Author's personal copy

7.22 Mass-Movement Causes: Glacier ThinningM Geertsema, Ministry of Forests, Lands, and Natural Resource Operations, Prince George, BC, CanadaM Chiarle, Consiglio Nazionale delle Ricerche – Istituto di Ricerca per la Protezione Idrogeologica, Strada delle Cacce, Italy

r 2013 Elsevier Inc. All rights reserved.

7.22.1 Introduction 217

7.22.2 Landslides in Soil 217 7.22.2.1 Exposure of Glacial Sediment 218 7.22.2.2 Paraglacial Dam Break Floods and Related Debris Flows 218 7.22.2.3 Melting of Ground Ice 219 7.22.3 Landslides in Rock 219 7.22.3.1 Glacial Conditioning of Rock Masses 219 7.22.3.2 Landslides on Glacially Conditioned Rock Slopes 220 7.22.4 Conclusions 221 References 221

Ge

In:

Ge

Hi

Tre

GlossaryGlacial debuttressing Refers to the loss of support to

valley walls upon glacier shrinkage, and is often

accompanied by the expansion of joints in rock masses

ertsema, M., Chiarle, M., 2013. Mass movement causes: glacier thinning.

Shroder, J. (Editor in Chief), Marston, R.A., Stoffel, M. (Eds.), Treatise on

omorphology. Academic Press, San Diego, CA, vol. 7, Mountain and

llslope Geomorphology, pp. 217–222.

atise on Geomorphology, Volume 7 http://dx.doi.org/10.1016/B978-0-12-3747

Jokulhlaup Outburst flood from a glacial dam breach.

Paraglacial process A glacially conditioned, nonglacial

process such as a landslide that happens long after glaciers

have left, but as a result of the glacier-imposed stresses.

Abstract

Glaciers have profound effects on the stability of slopes. Receding glaciers expose soils, commonly in steep slope positions.

The soils are rapidly eroded and transported by debris slides and flows. Outburst floods from temporary lakes may also

occur. Glaciers load bedrock, and following deglaciation stress release and slope relaxation from glacial debuttressing can

result in a variety of bedrock landslides. As glaciers continue to recede in this century, we expect continued associatedlandslide activity.

7.22.1 Introduction

Mass movements can have a variety of causes. Earthquakes,

permafrost degradation, wildfire, and heavy rainfall are com-

mon contributors to natural landslides. Tectonics, marked

climate change, volcanic activity, and inherent weaknesses in

soil and rock are some of the factors that may distinguish one

region from another in terms of landslide activity, and indeed

these sorts of factors contribute to global and regional land-

slide hot spots (Nadim et al., 2006). Glaciers also play a strong

role in conditioning slopes to mass movement (Evans and

Clague, 1994), and the impacts on hillslopes persist after

glaciers disappear.

Paraglacial processes (i.e., glacially conditioned, nonglacial

processes) were first introduced to the literature by Ryder

(1971a, b) and defined by Church and Ryder (1972) to de-

scribe sedimentation rates on alluvial fans. Since then much

work has been done to extend the concept of paraglacial

geomorphology to other processes (see Ballantyne, 2002a, b

and references therein) including landslides.

Glaciers play an important role in conditioning mountain

slopes for mass movement. Mass movements in mountainous

terrain are strongly influenced by the advance and retreat of

glaciers (Evans and Clague, 1994). Many studies show that

recently deglaciated areas are hot spots for a variety of land-

slide types (e.g., Bovis, 1982; Ballantyne, 2002a, b; Holm

et al., 2004; Geertsema et al., 2006; Cossart et al., 2008). We

note that glaciers are agents of erosion and deposition. Al-

though some valleys are deepened by glaciers, others may be

filled with glacigenic sediments. Both scenarios present chal-

lenges for slope instability. Here, we restrict our discussion to

the effects of glacial erosion and thinning on mass movement.

We use the word ‘landslide’ as a generic term for a variety of

mass-movement types and processes (Cruden and Varnes,

1996). Although we recognize that landslides are commonly

complex, involving movements in both rock and soil

(Geertsema et al., 2006), here we consider the influence of

glacier thinning on landslides in soil and rock separately.

