Volcano, Alaska.

Journal of Geophysical Research 112 (B07312), http://dx.doi.org/10.1029/ 2006JB004751. 24 pp. Diefenbach, A.K., Bull, K.F., Wessels, R.L., McGimsey, R.G., 2013. Photogrammetric monitoring of lava dome growth during the 2009 eruption of Redoubt Volcano. Journal of Volcanology and Geothermal Research 259, 308–316. Dorava, J.M., Meyer, D.F., 1994. Hydrologic hazards in the lower Drift River basin associated with the 1989–1990 eruptions of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 62, 387–407. Ekstrand, A.L., Webley, P.W., Garay, M.J., Dehn, J., Prakash, A., Nelson, D.L., Dean, K.G., Steensen, T., 2013. A multi-sensor plume height analysis of the 2009 Redoubt eruption. Journal of Volcanology and Geothermal Research 259, 170–184. Fee, D., McNutt, S.R., Lopez, T.M., Arnoult, K.M., Szuberla, C.A.L., Olson, J.V., 2013. Combining local and remote infrasound recordings from the 2009 Redoubt Volcano eruption. Journal of Volcanology and Geothermal Research 259, 100–114. Fierstein, J., Nathenson, M., 1992. Another look at calculation of fallout tephra volumes. Bulletin of Volcanology 54, 156–167. Gardner, C.A., Neal, C.A., Waitt, R.B., Janda, R.J., 1994. Proximal pyroclastic flow deposits from the 1989–1990 eruption of Redoubt Volcano, Alaska — stratigraphy, distribution, and physical characteristics. Journal of Volcanology and Geothermal Research 62, 213–250. Grapenthin, R., Freymueller, J.T., Kaufman, A.M., 2013. Geodetic observations during the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 115–132. Haney, M.M., Chouet, B.A., Dawson, P.B., Power, J.A., 2013. Source characterization for an explosion during the 2009 eruption of Redoubt Volcano from verylong-period seismic waves. Journal of Volcanology and Geothermal Research 259, 77–88. Hotovec, A.J., Prejean, S.G., Vidale, J.E., Gomberg, J., 2013. Strongly gliding harmonic tremor during the 2009 eruption of Redoubt Volcano. Journal of Volcanology and Geothermal Research 259, 89–99. Kelly, P.J., Kern, C., Roberts, T.J., Lopez, T., Werner, C., Aiuppa, A., 2013. Rapid chemical evolution of tropospheric volcanic emissions from Redoubt Volcano, Alaska, based on observations of ozone and halogen-containing gases. Journal of Volcanology and Geothermal Research 259, 317–333. Ketner, D.M., Power, J.A., 2013. Characterization of seismic events during the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 45–62. Larsen, J.F., Nye, C.J., Coombs, M.L., Tilman, M., Izbekov, P., Cameron, C., 2010. Petrology and geochemistry of the 2006 eruption of Augustine Volcano. In: Power, J.A.,

