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Monitoring periglacial processes: Towards construction of a global network
Geomorphology 80 (2006) 20 – 31 www.elsevier.com/locate/geomorph
Monitoring periglacial processes: Towards construction of a global network Norikazu Matsuoka Geoenvironmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan Received 5 November 2004; received in revised form 27 September 2005; accepted 27 September 2005 Available online 3 March 2006
Abstract This paper outlines the strategy for constructing a global monitoring network for periglacial processes. The monitoring system should be designed with appropriate choices of parameters and techniques, which depend on the purpose of monitoring (e.g. modelling individual processes or assessing the sediment budget of a catchment). Acquisition of comparable data from globally distributed sites requires standardized techniques and instruments. In addition, expansion of the monitoring network to poorly accessible periglacial sites benefits from compact, cold-resistant and maintenance-free instruments; priority is given to automatic acquisition of year-round data that promote understanding of interactions between ground movements and environmental factors. Examples of previous process monitoring (frost wedging, solifluction and permafrost creep) suggest the significances of (1) high resolution of data for short-term, small-scale processes, (2) combination of movement and its major variables and (3) long-lasting monitoring that distinguishes long-term trend from interannual fluctuation. As the first stage of the monitoring network, a model experimental site is under construction in Svalbard where a variety of periglacial processes coexist in a small area, to test and compare various techniques to be standardized. © 2006 Elsevier B.V. All rights reserved. Keywords: Field monitoring; Periglacial processes; Frost wedging; Solifluction; Permafrost creep
1. Background The cryosphere is susceptible to climate changes at various time scales. Most of the periglacial environments, for instance, experience rapid changes in the ground thermal regime in response to both annual and long-term climatic variations. The resulting annual frost alternations and/or growth and decay of permafrost may destabilize rock slopes or mobilize soil slopes, and eventually lead to a significant geomorphic change often accompanied by a hazard (e.g. Harris et al., 2001a; Haeberli and Burn,
E-mail address: [email protected]. 0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2005.09.005
2002). To predict such a potential hazard is a priority issue of periglacial geomorphology. Nevertheless, prediction is rarely successful due to the lack of predictive models of the climatic control on periglacial processes. In this context, the International Permafrost Association (IPA) organized a new Working Group (WG) on ‘Periglacial Landforms, Processes and Climate’ (cochairs: Ole Humlum and Norikazu Matsuoka) in 2004, aiming at making a database for temporal and spatial variability of periglacial processes with special attention to the impact of climatic change. To achieve this goal, the WG plans to establish a global network for monitoring periglacial processes, which is possibly combined with the SEDIFLUX research network.
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Monitoring networks are already in progress in periglacial environments, but focusing on the ground thermal regimes (active layer depths and permafrost temperatures) in the circumpolar areas (Brown et al., 2000) and European high mountains (Harris et al., 2001b). The planned network highlights geomorphic processes associated with the ground thermal regimes. What is the advantage of the global network? There have been a number of long-term observations of periglacial processes including the growth of ice wedges and pingos in the Canadian Arctic (Mackay, 1998, 2000), movement of rock glaciers in the Swiss Alps (Haeberli et al., 1998), solifluction in Svalbard (Åkerman, 1996), and frost wedging and solifluction in the Swiss and Japanese Alps (Matsuoka et al., 2003; Matsuoka, 2005). These observations have revealed the average and fluctuation of movement over 10–50 years and their association with the local climate and/or hydrology. However, to reconstruct past periglacial conditions or to predict future geomorphic changes, universal process models should be developed by integrating data from a variety of periglacial climates. In this respect, recent advances in the data logging technology have popularized field monitoring in cold regions, but different methodologies have been used at each site. The global promotion of the monitoring campaign requires standardization of monitoring parameters and techniques. This paper outlines the process towards constructing a global monitoring network. The next section describes the fundamental step to design a monitoring system:
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how to choose (1) parameters to be measured and how to choose (2) techniques for measuring the parameters. In the third section, some actual examples of field monitoring are presented with techniques that are useful but partly need further improvement. Finally, we propose establishing a model experimental site that allows us to test, compare and improve the techniques. 2. Design of monitoring 2.1. Choice of parameters: individual processes or sediment budget? The parameters to be measured depend primarily on the purpose of the study and the spatial scale. A cold drainage basin is subjected to a variety of geomorphic processes, including glacial, periglacial, fluvioglacial, nival, gravitational and eolian processes. One school may focus on the mechanism of a specific process like solifluction or pingo growth, whereas another aims at evaluating the sediment budget of the whole catchment (Fig. 1). Individual process studies explore functional relationships between movement and its variables, which can be written as: Rate of movement ¼ f ðClimate; Hydrology; Topography; GeologyÞ: ð1Þ Numerical modelling of the process thus calls for comprehensive monitoring of both the rate of movement
Fig. 1. Landscape of a periglacial catchment (Reindalen, Svalbard) illustrating the various scales at which monitoring is needed.
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and variables (e.g. Haeberli et al., 1998; Matsuoka, 1998). These models are used to predict the amount of past or future movement at a site. They are also integrated to simulate long-term landform evolution (e.g. Anderson, 2002) or applied to the assessment of potential hazards. The individual process studies benefit from year-round, continuous data that promote understanding of interactions between environmental parameters and movement. Sediment budgets in a landscape element are expressed as a continuity equation: QðinputÞ ¼ QðoutputÞ þ QðstorageÞ
ð2Þ
where Q denotes the sediment quantity per unit time. This approach addresses the rates of sediment transfer by individual processes and the interactions between the processes (e.g. Rapp, 1960; Reid and Dunne, 2002), while it may not always require data on the factors controlling the processes. The difference in the purpose of monitoring suggests that a distinction should be made between the ‘core parameters’, which are recommended to be monitored at every site, and ‘site-specific’ (or topicdependent) parameters, which depend on the purpose.
The choice of parameters is affected also by the spatial factors. Fig. 2 illustrates periglacial processes operative in a periglacial catchment and associated parameters. A number of processes may take place within a small area, depending primarily on the bedrock geology and the presence of permafrost. Resistant rocks with widely spaced joints and a large interjoint strength produce blocky materials, and where permafrost is present, constitute a landform sequence composed of a rockwall, talus and rock glacier. Densely jointed, less resistant rocks cannot support a high rockwall and tend to produce much finer materials; these conditions lead to debris-mantled slopes often accompanied by miniature periglacial features like patterned ground and solifluction lobes. Individual process researchers choose a single process or sequential processes operative in the catchment; then, their monitoring is designed to include the major parameters (see Fig. 2). The parameters chosen by sediment budget researchers vary also with the prevailing geology and subsurface frost conditions in the catchment. Although comprehensive monitoring promotes numerical modelling of periglacial processes or sediment budgets, it also involves significant limitations.
Fig. 2. A scheme of processes and landforms in a periglacial catchment, reflecting bedrock geology and frost regime. Parameters for monitoring are indicated.