7.22.2 Landslides in Soil

Glaciers erode, redistribute, and deposit sediment. As glaciers

retreat and thin, they expose both scoured bedrock and glaci-

genic sediment (Figure 1). Exposed soils can range from thin

veneers over bedrock to complex packages of sediment that are

tens of meters thick. Genetic materials can include till,

39-6.00168-8 217

Figure 2 Heavy rainfall on 24 July 1996 led to gully deepening(arrows) and debris flow and flooding on a fan in the forefield of theOrmelune Glacier (Aosta Valley, NW Italy). Photo Giovanni Mortara,Consiglio Nazionale delle Ricerche – Istituto di Ricerca per laProtezione Idrogeologica, Torino, Italy.

Figure 1 Thinning and retreat of Llewellyn Glacier in northernBritish Columbia (Clague et al., 2010) has exposed steep rock,soil-covered slopes, and an unvegetated forefield with amoraine-dammed lake (far right). Previous glacier thickness isevident from two trimlines (arrows). Note the variable size of gullies,related in part to the age of surface exposure. The oversteepenedslope below the lowest trimline is especially at risk for gully erosion(as is happening in the inset photo). Photos by Marten Geertsema,British Columbia Ministry of Forests and Range.

218 Mass-Movement Causes: Glacier Thinning

Author's personal copy

glaciolacustrine deposits, colluvium, glaciofluvial, and aeolian

sediments. In some cases, the landforms are arranged in such

a way that they become dams for temporary lakes. The unve-

getated, and, in some cases, ice-cored sediments, are subject to a

variety of hillslope processes (Ballantyne, 2002a) and can be

readily mobilized by heavy precipitation, snow and ice melt,

and dam-burst floods (Chiarle et al., 2007).

Figure 3 Glacier thinning along Tulsequah Glacier is responsible forthe development of ice-dammed lakes such as this one. Lake NoLake (arrow) drains subglacially 1 or 2 times annually, resulting inlarge outburst floods on Tulsequah River (Geertsema and Clague,2005). Photo by Marten Geertsema, British Columbia Ministry ofForests and Range.

7.22.2.1 Exposure of Glacial Sediment

Retreating and thinning glaciers commonly expose extensive

areas of bare sediment (Figure 1). Where soil is exposed on

steep slopes, debris flows (Figure 2) are the main (most effi-

cient) agents of erosion and sediment transport (Ballantyne,

2002a). Bulking of sediment to channels from surface erosion

or debris slides generally leads to debris flows with longer travel

distances. In addition, channelized runoff may entrain sedi-

ment and transform movements into debris flows. Although

intense rainstorms and rapid snow melt are the principal trig-

gers of debris flows, the available sediment supply, the young

steep slopes, and the lack of vegetative cover set these recently

deglaciated areas apart from other landslide-prone regions.

In a survey of 19 alpine basins in the Lillooet River valley,

Holm et al. (2004) found that debris movements were con-

centrated along Little Ice Age lateral moraines and trimlines.

Similarly, Zimmermann and Haeberli (1992) found that more

than half of the debris flows triggered by intense rain in the

Swiss Alps in 1987 initiated on steep, Little Ice Age vintage,

till-covered slopes.

7.22.2.2 Paraglacial Dam Break Floods and RelatedDebris Flows

Retreating and thinning glaciers may produce a variety of

(usually short lived) lakes (Clague and Evans, 1994). Glacial

lakes may be dammed by moraines, landslides, alluvial fans,

and the glaciers themselves. Outburst floods from glacier-dam-

med lakes (Figure 3) can happen annually, and the lakes may

experience a jokulhlaup cycle (Geertsema and Clague, 2005).

Conversely, lakes behind moraine dams do not refill once the

dams are breached. Floods and debris flows from the escaping

waters can be catastrophic because of the large volumes in-

volved, the long travel distances, and their unpredictability.

