C

CALVING GLACIERS depth (hw) is linear, and can be simply expressed as u c = chw. The value of the coefficient c varies greatly in different settings, being highest for temperate gla- Charles R. Warren ciers and lowest for polar glaciers. Also, for any given School of Geography and Geosciences, University of water depth, calving is an order of magnitude faster in St. Andrews, St. Andrews, Scotland, UK fjords (Fjords) than in lakes, largely as a result of the effect of the different water densities on the buoyancy Calving glaciers terminate in water and lose mass by calv- forces acting on the ice. Much of our understanding ing, the process whereby masses of ice break off to form of the dynamics of calving glaciers stems from inten- icebergs. Since they may consist of temperate or polar sive studies of a small number of Alaskan glaciers ice, may be grounded or floating, and may flow into the (Alaskan Glaciers), particularly Columbia Glacier and sea or into lakes, many types exist. They are widely dis- LeConte Glacier (Meier, 1997; O’Neel et al., 2001). tributed, but while lake-calving glaciers may exist in any This work established the empirical uc/hw relationship, glacierized mountain range, tidewater glaciers but left the physical processes behind it unclear. Model- (Tidewater Glaciers) are currently confined to latitudes ing has subsequently shown that this relationship, and higher than 45 . Typically, calving glaciers are fast the contrasting calving rates in tidewater and freshwa- flowing and characterized by extensional (stretching) flow ter, can be understood with reference to intricate feed- near their termini, resulting in profuse crevassing backs between calving and glacier dynamics (Crevasses). They usually terminate at near-vertical ice (Dynamics of Glaciers) (Van der Veen, 2002; Benn cliffs, which are typically a few tens of meters in height et al., 2007). In essence, calving rates are controlled but are sometimes as much as 80 m high. Calving activity primarily by variations in longitudinal strain rates and above the waterline comprises a continuum from small ice velocities (especially sliding speeds), which deter- fragments of ice to pillars the full height of the cliff. Below mine the density and depth of crevassing. the waterline much ice may be lost through melting, but, in Calving glaciers are significant for three main reasons: deep water, buoyancy causes infrequent but high magni- tude calving events. In some settings, thermal erosion 1. Glacier dynamics. Calving glaciers comprise the most (melting) at the waterline can cause calving by undercut- dynamic elements of many of the world’s ice masses, ting the cliff. The calving process permits much larger vol- and calving is the major means of ice loss from umes of ice to be lost over a given time than melting; this is the two continental ice sheets of Antarctica and seen spectacularly at the margins of ice shelves (Ice Shelf ) Greenland (Antarctica and Greenland Ice Sheet) from which tabular icebergs (Iceberg) with surface areas (Rignot and Kanagaratnam, 2006). An understanding of many tens of square kilometers can be released. For of calving processes is therefore critical for predicting example, over 35 days in 2002, an area of 3,250 km2 of cryospheric response to future climate change and con- the Larsen Ice Shelf in Antarctica calved catastrophically, sequent sea-level rise; our present limited understand- releasing 720 km3 of ice into the ocean. ing of the links between climate and ice dynamics Glaciers calve faster in deeper water. This correlation hinders such predictions (Nick et al., 2009). During between calving rate (u c in meters per annum) and water the waning stages of Quaternary glacial periods

Vijay P. Singh, Pratap Singh & Umesh K. Haritashya (eds.), Encyclopedia of Snow, Ice and Glaciers, DOI 10.1007/978-90-481-2642-2, # Springer Science+Business Media B.V. 2011 106 CANADIAN ROCKIES AND COAST MOUNTAINS OF CANADA

(Quaternary Glaciation), calving was the dominant Cross-references process of mass loss around the midlatitude ice Alaskan Glaciers sheets, and calving processes strongly affected their Antarctica patterns of growth and decay. Armadas of icebergs Dynamics of Glaciers discharged during ice sheet collapses are believed to Fjords have caused global climate change by altering Glacier Lake Outburst Floods oceanic circulation. Calving has also accounted for Global Warming and its Effect on Snow/Ice/Glaciers Greenland Ice Sheet the rapid collapse of ice shelves around the Antarctic Ice Shelf Peninsula in recent decades, most notably the Larsen Marine Ice Sheet ice shelves. Quaternary Glaciation 2. Non-climatic behavior. Calving glacier fluctuations are Sea-Level highly sensitive to topographic controls, with advances Tidewater Glaciers and retreats often being punctuated by stillstands at topographic pinning points – locations of relative narrowing and shallowing. Some tidewater glaciers fluctuate cyclically, in ways unrelated to climate, over CANADIAN ROCKIES AND COAST MOUNTAINS distances of tens of kilometers and over timescales of OF CANADA centuries to millennia. Therefore, neither the contem- porary behavior of calving glaciers nor the geomorpho- John J. Clague1, Brian Menounos2, Roger Wheate2 logical records from past fluctuations can be 1Department of Earth Sciences, Simon Fraser University, interpreted straightforwardly as indicators of climatic Burnaby, BC, Canada change (Warren, 1992; Vieli et al., 2001). 2Geography Program and Natural Resources and 3. Socioeconomic impacts. Calving glaciers can provide Environmental Studies Institute, University of Northern resources for society, but they also represent significant British Columbia, Prince George, BC, Canada hazards. Resources include tourism and the medium- term possibility of harnessing Antarctic tabular ice- Definition bergs as a source of freshwater, while hazards include 2 icebergs and glacier lake outburst floods (Glacier Lake Alpine glaciers cover about 26,000 km of British Colum- Outburst Floods). With continued global warming bia and westernmost Alberta. The glacier source areas are (Global Warming and Its Effect on Snow/Ice/Glaciers), cirques and plateaus above about 1,500-m elevation in calving may lead to rapid and sustained loss of ice several mountain ranges that trend northwest through the from the marine ice sheet (Marine Ice Sheet) of two provinces. Some glaciers in the Coast and St. Elias West Antarctica, in turn causing global sea-level rise Mountains extend down to elevations below 500 m asl of 3–4 m (Sea-Level). and one (Grand Pacific Glacier) calves into the sea. This article summarizes the distribution of glaciers in British Columbia (B.C.) and Alberta, discusses the mass balance Bibliography and climatology of the glaciers, and describes historical Benn, D. I., Warren, C. R., and Mottram, R. H., 2007. Calving pro- changes in ice cover. cesses and the dynamics of calving glaciers. Earth Science Reviews, 82, 143–179. Meier, M. F., 1997. The iceberg discharge process: observations and Introduction inferences drawn from the study of Columbia Glacier. In van der The total area of glaciers in British Columbia (B.C.) and Veen, C. J. (eds.), Calving Glaciers: Report of a Workshop, 2 Febuary. 28–March 2, 1997. Byrd Polar Research Centre Alberta is about 26,000 km , which is about one quarter Report No. 15. Columbus, Ohio: The Ohio State University, of the area of alpine ice cover in North America, but only pp. 109–114. 0.2% of the total on Earth. The number of glaciers, Nick, F. M., Vieli, A., Howat, I. M., and Joughin, I., 2009. Large- although difficult to establish, is approximately 15,000, scale changes in Greenland outlet glacier dynamics triggered at of which about 1,000 are in Alberta. Nearly 70% of the 2 – the terminus. Nature Geoscience, ,110 114. total glacierized area in B.C. and Alberta is in the Coast O’Neel, S., Echelmeyer, K. A., and Motyka, R. J., 2001. Short-term flow dynamics of a retreating tidewater glacier: LeConte Glacier, Mountains, a series of northwest-trending ranges border- Alaska, U.S.A. Journal of Glaciology, 47, 567–578. ing the Pacific coast and extending about 1,000 km from Rignot, E., and Kanagaratnam, P., 2006. Changes in the velocity the B.C.–Washington border on the south to the B.C.– structure of the Greenland Ice Sheet. Science, 311, 986–990. Yukon border on the north (Figure 1). The highest peaks Van der Veen, C. J., 2002. Calving glaciers. Progress in Physical in the Coast Mountains are in the southern part of the Geography, 26,96–122. mountain system, culminating in Mount Waddington Vieli, A., Funk, M., and Blatter, H., 2001. Flow dynamics of tidewa- ter glaciers: a numerical modelling approach. Journal of Glaciol- (4,016 m asl). The southern part of the St. Elias Mountains ogy, 47, 595–606. extends into northern B.C. along its border with Alaska, Warren, C. R., 1992. Iceberg calving and the glacioclimatic record. and peaks in that area exceed 4,000 m asl, the highest Progress in Physical Geography, 16, 253–282. being Mount Fairweather (4,663 m asl). CANADIAN ROCKIES AND COAST MOUNTAINS OF CANADA 107

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Canadian Rockies and Coast Mountains of Canada, Figure 1 Relief map of western Canada, showing major mountain systems and ranges. Blue shading shows present-day ice cover. Ice cover is greater in the northern and southern Coast generally lower amounts of precipitation in the interior Mountains than in the central part of the system, where ranges than along the coast (Østrem, 1966). The total lower elevations limit the size and number of glaciers. glacierized area in the B.C. interior ranges and Alberta Overall elevations are greater in the southern Coast Moun- Rocky Mountains thus is much less than in the Coast tains than in the northern Coast Mountains. More exten- Mountains – glaciers in the Rocky Mountains represent sive ice cover in the northern Coast Mountains results 8.7% of the total area of ice cover; those in the southern from the decrease in the glaciation limit from south to B.C. interior, 7.5%; and those in the mountains of the north due to lower mean temperatures and locally greater northern interior, 2.3%. Approximately 60 small glaciers precipitation (Østrem, 1966). As a consequence, 36% of on Vancouver Island have a combined area of only 20 km2. the total glacierized area in B.C. and Alberta is in the Most glaciers are remote and not easily accessible northern Coast Mountains, 26% in the southern Coast except by helicopter, but some are close to roads or Mountains, and 7% in the central part. The B.C. portion established hiking trails. Notable among these are Atha- of the St. Elias Mountains has about 12% of the total ice basca and Saskatchewan glaciers in the Alberta Rocky cover. Mountains; Illecillewaet Glacier in the Selkirk Mountains The glaciation limit generally rises to the east across of eastern B.C.; Hudson Bay Glacier near Smithers, B.C.; B.C. due to the more continental environment and Helm, Sphinx, and Sentinel glaciers in the southern Coast 108 CANADIAN ROCKIES AND COAST MOUNTAINS OF CANADA