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Monitoring favours slow and frequent processes like soil creep and slow landslide, but may not suit rapid or sporadic processes like rockfall and debris flow, unless a large-scale, expensive system is introduced. Moreover, most of the small sensors fail to detect large-scale processes like rock avalanche. Such a problem is now partly overcome by the advance of remote-sensing techniques (see below). 2.2. Choice of techniques
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al., 2002). Automatic cameras reveal the timing of movement with photographs taken at regular intervals (cf. Christiansen, 2001). These automatic techniques, when standardized and spread, allow us to collect comparable data from various periglacial environments. To promote this monitoring campaign, the standard techniques must have advantages of: •
Inclusion of all necessary parameters; High resolution data acquisition; • Solid devices ensuring long-term monitoring under harsh climates; • Handy and portable equipment; • Minimum disturbance of ground upon installation; • Least maintenance (e.g. once per year); and • Reasonable price. •
Automated monitoring generally favours process studies in periglacial environments, most of which are located distant from the researcher's office or even beyond any permanent residence. A variety of sensors, either commercial or handmade, are currently available for automatic logging of movements and their variables, although conventional manual methods are still useful for measurements difficult to be automated (Fig. 2). Reflecting the availability of commercial sensors, automatic monitoring has mainly targeted environmental factors. For instance, various sensors set together on an observation tower have recorded meteorological parameters. Monitoring of rock and soil temperatures becomes increasingly popular with the progress of inexpensive miniature loggers (e.g. Hoelzle et al., 1999). Data loggers also accept hydrological quantities converted to electric signals, such as precipitation, soil moisture, groundwater level and stream discharge. In contrast to the environmental factors, movements of rock debris or soils have mostly been measured by manual methods at intervals of a few months to several years. The lack of continuous measurements has long prevented identifying the exact timing and trigger of the movement, but the situation is improving. Strain-gauge type sensors permit monitoring of slow ground movements. Examples include a crack extensometer for frost wedging (Matsuoka, 2001), a displacement transducer for frost heave (Matsuoka, 1998) and an inclinometer for permafrost creep (Arenson et al., 2002). Potentiometers that convert rotation to voltage are used in recording solifluction or landslides (Lewkowicz, 1992; Jaesche et al., 2003). Photo-electronic sensors can record the depth of erosion or deposition by wind, stream or needle ice (e.g. Lawler, 1991). Shock sensors and seismographs detect the generation of cracking in bedrock or frozen ground (Christiansen, 2005) and of rockfalls (Mills, 1999), although the data possibly include noises from other sources. The most recent advance is achieved in the remotesensing technology. GPS is applied to monitor displacement by relatively rapid mass movement (e.g. Malet et
In particular, the operation at periglacial sites, often located in remote areas like high mountains, requires a compact, cold-resistant and maintenance-free system. Some useful techniques are listed in a provisional version of ‘A Handbook on Periglacial Field Methods’ which can be downloaded from the IPA web site (Humlum and Matsuoka, 2004). 3. Examples of monitoring This section highlights the advantages and problems of monitoring, with examples from the Swiss and Japanese mountains. The examples feature three processes representing different time scales: (1) frost wedging associated with diurnal freeze–thaw cycles; (2) solifluction reflecting seasonal processes; and (3) permafrost creep subject to an interannual variation. 3.1. Diurnal variation: frost wedging in the Japanese Alps Opening of a rock joint was monitored on a cirque wall in the Japanese Alps (Fig. 3A). A crack extensometer (Kyowa, BCD-5A: Fig. 3B) attached to the rock face detected widening of a crack of up to 10 mm with a resolution of 2.5 × 10− 3 mm. This sensor is used to measure both frost wedging (Matsuoka, 2001) and thermal expansion (Ishikawa et al., 2004). Signals from the sensor were recorded at 1-h intervals with a data logger. This time resolution (constrained by the logger capacity) is appropriate to show diurnal movement, although higher resolution provides more accurate timing of a spiky movement. A thermal probe sensed the temperature at the top of the joint at 5-min intervals
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Fig. 3. Monitoring frost wedging in southern Japanese Alps. (A) Location of the monitoring site near the base of an east-facing rockwall. (B) Instrumentation: a crack extensometer (CE) senses widening of a rock joint; a thermal probe (location at J) measures temperature at the top of the joint. (C) Rock joint movement at 60-min intervals and joint-top temperature at 5-min intervals in the autumn freeze–thaw period in 2002. Encircled highlights supercooling and/or brief zero-curtain indicating water freezing in the joint.
during the autumn freeze–thaw periods and at 0.5- to 1-h intervals in the rest of year. The former interval favours detecting the freezing of water in the joint. Another thermal probe was attached to the extensometer for calibration of the strain records against temperature (Matsuoka, 2001). Fig. 3C displays an example of diurnal events. The high resolution recording detected a brief period of supercooling followed by sudden heating and zerocurtain, which indicates the latent heat release by freezing of water in the joint. Joint opening (0.05–0.1 mm) always followed this freezing pulse with a significant time lag (ca. 5 h). The time lag between the freezing pulse at the top of joint and the beginning of expansion indicates that frost penetration in the joint finally
produced significant widening at a certain depth. Consequently, these events are attributed to expansion due to water freezing in the joint. The rock joint also responded to autumn freeze–thaw cycles, and the repetition of expansion and contraction led to interannual opening (Matsuoka, 2001; Matsuoka et al., 2003). These results suggest that identification of frost wedging requires both high resolution and long-term monitoring. 3.2. Seasonal variation: solifluction in the Swiss Alps Movement of a solifluction lobe has been monitored together with environmental parameters since 1994 in the Upper Engadin, Swiss Alps (Fig. 4A). A displacement transducer fixed to an iron angle frame
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Fig. 4. Monitoring solifluction in Upper Engadin (Swiss Alps). (A) The instrumented east-facing stone-banked lobe. (B) Deformation of a strain probe over a 4 yr period. The base of movement lies at 50 cm depth. (C) Annual variation in surface heave, subsurface inclination, soil moisture content and temperature.
sensed the vertical soil movement (frost heave). Downslope movement was observed with two types of sensors: a flexible strain probe (Fig. 4B) and a rigid inclinometer. The former is a handmade probe sensing millimetre-scale movement. Five bridge circuits, each made of two pair of strain gauges, detected bending of the probe at 12-cm depth intervals to a depth of 60 cm (Matsuoka et al., 1997). The inclinometer (Kyowa, BKJ-A-10) can record inclination within ± 10°, but the rigid, 25-cm-long probe can only respond to deep movement (probably >10 cm). Concurrently monitored were soil temperature at different depths (down to 225 cm) and soil moisture at 20 and 40 cm, sensed with platinum probes and TDR (Time Domain Reflectometry) probes, respectively. The recorded volumetric water content was calibrated by direct weighing of soil samples recovered several times from the same depth. All data were stored in data loggers at 1- to 4-h intervals. Fig. 4C summarizes annual variations in four parameters, frost heave, internal deformation (data from an inclinometer), soil moisture and temperature at four depths, from the 2001 summer to the 2002
summer. During this year, the strain probe failed to record movement due to an electric problem. The soil temperatures at 225 cm were positive in summer, which indicate the absence of subsurface permafrost, while in winter they were close to 0 °C indicative of deep seasonal frost penetration (ca. 200 cm). The seasonal frost depth fluctuated interannually between 50 and 200 cm (Matsuoka et al., 2003). Frost heave took place in two periods. A few short-term frost heave cycles happened in autumn but essentially heave was absent in spring under the latelying snow cover (Fig. 4C). The heave amount of the former rarely exceeded 1 cm. Much larger heave (ca. 3 cm) was produced during seasonal freezing in winter. A large part of the seasonal heave occurred before the frost table reached 50 cm depth, suggesting that ice lenses formed largely within the top 50 cm. This coincides with the depth of the maximum downslope movement displayed by an excavated strain probe (Fig. 4B). The inclinometer did not respond to the short-term frost heave cycles in autumn, implying that short-term frost heaving can produce only surficial soil movement
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(shallower than 10 cm). Instead, the sensor recorded significant downslope tilting in the early seasonal freezing period and in a short period at the beginning of seasonal thawing (Fig. 4C). The former tilting probably arose from seasonal frost heave intersecting with the axis of the inclinometer; hence, this was an apparent movement. The latter tilting probably resulted from gelifluction accompanying thaw consolidation at a few decimetres depth. The volumetric moisture content of soil fluctuated between 15% and 20% at both 20 and 40 cm depths during the frost-free period (Fig. 4C). The fluctuation is likely due to precipitation and subsequent desiccation (cf. Matsuoka, 1996). When frozen, the soil holds 7–8% of moisture, which might represent the unfrozen water content. The seasonal thaw consolidation in middle June resulted in a rapid rise in moisture reaching the annual maximum of 23% (Fig. 4C), which implies supersaturation and possible softening of the soil (cf. Harris et al., 1995); the data support the significance of gelifluction during seasonal thawing. Consequently, a combination of parameters documents the primary role of gelifluction in the development of the solifluction lobe and reinforces understanding of the mechanism of soil movement.
3.3. Interannual variation: permafrost creep in the Swiss Alps The final example is movement of a small rock glacier (Büz-N rock glacier) in the Upper Engadin, Swiss Alps, which occurs as bulging of a talus slope (Fig. 5A). The rock glacier has a lobate-type plan shape (50 m long and 130 m wide) and faces northeast. Unlike typical, large rock glaciers in this region (e.g. Murtèl, Muragl and Schafberg rock glaciers: Arenson et al., 2002) which have a bouldery (open-work) active layer, this rock glacier displays a pebbly surface filled with fine debris (Ikeda et al., 2003). Bulging terminated in a steep front 10 m high, which is located at 2800 m ASL. Since this elevation is close to the lower limit of permafrost indicated by intact pebbly rock glaciers (Matsuoka et al., 2005), the rock glacier is expected to be sensitive to climatic variation. The automatic monitoring system comprised two inclinometers installed at 4 and 5 m depths, thermistor probes at the surface and 0.5, 1, 2, 3, 4 and 5 m depths in a borehole reaching well below the permafrost table (ca. 2 m) and data loggers. The inclinometers (Kyowa, BKJA-10-D) measure tilting for two axes crossing at right angles, and the downslope inclination is determined
Fig. 5. Monitoring permafrost creep in Upper Engadin (Swiss Alps). (A) The instrumented northeast-facing pebbly rock glacier (Büz-N). (B) Annual velocity profiles computed from the surface velocity and inclinations at 4 and 5 m depths, using the power-law flow model (after Ikeda, 2004). (C) Internal deformation and thermal regime in 2000–2003.