Dam-burst floods tend to be much larger than nival floods;

because river systems are rarely plumbed for extreme events, a

suite of cascading effects may result, including secondary

debris slides from valley walls and sometimes large debris

flows. An example of such a suite of events comes from mo-

raine-dammed Klattasine Lake in British Columbia. The lake

drained catastrophically sometime between June 1971 and

September 1973, releasing about 1.7�106 m3 of water. The

resultant flow dissected the moraine and mobilized large

Figure 4 Glaciers erode and steepen mountain valleys, but provide

Mass-Movement Causes: Glacier Thinning 219

Author's personal copy

quantities of sediment from the channel and valley margins.

As the sediment concentration increased, the flood rapidly

transformed into a debris flow that traveled 8 km downstream

(Clague et al., 1985). The debris flow destabilized adjacent

valley slopes causing secondary landslides.

Outbursts floods from englacial and subglacial lakes can be

insidious because the water pockets are difficult to detect. An

englacial lake with a volume of 65 000 m3 was recently

identified with Tete-Rousse Glacier on Mont Blanc, France.

Local authorities, concerned about the threat an outburst

flood posed to several villages in the valley below, decided to

drain the water through vertical holes drilled into the glacier

(Chiarle et al., 2011). In 1892, a 200 000-m3 englacial lake

drained in the same area, triggering an 800 000-m3 debris

flow. The flow, which ran through the village of Saint Gervais

and killed 175 people, is one of the worst glacier-caused dis-

asters in Europe (Vincent et al., 2010).

support to the valley walls. When glaciers waste out of the valleysstress release occurs, which may lead to joint expansion (yellowarrows), as seen here in the Telkwa Mountains, British Columbia.Further expansion of these joints places this site at risk for topplingand rock fall–cliff collapse. Photos by Marten Geertsema, BritishColumbia Ministry of Forests and Range.

7.22.2.3 Melting of Ground Ice

Dead glacier ice (ground ice) is common around the margins of

retreating glaciers. Even when it is no longer in equilibrium

with climate, such ice may persist primarily because of the in-

sulating effect of overlying debris. Slow thawing of the ice,

particularly under a warming climate, can contribute to debris

flow initiation. Although many flows are triggered by rainfall,

some may occur simply from melting of the ice. Mass move-

ments on rupture surfaces of buried glacial ice are similar to

those that involve ice-rich permafrost. The ice acts as a barrier to

water movement and, therefore, concentrates flow. Meltwater

and rainfall can be concentrated along a frozen rupture surface.

Ice-rich debris and ice lenses have been observed in many

debris flow initiation zones (Chiarle et al., 2007). Thawing of

ground ice likely contributed to a debris flow on 29 July 2005

in Val di Fosse in the eastern Italian Alps. Melting of a buried

ice mass, exposed in a 20-m-long detachment zone at 3000 m

asl, triggered a 15 000-m3 debris flow (Chiarle et al., 2011).

Similarly, Mattson and Gardner (1991) documented 25

landslides in ice-cored moraines in the Alberta Rockies. The

landslides initiated at the ice–debris interface and were trig-

gered by rainfall as well as melting of ice.

We expect thawing of ground ice to increase in importance

as a paraglacial contributor to alpine debris flows as glaciers

continue to thin. Resulting debris flow activity may lag behind

glacier retreat because of the lack of direct contact of the

buried ice with the atmosphere. Once debris is removed by an

initial landslide, or becomes thinner, we expect melting of ice

to accelerate and to lead to more debris flows.

7.22.3 Landslides in Rock

Glacier dynamics can have profound effects on the stability of

rock slopes. Both glaciation and deglaciation weaken rock

masses (Augustinus, 1995; Ballantyne, 2002a; Cossart et al.,

2008). This happens in a four-step process: (1) deepening and

widening of valleys (glacial erosion); (2) ice loading resulting

in the development of stress fractures; (3) debuttressing

(during deglaciation); and (4) stress release as manifested by

joint expansion (Figures 4 and 5).