Mountains, and Salmon Glacier in the northern Coast summer and steers storm systems along more northerly Mountains. Athabasca Glacier, located along the Icefields tracks. Summer is thus typically warm and dry in southern Parkway in Jasper National Park, is the most visited B.C. and Alberta (Moore et al., 2009). The interior ranges glacier in North America (Figure 2). It flows from the of B.C. and the Canadian Rockies experience frequent Columbia Icefield, which has an area of nearly 325 km2 convective storms during summer, and snow can fall dur- and feeds six major glaciers. Athabasca Glacier is pres- ing these storms at high elevations. ently about 6 km long, has an area of about 6 km2, and The strongest links between regional climate and gla- a maximum thickness of about 300 m. cier mass balance in B.C. are during winter when the atmosphere is most active. Wintertime circulation is Mapping British Columbia and Alberta glaciers strongly influenced by the Pacific North American Pattern Western Canadian glaciers were mapped at scales of (PNA), a recurring pattern of high-and low-pressure cen- 1:50,000 and 1:250,000 as part of the National Topo- ters (Wallace and Gutzler, 1981) that can either direct or graphic Survey (NTS) completed during the second half divert winter storms across southern and middle latitudes of the twentieth century. No single date can be associated of B.C. A persistent ridge of high pressure over B.C. dur- with the areal extent of the glaciers depicted on NTS maps. ing the strong phase of the PNA favors reduced snowfall. Glaciers in B.C. were mapped at 1:20,000-scale during In contrast, cool, wet conditions characterize the weak the initial Terrain Resources Inventory Management phase of the PNA, especially in maritime locations of (TRIM) program between 1981 and 1989. The total gla- southern B.C. and the U.S. Pacific Northwest (Moore, cier cover, estimated from aerial photographs acquired 1996; Moore and McKendry, 1996). for TRIM mapping, is about 28,500 km2 (Schiefer et al., PNA-like atmospheric patterns are linked to large sea- 2007). Glacier cover in the Alberta Rocky Mountains for surface temperature anomalies in the equatorial Pacific the same period was approximately 1,050 km2. Some or in the North Pacific. These temperature anomalies are small glaciers have subsequently disappeared, and others associated with the El Niño-Southern Oscillation (ENSO) have disintegrated into multiple smaller ice masses. and the Pacific Decadal Oscillation (PDO). ENSO events typically last 1–2 years and recur every 2–7 years, whereas PDO events tend to last for periods of one to Links between climate and glaciers several decades (Mantua et al., 1997). Both El Niño condi- A prominent feature of British Columbia’s climate is the tions and the warm phase of the PDO favor higher-than- regular occurrence of mid-latitude cyclones during winter. average sea surface temperatures along the west coast of These systems originate in the North Pacific Ocean, track North America and lower-than-average sea-surface tem- eastward across the coast, and deliver large amounts of peratures in the central North Pacific. In contrast, cool snow to the mountains of B.C. A high-pressure center sea surface temperatures are common during La Niña commonly forms off western North America during events and the cold phase of the PDO.

Canadian Rockies and Coast Mountains of Canada, Figure 2 Athabasca Glacier, the most visited glacier in North America. The glacier has retreated more than 1.5 km since the middle 1800s. CANADIAN ROCKIES AND COAST MOUNTAINS OF CANADA 109

Glacier mass balance and frontal variations climate involving the warm phase of the PDO and more Mountain glaciers respond to climate over a range of tem- frequent El Niño conditions (McCabe and Fountain, poral scales. At annual timescales, for example, glaciers 1995; Moore and Demuth, 2001). may gain mass if winter accumulation outpaces melting during summer. A persistent imbalance between accumu- Historical glacier changes and links to climate lation and ablation will eventually cause glaciers to adjust Glaciers in B.C. and Alberta remained near their Little Ice their thickness, length, or area to reach a new equilibrium Age positions until the early twentieth century, when cli- with climate. Adjustments in length and area can take mate abruptly warmed in western North America (Jones decades or centuries, whereas changes in thickness occur et al., 1999; Menounos, 2006; Koch et al., 2009). Atha- over timescales of years. basca Glacier in the Rocky Mountains retreated only about Detailed glacier mass balance studies in western 200 m between 1844 and 1906, but receded over 1 km dur- Canada began at the start of the International Hydrologic ing the next 75 years and lost nearly half its volume Decade in 1965. Early researchers chose glaciers along (Luckman et al., 1999). Likewise, Helm Glacier in the a west–east transect through southern B.C. and western- southern Coast Mountains and Illecillewaet Glacier in most Alberta to examine links between climate and Columbia Mountains retreated about 200 m in the late mass balance from maritime (Sentinel and Helm glaciers) 1800s, followed by about 1 km of retreat between 1900 to continental (Peyto and Ram River glaciers) and 1988 (Osborn and Luckman, 1988; Koch et al., 2009). environments (Østrem, 1966). Berendon Glacier in the Fluctuations of glaciers in B.C. and Alberta also mirror northern Coast Mountains was added after 1965 to changes in climate on decadal timescales. Most glaciers establish a north–south transect. Only Place and Peyto rapidly retreated during the period 1920–1950. Glacier glaciers, however, have mass balance records longer recession slowed after 1950, and in some cases glaciers than 30 years. advanced during the 1960s and 1970s. After about 1980, Yarnal (1984) showed that mass balance changes at glaciers resumed their retreat, a trend that has continued Sentinel and Peyto glaciers are partly controlled by to the present (Koch et al., 2009; Moore et al., 2009). recurring synoptic features during the accumulation Periods of glacier recession coincide with positive phases and ablation seasons, determined from charts of the of the PDO, when the climate of B.C. was relatively warm geopotential surface (500 hPa). Both glaciers gain mass and dry. The minor advances of the 1960s and 1970s during periods of cyclonic activity in winter and under occurred during a negative, cool phase of the PDO. Rates of glacier retreat in the southern Coast Mountains were synoptic conditions that favor cloudy conditions. Simi- lar synoptic mass balance relations were shown by highest (30 m a 1) between about 1920 and 1950 Walters and Meier (1989), who analyzed a longer and (Menounos et al., 2005; Koch et al., 2009). Illecillewaet Glacier in eastern B.C. retreated 20–40 m a1 between more complete data set for other North Pacific glaciers (South Cascade, Sentinel, Place, Peyto, Wolverine, and 1900 and 1960, but only about 6 m a 1 between 1960 Gulkana glaciers). They suggested that wintertime mass and 1980 (Osborn and Luckman, 1988). balance variability can be largely explained by changes Analysis of 2005 Landsat satellite imagery shows that in atmospheric circulation similar to those controlled by the total glacierized area in B.C. and Alberta decreased the PNA. 10.8% (2.9%) and 25.4 (3.4%), respectively, over the preceding 20-year period (Bolch et al., 2010). The The mass balance of western Canadian glaciers is strongly affected by winter precipitation (Hodge et al., average annual retreat rate of 0.55% a 1 is comparable to 1998; Bitz and Battisti, 1999). In addition to the direct late twentieth century rates reported for other mountain influence of precipitation on accumulation, winter precip- regions, including the European Alps and the Himalayas. itation can also influence summer ablation (Moore et al., 2009): years with heavy snowfall can delay exposure of Areal changes in ice cover during the past 3 ice in the ablation season, thus maintaining a high surface decades albedo and reducing melt during summer (Young, 1981; The Coast and St. Elias Mountains have the greatest Moore and Demuth, 2001). Weather and synoptic condi- glacierized area and show the greatest total ice loss – tions during summer influence the balance of glaciers in about 2,400 km2 between 1985 and 2000. Regions with the interior ranges and Rocky Mountains (Letréguilly, less ice cover, however, have the highest relative areal 1988; Bitz and Battisti, 1999). ice losses – 24% in the northern interior ranges and The average winter balance at Peyto Glacier averaged 25.4% in the Alberta Rocky Mountains, compared with 1.51 m water equivalent (we) per year from 1965 to 7.7% and 10.3% in the northern and southern Coast 1976, but decreased to 1.01 m we per year over the Mountains, respectively. These losses are only part of period 1977–1999 interval, following a Pacific climate the total reduction in ice cover since the Little Ice Age. shift in 1976 (Watson and Luckman 2004; Moore et al., For example, in Garibaldi Provincial Park, ice cover was 2009). Place Glacier and glaciers in the U.S. Pacific 16% less in 2005 than in 1987, but was 49% less in Northwest experienced similar declines in winter 2005 than in the eighteenth century (Koch et al., 2009). mass balance following 1976, in concert with a shift in Many valley glaciers have retreated more than 1 km since 110 CANADIAN ROCKIES AND COAST MOUNTAINS OF CANADA

Thinning of Klinaklini glacier

1987–1970 2000–1987 2000–1970

2.59 km3 5.36 km3 7.95 km3

–10 m

–100 m 0 4.5 9 18 Kilometers –300 m

Canadian Rockies and Coast Mountains of Canada, Figure 3 Elevation change of Klinklini Glacier between 1970 and 2000. Colors denote elevation loss in the ablation zone of the glacier over three periods. Changes in the glacier surface were obtained by differencing digital elevation models produced from the National Topographic Database maps (1970), Terrain Resource Inventory Maps (1987), and Shuttle Radar Topographic Mission imagery (2000).

1900, based on visible trim lines. Small glaciers have Columbia is controlled by the Pacific North American Pat- experienced the highest percentage areal losses and, in tern (PNA). A persistent ridge of high pressure over B.C. some cases, have disappeared. Conversely, many small during the strong phase of the PNA favors reduced snow- cirque glaciers in sheltered topographic locations experi- fall. In contrast, cool, wet conditions typify the weak enced relatively little reduction in area (DeBeer and Sharp, phase of the PNA, especially in maritime locations of 2007, 2009). southern B.C. PNA-like atmospheric patterns are linked to large sea-surface temperature anomalies in the equato- Volume losses rial Pacific or in the North Pacific, which in turn are asso- Geodetic methods and area-volume scaling provide volume ciated with the El Niño-Southern Oscillation (ENSO) and loss estimates for glaciers in B.C. and Alberta (Schiefer the Pacific Decadal Oscillation (PDO). et al., 2007; Bolch et al., 2010). In the case of small glaciers, Most glaciers in British Columbia and Alberta retreated terminus retreat explains much of the volume loss; for large between 1920 and 1950. Glacier recession slowed after glaciers, downwasting in the ablation zone dominates mass 1950, and in some cases glaciers advanced during the loss. The total estimated ice loss in B.C. between 1985 and 1960s and 1970s. After about 1980, glaciers continued 2000, based on the TRIM and the Shuttle Radar Topo- their retreat, a trend that has continued to the present. graphic Mission (SRTM) digital elevation models, is 22.5 Periods of glacier recession coincide with positive phases (5.5) km3 a1, which corresponds to an average thinning of the PDO. The minor advances of the 1960s and 1970s rate of 0.78 0.19 m a1. Thinning rates are highest where occurred during a negative, cool phase of the PDO. Glacier cover in the Coast and St. Elias Mountains ice cover is greatest (i.e., the Coast and St. Elias Mountains) 2 and lowest in the B.C. interior and the northern Rocky decreased by about 2,400 km between 1985 and 2000. Mountains (Figure 3). The average annual loss in ice volume over this period is 22.5 (5.5) km3 a1, which corresponds to an average thinning rate of 0.78 0.19 m a1. Summary There are about 15,000 glaciers, covering a total area of 26,000 km2, in British Columbia and western Alberta. Bibliography About 36% of the ice cover is in the northern Coast Moun- Bitz, C. M., and Battisti, D. S., 1999. Interannual to decadal vari- tains, 26% is in the southern Coast Mountains, and 12% is ability in climate and the glacier mass balance in Washington, in the B.C. portion of the St. Elias Mountains; the remain- western Canada, and Alaska. Journal of Climate, 12, der is in the central part of the Coast Mountains. 3181–3196. The mass balance of western Canadian glaciers is Bolch, T., Menounos, B., and Wheate, R., 2010. Landsat-based inventory of glaciers in western Canada, 1985 to 2005. Remote strongly affected by winter precipitation, although Sensing of the Environment, 114, 127–137. weather and synoptic conditions during summer influence DeBeer, C. M., and Sharp, M. J., 2007. Recent changes in glacier the summer balance of glaciers in the interior ranges and area and volume within the southern Canadian Cordillera. Rocky Mountains. Wintertime circulation in British Annals of Glaciology, 46, 215–221. CASCADE MOUNTAINS, USA 111