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geometrically from the two values. Each axis senses tilts within ±10° from the vertical. When one axis reaches this limit, however, another axis still senses tilting, and the downslope component is estimated from the latter values assuming the ratio of inclinations between the two axes. In addition to the internal deformation, annual displacements of surface stones were manually measured by a triangulation survey (Ikeda et al., 2003). Most of the surface displacement was attributed to permafrost creep, since strain probes installed in the active layer documented movement negligible compared with the surface displacement (Ikeda, 2004). Consequently, the annual surface displacement and tilts at two depths were integrated to compute the annual velocity profile by using a power law flow model (Fig. 5B; Ikeda, 2004). Monitoring for 3 years (2000–2003) showed a large interannual fluctuation in ground temperature (Fig. 5C). The ground surface temperature never fell below − 0.6 °C during the first winter. The warm ground temperature resulted from an extraordinary deep snow cover (e.g. 5 m at Büz-N rock glacier on 22 March 2001). In contrast, the ground surface temperature lowered to − 5 °C during the second winter, reflecting the thin snow (e.g. 2 m at Büz-N rock glacier on 6 March 2002). Regardless of the fluctuation within the active layer, temperatures at 4 and 5 m depths were constant at 0.0 to − 0.1 °C. The inclinometers tilted rapidly during the first year (2000–2001), at a rate of 9° year− 1 at 5 m depth (Fig. 5C). They still maintained rapid tilting until the early winter of 2001, but thereafter decelerated; as a result, the annual tilt at 5 m depth decreased to 5° year− 1 in the second year. Tilting accelerated again in the third year. The two inclinometers tilted consistently. Such a tilting history followed the near-surface temperature: the large deformation corresponded to warmer ground in winter and smaller deformation to colder ground (Fig. 5C). The internal deformation was reflected in the surface velocity determined by the triangulation survey. The
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largest surface velocities (1.1–1.5 m year− 1) paralleled the large internal deformation in the first year, whereas the smallest velocities (0.8–1.0 m year− 1) in the second year coincided with the small deformation. The computed velocity profiles also highlight the difference between the 3 years and suggest that most of the deformation has occurred between 4 and 8 m depth within the permafrost (Fig. 5B). The integration of these data lead to a conclusion that the near-surface temperature, which depends on the winter snow depth, is most responsible for the interannual fluctuation in the movement of this rock glacier. 3.4. Summary: process variability vs. monitoring period The above examples demonstrate the significance of (1) automated, concurrent monitoring of movement and its major controls and (2) long-term continuous monitoring (> 5 years) that documents interannual fluctuation. The former permits us to relate the timing of movement to the triggering parameter and also to model the rate of movement as a function of environmental and other parameters (Eq. (1)). Such a model can, in turn, predict the temporal variation in the rate at the monitoring site as a result of interannual or longterm climatic variation. Sediment budget studies also benefit from concurrent monitoring, since numerical process models promote understanding of the temporal variation in the sediment flux (Eq. (2)) due to changes in climatic and hydrological regimes. Long-term monitoring is particularly significant to identify the type of temporal variation in the rate of movement, because the ground may experience both chronic (frequently recurring) and discrete (episodic) processes (Reid and Dunne, 2002). Fig. 6 schematically illustrates three examples of variations. Type A represents nearly constant, but gradually increasing movement. Type B shows also nearly constant
Fig. 6. Three types of temporal process variability. See text for explanation.
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movement but includes episodic events. Type C shows large interannual variability. Such variations can occur either in a single process or in a landform unit. The type to which the process (or landform) belongs should be taken into account when choosing the monitoring parameters and periods. This is because, if the monitoring is restricted to the PhD period (e.g. a few years), the measured movement may overestimate the long-term average of Type C process, or underestimate the long-term average of Type B; furthermore, where disturbance is significant during the installation of a sensor monitoring may finish before the sensor is stabilized (Smith, 1992). Monitoring that continues over several decades allows more precise understanding of the long-term average or trend of Types A and C. Such a multidecadal monitoring may finally find or miss an episodic event in Type B, which can be the largest component of the geomorphic change. In a large-scale drainage basin, a multidecadal monitoring may still be too short to represent a long-term average, because more catastrophic large events with recurrence intervals in excess of 102 years somewhere in the basin can significantly raise the average denudation rate in the basin for the Holocene (e.g. Kirschner et al., 2001), whereas in a small catchment the current slope instability can cause the reverse condition (e.g. Clapp et al., 2000). In summary, monitoring should be continued as long as possible and even passed on to the next generation of scientists (e.g. Mackay and Burn, 2002). Monitoring should also involve both movement and its controlling
variables, which enables us to obtain a functional relationship and, as a consequence, to predict the movement beyond the monitoring period. Finally, a global monitoring network will provide widely applicable relationships between the process and its variables by integrating data from different environments. 4. Strategy: model experimental site To expand periglacial monitoring sites worldwide, the fundamental step is standardization of methodology. Towards the standardization, the WG project starts with constructing a model experimental site in a typical periglacial area. The model site promotes (1) comparing various methods and instruments, (2) testing performance of the instruments in a cold, harsh environment and (3) defining core parameters and site-specific parameters. Central Spitsbergen, Svalbard, was chosen for the model site. The primary advantage of central Spitsbergen is the good accessibility from the European mainland, which allows a number of periglacial geomorphologists to participate in the project. Year-round maintenance and frequent data collection are also provided. One of the scientific advantages of central Spitsbergen is a variety of periglacial landforms coexisting in a small area: including rockwalls, talus slopes, rock glaciers, block fields, landslide features, solifluction lobes, non-sorted polygons, sorted circles, pingos,
Fig. 7. Construction of the model ice-wedge site near Longyearbyen, Svalbard (September 2004, photographs by Andreas Kellerer). (A) A portable handy auger that can penetrate into frozen soil. (B) Setting instruments on an ice wedge trough.