Landslides resulting from glacially conditioned, rock mass

instability include rock topples and falls, slow deep-seated

slope deformation, and catastrophic rock avalanches. Rockfall

(cliff collapse) and slow rock slope deformation (and sagging)

can transform into long runout rock avalanches (Figure 5)

(Chigira, 1992; Geertsema et al., 2006). The spatial and tem-

poral association of rock landslides with previously glaciated

areas suggests that glacial conditioning of rock slopes plays an

important role in their occurrence.

7.22.3.1 Glacial Conditioning of Rock Masses

Eroding glaciers deepen valleys and steepen valley walls, par-

ticularly where ice flow is parallel to the long axis of valleys.

The deepening of valleys increases rock wall heights, which, in

turn, elevates the self-weight shear stresses of the rock mass

(Bovis, 1982; Ballantyne, 2002a) and may increase tensile

stresses in toe slopes (Augustinus, 1995).

Glacial loading, in addition to having regional isostatic

impacts, imparts stresses on both valley walls and floors (Bal-

lantyne, 2002a). Fracture orientation from glacial loading can

be distinguished from structural joint sets because of a similar

orientation to glacier movement (e.g., Bovis, 1990). According

to Benn and Evans (1998), glacier loading stresses vary at dif-

ferent scales. At the regional scale stress is a function of ice

thickness and surface gradient, at the mountain slope scale

stresses increase toward the valley floor, and at the site level

stresses are greater on stoss faces of rock ridges. Cossart et al.

(2008) calculated stresses at these various scales in an investi-

gation of glacial debuttressing on landslides in southeastern

France. They calculated values of up to 9000 and 300 kPa for

normal and longitudinal ice-loading stresses, respectively.

Glacial debuttressing is one of the most important

consequences of deglaciation in mountain environments

(Ballantyne, 2002a) and involves the expansion of joint sets in

Figure 6 Rotational rock slide (A) of mountain side as a result ofglacial debuttressing at Neves Creek, northern Rocky Mountains,British Columbia. View is to the South. Inset (view to the northwest)shows the effects of glacial debuttressing in (A), the same rotationalrock slide as in the main image, and (B) a prehistoric rock avalanche.The inset image was created by draping a 1999 orthophoto over a20-m digital elevation model. Vertical exaggeration is 1. Photo byMarten Geertsema, British Columbia Ministry of Forests and Range.

Figure 5 Joint expansion such as seen in Figure 4 and at the mainscarp (arrows) contributed to the cliff collapse that led to the2.7-km-long 1999 Howson rock avalanche in British Columbia’sTelkwa Mountains (Geertsema et al., 2006). Photos by MartenGeertsema, British Columbia Ministry of Forests and Range.

220 Mass-Movement Causes: Glacier Thinning

Author's personal copy

the rock mass (Figure 4). As glaciers retreat and thin valley

walls, they cease to support valley walls. Most rock masses dis-

play some degree of elasticity and will rebound to some degree

in response to the removed load. Note that this is different from

isostatic rebound. When rock slopes are exposed by glacier

thinning, relaxation of tensile stresses in the rock mass is re-

leased to a degree dependent on the amount of residual strain

energy and the modulus of elasticity of the rock (Ballantyne,

2002a). This rebound in response to debuttressing may result in

the opening of joints (Figure 4). The joints develop independ-

ently of regional structure – the response is to glacial loading –

and correspond to the direction of ice flow. This paraglacial

relaxation of rock masses conditions them for mass movement.

7.22.3.2 Landslides on Glacially Conditioned Rock Slopes

Although glaciers can condition rock slopes for failure, stability

is still largely controlled by lithology and structure. Augustinus

(1995) in New Zealand and Holm et al. (2004) in British

Columbia observed few landslides in glacially debuttressed

plutonic rock in contrast to abundant landslides in weaker,

sedimentary, metamorphic, or volcanic bedrock. In some cases,

it becomes difficult to distinguish the influences of tectonic

stresses, faulting, extension, compression, mountain building,

river incision, volcanic influences, and similar factors from the

effects of glacial debuttressing (see, e.g., Hermans et al., 2001;

Prager et al., 2008). Nonetheless, the evidence supporting a

relationship between glacial debuttressing and the failure of

rock slopes is strong (e.g., Panizza, 1973; McSaveney, 1993;

Hancox and Perrin, 1994; Abele, 1997; Ballantyne et al., 1998;

Fort, 2000; Holm et al., 2004; Strom, 2004; Geertsema et al.,

2006; Cossart et al., 2008; Hewitt et al., 2008).