DeBeer, C. M., and Sharp, M. J., 2009. Topographic influences on Yarnal, B., 1984. Relationships between synoptic-scale atmospheric recent changes of very small glaciers in the Monashee Mountains, circulation and glacier mass balance in south-western Canada British Columbia, Canada. Journal of Glaciology, 55,1–10. during the International hydrological Decade, 1965–1974. Jour- Hodge, S. M., Trabant, D. M., Krimmel, R. M., Heinrichs, T. A., nal of Glaciology, 30, 188–198. March, R. S., and Josberger, E. G., 1998. Climate variations Young, G. J., 1981. The mass balance of Peyto Glacier, Alberta, and changes in mass of three glaciers in western North America. Canada, 1965 to 1978. Arctic and Alpine Research, 13, Journal of Climate, 11, 2161–2179. 307–318. Jones, P. D., New, M., Parker, D. E., Martin, S., and Rigor, I. G., 1999. Surface air temperature and its changes over the past 150 Cross-references years. Review of Geophysics, 37, 173–199. Koch, J., Menounos, B., and Clague, J. J., 2009. Glacier change in Alaskan Glaciers Garibaldi Provincial Park, southern Coast Mountains, British Cascade Mountains, USA Columbia, since the Little Ice Age. Global and Planetary Climate Change and Glaciers Change, 66, 161–178. Rocky Mountains Letréguilly, A., 1988. Relation between mass balance of western Canadian mountain glaciers and meteorological data. Journal of Glaciology, 34,11–18. Luckman, B. H., Kavanagh, T. A., Craig, I., and St. George, R. S., CASCADE MOUNTAINS, USA 1999. Earliest photograph of Athabasca and Dome glaciers, Alberta. Géographie physique et Quaternaire, 53, 401–504. Mantua, N. J., Hare, S. R., Zhang, Y., Wallace, J. M., and Francis, Rijan B. Kayastha R. C., 1997. A Pacific interdecadal climate oscillation with Himalayan Cryosphere, Climate and Disaster Research impacts on salmon production. Bulletin of the American Meteo- Center (HiCCDRC), Kathmandu University, Dhulikhel, rological Society, 78, 1069–1079. Kavre, Kathmandu, Nepal McCabe, G. J., and Fountain, A. G., 1995. Relations between atmo- spheric circulation and mass balance of South Cascade Glacier, Washington, USA. Arctic and Alpine Research, 27, 226–233. Synonyms Menounos, B., 2006. Anomalous early 20th century sedimentation Canadian cascade; Cascade range; Cascadia; North in proglacial Green Lake, British Columbia, Canada. Canadian cascade Journal of Earth Sciences, 43, 671–678. Menounos, B., Clague, J., Gilbert, R., and Slaymaker, O., 2005. Environmental reconstruction from a varve network in the south- Definition ern Coast Mountains, British Columbia, Canada. Holocene, 15, 1163–1171. The Cascade Mountains, USA, is a major mountain range Moore, R. D., 1996. Snowpack and runoff responses to climatic var- of western North America. It extends for about 1120 km iability, southern Coast Mountains, British Columbia. Northwest in the north–south direction from northern California Science, 70, 321–333. through Oregon and Washington State, and for a short Moore, R. D., and Demuth, M. N., 2001. Mass balance and distance into British Columbia, Canada. The Cascades streamflow variability at Place Glacier, Canada, in relation to 15 – derive their name from the cascades (waterfalls) of the recent climate fluctuations. Hydrological Processes, , 3473 Columbia River. The Cascade Mountains include both 3486. Moore, R. D., and McKendry, I. G., 1996. Spring snowpack anom- nonvolcanic mountains, including the rugged spires aly patterns and winter climatic variability, British Columbia, of the North Cascades and the notable volcanoes known Canada. Water Resources Research, 32, 623–632. as the High Cascades. Major peaks in Cascade Mountains Moore, R. D., Fleming, S., Menounos, B., Wheate, R., Fountain, A., in California are Lassen Peak and Mount Shasta; in Holm, C., and Jakob, M., 2009. Glacier change in western North Oregon are Mount Hood and Mount Jefferson and in America: influences on hydrology and geomorphic hazards and Washington State are Mount Adams, Mount Baker, Mount water quality. Hydrologic Processes, 23,42–61. Osborn, G. D., and Luckman, B. H., 1988. Holocene glacier fluctu- St Helens, and Mount Rainier. ations in the Canadian Cordillera (Alberta and British Colum- The Cascade Mountains are part of the Pacific Ring of bia). Quaternary Science Reviews, 7,115–128. Fire, the ring of volcanoes and associated mountains Østrem, G., 1966. The height of the glaciations limit in the southern around the Pacific Ocean. The most active volcanoes in British Columbia and Alberta. Geografiska Annaler, 48A, 126– the USA, excluding Alaska and Hawaii, are found in the 138. Cascade Range, e.g., Mount Rainier (4,392 m), Mount Schiefer, E., Menounos, B., and Wheate, R., 2007. Recent volume loss of British Columbian glaciers, Canada. Geophysical Shasta (4,317 m), and Mount Adams (3,751 m). Mount Research Letters, 34, L16503, doi:10.1029/2007GL030780. Rainier is the highest Peak in the Cascade Mountain Wallace, J., and Gutzler, D., 1981. Teleconnections in the USA. Mount St Helens in Washington (2,549 m), which geopotential height field during the Northern Hemisphere win- had been dormant since 1857, erupted violently in 1980 ter. Monthly Weather Review, 109, 784–812. and 1982. Minor eruptions of Mount St. Helens have also Walters, R. A., and Meier, M. F., 1989. Variability of glacier mass occurred, most recently in 2006. balances in western North America. In Peterson, D. H. (ed.), The core of the Cascade Mountains is formed by old Aspects of Climate Variability in the Pacific and Western Americas. Geophysical Monographs, Vol. 55, pp. 365–374. crystalline rocks but above their crest line are many volca- Watson, E., and Luckman, B. H., 2004. Tree-based mass-balance nic cones, whose lava flows have covered much of the estimates for the past 300 years at Peyto Glacier, Alberta, lower slopes. Because of the Cascade Mountain’s proxim- Canada. Quaternary Research, 62,9–18. ity to the Pacific Ocean, these mountains receive good 112 CASCADE SYSTEM precipitation, especially on the western slopes, with annual accumulations of up to 3,800 mm in some areas. CATASTROPHIC FLOODING It is not uncommon for some places in the Cascades to have over 5,500 mm of snow accumulation, such as at Fiona Tweed Lake Helen (near Lassen Peak), one of the snowiest places Department of Geography, Staffordshire University, in the world. Most of the High Cascades are therefore Stoke-on-Trent, Staffordshire, UK white with snow and ice year round. However, the annual rainfall drops to 200 mm on the eastern foothills due to Synonyms a rain shadow effect. High magnitude floods; Superfloods

Definition CASCADE SYSTEM The term “catastrophic flooding” is generally used to describe the occurrence of exceptional or rare high magni- Rijan B. Kayastha tude floods. Himalayan Cryosphere, Climate and Disaster Research The term catastrophic flooding has its origins in the Center (HiCCDRC), Kathmandu University, Dhulikhel, diluvial theory of the biblical flood and derives from the Kavre, Kathmandu, Nepal thinking that catastrophic events shaped the Earth’s sur- face. Floods can be attributed catastrophic status on the Definition basis of their impacts on channel morphology and/or sed- imentology or the amount of sediment that they transport. Cascade system is defined as a system in which the flow of Catastrophic floods create substantial monetary and energy and/or matter from one element passes to next ele- human losses in the areas in which they occur. Whether ment in the series. The concept of cascade system is used a flood is catastrophic or not can depend on the timescale in the distributed hydrological modeling for simulating over which the impacts of the flood are considered; for runoff from a basin. In this concept, a basin is divided into ... example, an event may appear catastrophic over a short number of sub-basins say, Tank 1, Tank 2, Tank 3, , timescale but over a longer timescale may be one of Tank n, from upstream to downstream as shown in a number of similar events and therefore be relatively Figure 1. The inflow on the starting tank, Tank 1, in the “non-catastrophic” (Wolman and Miller, 1960; Wolman upstream end of the basin will be rainfall and after evapo- and Gerson, 1978; Maizels and Russell, 1990a, b; Russell, transpiration, infiltration, and other initial losses, the 2004). Preservation of erosional landforms and sedimen- remaining water (outflow of Tank 1) will be inflow to tary evidence of floods over geological timescales is likely the lower tank, Tank 2. Similarly, outflow of the Tank 2 to reflect truly catastrophic events and the conditions will be will become the inflow to Tank 3 in the series appropriate for their impacts to be preserved (Russell, and so on. This process will continue to the lowermost 2004). If considered over shorter timescales a flood could tank of the basin which will give the actual runoff from be defined as catastrophic if it results in irreversible the basin. changes in fluvial systems. The largest known catastrophic floods are associated with deglaciation as well as high-intensity rainfall. In gla- Rainfall ciated environments, catastrophic processes associated with high-energy flows (such as Ice-Dammed Lakes, Tank 1 jökulhlaups/glacier lake outburst floods (GLOFs), etc., see entries Hydrology of Jökulhlaups; Glacier Lake Out- Q 1 burst Floods.) can cause substantial landscape change. The main causes of catastrophic flooding in glaciated ter- Tank 2 rain comprise rainfall, melting of ice, and natural or man- Q made dam failure, which generate sudden and large inputs 2 of water to flood routeways (e.g., Mayer and Nash, 1987; Tank 3 Evans and Clague, 1994; Tweed and Russell, 1999; Clague and Evans, 2000; Martini et al., 2002). The Q 3 Channeled Scablands of Washington, USA, are believed to have been shaped by catastrophic flooding from the Q n−1 drainage of proglacial lakes during the late Pleistocene Tank n Epoch (Baker, 1981).