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palsas, seasonal frost mounds, thermokarst depressions, tafoni, wind erosion features (e.g. Åkerman, 1987; Humlum et al., 2003; Matsuoka et al., 2004). Such a variety enables us to concentrate various technologies within a study area. The landscape variety reflects the location transitional between warm and cold permafrost. High relief further reinforces the spatial contrasts in periglacial conditions: warm permafrost with a thick active layer (> 1 m) vs. cold permafrost with a thin active layer (< 1 m); dry sites (e.g. convex upper slopes) vs. wet sites (e.g. concave lower slopes); and steep rockwalls to flat terraces or strandflats. These conditions promote determination of the thresholds for the generation of the above landforms. Another scientific advantage of central Spitsbergen is that there are already a number of quantitative data on various processes: rock weathering (e.g. Matsuoka, 1991; Prick, 2003); permafrost creep (e.g. Isaksen et al., 2000; Kääb et al., 2002); frost heave and gelifluction (e.g. Åkerman, 1996; Matsuoka and Hirakawa, 2000; Sørbel and Tolgensbakk, 2002); frost sorting (e.g. Hallet et al., 1988; Hallet, 1998); ice-wedge cracking (Matsuoka, 1999; Christiansen, 2005); pingo growth (Yoshikawa and Harada, 1995; Matsuoka et al., 2004); and fluvial sediment transport (Bogen and Bønsnes, 2003). Also available are climatological parameters (e.g. Humlum, 2004) and permafrost structure and temperature (Isaksen et al., 2001; Christiansen et al., 2003). These data are useful for determination of monitoring parameters and techniques and for inter-site comparison of movements and variables. In September 2004, the first attempt was undertaken on constructing a model ice wedge site near Longyearbyen, central Spitsbergen (Fig. 7). Seven scientists participated in this campaign. This site had already experienced 1–2 years of monitoring with sensors installed in 2002–2003, which consisted of shock sensors for detecting thermal cracking, thermistor cables for monitoring ground temperatures, and an automatic camera that displays snow depth (Christiansen, 2005). The existing system was reinforced in 2004 by installation of additional thermistor cables down to 2 m depth, two kinds of soil moisture sensors, breaking cables (copper wires: Mackay, 1974) that record the timing of thermal cracking, and dilatometers for recording the widening of an icewedge trough (Matsuoka, 1999) and the vertical movement at an ice wedge rampart (Fig. 7B). A portable engine auger (Fig. 7A) was used to install sensors and frames well into permafrost with minimum disturbance of the structure and thermal regime of the ground. The installation was followed by an
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excursion of the PACE21 (Permafrost and Climate in the 21st Century) workshop, when advantages and possible improvements of the monitoring system were discussed at the model site. Acknowledgements I would like to thank Achim A. Beylich for his invitation to the 1st SEDIFLUX workshop and giving a chance to demonstrate the new IPA-sponsored project. I am also grateful to Ole Humlum and Hanne Christiansen for fruitful discussion on the strategy of the project, and to Frank Ahnert and Olav Slaymaker for their helpful comments on the manuscript. References Åkerman, H.J., 1987. Periglacial forms of Svalbard: a review. In: Boardman, J. (Ed.), Periglacial Processes and Landforms in Britain and Ireland. Cambridge University Press, Cambridge, pp. 9–25. Åkerman, H.J., 1996. Slow mass movements and climatic relationships, 1972–1994, Kapp Linné, West Spitsbergen. In: Anderson, M.G., Brooks, S.M. (Eds.), Advances in Hillslope Processes, vol. 2. Wiley, Chichester, pp. 1219–1256. Anderson, R.S., 2002. Modeling the tor-dotted crests, bedrock edges, and parabolic profiles of high alpine surfaces of the Wind River Range, Wyoming. Geomorphology 46, 35–58. Arenson, L., Hoelzle, M., Springman, S., 2002. Borehole deformation measurements and internal structures of some rock glaciers in Switzerland. Permafrost and Periglacial Processes 13, 117–135. Bogen, J., Bønsnes, T.E., 2003. Erosion and sediment transport in High Arctic Rivers, Svalbard. Polar Research 22, 175–189. Brown, J., Hinkel, K.M., Nelson, F.E., 2000. The Circumpolar Active Layer Monitoring CALM) program: research designs and initial results. Polar Geography 24, 165–258. Christiansen, H.H., 2001. Snow-cover depth, distribution and duration data from northeast Greenland obtained by continuous automatic digital photography. Annals of Glaciology 32, 102–108. Christiansen, H.H., 2005. Ice-wedge dynamics in Svalbard: evidence for thermal contraction cracking. Permafrost and Periglacial Processes, 87–98. Christiansen, H.H., Åkerman, H.J., Repelewska-Pekalowa, J., 2003. Active layer dynamics in Greenland, Svalbard and Sweden. In: Haeberli, W., Brandová, D. (Eds.), Extended Abstracts, Reporting Current Research and New Information, 8th International Conference on Permafrost. Balkema, Lisse, pp. 19–20. Clapp, E.M., Bierman, P.R., Schick, A.P., Lekach, J., Enzel, Y., Caffee, M., 2000. Sediment yield exceeds sediment production in arid region drainage basins. Geology 28, 995–998. Haeberli, W., Burn, C.R., 2002. Natural hazards in forests: glacier and permafrost effects as related to climate change. In: Sidle, R.C. (Ed.), Environmental Changes and Geomorphic Hazards in Forests. CABI Publishing, Oxfordshire, pp. 167–202. Haeberli, W., Hoelzle, M., Keller, F., Vonder Mühll, D., Wagner, S., 1998. Ten years after the drilling through the permafrost of the active rock glacier Murtèl, eastern Swiss Alps: answered questions and new perspectives. In: Lewkowicz, A.G., Allard, M. (Eds.), Proceedings of the 7th International Conference on Permafrost. Centre d'études Nordiques, Sainte-Foy, pp. 403–410.
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Hallet, B., 1998. Measurement of soil motion in sorted circles, western Spitsbergen. In: Lewkowicz, A.G., Allard, M. (Eds.), Proceedings of the 7th International Conference on Permafrost. Centre d'études Nordiques, Sainte-Foy, pp. 415–420. Hallet, B., Prestrud Anderson, S., Stubbs, C.W., Gregory, C.E., 1988. Surface soil displacement in sorted circles, western Spitsbergen. In: Senneset, K. (Ed.), Proceedings of the 5th International Conference on Permafrost, vol. 1. Tapir Publishers, Trondheim, pp. 770–775. Harris, C., Davies, M.C.R., Coutard, J.-P., 1995. Laboratory simulation of periglacial solifluction: significance of porewater pressures, moisture contents and undrained shear strength during thawing. Permafrost and Periglacial Processes 6, 293–311. Harris, C., Davies, M.C.R., Etzelmüller, B., 2001a. The assessment of potential geotechnical hazards associated with mountain permafrost in a warming global climate. Permafrost and Periglacial Processes 12, 145–156. Harris, C., Haeberli, W., Vonder Mühll, D., King, L., 2001b. Permafrost monitoring in the high mountains of Europe: the PACE Project in its global context. Permafrost and Periglacial Processes 12, 3–11. Hoelzle, M., Wegmann, M., Krummenacher, B., 1999. Miniature temperature dataloggers for mapping and monitoring of permafrost in high mountain areas: first experience from the Swiss Alps. Permafrost and Periglacial Processes 10, 113–124. Humlum, O., 2004. Monitoring surface climate around Longyearbyen, Svalbard. http://www.unis.no/RESEARCH/GEOLOGY/Geo_ research/Ole/MonitoringSurfaceClimate.htm. Humlum, O., Matsuoka, N., 2004. A Handbook on Periglacial Field Methods. http://www.geo.uio.no/IPA/A Handbook on Periglacial Field Methods.pdf. Humlum, O., Instanes, A., Sollid, J.L., 2003. Permafrost in Svalbard: a review of research history, climatic background and engineering challenges. Polar Research 22, 191–215. Ikeda, A., 2004. Rock glacier dynamics near the lower limit of Mountain Permafrost in the Swiss Alps. Unpublished Doctor Thesis, University of Tsukuba. 107 pp. Ikeda, A., Matsuoka, N., Kääb, A., 2003. A rapidly moving small rock glacier at the lower limit of the mountain permafrost belt in the Swiss Alps. In: Phillips, M., Springman, S.M., Arenson, L. (Eds.), Proceedings of the 8th International Conference on Permafrost, vol. 1. Balkema, Lisse, pp. 455–460. Isaksen, K., Ødegård, R.S., Eiken, T., Sollid, J.L., 2000. Composition, flow and development of two tongue-shaped rock glaciers. Permafrost and Periglacial Processes 11, 241–257. Isaksen, K., Holmund, P., Sollid, J.H., Harris, C., 2001. Three deep alpine-permafrost boreholes in Svalbard and Scandinavia. Permafrost and Periglacial Processes 12, 13–25. Ishikawa, M., Kurashige, Y., Hirakawa, K., 2004. Analysis of crack movements observed in an alpine bedrock cliff. Earth Surface Processes and Landforms 29, 883–891. Jaesche, P., Veit, H., Huwe, B., 2003. Snow cover and soil moisture controls on solifluction in an area of seasonal frost, eastern Alps. Permafrost and Periglacial Processes 14, 399–410. Kääb, A., Isaksen, K., Eiken, T., Farbrot, H., 2002. Geometry and dynamics of two lobe-shaped rock glaciers in the permafrost of Svalbard. Norsk Geografisk Tidsskrift 56, 152–160. Kirschner, J.W., Finkel, R.C., Riebe, C.S., Granger, D.E., Clayton, J. L., King, J.G., Megahan, W.F., 2001. Mountain erosion over 10 yr, 10 k.y., and 10 m.y. time scales. Geology 29, 591–594. Lawler, D.M., 1991. A new technique for automatic monitoring of erosion and deposition rates. Water Resources Research 27, 2125–2128.