Paraglacial rockfall contributes to the development of talus

aprons at the base of cliffs. Many authors (see Ballantyne,

2002a) have shown that present-day rockfall accumulation

rates are much too small (order of magnitude too small) to

account for the amount of postglacial talus accumulation. The

conclusion is that rockfall rates were much greater in the early

paraglacial phase of the postglacial period. In a few cases,

rockfall (cliff collapse) can transform into long runout rock

avalanches.

Another response of rock slopes to glacial debuttressing is

slow deformation, or gravitational sagging, or spreading.

These slow movements commonly display horst and graben

topography, gulls, and uphill-facing scarps. Bovis (1982,

1990) confirmed that 3�107 m3 of rock was deforming as a

result of post-Little Ice Age glacial debuttressing following

downwasting of Affliction Glacier in British Columbia. Simi-

larly, Evans and Clague (1994) reported on post-Little Ice Age

sackung development above Melbern Glacier in the St. Elias

Mountains of British Columbia. Slow rock deformation can be

a precursor to catastrophic rock slope failure (Chigira, 1992;

Geertsema et al., 2006). In some cases, similar lithologies can

result in different types of rock failure. A slope in the northern

Rocky Mountains of British Columbia responded to debut-

tressing with a slow, deep-seated rotational slide as well as a

rock avalanche (Figure 6).

Rock avalanches are generally characterized by their large

volumes, long runout distances, and low travel angles. Many

rock avalanches after the Little Ice Age occur on rock slopes

above glaciers (McSaveney, 1993; Evans and Clague, 1994;

Holm et al., 2004). For example, two-thirds of the rock ava-

lanches in northern British Columbia that occurred between

1973 and 2003 (Geertsema et al., 2006) occurred on cirque

Mass-Movement Causes: Glacier Thinning 221

Author's personal copy

walls where glaciers have thinned up to several hundred

meters. Some early Holocene rock avalanches are measured in

volumes of tens of cubic kilometers. Examples occur in many

parts of the world (e.g., Hancox and Perrin, 1994; Hewitt

et al., 2008), and most of these gigantic events occurred very

shortly after deglaciation.

Further evidence for paraglacial debuttressing causes of

landslides is provided by an exhaustion model of Cruden

and Hu (1993) applied to the Canadian Rockies. The model

assumes that a limited number of failure sites exist and that

failure occurs only once at a given site. This causes the prob-

ability of failure to diminish exponentially over time and goes

a long way to explain some of the immense prehistoric

landslide deposits. Of course, we do see evidence of repeated

rock avalanches in the same areas, but their model provides a

good general framework. The other problem with rock ava-

lanches is that they may happen after a long period of con-

ditioning by slope deformation. So while rockfall and slope

deformation may be immediate responses to glacial thinning,

some rock avalanches require more specific conditions –

which develop overtime (e.g., Abele, 1997). Ultimately, some

mid-Holocene rock avalanches may still be occurring as

paraglacial responses to deglaciation.

7.22.4 Conclusions

Glaciers play an important role in conditioning landscapes for

mass movement. Glaciers rearrange and override sediments,

only to expose them to elements when the glaciers recede. The

exposed and commonly steep soils are rapidly modified by

erosion and debris slides and flows. Outburst floods from

temporary lakes also occur, and these may also transform into

debris flows. Not only do glacial loads impart stress fractures

to bedrock, the stress release and associated slope relaxation

can result in rockfall, slow deep-seated slope deformation, and

(under the right circumstances) rock avalanches. As glaciers

continue to thin in the twenty-first century, we can expect

continued associated landslide activity.

References

Abele, G., 1997. Influence of glacier and climate variation on rock slide activity inthe Alps. Palaoklimaforschung 19, 1–6.