Qn Bibliography Baker, V. R., 1981. Catastrophic flooding: The Origin of the Cascade System, Figure 1 Cascade system in runoff modeling. Channeled Scabland. Stroudsburg: Dowden, Hutchinson & Ross. CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS 113

Baker, V.R., 1996. Megafloods and glaciation. In Martini, I. P. (ed.), to rest, in some instances kilometers beyond the source. Late Glacial and Postglacial Environmental Changes. The mobility of the streaming debris is enhanced as it – New York: Oxford University Press, pp. 98 108. travels over snow and ice. Catastrophic rock slope fail- Clague, J. J., and Evans, S. G., 2000. A review of catastrophic drain- age of moraine-dammed lakes in British Columbia. Quaternary ures and other types of landslides are common in Science Reviews, 19, 1763–1783. mountains around the world, but are particularly numer- Evans, S. G., and Clague, J. J., 1994. Recent climate change and cat- ous in high glacierized ranges where glaciers have astrophic geomorphic processes in mountain environments. eroded steep slopes and where recent glacier retreat Geomorphology, 10, 107–128. has left unstable slopes unsupported. Thaw of alpine Maizels, J. K., and Russell, A. J., 1990a. Catastrophic drainage and permafrost in a warming climate has also been impli- the quaternary record. I. Criteria for defining ‘catastrophic’ drainage. Quaternary Newsletter, 61,12–18. cated in many landslides in glacierized mountains. We Maizels, J. K., and Russell, A. J., 1990b. Catastrophic drainage describe the interplay between catastrophic rock slope and the quaternary record II. Environmental significance of failures and glaciers in the Karakoram Himalaya and ‘catastrophic’ floods: possible applications in the UK western North America, two areas with some of the and development of a database. Quaternary Newsletter, 61, highest relief and largest alpine glaciers on Earth, and 18–23. thirdly in the European Alps, with one of the most Martini, P.I., Baker, V.R., and Garzón, G. (eds.), 2002. Flood and detail records. Megaflood Processes and deposits: Recent and Ancient Exam- ples, International Association of Sedimentologists, Special Publication, 32. Mayer, L., and Nash, D., 1987. Catastrophic Flooding. Binghamton Introduction Symposium in Geomorphology, 18. London: Allen & Unwin. Rock slope failures in glacierized mountains may gen- Russell, A. J., 2004. Sedimentary processes – catastrophic floods. erate rock avalanches that affect mountain glaciers In Selley, R. C., Cocks, L. R. M., and Plimer, I. R. (eds.), Ency- (Figure 1). The runout and emplacement geometry of clopedia of Geology. Oxford: Elsevier B.V, pp. 628–641. Tweed, F. S., and Russell, A. J., 1999. Controls on the formation and rock avalanches are affected when they travel over ice sudden drainage of glacier-impounded lakes: implications for (Evans and Clague, 1988; Deline, 2009), and substan- jökulhlaup characteristics. Progress in Physical Geography, tial modifications of glacier activity, mass balance, 23,79–110. and sedimentation can follow (Huggel, 2008; Hewitt, Wolman, M. G., and Gerson, R., 1978. Relative scales of time and 2009). If the landslides descend over glaciers into ice- effectiveness of climate in watershed geomorphology. Earth free valleys, they can develop even greater mobility Surface Processes and Landforms, 3, 189–203. Wolman, M. G., and Miller, J. P., 1960. Magnitude and frequency and can, if they reach inhabited areas, result in singular of forces in geomorphic processes. Journal of Geology, 68, catastrophes (Pflaker and Ericksen, 1978; Hauser, 2002; 54–74.

Cross-references Glacier Lake Outburst Floods Hydrology of Jökulhlaups Ice-Dammed Lakes Pleistocene Epoch

CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS

Kenneth Hewitt1, John J. Clague2, Philip Deline3 1Cold Regions Research Centre, Wilfrid Laurier University, Waterloo, ON, Canada 2Centre for Natural Hazard Research, Department of Earth Sciences, Simon Fraser University, Burnaby, BC, Canada 3EDYTEM Lab, Université de Savoie, CNRS, Le Bourget-du-Lac, France

Definition “Catastrophic rock slope failure” is the sudden failure and downslope movement of a large mass of intact rock. The Catastrophic Rock Slope Failures and Mountain Glaciers, failed rock mass rapidly disintegrates and may flow – Figure 1 Rock avalanche onto the accumulation zone of a long distance at speeds up to 100 m s 1 before coming a glacier in the Southern Alps of New Zealand. 114 CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS

Huggel et al., 2008). Rock avalanches occurring in ice- Rock avalanches occur in almost all mountain ranges free areas below glaciers can affect ice-margin and (Table 1), but most reported examples are in presently or proglacial sedimentation, even terminal fluctuations. formerly glacierized mountain valleys. Many detachment When landslides dam valleys at or near glacier termini, zones are on slopes over-steepened by glacial erosion. lakes may cause the ice to float (Hewitt, 2001; Deline, Glacial retreat and debuttressing may be important factors 2005b). in destabilizing such slopes (Evans and Clague, 1993;

Catastrophic Rock Slope Failures and Mountain Glaciers, Table 1 Examples of large (>106 m3) rock avalanches descending onto glaciers

Mountain system Examples No. Reference

North American Cordillera Alaska 1945–1963 11 Post, 1967 1964 earthquake >50 McSaveney, 1978 1964–1965 4 Reid, 1969 British Columbia Pandemonium Creek 1959 Evans and Clague, 1988 Devastation Glacier 1975 North Creek 1986 Mount Meager 1986 Washington, USA Mount Rainier: Crandell 1971 Prehistoric “frequent” Fahnestock, 1978 Emmons Glacier 1963 “several” Greenland Holsteinsborg sixteenth to seventeenth Kelly, 1980 centuries South American Cordillera Peru, Cordillera Blanca Nevados Hascaran Pflaker and Ericksen, 1978 Prehistoric, 1962, 1970 >3 Chile, Andes Rio Colorado, Hauser, 2002 Three prehistoric Estero Paraguirre 1987 Argentina, Andes Aconcagua 2 R. Hermanns, pers. comm. Antarctica, S.Georgia, Lyell Glacier 1975 1 Gordon et al., 1978

New Zealand, S. Alps Mt. Cook 1873, 1991 McSaveney, 2002 Mt. Fletcher 1991 Mt. Thomson 1996 Mueller Glacier 1960 Mt. Isobel 1950s European Alps Triolet Glacier, Italy < 1000, 1717 2 Porter and Orombelli, 1980 Deline and Kirkbride, 2009 Brenva Glacier, Italy, >10 Valbusa, 1921 c. 2500 BP, c. 500, 1300, 1767, 1920, 1997 Deline, 2001, 2005a, 2005b Rossbodergletscher, Switzerland, 1901 Miage Glacier, Italy, 1921, >10 Deline, 2009 1945, 1988 Aletsch Glacier, >3 Alean, 1984 Switzerland, 1937 Thurwieser, Italy, 2004 Sosio et al., 2008 Caucasus Urukh River/Glacier ca. 1959 A Strom, personal communication Kolka-Karmadon 2002 Haeberli et al., 2004 Huggel et al., 2005 Pamir Rgo Glacier 2003? Schneider, 2004 Karakoram Himalaya Prehistoric 21 This article Historic 8 Bualtar Glacier 1986 Chillinji Glacier 1991 Aling Glacier 1990? North Te-Rong 2002 Nepal Himalaya Kali Gandaki, prehistoric “many” Fort, 2000 Ghasa Gompa, Dhampu Annapurna Weidinger, 2004 Langthang, “Tsergo Ri” Heuberger et al., 1984 CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS 115