K.F. Bull, H. Buurman / Journal of Volcanology and Geothermal Research 259 (2013) 2–15 Coombs, M.L., Freymueller, J.T. (Eds.), The 2006 Eruption of Augustine Volcano, Alaska: U.S. Geol. Surv. Prof. Paper, 1769, pp. 335–382. Lopez, T., Carn, S., Werner, C., Fee, D., Kelly, P., Doukas, M., Pfeffer, M., Webley, P., Cahill, C., Schneider, D., 2013. Evaluation of Redoubt Volcano's sulfur dioxide emissions by the Ozone Monitoring Instrument. Journal of Volcanology and Geothermal Research 259, 290–307. McGimsey, R.G., Neal, C.A., Miller, T.P., Power, J.A., Wallace, K.L., Diefenbach, A.K., Larsen, J.F., Waythomas, C.F., 2009. Comparing and contrasting the 2009 and 1989–90 eruptions of Redoubt Volcano. Alaska. EOS. Transactions of the AmericanGeophysical Union 90 (52) (Fall Meet. Suppl., Abstract V43A-2219). McNutt, S.R., Tytgat, G., Estes, S.A., Stihler, S.D., 2010. A parametric study of the January 2006 explosive eruptions of Augustine Volcano, using seismic, infrasonic, and lightning data. In: Power, J.A., Coombs, M.L., Freymueller, J.T. (Eds.), The 2006 Eruption of Augustine Volcano, Alaska: U.S. Geol. Surv. Profess. Paper, 1769, pp. 85–102. McNutt, S.R., Thompson, G., West, M.E., Fee, D., Stihler, S., Clark, E., 2013. Local seismic and infrasound observations of the 2009 explosive eruptions of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 63–76. Miller, T.P., 1994. Dome growth and destruction during the 1989–1990 eruption of Redoubt Volcano. Journal of Volcanology and Geothermal Research 62, 197–212. Miller, T.P., Chouet, B.A., 1994. The 1989–1990 eruptions of Redoubt Volcano: an introduction. Journal of Volcanology and Geothermal Research 62, 1–10. Pfeffer, M.A., Doukas, M.P., Werner, C.A., Evans, W.C., 2013. Airborne filter pack measurements of S and Cl in the plume of Redoubt Volcano, Alaska February–May 2009. Journal of Volcanology and Geothermal Research 259, 285–289. Power, J.A., Lahr, J.C., Page, R.A., Chouet, B.A., Stephens, C.D., Harlow, D.H., Murray, T.L., Davies, J.N., 1994. Seismic evolution of the 1989–1990 eruption sequence of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 62, 69–94. Power, J.A., Stihler, S.D., Chouet, B.A., Haney, M.M., Ketner, D.M., 2013. Seismic observations of Redoubt Volcano, Alaska — 1989–2010 and a conceptual model of the Redoubt magmatic system. Journal of Volcanology and Geothermal Research 259, 31–44. Pyle, D.M., 1989. The thickness, volume, and grain size of tephra-fall deposits. Bulletin of Volcanology 51, 1–15. Riehle, J.R., Kienle, J., Emmel, K.S., 1981. Lahars in Crescent River valley, lower Cook Inlet, Alaska. Alaska Division of Geological and Geophysical Surveys GR 0053. 10 pp. Ripepe, M., De Angelis, S., Lacanna, G., Voight, B., 2010. Observation of infrasonic and gravity waves at Soufrière Hills Volcano, Montserrat. Geophysical Research Letters 37 (L00E14) 5 pp.

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Schaefer, J.G., 2012. The eruption of Redoubt Volcano, Alaska. Alaska Division of Geological and Geophysical Surveys Report of Investigations, pp. 2012–2015. 45 pp. Schneider, D.J., Hoblitt, R.P., 2013. Doppler weather radar observations of the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 133–144. Scott, W.E., McGimsey, R.G., 1994. Character, mass, distribution and origin of tephrafall deposits of the 1989–1990 eruption of Redoubt Volcano, south-central Alaska. Journal of Volcanology and Geothermal Research 62, 251–272. Sturm, M., Benson, C., MacKeith, P., 1986. Effects of the 1966–1968 eruptions of Mount Redoubt on the flow of Drift glacier. Journal of Glaciology 32, 335–362. Till, A.B., Yount, M.E., Bevier, M.L., 1994. The geologic history of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 62, 11–30. Trabant, D.C., Waitt, R.B., Major, J.J., 1994. Disruption of Drift glacier and origin of floods during the 1989–1990 eruptions of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 62, 369–385. Wallace, K.L., Schaefer, J.R., Coombs, M.L., 2013. Character, mass, distribution, and originof tephra-fall deposits from the 2009 eruption of Redoubt Volcano, Alaska— Highlighting the significance of particle aggregation. Journal of Volcanology and Geothermal Research 259, 145–169. Waythomas, C.F., Pierson, T.C., Major, J.J., Scott, W.E., 2013. Voluminous ice-rich and water-rich lahars generated during the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 389–413. Werner, C.A., Evans, W.C., Kelly, P., McGimsey, R.G., Pfeffer, M.A., Doukas, M.P.P., Neal, C.A., 2012. Deep magmatic degassing vs. scrubbing: elevated CO2 emissions and C/ S in the lead-up to the 2009 eruption of Redoubt Volcano, Alaska. Geochemistry, Geophysics, Geosystems 13, 18, http://dx.doi.org/10.1029/2011GC003794. Werner, C., Kelly, P.J., Doukas, M., Lopez, T., Pfeffer, M., McGimsey, R., Neal, C., 2013. Degassing of CO2, SO2, and H2S associated with the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 270–284. Wessels, R.L., Vaughan, R.G., Patrick, M.R., Coombs, M.L., 2013. High-resolution satellite and airborne thermal infrared imaging of precursory unrest and 2009 eruption at Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research 259, 248–269. Wolf, K.J., Eichelberger, J.C., 1997. Syneruptive mixing, degassing, and crystallization at Redoubt Volcano, eruption of December, 1989 to May 1990. Journal of Volcanology and Geothermal Research 75, 19–38.