Lewkowicz, A.G., 1992. A solifluction meter for permafrost sites. Permafrost and Periglacial Processes 3, 11–18. Mackay, J.R., 1974. Ice-wedge cracks, Garry Island, Northwest Territories. Canadian Journal of Earth Sciences 11, 1366–1383. Mackay, J.R., 1998. Pingo growth and collapse, Tuktoyakytuk Peninsula area, Western Arctic Coast, Canada: a long-term field survey. Géographie Physique et Quaternaire 52, 271–323. Mackay, J.R., 2000. Thermally induced movements in ice-wedge polygons, Western Arctic Coast: a long-term study. Géographie Physique et Quaternaire 54, 41–68. Mackay, J.R., Burn, C.R., 2002. The first 20 years (1978–1979 to 1998–1999) of ice-wedge growth at the Illisarvik experimental drainage lake site, western Arctic coast, Canada. Canadian Journal of Earth Sciences 39, 95–111. Malet, J.-P., Maquaire, O., Calais, E., 2002. The use of Global Positioning System techniques for the continuous monitoring of landslides: application to the Super-Sauze earthflow (Alpes-deHaute-Provence, France). Geomorphology 43, 33–54. Matsuoka, N., 1991. A model of the rate of frost shattering: application to field data from Japan, Svalbard and Antarctica. Permafrost and Periglacial Processes 2, 271–281. Matsuoka, N., 1996. Soil moisture variability in relation to diurnal frost heaving on Japanese high mountain slopes. Permafrost and Periglacial Processes 7, 139–151. Matsuoka, N., 1998. Modelling frost creep rates in an alpine environment. Permafrost and Periglacial Processes 9, 397–409. Matsuoka, N., 1999. Monitoring of thermal contraction cracking at an ice wedge site, central Spitsbergen. Polar Geoscience 12, 258–271. Matsuoka, N., 2001. Direct observation of frost wedging in alpine bedrock. Earth Surface Processes and Landforms 26, 601–614. Matsuoka, N., 2005. Temporal and spatial variations in periglacial soil movements on alpine crest slopes. Earth Surface Processes and Landforms 30, 41–58. Matsuoka, N., Hirakawa, K., 2000. Solifluction resulting from onesided and two-sided freezing: field data from Svalbard. Polar Geoscience 13, 187–201. Matsuoka, N., Hirakawa, K., Watanabe, T., Moriwaki, K., 1997. Monitoring of periglacial slope processes in the Swiss Alps: the first two years of frost shattering, heave and creep. Permafrost and Periglacial Processes 8, 155–177. Matsuoka, N., Ikeda, A., Hirakawa, K., Watanabe, T., 2003. Contemporary periglacial processes in the Swiss Alps: seasonal, inter-annual and long-term variations. In: Phillips, M., Springman, S.M., Arenson, L. (Eds.), Proceedings of the 8th International Conference on Permafrost, vol. 2. Balkema, Lisse, pp. 735–740. Matsuoka, N., Sawaguchi, S., Yoshikawa, K., 2004. Present-day periglacial environments in central Spitsbergen, Svalbard. Geographical Review of Japan 77, 276–300. Matsuoka, N., Ikeda, A., Date, T., 2005. Morphometric analysis of solifluction lobes and rock glaciers in the Swiss Alps. Permafrost and Periglacial Processes, 99–113. Mills, H.H., 1999. Temporal variation of mass-wasting activity in Mount St. Helens Crater, Washington, U.S.A. Arctic and Alpine Research 23, 417–423. Prick, A., 2003. Frost weathering and rock fall in an arctic environment, Longyearbyen, Svalbard. In: Phillips, M., Springman, S.M., Arenson, L. (Eds.), Proceedings of the 8th International Conference on Permafrost, vol. 2. Balkema, Lisse, pp. 907–917. Rapp, A., 1960. Recent development of mountain slopes in Kärkevagge and surroundings, Northern Scandinavia. Geografiska Annaler 42A, 65–200.
N. Matsuoka / Geomorphology 80 (2006) 20–31 Reid, L.M., Dunne, T., 2002. Sediment budgets as an organizing framework in fluvial geomorphology. In: Kondolf, M., Piegay, H. (Eds.), Tools in Fluvial Geomorphology. Wiley, Chichester, pp. 463–500. Smith, D.J., 1992. Long-term rates of contemporary solifluction in the Canadian Rocky Mountains. In: Dixon, J.C., Abrahams, A.D. (Eds.), Periglacial Geomorphology. Wiley, Chichester, pp. 203–221.
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Sørbel, L., Tolgensbakk, J., 2002. Ice-wedge polygons and solifluction in the Adventdalen area, Spitsbergen, Svalbard. Norsk Geografisk Tidsskrift 56, 62–66. Yoshikawa, K., Harada, K., 1995. Observations on nearshore pingo growth, Adventdalen, Spitsbergen. Permafrost and Periglacial Processes 6, 361–372.
Monitoring periglacial processes: Towards construction of a global network Norikazu Matsuoka Geoenvironmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan Received 5 November 2004; received in revised form 27 September 2005; accepted 27 September 2005 Available online 3 March 2006
Abstract This paper outlines the strategy for constructing a global monitoring network for periglacial processes. The monitoring system should be designed with appropriate choices of parameters and techniques, which depend on the purpose of monitoring (e.g. modelling individual processes or assessing the sediment budget of a catchment). Acquisition of comparable data from globally distributed sites requires standardized techniques and instruments. In addition, expansion of the monitoring network to poorly accessible periglacial sites benefits from compact, cold-resistant and maintenance-free instruments; priority is given to automatic acquisition of year-round data that promote understanding of interactions between ground movements and environmental factors. Examples of previous process monitoring (frost wedging, solifluction and permafrost creep) suggest the significances of (1) high resolution of data for short-term, small-scale processes, (2) combination of movement and its major variables and (3) long-lasting monitoring that distinguishes long-term trend from interannual fluctuation. As the first stage of the monitoring network, a model experimental site is under construction in Svalbard where a variety of periglacial processes coexist in a small area, to test and compare various techniques to be standardized. © 2006 Elsevier B.V. All rights reserved. Keywords: Field monitoring; Periglacial processes; Frost wedging; Solifluction; Permafrost creep
1. Background The cryosphere is susceptible to climate changes at various time scales. Most of the periglacial environments, for instance, experience rapid changes in the ground thermal regime in response to both annual and long-term climatic variations. The resulting annual frost alternations and/or growth and decay of permafrost may destabilize rock slopes or mobilize soil slopes, and eventually lead to a significant geomorphic change often accompanied by a hazard (e.g. Harris et al., 2001a; Haeberli and Burn,
E-mail address: [email protected]. 0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2005.09.005
2002). To predict such a potential hazard is a priority issue of periglacial geomorphology. Nevertheless, prediction is rarely successful due to the lack of predictive models of the climatic control on periglacial processes. In this context, the International Permafrost Association (IPA) organized a new Working Group (WG) on ‘Periglacial Landforms, Processes and Climate’ (cochairs: Ole Humlum and Norikazu Matsuoka) in 2004, aiming at making a database for temporal and spatial variability of periglacial processes with special attention to the impact of climatic change. To achieve this goal, the WG plans to establish a global network for monitoring periglacial processes, which is possibly combined with the SEDIFLUX research network.
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Monitoring networks are already in progress in periglacial environments, but focusing on the ground thermal regimes (active layer depths and permafrost temperatures) in the circumpolar areas (Brown et al., 2000) and European high mountains (Harris et al., 2001b). The planned network highlights geomorphic processes associated with the ground thermal regimes. What is the advantage of the global network? There have been a number of long-term observations of periglacial processes including the growth of ice wedges and pingos in the Canadian Arctic (Mackay, 1998, 2000), movement of rock glaciers in the Swiss Alps (Haeberli et al., 1998), solifluction in Svalbard (Åkerman, 1996), and frost wedging and solifluction in the Swiss and Japanese Alps (Matsuoka et al., 2003; Matsuoka, 2005). These observations have revealed the average and fluctuation of movement over 10–50 years and their association with the local climate and/or hydrology. However, to reconstruct past periglacial conditions or to predict future geomorphic changes, universal process models should be developed by integrating data from a variety of periglacial climates. In this respect, recent advances in the data logging technology have popularized field monitoring in cold regions, but different methodologies have been used at each site. The global promotion of the monitoring campaign requires standardization of monitoring parameters and techniques. This paper outlines the process towards constructing a global monitoring network. The next section describes the fundamental step to design a monitoring system:
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how to choose (1) parameters to be measured and how to choose (2) techniques for measuring the parameters. In the third section, some actual examples of field monitoring are presented with techniques that are useful but partly need further improvement. Finally, we propose establishing a model experimental site that allows us to test, compare and improve the techniques. 2. Design of monitoring 2.1. Choice of parameters: individual processes or sediment budget? The parameters to be measured depend primarily on the purpose of the study and the spatial scale. A cold drainage basin is subjected to a variety of geomorphic processes, including glacial, periglacial, fluvioglacial, nival, gravitational and eolian processes. One school may focus on the mechanism of a specific process like solifluction or pingo growth, whereas another aims at evaluating the sediment budget of the whole catchment (Fig. 1). Individual process studies explore functional relationships between movement and its variables, which can be written as: Rate of movement ¼ f ðClimate; Hydrology; Topography; GeologyÞ: ð1Þ Numerical modelling of the process thus calls for comprehensive monitoring of both the rate of movement
Fig. 1. Landscape of a periglacial catchment (Reindalen, Svalbard) illustrating the various scales at which monitoring is needed.