Ballantyne and Benn, 1996; Bovis and Stewart, 1998; path, the orientation of path relative to that of the glacier, Dadson and Church, 2005). and the steepness of the glacier bed and surface are impor- Investigations are revealing a much higher incidence of tant factors. rock avalanches in glacierized mountains than formerly Several distinct contexts and some sub-types can be realized and impacts there have been underestimated recognized. First are rock avalanches that occur entirely (McSaveney, 2002; Deline, 2009). As such, they must be on ice and do not reach beyond the margins of the gla- considered an important factor in denudation, sedimenta- cier. Important sub-categories are events largely tion, and landscape evolution in these mountains. restricted to the glacier’s accumulation area (Figure 1) Our topic involves new and challenging notions for the and those affecting mainly the ablation zone relations between mass movements and mountain gla- (Figure 2). Second are rock avalanches that originate ciers. Hitherto, studies of the phenomenon have focused in glacierized basins and travel onto ice-free valley mainly on modern events, commonly treated as singular floors (Figure 3). A rare variant of this group is rock cases (Voight, 1978). These studies have elucidated the avalanches that significantly erode the glaciers onto processes involved, but the broader implications of which they fall, producing highly mobile, mixed flows regional concentrations of events received little attention of debris, and ice that travel far beyond the glacier ter- until recently. minus. An example is the disastrous 2002 Kolka- Karmadon event in the Russian Caucasus (Haeberli Rockslide-rock avalanches et al., 2004; Huggel et al., 2005). An avalanche of rock Catastrophic rock slope failures are referred to as rockslide- and ice fell onto Kolka Glacier, eroding almost all its rock avalanches (Mudge, 1965), rock avalanches ice. A massive flow of rock and ice continued 20 km (Eisbacher and Clague, 1984), and sturzstroms (Heim, down valley, where it came to rest at the entrance to 1932; Hsü, 1975, 1978; Hutchinson, 1988). They are char- a gorge. There, it transformed into a mudflow that trav- acterized by sudden failures of large (106–1010 m3)intact eled for another 15 km. The rock-ice avalanche killed masses of rock, followed by rapid runout and emplacement about 140 people and caused massive destruction. Third of relatively thin sheets of crushed and pulverized debris. are rock avalanches that originate on slopes of ice-free Maximum runout distances are commonly five to ten times valleys and travel over the termini of active glaciers. total fall height. The debris generally travels at velocities In addition, rock avalanches that originate and are exceeding 100 km h1, in some instances more than 250 wholly emplaced in ice-free valleys may affect up-valley km h1. When the speed falls below a threshold, the debris glacier behavior (Figure 4). This article deals mainly with comes to an abrupt halt through frictional “freezing” the first group of events, where landslide material is (Hewitt et al., 2008). emplaced on active ice, but in terms of natural hazards The majority of known rock avalanches are in the second and third types are more dangerous (Figure 5). glacierized mountains, but those actually falling on gla- An important contextual variant, not dealt with here, ciers must be greatly underestimated, mainly because they is glacierized volcanoes. The cataclysmic eruption of are unlikely to be recognizable after a few decades. Burial Mt. St. Helens in 1980 triggered a huge rock avalanche of landslide debris by snow in glacier accumulation zones, and lahars, and indicated something of the scale and diver- or its dispersal by ice movement and ablation as described sity of mass movements that occur on glacier-clad volca- below, greatly reduce the chances that their legacy will be noes during eruptions (Waitt et al., 1983). recognized (McSaveney, 2002). Because most occur in rugged, often uninhabited terrain that is difficult of access, many modern events must have been missed, at least prior Significant processes and developments to satellite imaging. Most catastrophic rock slope failures Glacier effects on rock-avalanche movement are triggered in earthquakes or severe weather, further From a study of 17 examples, Evans and Clague (1988) reducing the chances of direct observation. And dozens concluded that travel over glaciers tends to increase of surviving rock-avalanche deposits have been rock-avalanche mobility. Snow and ice surfaces over misidentified as moraines or till (Heim, 1932; Porter and which the debris travels are typically flat or gently sloping, Orombelli, 1980; Hewitt, 1999; Blikra et al., 2006; Deline allowing unobstructed flow, and frictional resistance is and Kirkbride, 2009). Misidentification is an understand- much lower than in situations where the landslide travels able mistake in rugged environments with many different over rock or sediment surfaces. During landslides in sources of coarse, poorly stratified, or massive debris. 1986 at Bualtar Glacier in the Karakoram Himalaya, rapid melting of ice by the frictionally heated debris helped to Landslide–glacier interactions remove surface irregularities (Hewitt, 1988). These condi- The impact of a landslide on a glacier depends partly on tions also mean the debris sheets on glaciers are character- the size and character of the rock slope failure, partly on istically thin; average thicknesses are generally 1–3m, its location relative to the glacier, and partly on the behav- and large areas of bare or nearly bare ice may occur within ior of the rock avalanche from inception to cessation of the sheet (Figure 6). flow. The size of the rock avalanche relative to that of Channeling by lateral moraines or in glacial troughs the glacier, the steepness and relief of the rock-avalanche increases the runout distances of rock avalanches by 116 CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 2 Rock-avalanche deposit on Black Rapids Glacier, Alaska. The deposit has a volume of about 10 106 m3 and averages about 2 m in thickness. The rock avalanche was triggered by a magnitude-7.9 earthquake in November 2002. (Photo: J. J. Clague, 2007.) limiting or preventing lateral spreading (Evans et al., supraglacial units derived from rock avalanches in his 1989). For instance, downwasting of the Brenva Glacier work on Miage Glacier, the main debris-covered glacier since 1988 had converted its moraines into ramparts that on the Mont Blanc massif. One type is flow-parallel channeled the 1997 rock avalanche. In contrast, most stripes derived from rock avalanches and rock falls in the deposition in the 1920 rock avalanche occurred outside accumulation zone that have subsequently been the moraines because the advance of the glacier that transported englacially. A straight stripe is associated with started in 1913 had raised its surface above the moraine a short englacial transport path, and a curved stripe results crests (Deline, 2009). from longer englacial transport. However, it is unlikely Observations of what happens in accumulation zones of debris transported from the accumulation zone will, when glaciers during rock avalanches are few because the land- it reemerges, be ablated out as a more or less continuous slide material is soon buried under new snow. Many high- and pure sheet of rock-avalanche debris. Rather, it will elevation landslides occurred during the 1964 and 2005 undergo irregular and gradual emergence at the surface earthquakes in Alaska; observations after these events over a long period with a degree of modification that is suggest that soft snow, ploughed up and melted by the greater than with earlier emergence. The second type com- landslide, may affect its movement (Post, 1967; prises irregular sheets of rock-avalanche and rock-fall McSaveney, 1978; Harp et al., 2003; Jibson et al., 2006). deposits emplaced on bare ice in the ablation zone and Debris typically moves away from the main body of the subsequently transported entirely supraglacially. rock avalanche in linear tongues, sometimes anchored by Whatever the origin of the debris, it is progressively large blocks of rock (Figure 7). Some rock avalanches, modified as it is transported down the glacier. The original such as at Brenva Glacier in 1997, erode through the firn form of the debris sheet is distorted by glacier flow that of the accumulation zone and incorporate large amounts occurs at typical rates of tens to hundreds of meters per of ice. At Kolka-Karmadon in 2002, a large part of the gla- year. Surface features common to rock-avalanche deposits cier was removed (Huggel, 2008). in other environments, including ridges transverse and parallel to rock-avalanche flow may be preserved for decades, but become less distinct with time. Even thin Effects of rock avalanches on glacier movement layers of rock debris insulate the underlying ice surface, and supraglacial debris leading to rapid and significant elevation of the debris A landslide onto the accumulation zone of a glacier may sheet above the surrounding bare ice. Debris-draped ice have some, as yet undetermined, effect on glacier flow. plateaus may develop at rates of several meters per year Clearer and more significant consequences for glacier and reach heights of many tens of meters as they move behavior and the fate of the landslide debris are in the abla- down valley toward the glacier terminus (Figure 8). tion zone where the debris is continuously exposed. Observations in the Karakoram, described below, indicate Deline (2009, 1073) has identified two types of a limit as to how high the protected ice will become, CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS 117

movement may lead to overriding of ice-free margins and advance of the glacier terminus. A consequence is that the normal relations between accumulation and ablation zones are compromised, and the glacier may respond in a different manner from other glaciers in the region. Fluc- tuations of Brenva Glacier, Italy, over the past century have been associated with repeated burial and reduced ablation under rock-avalanche debris (Valbusa, 1921; d’Agata et al., 2005; Deline, 2005a). The 1920 rock ava- lanche augmented the debris cover in the ablation zone, causing the glacier to advance 490 m between 1920 and 1941; in contrast, neighboring glaciers retreated from the mid-1920s onward. Bualtar and Aling glaciers in the Karakoram continued advancing for almost 15 years after being blanked by rock-avalanche debris, while surround- ing glaciers retreated (Hewitt, 2009). These two also are examples of glaciers that have surged following rock ava- lanches (Gardner and Hewitt, 1989). Unlike typical surges, however, the advances may continue long after the surge. Landslide debris alters sedimentation at the glacier mar- gin. Ice-margin and proglacial fluvial sedimentation may, over the course of a disturbance episode, exceed normal rates by one or two orders of magnitude. Most of the rock-avalanche material is dispersed to the glacier margin and forefield within a few decades or centuries. In con- trast, rock avalanches emplaced on ice-free ground may resist removal for millennia, even tens of millennia (Voight, 1978; Hewitt, 2002). A consequence is that many lateral and end moraines may include a substantial legacy of reworked and transported rock-avalanche debris. They may even be, as Deline (2009, 1082) suggests “...long- ” Catastrophic Rock Slope Failures and Mountain Glaciers, term archives of rock-avalanche activity. In some cases, Figure 3 Rock-avalanche debris (foreground) blocks the Hunza moraines may consist entirely of rock-avalanche debris, and Hispar valleys, Central Karakoram. The rock avalanche in which case they carry no climatic implications. The dis- originated on the rock walls of Ultar Peak (7,388 m asl) tal flank of one of Brenva Glacier’s lateral moraines has and traveled down the glacier in the background. a pronounced concave slope that differs from the typical (Photo: K. Hewitt, 2005.) rectilinear distal slope of a dump moraine; it is attributed to successive deposits of Holocene rock avalanches. Finally, certain morainic complexes extend farther down probably as a result of compensating flow displacement at valley than neighboring ones and lack ordered concentric depth (Hewitt, 2009). Eventually, debris adjusts to surface moraines. They record glacier advances driven, not by cli- irregularities by sliding into depressions or moulins. mate, but by rock avalanches. Examples have been The fabric and thickness of the debris change as a result described in the Barpu-Bualtar basin, Pakistan (Hewitt, of these processes. In glaciers with tributaries, crevasse 2009) and at Triolet Glacier, Italy (Deline, 2009; Deline fields, icefalls, and changes of direction, there is ample and Kirkbride, 2009). opportunity for redistribution and modification of the Glaciers affected by rock avalanches also have signifi- debris. With time, it becomes difficult to distinguish cant contributions from smaller, but far more frequent rock rock-avalanche debris from other supraglacial materials. fall. Patches or tongues of rock-fall debris are common on The impacts on glacial transport and ablation are likely these glaciers. The two need to be considered together to be significant, but techniques hardly exist to even iden- when assessing the role of rock-wall processes on long- tify the phenomenon, let alone the scale of the impacts. term denudation in glacierized terrain (Deline, 2009). When a rock avalanche blankets part or all of the abla- The large amounts of fine debris emplaced during rock tion zone with debris, it initiates a series of disturbances avalanches are readily flushed away by on-ice processes, that affect mass balance and ice dynamics. A source of making it progressively more difficult to distinguish the positive mass balance – a large area of insulated glacier residual coarse fraction from rock-fall material. Neverthe- ice – becomes a moving “accumulation” anomaly local- less, it is now evident that in many glaciated mountains, ized in the ablation zone. Ice thickening and accelerated moraines may include a substantial legacy of reworked 118 CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 4 The Bhurt rock avalanche in the Western Karakoram crossed the Karambar valley from a source behind the camera. Rock-avalanche debris blocks the valley of the tributary Bhurt Glacier (upper background); almost all sediment from the glacier is trapped behind the debris barrier. (Photo: K. Hewitt, 1998.)