Augustinus, P.C., 1995. Glacial valley cross-profile development: the influence ofin situ rock stress and rock mass strength, with examples from the SouthernAlps, New Zealand. Geomorphology 14, 87–97.

Ballantyne, C.K., 2002a. Paraglacial geomorphology. Quaternary Science Reviews21, 1935–2017.

Ballantyne, C.K., 2002b. A general model of paraglacial landscape response. TheHolocene 12, 371–376.

Ballantyne, C.K., Stone, J.O., Fifield, L.K., 1998. Cosmogenic Cl-36 dating ofpostglacial landsliding at The Storr, Isle of Skye, Scotland. The Holocene 8,347–351.

Benn, D.I., Evans, D.J.A., 1998. Glaciers and Glaciation. Arnold, London, 734 pp.Bovis, M.J., 1982. Uphill-facing (antislope) scarps in the Coast Mountains,

southwest British Columbia. Geological Society of America Bulletin 93,804–812.

Bovis, M.J., 1990. Rock-slope deformation at Affliction Creek, southern CoastMountains, British Columbia. Canadian Journal of Earth Sciences 27, 243–254.

Chiarle, M., Geertsema, M., Mortara, G., Clague, JJ., 2011. Impacts of climatechange on debris flow occurrence in the Cordillera of western Canada and theEuropean Alps. In: Genevois, R., Hamilton, D.L., Prestininzi, A. (Eds.),

Proceedings of the 5th International Conference on Debris-Flow HazardsMitigation. Mechanics, Prediction and Assessment. Padua, Italy 14–17 June2011. Universita La Sapienza, Roma, pp. 45–52.

Chiarle, M., Iannotti, S., Mortara, G., Deline, P., 2007. Recent debris flowoccurrences associated with glaciers in the Alps. Global and Planetary ChangeSpecial Issue on "Climate Change Impacts on Mountain Glaciers andPermafrost" 56, 123–136.

Chigira, M., 1992. Long term gravitational deformation of rocks by mass creep.Engineering Geology 32, 157–184.

Church, M., Ryder, J.M., 1972. Paraglacial sedimentation: a consideration of fluvialprocesses conditioned by glaciations. Geological Society of America Bulletin 83,3059–3071.

Clague, J.J., Evans, S.G., 1994. Formation and failure of natural dams in theCanadian Cordillera. Geological Survey of Canada Bulletin 464, 35 pp.

Clague, J.J., Evans, S.G., Blown, I.G., 1985. A debris flow triggered by thebreaching of a moraine-dammed lake, Klattasine Creek, British Columbia.Canadian Journal of Earth Sciences 22, 1492–1502.

Clague, J.J., Koch, J., Geertsema, M., 2010. Expansion of outlet glaciers of theJuneau Icefield before and during the last two millenia. The Holocene, http://dx.doi.org/10.1177/00959683609353433.

Cossart, E., Braucher, R., Fort, M., Bourles, D.L., Carcaillet, J., 2008. Slopeinstability in relation to glacial debuttressing in alpine areas (Upper Durancecatchment, southeastern France): evidence from field data and 10Be cosmic rayexposure ages. Geomorphology 95, 3–26.

Cruden, D.M., Hu, X.Q., 1993. Exhaustion and steady state models for predictinglandslide hazardsin the Canadian Rocky Mountains. Geomorphology 8, 279–285.

Cruden, D.M., Varnes, D.J., 1996. Landslide types and processes. In: Turner, A.K.,Schuster, R.L. (Eds.), Special Report 247: Landslide Investigation and Mitigation.National Research Council, Transportation Research Board, Washington, DC,pp. 36–75.

Evans, S.G., Clague, J.J., 1994. Recent climatic change and catastrophicgeomorphic processes in mountain environments. Geomorphology 10, 107–128.

Fort, M., 2000. Glaciers and mass wasting processes: their influence on theshaping of the Kali Gandaki valley (higher Himalya of Nepal). QuaternaryInternational 65/66, 101–119.

Geertsema, M., Clague, J.J., 2005. Jokulhlaups at Tulsequah Glacier, northwesternBritish Columbia, Canada. The Holocene 15, 310–316.