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and variables (e.g. Haeberli et al., 1998; Matsuoka, 1998). These models are used to predict the amount of past or future movement at a site. They are also integrated to simulate long-term landform evolution (e.g. Anderson, 2002) or applied to the assessment of potential hazards. The individual process studies benefit from year-round, continuous data that promote understanding of interactions between environmental parameters and movement. Sediment budgets in a landscape element are expressed as a continuity equation: QðinputÞ ¼ QðoutputÞ þ QðstorageÞ
ð2Þ
where Q denotes the sediment quantity per unit time. This approach addresses the rates of sediment transfer by individual processes and the interactions between the processes (e.g. Rapp, 1960; Reid and Dunne, 2002), while it may not always require data on the factors controlling the processes. The difference in the purpose of monitoring suggests that a distinction should be made between the ‘core parameters’, which are recommended to be monitored at every site, and ‘site-specific’ (or topicdependent) parameters, which depend on the purpose.
The choice of parameters is affected also by the spatial factors. Fig. 2 illustrates periglacial processes operative in a periglacial catchment and associated parameters. A number of processes may take place within a small area, depending primarily on the bedrock geology and the presence of permafrost. Resistant rocks with widely spaced joints and a large interjoint strength produce blocky materials, and where permafrost is present, constitute a landform sequence composed of a rockwall, talus and rock glacier. Densely jointed, less resistant rocks cannot support a high rockwall and tend to produce much finer materials; these conditions lead to debris-mantled slopes often accompanied by miniature periglacial features like patterned ground and solifluction lobes. Individual process researchers choose a single process or sequential processes operative in the catchment; then, their monitoring is designed to include the major parameters (see Fig. 2). The parameters chosen by sediment budget researchers vary also with the prevailing geology and subsurface frost conditions in the catchment. Although comprehensive monitoring promotes numerical modelling of periglacial processes or sediment budgets, it also involves significant limitations.
Fig. 2. A scheme of processes and landforms in a periglacial catchment, reflecting bedrock geology and frost regime. Parameters for monitoring are indicated.
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Monitoring favours slow and frequent processes like soil creep and slow landslide, but may not suit rapid or sporadic processes like rockfall and debris flow, unless a large-scale, expensive system is introduced. Moreover, most of the small sensors fail to detect large-scale processes like rock avalanche. Such a problem is now partly overcome by the advance of remote-sensing techniques (see below). 2.2. Choice of techniques
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al., 2002). Automatic cameras reveal the timing of movement with photographs taken at regular intervals (cf. Christiansen, 2001). These automatic techniques, when standardized and spread, allow us to collect comparable data from various periglacial environments. To promote this monitoring campaign, the standard techniques must have advantages of: •
Inclusion of all necessary parameters; High resolution data acquisition; • Solid devices ensuring long-term monitoring under harsh climates; • Handy and portable equipment; • Minimum disturbance of ground upon installation; • Least maintenance (e.g. once per year); and • Reasonable price. •
Automated monitoring generally favours process studies in periglacial environments, most of which are located distant from the researcher's office or even beyond any permanent residence. A variety of sensors, either commercial or handmade, are currently available for automatic logging of movements and their variables, although conventional manual methods are still useful for measurements difficult to be automated (Fig. 2). Reflecting the availability of commercial sensors, automatic monitoring has mainly targeted environmental factors. For instance, various sensors set together on an observation tower have recorded meteorological parameters. Monitoring of rock and soil temperatures becomes increasingly popular with the progress of inexpensive miniature loggers (e.g. Hoelzle et al., 1999). Data loggers also accept hydrological quantities converted to electric signals, such as precipitation, soil moisture, groundwater level and stream discharge. In contrast to the environmental factors, movements of rock debris or soils have mostly been measured by manual methods at intervals of a few months to several years. The lack of continuous measurements has long prevented identifying the exact timing and trigger of the movement, but the situation is improving. Strain-gauge type sensors permit monitoring of slow ground movements. Examples include a crack extensometer for frost wedging (Matsuoka, 2001), a displacement transducer for frost heave (Matsuoka, 1998) and an inclinometer for permafrost creep (Arenson et al., 2002). Potentiometers that convert rotation to voltage are used in recording solifluction or landslides (Lewkowicz, 1992; Jaesche et al., 2003). Photo-electronic sensors can record the depth of erosion or deposition by wind, stream or needle ice (e.g. Lawler, 1991). Shock sensors and seismographs detect the generation of cracking in bedrock or frozen ground (Christiansen, 2005) and of rockfalls (Mills, 1999), although the data possibly include noises from other sources. The most recent advance is achieved in the remotesensing technology. GPS is applied to monitor displacement by relatively rapid mass movement (e.g. Malet et
In particular, the operation at periglacial sites, often located in remote areas like high mountains, requires a compact, cold-resistant and maintenance-free system. Some useful techniques are listed in a provisional version of ‘A Handbook on Periglacial Field Methods’ which can be downloaded from the IPA web site (Humlum and Matsuoka, 2004). 3. Examples of monitoring This section highlights the advantages and problems of monitoring, with examples from the Swiss and Japanese mountains. The examples feature three processes representing different time scales: (1) frost wedging associated with diurnal freeze–thaw cycles; (2) solifluction reflecting seasonal processes; and (3) permafrost creep subject to an interannual variation. 3.1. Diurnal variation: frost wedging in the Japanese Alps Opening of a rock joint was monitored on a cirque wall in the Japanese Alps (Fig. 3A). A crack extensometer (Kyowa, BCD-5A: Fig. 3B) attached to the rock face detected widening of a crack of up to 10 mm with a resolution of 2.5 × 10− 3 mm. This sensor is used to measure both frost wedging (Matsuoka, 2001) and thermal expansion (Ishikawa et al., 2004). Signals from the sensor were recorded at 1-h intervals with a data logger. This time resolution (constrained by the logger capacity) is appropriate to show diurnal movement, although higher resolution provides more accurate timing of a spiky movement. A thermal probe sensed the temperature at the top of the joint at 5-min intervals
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Fig. 3. Monitoring frost wedging in southern Japanese Alps. (A) Location of the monitoring site near the base of an east-facing rockwall. (B) Instrumentation: a crack extensometer (CE) senses widening of a rock joint; a thermal probe (location at J) measures temperature at the top of the joint. (C) Rock joint movement at 60-min intervals and joint-top temperature at 5-min intervals in the autumn freeze–thaw period in 2002. Encircled highlights supercooling and/or brief zero-curtain indicating water freezing in the joint.
during the autumn freeze–thaw periods and at 0.5- to 1-h intervals in the rest of year. The former interval favours detecting the freezing of water in the joint. Another thermal probe was attached to the extensometer for calibration of the strain records against temperature (Matsuoka, 2001). Fig. 3C displays an example of diurnal events. The high resolution recording detected a brief period of supercooling followed by sudden heating and zerocurtain, which indicates the latent heat release by freezing of water in the joint. Joint opening (0.05–0.1 mm) always followed this freezing pulse with a significant time lag (ca. 5 h). The time lag between the freezing pulse at the top of joint and the beginning of expansion indicates that frost penetration in the joint finally
produced significant widening at a certain depth. Consequently, these events are attributed to expansion due to water freezing in the joint. The rock joint also responded to autumn freeze–thaw cycles, and the repetition of expansion and contraction led to interannual opening (Matsuoka, 2001; Matsuoka et al., 2003). These results suggest that identification of frost wedging requires both high resolution and long-term monitoring. 3.2. Seasonal variation: solifluction in the Swiss Alps Movement of a solifluction lobe has been monitored together with environmental parameters since 1994 in the Upper Engadin, Swiss Alps (Fig. 4A). A displacement transducer fixed to an iron angle frame
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Fig. 4. Monitoring solifluction in Upper Engadin (Swiss Alps). (A) The instrumented east-facing stone-banked lobe. (B) Deformation of a strain probe over a 4 yr period. The base of movement lies at 50 cm depth. (C) Annual variation in surface heave, subsurface inclination, soil moisture content and temperature.