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 5 Up to 200 m of debris filling the valley in the foreground originated as a rock avalanche from Mount Aconcagua (6,962 m asl; top right background). The landslide traveled over Horcones Glacier and incorporated large quantities of ice, snow, and additional debris to become an extremely large (>3 km 3) and very mobile mass flow. The landslide traveled another 15 km down the valley below the photograph to dam the main valley where the Trans- Andean Highway is located today. (Photo: K. Hewitt, 2006.) and transported rock-avalanche debris produced by the glacierized mountains (Evans and Clague 1994, 1999; same events that left intact, unmodified deposits at the gla- Holm et al., 2004). Many marginally stable slopes that cier margins (Hewitt, 2002). were buttressed by glacier ice during the Little Ice Age failed after they became deglaciated in the twentieth cen- Effects of recent glacier retreat on slope stability tury. An ancillary factor that may have contributed to such Thinning and retreat of alpine glaciers appear to be failures is steepening of rock slopes by cirque and valley responsible for some catastrophic rock slope failures in glaciers during the Little Ice Age. CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS 119

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 6 The boulder surface of the 1986 rock avalanche on Bualtar Glacier, Karakoram Himalaya. (Photo: K. Hewitt, 1987.)

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 7 Aerial photograph of the deposit of the 1964 Sherman Glacier rock avalanche, taken in August 1967. Note the digitate margin of the debris sheet; lobes of debris ploughed through snow ahead of the main body of debris.

These effects are most pronounced in mountain ranges the land is rising due to isostatic rebound (Larson et al., with the greatest ice cover (Himalaya, St. Elias Mountains, 2005). and Coast Mountains) because it is there that ice losses in Other mechanisms besides debuttressing can cause or the twentieth century have been largest. An extreme trigger landslides. Temperatures in high glacierized moun- example is Glacier Bay, Alaska, which until the end of tains are normally below freezing. They may rise rapidly, the eighteenth century was completely occupied by glacier however, during warm spells, melting snow and ice. The ice. Since then, the bay has become deglaciated, with the water generated by this melting can infiltrate fractures in loss of over 1,000 km2 of ice. The ice loss is so great that marginally stable rock masses (Davies et al., 2001). When 120 CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 8 Thin sheet of rock-avalanche debris overlying an ice platform in the ablation zone of Black Rapids Glacier. The debris sheet, which is 2 m thick, insulates the underlying ice. In the 7 years since the rock avalanche, the bare glacier surface adjacent to the debris sheet has downwasted nearly 20 m, leaving the elevated platform of debris-covered ice. (Photo: J.J. Clague.) temperatures fall below freezing, water within the frac- and arêtes, abound. Glaciers remain common within the tures may freeze or the fractures may be sealed by freezing Cordillera, covering approximately 125,000 km2 of region. at the surface. In either case, pore water pressures rise, pro- ducing extensional forces on an already weak rock mass. A related process is thawing of permafrost beneath high- Pandemonium Creek elevation rock slopes (Gruber et al., 2004; Fischer et al., In 1959, a rock spur became detached from the glacially 2006; Gruber and Haeberli, 2007; Noetzli and Gruber, debuttressed headwall of a cirque near Pandemonium 2009). The lowest elevation of alpine permafrost has risen Creek in the southern Coast Mountains of British Colum- in most or all mountains in the twentieth century due to bia (Evans et al., 1989). Approximately 5 106 m3 of global warming (Zhang et al., 2006). Thawing has blocky, gneissic quartz diorite debris traveled across lowered the strength of rock with fractures or other struc- a small glacier and then 9 km along a highly irregular path, tural discontinuities, because water in the fractures melts. descending a vertical distance of 2 km to the valley of Illustrative of these processes is the unusually large South Atnarko River (Figure 9). The high mobility of number of rock falls that happened in the European Alps the rock avalanche is manifested by super-elevation in val- during the exceptionally warm summer of 2003. The rock ley bends, two runups, and two right-angle changes in falls posed a significant hazard to climbers and attracted flow direction. This mobility is due, in part, to peculiari- the attention of scientists and the public. Larger landslides ties in the path of the landslide (lateral moraines, for exam- have also occurred more recently, for example in 2004 at ple, funneled and accelerated the debris) and, in part, to Thurwieser Peak in the central Italian Alps and in 2007 travel over a glacier below the detachment zone. Although at Monte Rosa in the northwestern Italian Alps, both areas most of the debris came to rest on the upper part of a fan at visited by large numbers of tourists. the mouth of Pandemonium Creek, one lobe traversed the fan and entered Knot Lakes, where it generated displace- ment waves that destroyed trees along the shore. Runup Examples from western North America and superelevation data indicate that the debris was mov- The Canadian and Alaskan parts of the North American ing between 81 and 100 m s1 as it entered the runup zone Cordillera have supported glaciers for at least 10 million at Pandemonium Creek and 21–38 m s1 in Pandemonium years, and during the Pleistocene much of this region valley to the east. The Pandemonium Creek landslide is repeatedly was enveloped by the Cordilleran ice sheet similar in many respects to much larger, highly mobile rock (Clague, 1989). This recurrent and repeated glaciation has avalanches involving glacier ice in other parts of the world, left a strong imprint on the physiography of the region: local for example, Huascaran, Peru (Pflaker and Ericksen, relief is great, steep slopes are common, and classic glacial 1978). It is illustrative of the extreme mobility of relatively landforms, including U-shaped valleys, fiords, cirques, small rock avalanches that interact with glaciers. CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS 121

1 1,300

1,200 2 1,200

1,100 3 1,100

1,100 4

1,100 5 Elevation (m) 1,000

1,000 6 900

7 Detachment zone 800

0 200 m

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 9 Topography, longitudinal profile, and cross-sections of the 1959 Pandemonium Creek rock avalanche, British Columbia. (Adapted from Evans et al., 1989, Figures 4 and 10.)

Mount Munday the width of the main debris sheet moved a distance of Sometime between May 25 and July 10, 1997, a large rock 900 m on a slope of 5 . avalanche occurred on the south flank of Mount Munday The geometry of the rock-avalanche path below the bobsled bed indicates a coefficient of kinetic friction of (3,367 m asl) in the British Columbia Coast Mountains (Evans and Clague, 1998). The site is 6.5 km southeast approximately 0.11 (6 ) for the interface between the of Mount Waddington (4,019 m asl), the highest peak in debris and snow. Clearly defined, overlapping flow lines the Coast Mountains. About 3.2 106 m3 of debris were evident in the debris following the rock avalanche. flowed across and down the Ice Valley Glacier, forming In places along the travel path, debris was thin or absent, a spectacular tongue-shaped deposit covering 220 ha of exposing the glacier surface beneath. the glacier surface (Figure 7). The landslide involved Glaciers in the Mount Waddington area have thinned highly resistant gneissic rocks that form a number of high and retreated due to atmospheric warming, and glacier peaks in the area. Failure was controlled by the foliation ice loss is likely a factor in the Mount Munday event. and by a steeply dipping planar fault surface that has The immediate trigger of the failure may be related to a more southerly strike and cuts across the foliation at the exceptional precipitation in southwest British Colum- a lower dip angle. bia during the first half of 1997 and a pronounced period The detached rock mass first traveled in a southwest of warm weather in the days before the failure. direction across Ice Valley Glacier. It ran up the opposing slope to a height of about 100 m above the glacier surface Examples from the European Alps and was deflected about 90 downglacier in a northwest A recent inventory of rock avalanches and rock falls in the direction, in a manner similar to a bobsled. Below the bob- Alps includes 301 events, of which about half are dated sled bend, the debris traveled up to 2.6 km over the snow- and most are historic (Schoeneich et al., 2008). Few of covered glacier surface on a slope of only 6 . Ridges of the landslides are known from glacierized environments, snow were pushed up at the margins of the debris. At the partly because the deposits in these environments typi- distal limit of the debris, a lobe approximately half cally are not preserved. However, since 1997 five rock 122 CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS avalanches have descended in part or totally on glaciers in Based on observations of these historic events, the strong the western Alps – Brenva Glacier (1997), Punta asymmetry of the south lateral moraine of Brenva Glacier Thurwieser (2004), the west face of Les Drus (2005), probably is the result of numerous rock avalanches onto and the east face of Monte Rosa (2006, 2007). Research the glacier during the Holocene. Thus far, however, only on the Italian side of the Mont Blanc massif suggests that four Holocene rock avalanches prior to the twentieth century many others occurred during the Holocene (Haeberli et al., have been identified – AD 1767 (Deline, 2005a), early four- 2002; Ravanel and Deline, 2008; Deline, 2009). teenth century, after AD 426–615, and 2750–2350 calendar years BP (Deline, 2005b). Brenva Glacier Small rock falls occur regularly on the steep slopes border- Examples from the Karakoram Himalaya ing Brenva Glacier. In addition, two large rock avalanches More than 320 rock avalanches have been identified in the have occurred during the twentieth century (Figures 10 Karakoram Himalaya, and at least 29 of them spread in and 11), and several others in the late Holocene. In January part or whole over glaciers. Most events in the inventory 1997, part of Eperon de la Brenva collapsed, mobilizing are prehistoric, but 11 rock avalanches descended onto 2 106 m3 of rock debris and >4.5 106 m3 of ice and glaciers between 1986 and 2009, and one is reported from snow. The avalanche of rock, ice, and snow traveled the nineteenth century (Table 2). For reasons noted earlier, 5,750 m horizontally and 2,325 m vertically before com- these numbers are underestimates. If recent reports are at ing to rest. On reaching the lower part of the glacier, it all representative, as many as 4,000 rock avalanches may spread in two directions: one lobe overflowed the south have traveled over glaciers in the Karakoram, Nanga lateral moraine, whereas the main lobe was channeled by Parbat, and Hindu Raj ranges in the Holocene. The gla- the lateral moraines and reached the glacier terminus. ciers have a total area of some 18,000 km2. By compari- In November 1920, four separate rock masses detached son, surveys of postglacial rock avalanches at lower from the east face of the Grand Pilier d’Angle. The total elevations and in ice-free areas suggest much lower inci- volume of failed rock is in the range 2.4–3.6 106 m3; dences – 1,000–1,500 Holocene events over an area of an additional 7.6–9.9 106 m3 of ice was mobilized in some 80,000 km2. Yet, even these rates are among the the four events. Maximal horizontal and vertical displace- highest global concentrations yet known. These lower ments were 5,150 m and 2,660 m, respectively (Figure 11). areas may also have experienced more frequent rock

RA ages Post-LIA N Little ice age

Medieval warm period A rock avalanche track represented Older than MWP by an arrow means an hypothetical location of its scar (circle)

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 10 Late Holocene rock avalanches on the Italian side of the Mont Blanc massif. Most of the rock avalanches traveled onto glaciers. CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS 123

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 11 Brenva rock avalanches in 1920 and 1997. 1 – 1920 scar. 2 – 14 November 1920 track. 3 – 19 November 1920 track. 4 – 1997 scar. 5 – 18 January 1997 track.