Geertsema, M., Clague, J.J., Schwab, J.W., Evans, S.G., 2006. An overview ofrecent large catastrophic landslides in northern British Columbia, Canada.Engineering Geology 83, 120–143.

Hancox, G.T., Perrin, N.D., 1994. Green Lake landslide: a very large ancient rockslide in Fiordland, New Zealand. Proceedings of the 7th International IAEGCongress. Balkema, Rotterdam, pp. 1677–1689.

Hewitt, K., Clague, J.J., Orwin, J.F., 2008. Legacies of catastrophic rock slopefailures in mountain landscapes. Earth Science Reviews 87, 1–38.

Hermans, R.L., Niedermann, S., Garcia, A.V., Gomez, J.S., Strecker, M.R., 2001.Neotectonics and catastrophic failure of mountain fronts in the southern intra-Andean Puna Plateau, Argentina. Geology 29, 619–623.

Holm, K., Bovis, M.J., Jakob, M., 2004. The landslide response of alpine basins topost-Little Ice Age glacial thinning and retreat in southwestern British Columbia.Geomorphology 57, 201–216.

Mattson, L.E., Gardner, J.S., 1991. Mass wasting on valley-side ice-cored moraines,Boundary Glacier, Alberta, Canada. Geografiska Annaler 73A, 123–128.

McSaveney, M.J., 1993. Rock avalanches of 2 May and 6 September 1992, MountFletcher, New Zealand. Landslide News 7, 2–4.

Nadim, F., Kjekstad, O., Peduzzi, P., Herold, C., Jaedicke, C., 2006. Global landslideand avalanche hotspots. Landslides 3, 159–173.

Panizza, M., 1973. Glacio pressure implications in the production of landslides inthe dolomitic area. Geologia Applicata e Idrogeologia 8, 289–297.

Prager, C., Zangerl, C., Patzelt, G., Brandner, R., 2008. Age distribution of fossillandslides in the Tyrol (Austria) and its surrounding areas. Natural Hazards andEarth Systems Science 8, 377–407.

Ryder, J.M., 1971a. The stratigraphy and morphology of paraglacial alluvial fans insouth-central British Columbia. Canadian journal of Earth Science 8, 279–298.

Ryder, J.M., 1971b. Some aspects of the morphometry of paraglacial alluvial fans insouth-central British Columbia. Canadian journal of Earth Science 8, 1252–1264.

Strom, A., 2004. Rock avalanches of the Ardon River valley at the southern foot ofthe Rocky Range, Northern Caucasus, North Osetia. Landslides 1, 237–241.

Vincent, C., Garambois, S., Thibert, E., Lefebvre, E., Le Meur, E., Six, D., 2010.Origin of the outburst flood from Glacier de Tete Rousse in 1892 (Mont Blancarea, France). Journal of Glaciology 56, 688–698.

Zimmermann, W., Haeberli, W., 1992. Climate change and debris flow activity in highmountain areas: a case study in the Swiss Alps. Catena Supplement 22, 59–72.

Author's personal copy

Biographical Sketch

Marten Geertsema, a geomorphologist, has worked for the British Columbia Forest Service since 1985. He is

interested in terrain hazards and their causes, including past, present, and future hazard regimes. Marten has

degrees in soil science and earth science from the University of Alberta, and a doctorate in physical geography

from the University of Utrecht in the Netherlands. He is a professional geoscientist and a professional agrologist,

and holds adjunct professor positions at the University of Northern British Columbia and Oklahoma State

University.

222 Mass-Movement Causes: Glacier Thinning

Marta Chiarle is a geomorphologic researcher with the Research Institute for Geo-hydrological Protection of

Turin, of the Italian National Research Council. Marta has also worked as a visiting scientist with the US Geo-

logical Survey in Colorado, and Simon Fraser University in British Columbia. She is interested in mountain

hazards and climate change, and has a special interest in alpine debris flows and periglacial geomorphology.

Marta has a degree in Earth Science from the University of Turin, and a doctorate in Geological Engineering from

the Politecnico di Torino, Italy.