sensed the vertical soil movement (frost heave). Downslope movement was observed with two types of sensors: a flexible strain probe (Fig. 4B) and a rigid inclinometer. The former is a handmade probe sensing millimetre-scale movement. Five bridge circuits, each made of two pair of strain gauges, detected bending of the probe at 12-cm depth intervals to a depth of 60 cm (Matsuoka et al., 1997). The inclinometer (Kyowa, BKJ-A-10) can record inclination within ± 10°, but the rigid, 25-cm-long probe can only respond to deep movement (probably >10 cm). Concurrently monitored were soil temperature at different depths (down to 225 cm) and soil moisture at 20 and 40 cm, sensed with platinum probes and TDR (Time Domain Reflectometry) probes, respectively. The recorded volumetric water content was calibrated by direct weighing of soil samples recovered several times from the same depth. All data were stored in data loggers at 1- to 4-h intervals. Fig. 4C summarizes annual variations in four parameters, frost heave, internal deformation (data from an inclinometer), soil moisture and temperature at four depths, from the 2001 summer to the 2002
summer. During this year, the strain probe failed to record movement due to an electric problem. The soil temperatures at 225 cm were positive in summer, which indicate the absence of subsurface permafrost, while in winter they were close to 0 °C indicative of deep seasonal frost penetration (ca. 200 cm). The seasonal frost depth fluctuated interannually between 50 and 200 cm (Matsuoka et al., 2003). Frost heave took place in two periods. A few short-term frost heave cycles happened in autumn but essentially heave was absent in spring under the latelying snow cover (Fig. 4C). The heave amount of the former rarely exceeded 1 cm. Much larger heave (ca. 3 cm) was produced during seasonal freezing in winter. A large part of the seasonal heave occurred before the frost table reached 50 cm depth, suggesting that ice lenses formed largely within the top 50 cm. This coincides with the depth of the maximum downslope movement displayed by an excavated strain probe (Fig. 4B). The inclinometer did not respond to the short-term frost heave cycles in autumn, implying that short-term frost heaving can produce only surficial soil movement
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(shallower than 10 cm). Instead, the sensor recorded significant downslope tilting in the early seasonal freezing period and in a short period at the beginning of seasonal thawing (Fig. 4C). The former tilting probably arose from seasonal frost heave intersecting with the axis of the inclinometer; hence, this was an apparent movement. The latter tilting probably resulted from gelifluction accompanying thaw consolidation at a few decimetres depth. The volumetric moisture content of soil fluctuated between 15% and 20% at both 20 and 40 cm depths during the frost-free period (Fig. 4C). The fluctuation is likely due to precipitation and subsequent desiccation (cf. Matsuoka, 1996). When frozen, the soil holds 7–8% of moisture, which might represent the unfrozen water content. The seasonal thaw consolidation in middle June resulted in a rapid rise in moisture reaching the annual maximum of 23% (Fig. 4C), which implies supersaturation and possible softening of the soil (cf. Harris et al., 1995); the data support the significance of gelifluction during seasonal thawing. Consequently, a combination of parameters documents the primary role of gelifluction in the development of the solifluction lobe and reinforces understanding of the mechanism of soil movement.
3.3. Interannual variation: permafrost creep in the Swiss Alps The final example is movement of a small rock glacier (Büz-N rock glacier) in the Upper Engadin, Swiss Alps, which occurs as bulging of a talus slope (Fig. 5A). The rock glacier has a lobate-type plan shape (50 m long and 130 m wide) and faces northeast. Unlike typical, large rock glaciers in this region (e.g. Murtèl, Muragl and Schafberg rock glaciers: Arenson et al., 2002) which have a bouldery (open-work) active layer, this rock glacier displays a pebbly surface filled with fine debris (Ikeda et al., 2003). Bulging terminated in a steep front 10 m high, which is located at 2800 m ASL. Since this elevation is close to the lower limit of permafrost indicated by intact pebbly rock glaciers (Matsuoka et al., 2005), the rock glacier is expected to be sensitive to climatic variation. The automatic monitoring system comprised two inclinometers installed at 4 and 5 m depths, thermistor probes at the surface and 0.5, 1, 2, 3, 4 and 5 m depths in a borehole reaching well below the permafrost table (ca. 2 m) and data loggers. The inclinometers (Kyowa, BKJA-10-D) measure tilting for two axes crossing at right angles, and the downslope inclination is determined
Fig. 5. Monitoring permafrost creep in Upper Engadin (Swiss Alps). (A) The instrumented northeast-facing pebbly rock glacier (Büz-N). (B) Annual velocity profiles computed from the surface velocity and inclinations at 4 and 5 m depths, using the power-law flow model (after Ikeda, 2004). (C) Internal deformation and thermal regime in 2000–2003.
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geometrically from the two values. Each axis senses tilts within ±10° from the vertical. When one axis reaches this limit, however, another axis still senses tilting, and the downslope component is estimated from the latter values assuming the ratio of inclinations between the two axes. In addition to the internal deformation, annual displacements of surface stones were manually measured by a triangulation survey (Ikeda et al., 2003). Most of the surface displacement was attributed to permafrost creep, since strain probes installed in the active layer documented movement negligible compared with the surface displacement (Ikeda, 2004). Consequently, the annual surface displacement and tilts at two depths were integrated to compute the annual velocity profile by using a power law flow model (Fig. 5B; Ikeda, 2004). Monitoring for 3 years (2000–2003) showed a large interannual fluctuation in ground temperature (Fig. 5C). The ground surface temperature never fell below − 0.6 °C during the first winter. The warm ground temperature resulted from an extraordinary deep snow cover (e.g. 5 m at Büz-N rock glacier on 22 March 2001). In contrast, the ground surface temperature lowered to − 5 °C during the second winter, reflecting the thin snow (e.g. 2 m at Büz-N rock glacier on 6 March 2002). Regardless of the fluctuation within the active layer, temperatures at 4 and 5 m depths were constant at 0.0 to − 0.1 °C. The inclinometers tilted rapidly during the first year (2000–2001), at a rate of 9° year− 1 at 5 m depth (Fig. 5C). They still maintained rapid tilting until the early winter of 2001, but thereafter decelerated; as a result, the annual tilt at 5 m depth decreased to 5° year− 1 in the second year. Tilting accelerated again in the third year. The two inclinometers tilted consistently. Such a tilting history followed the near-surface temperature: the large deformation corresponded to warmer ground in winter and smaller deformation to colder ground (Fig. 5C). The internal deformation was reflected in the surface velocity determined by the triangulation survey. The
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largest surface velocities (1.1–1.5 m year− 1) paralleled the large internal deformation in the first year, whereas the smallest velocities (0.8–1.0 m year− 1) in the second year coincided with the small deformation. The computed velocity profiles also highlight the difference between the 3 years and suggest that most of the deformation has occurred between 4 and 8 m depth within the permafrost (Fig. 5B). The integration of these data lead to a conclusion that the near-surface temperature, which depends on the winter snow depth, is most responsible for the interannual fluctuation in the movement of this rock glacier. 3.4. Summary: process variability vs. monitoring period The above examples demonstrate the significance of (1) automated, concurrent monitoring of movement and its major controls and (2) long-term continuous monitoring (> 5 years) that documents interannual fluctuation. The former permits us to relate the timing of movement to the triggering parameter and also to model the rate of movement as a function of environmental and other parameters (Eq. (1)). Such a model can, in turn, predict the temporal variation in the rate at the monitoring site as a result of interannual or longterm climatic variation. Sediment budget studies also benefit from concurrent monitoring, since numerical process models promote understanding of the temporal variation in the sediment flux (Eq. (2)) due to changes in climatic and hydrological regimes. Long-term monitoring is particularly significant to identify the type of temporal variation in the rate of movement, because the ground may experience both chronic (frequently recurring) and discrete (episodic) processes (Reid and Dunne, 2002). Fig. 6 schematically illustrates three examples of variations. Type A represents nearly constant, but gradually increasing movement. Type B shows also nearly constant
Fig. 6. Three types of temporal process variability. See text for explanation.