Catastrophic Rock Slope Failures and Mountain Glaciers, Table 2 Selected rock avalanches that have descended onto glaciers in the Karakoram Himalaya and their dimensions

Rock avalanche River Glacier Volume (106 m3) Area (km2) Comment

Ghorsit Hushe/Shyok Charakusa 300 2.5+ Prehistoric, partly covered terminus Lokpar Hushe/Shyok Aling 20 3.0 1992; surge of Lokpar and Aling terminus Masherbrum Hushe/Shyok Masherbrum 2 1.5 Late 1980s Unnamed Shyok Unnamed 600+ >30 Prehistoric; from small glacier basins Tsok Dumordo Unnamed 150 8 Descent over small tributary below Panmah Glacier Naltar Lakes Naltar Kuto 300 14 Dams outflow of glacier Baltit-Sumayar Hunza Ultar 400 8 Dammed ice-free Hunza and Hispar valleys Yashbandan- Hunza Pasu and Ghulkin >250 21 Covered termini of two glaciers Barut Bligim Platt I Hunza Batura 5 3 Covered outer moraines Bilgim Platt II Hunza Batura 3 2 Covered outer moraines Shikarjerab Hunza Unnamed 12 >8 Prehistoric Qalandar Uwin Karambar Chhateboi >600 >15 Prehistoric North Te-Rong Nubra North Te-Rong ? 5 2002 Buldar Basin Nanga Parbat Kappen 11 2.3 2003 Astor basin Nanga Parbat Chhichi 1.5 0.5 2005?

avalanches in late-glacial time, as glaciers that covered By 2005, the landslide debris had been transported about almost the entire region thinned and retreated. If so, the 9 km down valley, about one-third of the distance in gla- evidence for this activity has been largely removed from cier surges (see below). During this 20-year period, the the landscape. landslide debris was fully reworked. The average debris thickness was reduced from about 7 to 8 m in 1986 to Bualtar and Aling glaciers, central Karakoram about 2 m in 2005, and the debris became less readily dis- In August 1986, three rock avalanches descended from the tinguishable from supraglacial debris generated by snow same rock wall onto the ablation zone of Bualtar Glacier. avalanches and rock fall, which are widely present on 124 CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS

Catastrophic Rock Slope Failures and Mountain Glaciers, Figure 12 A rock avalanche descended onto the Lokpar tributary glacier (upper left) in 1992. The following year the glacier surged into the main Aling Glacier which rapidly advanced 2.5 km. (Photo: K. Hewitt, 1999.)

Karakoram glaciers. Nevertheless, throughout this time, The surges initially did not affect the terminus, but over the debris sheet remained much thicker than debris any- the next 5 years the glacier advanced some 2.5 km and it where else on Bualtar Glacier before 1986, and thicker continued to advance more slowly for another 10 years. than most debris covers on glaciers examined elsewhere It reached to within a kilometer of the Hispar River, farther in the region. As a result, it reduced ablation to a much than at any time since the 1920s (Mason, 1930). greater extent, and a large area of thickened ice persisted A rock avalanche appears to have been responsible for beneath the rock avalanche material. The debris cover another glacier surge in the Karakoram. The rock ava- had a positive impact on mass balance, equivalent to lanche descended onto Lokpar Glacier, a tributary of a 20% increase in annual accumulation (Hewitt, 2009). Aling Glacier (Figure 12). Shortly thereafter, Lopkar Gla- The area of thickened ice moved along with debris cier surged, in turn causing Aling Glacier to advance some through the ablation zone, and within 10 years it was 3 km. In other recent cases, glaciers affected by rock ava- equivalent to the mass transferred in the surges. lanches did not surge, but their rates of flow increased and The 1986 Bualtar rock avalanches represent a fivefold they thickened down valley (Hewitt, 2009). increase in supraglacial debris on the glacier. Rock- avalanche debris carried to the margins of the glacier within 30 years of the failures will equal almost 500 years Concluding remarks of normal supraglacial transport by the glacier. Similarly, Rock avalanche–glacier interactions involve mutual dis- the events represent a doubling of average rate of denuda- turbance of two different Earth surface process systems. tion during this period. The behavior and deposits of one process system cannot A few months after the rock avalanches, in January be understood without reference to the other. Glacier 1987, Bualtar Glacier surged at and below the debris behavior, landforms, and sedimentary deposits are sheet (Gardner and Hewitt, 1989). Over the summer, affected by landslides throughout an extended period of a wave of fast-moving ice traveled down the valley from debris transport, disturbed mass balance, and sedimenta- the vicinity of the rock avalanches. Measured ice veloc- 1 tion. Each period has a distinctive character and sequence, ities were between 7 and 11 m day , an order of mag- and spatial relations are organized and lagged accordingly. nitude higher than pre-surge rates (<0.8 m day1). A second surge of similar scale occurred in 1989. Dur- ing the two surges, ice overtopped lateral moraines that Bibliography had been ice-free for at least a few decades. Ice and Alean, J., 1984. Ice avalanches and a landslide on Grosser meltwater undercut the glacier margins and triggered Aletschgletscher. Zeitschrift für Gletscherkunde und landslides and debris flows. Meltwater that had ponded Glazialgeologie, 20,9–25. at the sides of the glacier escaped in a series of small Ballantyne, C. K., and Benn, D. I., 1996. Paraglacial slope adjust- outburst floods. ment during recent deglaciation and its implication for slope CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS 125

evolution in formerly glaciated environments. In Anderson, Evans, S. G., and Clague, J. J., 1998. Rock avalanche from Mount M. G., and Brooks, S. M. (eds.), Advances in Hillslope Pro- Munday, Waddington Range, British Columbia, Canada. Land- cesses. British Geomorphological Research Group Symposia slide News, 11,23–25. Series, Vol. 12, 1173–1195. Evans, S. G., and Clague, J. J., 1999. Rock avalanches on glaciers in Blikra, L. H., Longva, O., Braathen, A., Anda, E., Dehl, J. F., and the Coast and St. Elias Mountains, British Columbia. In Stalsberg, K., 2006. Rock slope failures in Norwegian fjord Proceedings of the 13th Annual Vancouver Geotechnical areas: Examples, spatial distribution and temporal patterns. Conference. Richmond: BiTech, BC, pp. 115–123. In Evans, S. G., Scarascia Mugnozza, G., Strom, A. L., and Evans, S. G., Clague, J. J., Woodsworth, G. J., and Hungr, O., 1989. Hermanns, R. L. (eds.), Landslides from Massive Rock Slope The Pandemonium Creek rock avalanche, British Columbia. Failure. Proceedings of NATO Advanced Research Workshop, Canadian Geotechnical Journal, 26, 427–446. Celano, Italy. Springer, Dordrecht, pp. 475–496. Fahnestock, R. K., 1978. Little Tahoma Peak rockfalls and ava- Bovis, M. J., and Stewart, T. W., 1998. Long-term deformation of lanches, Mount Rainier, Washington, U.S.A. In Voight, B. a glacially undercut rock slope, southwest British Columbia. In (ed.), Rockslides and Avalanches 1: Natural Phenomena. New Moore, D., and Hungr, O. (eds.), Proceedings of the Eight Inter- York: Elsevier, pp. 181–196. national Congress. International Association for Engineering Fischer, L., Kääb, A., Huggel, C., and Noetzli, J., 2006. Geology, Geology and the Environment. Rotterdam: A. A. Balkema, glacier retreat and permafrost degradation as controlling factor pp. 1267–1276. of slope instabilities in a high-mountain rock wall: The Monte Clague, J. J., 1989. Quaternary geology of the Canadian Cordillera. Rosa east face. Natural Hazards and Earth System Sciences, 6, Chapter 1, In Fulton, R. J. (ed.), Quaternary Geology of Canada 761–772. and Greenland. Geological Survey of Canada Geology of Fort, M., 2000. Glaciers and mass wasting processes: Their influ- Canada, Vol. 1, pp. 15–96. ence on the shaping of Kali Gandaki valley, Nepal. Quaternary Clague, J. J., 1997. Evidence for large earthquakes at the Cascadia International, 65(66), 101–119. subduction zone. Reviews of Geophysics, 35, 439–460. Gardner, J. S., and Hewitt, K., 1989. Surge of the Bualtar Glacier, Crandell, D. R., 1971. Postglacial lahars from Mount Rainier Karakoram Ranges, Pakistan: A possible landslide trigger. Jour- Volcano, Washington. U. S. Geological Survey Professional nal of Glaciology, 32,27–29. Paper, 677. Gordon, J. E., Birnie, R., and Timmis, R., 1978. A major rockfall D’Agata, C., Smiraglia, C., Zanutta, A., and Mancini, F., 2005. and debris slide on the Lyell Glacier, South Georgia. Arctic Recent variations of a debris-covered glacier (Brenva glacier) and Alpine Research, 10,49–60. in the Italian Alps monitored by comparison of maps and digital Gruber, S., and Haeberli, W., 2007. Permafrost in steep bedrock orthophotos. Journal of Glaciology, 51, 183–185. slopes and its temperature-related destabilization following cli- Dadson, S. J., and Church, M., 2005. Postglacial topographic evolu- mate change. Journal of Geophysical Research, 112, F02S18, tion of glaciated valleys; a stochastic landscape evolution model. doi:10.1029/2006JF000547. Earth Surface Processes and Landforms, 30, 1387–1403. Gruber, S., Hoelzle, M., and Haeberli, W., 2004. Permafrost thaw Davies, M. C. R., Hamza, O., and Harris, C., 2001. The effect of rise and destabilization of alpine rock walls in the hot summer of in mean annual temperature on the stability of rock slopes 2003. Geophysical Research Letters, 31, 4pp. containing ice-filled discontinuities. Permafrost and Periglacial Haeberli, W., Käab, A., Paul, F., Chiarle, M., Mortara, G., Mazza, Processes, 12, 137–144. A., Deline, P., and Richardson, S., 2002. A surge-type movement Deline, P., 2001. Recent Brenva rock avalanches (Valley of Aosta): at Ghiacciaio del Belvedere and a developing slope instability in New chapter in an old story? Supplementi di Geografia Fisica the east face of Monte Rosa, Macugnaga, Italian Alps. Norsk e Dinamica Quaternaria, 5,55–63. Geografisk Tidsskrift, 56, 104–111. Deline, P., 2005a. Change in surface debris cover on Mont Blanc Haeberli, W., Huggel, C., Kääb, A., Zgraggen-Oswald, S., Pollkvoj, massif glaciers after the ‘Little Ice Age’ termination. Holocene, A., Galushkin, I., Zotikov, I., and Osokin, N., 2004. The Kolka- 15, 302–309. Karmadon rock/ice slide of 20 September 2002; an extraordinary Deline, P., 2005b. Large rock avalanches on glaciers since 2500 BP event of historical dimensions in North Ossetia, Russian Cauca- on the Italian flank of the Mont Blanc massif. European sus. Journal of Glaciology, 50, 533–546. Geosciences Union, General Assembly, Vienna, Austria, Harp, E. L., Jibson, R. W., Kayen, R. E., Keefer, D. K., Sherrod, Abstracts, EGU05-A-03434. B. L., Carver, G. A., Collins, B. D., Moss, R. E. S., and Sitar, Deline, P., 2009. Interactions between rock avalanches and glaciers N., 2003. Landslides and liquefaction triggered by the M 7.9 in the Mont Blanc massif during the late Holocene. Quaternary Denali Fault earthquake of 3 November 2002. GSA Today, Science Reviews, doi:10.1016/j. quascirev. 2008.09.025. 13(8), 4–10. Deline, P., and Kirkbride, M. P., 2009. Rock avalanches on a glacier Hauser, A., 2002. Rock avalanche and resulting debris flow in and morainic complex in Haut Val Ferret (Mont Blanc massif, Estero Parraguire and Rio Colorado, Region Metropolitana, Italy). Geomorphology, 103,80–92. Chile. In Evans, S. G., and Degraff, J. V. (eds.), Catastrophic Eisbacher, G. H., and Clague, J. J., 1984. Destructive Mass Move- Landslides: Effects, Occurrence, and Mechanisms. Geological ments in High Mountains. Geological Survey of Canada Paper, Society of America Reviews in Engineering Geology, Vol. 15, 84–16. pp. 135–148. Evans, S. G., and Clague, J. J., 1988. Catastrophic rock avalanches Heim, A., 1932. Bergsturz und Menschenleben. Zürich: Fretz and in glacial environments. In Bonnard, C. (ed.), Landslides: Wasmuth. Proceedings of Fifth International Symposium on Landslides. Heuberger, H., Masch, L., Preuss, E., and Strecker, A., 1984. Rotterdam: Balkema, pp. 1153–1158. Quaternary landslides and rock fusion in Central Nepal and Evans, S. G., and Clague, J. J., 1993. Glacier-related hazards and the Tyrolean Alps. Mountain Research and Development, 4, climate change. In Bras, R. (ed.), The World at Risk: Natural 345–362. Hazards and Climate Change. American Institute of Physics Hewitt, K., 1988. Catastrophic landslide deposits in the Karakoram Conference Proceedings, Vol. 277, pp. 48–59. Himalaya. Science, 242,64–67. Evans, S. G., and Clague, J. J., 1994. Recent climatic change and Hewitt, K., 1999. Quaternary moraines vs catastrophic rock ava- catastrophic geomorphic processes in mountain environments. lanches in the Karakoram Himalaya, Northern Pakistan. Quater- Geomorphology, 10, 107–128. nary Research, 51, 220–237. 126 CATASTROPHIC ROCK SLOPE FAILURES AND MOUNTAIN GLACIERS

Hewitt, K., 2001. Catastrophic rock slides and the geomorphology Mudge, M. R., 1965. Rock avalanche and rockslide avalanche of the Hunza and Gilgit Basins, Karakoram Himalaya. deposits at Sawtooth Range, Montana. Geological Society of Erdkunde, 55,72–93. America Bulletin, 76, 1003–1014. Hewitt, K., 2002. Styles of rock avalanche depositional complex in Noetzli, J., and Gruber, S., 2009. Transient thermal effects in Alpine very rugged terrain, Karakoram Himalaya, Pakistan. In Evans, permafrost. The Cryosphere, 3,85–99. S. G., and Degraff, J. V. (eds.), Catastrophic Landslides: Pflaker, G., and Ericksen, G. E., 1978. Nevados Huascaran ava- Effects, Occurrence, and Mechanisms. Geological Society lanche, Peru. In Voight, B. (ed.), Rockslides and Avalanches, of America Reviews in Engineering Geology, Vol. 15, pp. 1 Natural Phenomena. New York: Elsevier, pp. 277–314. 345–378. Porter, S. C., and Orombelli, G., 1980. Catastrophic rockfall of Hewitt, K., 2009. Rock avalanches that travel onto glaciers: Distur- September 12, 1717 on the Italian flank of the Mont Blanc massif. bance regime landscapes, Karakoram Himalaya, Inner Asia. Zeitschrift fur Geomorphologie, N.F., 24,200–218. Geomorphology, 103,66–79. Post, A. S., 1967. Effects of the March 1964 Alaska Earthquake on Hewitt, K., Clague, J. J., and Orwin, J., 2008. Legacies of cata- Glaciers. U.S. Geological Survey Professional Paper, 544-D. strophic rock slope failures in mountain landscapes. Earth Ravanel, L., and Deline, P., 2008. La face ouest des Drus (massif du Science Reviews, 87,1–38. Mont-Blanc): Évolution de l’instabilité d’une paroi rocheuse Holm, K., Bovis, M., and Jakob, M., 2004. The landslide response dans la haute montagne alpine depuis la fin du petit âge glaciaire. of alpine basins to post- Little Ice Age glacial thinning and Géomorphologie, 4, 261–272. retreat in southwestern British Columbia. Geomorphology, 57, Reid, J. R., 1969. Effects of a debris slide on ‘Sioux Glacier’, south- 201–216. central Alaska. Journal of Glaciology, 8, 353–367. Hsü, K. J., 1975. Catastrophic debris streams (sturzströms) gener- Schneider, J. F., 2004. Risk assessment of remote geohazards in ated by rock falls. Geological Society of America Bulletin, 86, Central and Southern Pamir/Tajikistan, Gbao, Tajikistan. In 129–140. Abdrakhmatov, K., Evans, S. G., Hermanns, R., Scarascia- Hsü, K. J., 1978. Albert Heim: Observations of landslides and rele- Mugnozza, G., and Strom, A. L. (eds.), Security of Natural and vance to modern interpretations. In Voight, B. (ed.), Rockslides Artificial Rockslide Dams: Extended Abstracts Volume. Bishkek, and Avalanches 1, Natural Phenomena. New York: Elsevier, Kyrgyzstan: NATO Advanced Research Workshop, pp. pp. 70–93. 164–169. Huggel, C., 2008. Recent extreme slope failures in glacial environ- Schoeneich, P., Hantz, D., Deline, P., and Amelot, F., 2008. A new ments: Effects of thermal perturbation. Quaternary Science database of Alpine rock falls and rock avalanches. In Proceed- Reviews, doi:10.1016/j.quascirev.2008.06.007. ings, Interpraevent 2008 – Dornbirn, Vol. 2, pp. 243–250. Huggel, C., Zgraggen-Oswald, S., Haeberli, W., Kääb, A., Polkvoj, A., Sosio, R., Crosta, G. B., and Hungr, O., 2008. Complete dynamic Galushkin, I., and Evans, S. G., 2005. The 2002 rock/ice avalanche modeling calibration for the Thurwieser rock avalanche (Italian at Kolka/Karmadon, Russian Caucasus; Assessment of extraordi- Central Alps). Engineering Geology, 100,11–26. nary avalanche formation and mobility, and application of Valbusa, U., 1921. La prima frana-valanga del Monte Bianco sul QuickBird satellite imagery. Natural Hazards and Earth System ghiacciaio della Brenva (14 novembre 1920). Societa Sciences, 5, 173–187. Geografica Italiana Bolletino, Series VI, Vol. 8, pp. 118–125. Huggel, C., Caplan-Auerbach, J., and Wessels, R., 2008. Recent Voight, B. (ed.), 1978. Rockslides and Avalanches, 1 Natural Phe- extreme avalanches triggered by climate change? EOS (Transac- nomena. New York: Elsevier. tions, American Geophysical Union), 89(47), 469–470. Waitt, R. B., Jr., Pierson, T. C., MacLeod, N. S., Janda, R. J., Voigt, B., Hutchinson, J. N., 1988. General report: morphological and geo- and Holcomb, R. T., 1983. Eruption-triggered avalanche, flood, and technical parameters of landslides in relation to geology and lahar at Mount St. Helens – Effects of winter snowpack. Science, hydrology. In Bonnard, C. (ed.), Landslides: Proceedings of 221, 1394–1397. Fifth International Symposium on Landslides. Rotterdam: Weidinger, J. T., 2004. Case histories of Pleistocene to Recent Balkema, pp. 3–35. rockslide dams in the Himalayas (India, Nepal) and Qin Ling Jibson, R. W., Harp, E. L., Schulz, W., and Keefer, D. K., 2006. Mountains (China). In Abdrakhmatov, K., Evans, S. G., Large rock avalanches triggered by the M 7.9 Denali Fault, Hermanns, R., Scarascia-Mugnozza, G., and Strom, A. L. Alaska, earthquake of 3 November 2002. Engineering Geology, (eds.), Security of Natural and Artificial Rockslide Dams: 83, 144–160. Extended Abstracts Volume. Bishkek, Kyrgyzstan: NATO Kelly, M., 1980. A prehistoric catastrophic rock avalanche at Advanced Research Workshop, pp. 189–201. Holsteinsborg, West Greenland. Geological Survey of Denmark Zhang, Y., Chen, W., and Riseborough, D. W., 2006. Temporal and Bulletin, 28,73–79. spatial changes of permafrost in Canada since the end of the Little Larson, C. F., Motyka, R. J., Freymueller, J. T., Echelmeyer, K. A., Ice Age. Journal of Geophysical Research, 111(D22), 14pp. and Ivins, E. R., 2005. Rapid viscoelastic uplift in Southeast Alaska caused by post-Little Ice Age glacial retreat. Earth and Planetary Science Letters, 237, 548–560. Cross-references Mason, K., 1930. The Glaciers of the Karakoram and Alaskan Glaciers Neighbourhood. Records of the Geological Survey of India, Alps LXIII/2, Government of India, Central Publications Branch, Canadian Rockies and Coast Mountains of Canada Calcutta. Debris-Covered Glaciers McSaveney, M. J., 1978. Sherman Glacier rock avalanche, Alaska, Glacier Surging USA. In Voight, B. (ed.), Rockslides and Avalanches, 1 Natural Glaciers of the Karakoram Himalaya Phenomena. New York: Elsevier, pp. 197–258. Himalaya McSaveney, M. J., 2002. Recent rockfalls and rock avalanches Hindu Kush in Mount Cook National Park, New Zealand. In Evans, Ice-Marginal Deposition S. G., and Degraff, J. V. (eds.), Catastrophic Landslides: Natural Hazards Associated with Glaciers and Permafrost Effects, Occurrence, and Mechanisms. Geological Society Optical Remote Sensing of Alpine Glaciers of America Reviews in Engineering Geology, Vol. 15, pp. Rocky Mountains 35–70. Sediment Entrainment, Transport, and Deposition