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movement but includes episodic events. Type C shows large interannual variability. Such variations can occur either in a single process or in a landform unit. The type to which the process (or landform) belongs should be taken into account when choosing the monitoring parameters and periods. This is because, if the monitoring is restricted to the PhD period (e.g. a few years), the measured movement may overestimate the long-term average of Type C process, or underestimate the long-term average of Type B; furthermore, where disturbance is significant during the installation of a sensor monitoring may finish before the sensor is stabilized (Smith, 1992). Monitoring that continues over several decades allows more precise understanding of the long-term average or trend of Types A and C. Such a multidecadal monitoring may finally find or miss an episodic event in Type B, which can be the largest component of the geomorphic change. In a large-scale drainage basin, a multidecadal monitoring may still be too short to represent a long-term average, because more catastrophic large events with recurrence intervals in excess of 102 years somewhere in the basin can significantly raise the average denudation rate in the basin for the Holocene (e.g. Kirschner et al., 2001), whereas in a small catchment the current slope instability can cause the reverse condition (e.g. Clapp et al., 2000). In summary, monitoring should be continued as long as possible and even passed on to the next generation of scientists (e.g. Mackay and Burn, 2002). Monitoring should also involve both movement and its controlling
variables, which enables us to obtain a functional relationship and, as a consequence, to predict the movement beyond the monitoring period. Finally, a global monitoring network will provide widely applicable relationships between the process and its variables by integrating data from different environments. 4. Strategy: model experimental site To expand periglacial monitoring sites worldwide, the fundamental step is standardization of methodology. Towards the standardization, the WG project starts with constructing a model experimental site in a typical periglacial area. The model site promotes (1) comparing various methods and instruments, (2) testing performance of the instruments in a cold, harsh environment and (3) defining core parameters and site-specific parameters. Central Spitsbergen, Svalbard, was chosen for the model site. The primary advantage of central Spitsbergen is the good accessibility from the European mainland, which allows a number of periglacial geomorphologists to participate in the project. Year-round maintenance and frequent data collection are also provided. One of the scientific advantages of central Spitsbergen is a variety of periglacial landforms coexisting in a small area: including rockwalls, talus slopes, rock glaciers, block fields, landslide features, solifluction lobes, non-sorted polygons, sorted circles, pingos,
Fig. 7. Construction of the model ice-wedge site near Longyearbyen, Svalbard (September 2004, photographs by Andreas Kellerer). (A) A portable handy auger that can penetrate into frozen soil. (B) Setting instruments on an ice wedge trough.
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palsas, seasonal frost mounds, thermokarst depressions, tafoni, wind erosion features (e.g. Åkerman, 1987; Humlum et al., 2003; Matsuoka et al., 2004). Such a variety enables us to concentrate various technologies within a study area. The landscape variety reflects the location transitional between warm and cold permafrost. High relief further reinforces the spatial contrasts in periglacial conditions: warm permafrost with a thick active layer (> 1 m) vs. cold permafrost with a thin active layer (< 1 m); dry sites (e.g. convex upper slopes) vs. wet sites (e.g. concave lower slopes); and steep rockwalls to flat terraces or strandflats. These conditions promote determination of the thresholds for the generation of the above landforms. Another scientific advantage of central Spitsbergen is that there are already a number of quantitative data on various processes: rock weathering (e.g. Matsuoka, 1991; Prick, 2003); permafrost creep (e.g. Isaksen et al., 2000; Kääb et al., 2002); frost heave and gelifluction (e.g. Åkerman, 1996; Matsuoka and Hirakawa, 2000; Sørbel and Tolgensbakk, 2002); frost sorting (e.g. Hallet et al., 1988; Hallet, 1998); ice-wedge cracking (Matsuoka, 1999; Christiansen, 2005); pingo growth (Yoshikawa and Harada, 1995; Matsuoka et al., 2004); and fluvial sediment transport (Bogen and Bønsnes, 2003). Also available are climatological parameters (e.g. Humlum, 2004) and permafrost structure and temperature (Isaksen et al., 2001; Christiansen et al., 2003). These data are useful for determination of monitoring parameters and techniques and for inter-site comparison of movements and variables. In September 2004, the first attempt was undertaken on constructing a model ice wedge site near Longyearbyen, central Spitsbergen (Fig. 7). Seven scientists participated in this campaign. This site had already experienced 1–2 years of monitoring with sensors installed in 2002–2003, which consisted of shock sensors for detecting thermal cracking, thermistor cables for monitoring ground temperatures, and an automatic camera that displays snow depth (Christiansen, 2005). The existing system was reinforced in 2004 by installation of additional thermistor cables down to 2 m depth, two kinds of soil moisture sensors, breaking cables (copper wires: Mackay, 1974) that record the timing of thermal cracking, and dilatometers for recording the widening of an icewedge trough (Matsuoka, 1999) and the vertical movement at an ice wedge rampart (Fig. 7B). A portable engine auger (Fig. 7A) was used to install sensors and frames well into permafrost with minimum disturbance of the structure and thermal regime of the ground. The installation was followed by an
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excursion of the PACE21 (Permafrost and Climate in the 21st Century) workshop, when advantages and possible improvements of the monitoring system were discussed at the model site. Acknowledgements I would like to thank Achim A. Beylich for his invitation to the 1st SEDIFLUX workshop and giving a chance to demonstrate the new IPA-sponsored project. I am also grateful to Ole Humlum and Hanne Christiansen for fruitful discussion on the strategy of the project, and to Frank Ahnert and Olav Slaymaker for their helpful comments on the manuscript. References Åkerman, H.J., 1987. Periglacial forms of Svalbard: a review. In: Boardman, J. (Ed.), Periglacial Processes and Landforms in Britain and Ireland. Cambridge University Press, Cambridge, pp. 9–25. Åkerman, H.J., 1996. Slow mass movements and climatic relationships, 1972–1994, Kapp Linné, West Spitsbergen. In: Anderson, M.G., Brooks, S.M. (Eds.), Advances in Hillslope Processes, vol. 2. Wiley, Chichester, pp. 1219–1256. Anderson, R.S., 2002. Modeling the tor-dotted crests, bedrock edges, and parabolic profiles of high alpine surfaces of the Wind River Range, Wyoming. Geomorphology 46, 35–58. Arenson, L., Hoelzle, M., Springman, S., 2002. Borehole deformation measurements and internal structures of some rock glaciers in Switzerland. Permafrost and Periglacial Processes 13, 117–135. Bogen, J., Bønsnes, T.E., 2003. Erosion and sediment transport in High Arctic Rivers, Svalbard. Polar Research 22, 175–189. Brown, J., Hinkel, K.M., Nelson, F.E., 2000. The Circumpolar Active Layer Monitoring CALM) program: research designs and initial results. Polar Geography 24, 165–258. Christiansen, H.H., 2001. Snow-cover depth, distribution and duration data from northeast Greenland obtained by continuous automatic digital photography. Annals of Glaciology 32, 102–108. Christiansen, H.H., 2005. Ice-wedge dynamics in Svalbard: evidence for thermal contraction cracking. Permafrost and Periglacial Processes, 87–98. Christiansen, H.H., Åkerman, H.J., Repelewska-Pekalowa, J., 2003. Active layer dynamics in Greenland, Svalbard and Sweden. In: Haeberli, W., Brandová, D. (Eds.), Extended Abstracts, Reporting Current Research and New Information, 8th International Conference on Permafrost. Balkema, Lisse, pp. 19–20. Clapp, E.M., Bierman, P.R., Schick, A.P., Lekach, J., Enzel, Y., Caffee, M., 2000. Sediment yield exceeds sediment production in arid region drainage basins. Geology 28, 995–998. Haeberli, W., Burn, C.R., 2002. Natural hazards in forests: glacier and permafrost effects as related to climate change. In: Sidle, R.C. (Ed.), Environmental Changes and Geomorphic Hazards in Forests. CABI Publishing, Oxfordshire, pp. 167–202. Haeberli, W., Hoelzle, M., Keller, F., Vonder Mühll, D., Wagner, S., 1998. Ten years after the drilling through the permafrost of the active rock glacier Murtèl, eastern Swiss Alps: answered questions and new perspectives. In: Lewkowicz, A.G., Allard, M. (Eds.), Proceedings of the 7th International Conference on Permafrost. Centre d'études Nordiques, Sainte-Foy, pp. 403–410.
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