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Catastrophic mass flows (CMF) in the mountain cryosphere are an important geomorphic process that may pose significant hazard to communities and infrastructure in cold mountains; they occur in association with snow, glaciers, and permafrost in environments that are particularly sensitive to changes in thermal regimes and heavy rainfall. CMF form a broad range of cryospheric hazards and include mass movements of glacial ice, rock avalanches, ice-rock avalanches, debris flows, and outburst-generated flows. In some high mountains, avalanches of glacial ice, rock, and ice-rock mixtures may be earthquake-triggered. Broadly, CMF in the mountain cryosphere are characterized by sudden onset, high mean velocity (≥ 5 m/s), and high mobility (i.e., long runout in relation to volume) and generally involve a mixture of earth materials, water, snow, and ice. In some cases, CMF runout may exceed 100 km from source. CMF commonly undergo dramatic process transformation during movement in response to melting of entrained ice and snow, entrainment of additional materials along their path, river-damming effects, and incorporation or displacement of water in the periglacial environment; process complexity, involving long and complex process chains with instantaneous and/or delayed cascades, thus represents a challenge to quantitative hazard assessment. CMF initiate in uninhabited or sparsely populated areas of the mountain cryosphere and frequently descend into denser populated areas where they impact on mountain communities and infrastructure. CMF have been responsible for several notable mountain disasters since 1940 resulting in the deaths of over 15,000 people worldwide. Our focus on an examination of process complexity illuminates an assessment of CMF hazard in ice-affected mountain regions and forms the basis for the development of mitigation strategies based on detection, warning, engineering techniques in source and runout areas, and land-use controls. The precise relationship between the magnitude/frequency of CMF and change in the mountain cryosphere since ca. 1900 remains uncertain.

In a 291 day period in the latter stages of WW2 (1944–45) 10,386 V1 cruise missiles were launched against the UK from ground ramps in France and Holland, and from modified He-111 bombers flying off the south and east coasts of England. The attack mainly targeted London and despite a highly effective British campaign of in-flight interception, 2420 V1 missiles (23% of those launched) made explosive impact on the London target area resulting in significant loss of life and massive damage to London's housing stock. Using data from The National Register of 1939 we reconstruct the target geography of London and utilising a vast body of archival data from The National Archives we also reconstruct the V1 impact geography; in doing so we evaluate the accuracy of the V1 attack. Most missiles struck near the centre of the London target in areas of high population density; 40% of the missiles fell on the County of London forming the inner core of the London Civil Defence Region containing 38% of its 1944 population in only 16% of its area. The overall Mean Point of Impact is within 3.5 km of the centroid of the County of London. V1 impact density showed similar Clarke-like distance-decay relations to population density in relation to an assumed Central London aiming point. We also determine the accuracy metrics for the V1 attack. Our results verify the idea that high-resolution accuracy is moot when missile systems with relatively low accuracy are launched against large area targets, such as large cities. Although compared to modern missile systems the V1 was “inaccurate”, we find that the German cruise missile system fulfilled the operational accuracy requirements to achieve its terror and urban damage objectives.

The remnants of rockslide dams are widespread in the deeply incised river valleys of the northwest Himalayas and adjacent Pamir Mountains of Central Asia. In January 2010 a major rockslide (estimated volume ~ 55 Mm3) dammed the Hunza River (NW Pakistan) and a rockslide-dammed lake (Lake Gojal) immediately began to form. The lake overtopped the rockslide dam 145 days later through a spillway excavated in the surface of the debris by Pakistan authorities. Lake Gojal successively reduced in volume in response to spillway widening and deepening in engineering works up to May 2013; on August 28, 2015 (Day 2063 of impoundment) a remnant lake still remains. Using SRTM 3-arc-second digital terrain data and ten high-resolution satellite images from the period March 2010–August 2015, we document the river-damming environment of the Attabad rockslide, track and quantify the development of rockslide-dammed Lake Gojal and calculate lake areas and volumes at various stages of filling, stable overtopping, and partial draining to a final stable configuration. We introduce a method of delimiting lake shorelines by a pixel method which produces a mean elevation surface in the SRTM DEM; this technique results in accurate estimates of shoreline elevation and corresponding lake areas and volumes. We estimate the maximum volume reached by Lake Gojal, 51 days after overtopping, to have been approximately 455 Mm3. Using this data we also evaluate the mitigation works carried out by Pakistan authorities and find that i) they achieved an initial reduction of about 26% in the maximum possible volume of Lake Gojal that would have been reached without engineering intervention, and ii) as of August 28, 2015, in drawing down the lake by ~ 40 m, they had achieved a 72% reduction in the maximum volume reached by Lake Gojal after overtopping without a catastrophic release taking place. The emplacement of rockslide dams and the behaviour of their impounded lakes are critical hazards to communities and the development of infrastructure, including hydroelectric facilities, in this region of Central Asia. We show that a combination of high-resolution optical satellite imagery and SRTM 3-arc-second digital topography is very effective in producing key first-order data on rockslide-dammed lakes for geomorphic and hydrological analysis as well as the evaluation of engineering mitigation.

In April 2000 a large-scale rock avalanche dammed the Yigong Zangpo River, forming an extensive rockslide-dammed lake. The impoundment lasted for 62 days before a catastrophic breaching caused a massive outburst flood in the Yarlung Zangpo (Tibet) and the Dihang rivers (India) that travelled downstream to the main floodplain of the Brahmaputra in northeastern India. In response to discrepancies in the published literature on the event, we present a review and re-evaluation of the characteristics of the rock avalanche and associated landslide-dammed lake. We use digital topographical data (SRTM-3) and dynamic landslide modelling (DAN-W and DAN3D) to determine the salient characteristics of the damming landslide and to characterise its behaviour. Our analysis indicates that the volume of the damming rockslide was ca. 115 Mm3, including 91 Mm3 from the initial rockslope failure (bulked during disaggregation to 109 Mm3) and 6 Mm3 from entrainment during its 10.1 km travel down Zhamulong gully. The debris travelled with an average velocity of 15–18 m/s and resulted in a landslide dam on the Yigong River with a minimum height of about 55 m. Using LANDSAT-7 imagery (obtained before, during, and after impoundment) in conjunction with an SRTM-3 DEM, we reproduced the filling of the lake. We determine that the landslide dam formed an extensive reservoir with an impounded volume of 2.015 Gm3 and a maximum possible lake level of 2264 m asl (rounded to 2265 m asl). Our figures differ from those previously published but are believed to be well-constrained verifiable estimates of the volumes of the 2000 Yigong events. The outburst occurred after an attempt by army personnel to manually dig a spillway over the landslide debris and resulted in the entire volume of the lake draining in about 12 h. The outburst flood travelled over 500 km south into India, with a recorded rise in river level of 5.5 m at the Pasighat gauging station, 462 km downstream. In terms of historical outburst volumes from rockslide-dammed lakes, the volume of the 2000 Yigong event is only exceeded by that of the 1841 outburst flood from the Indus River rockslide-dammed lake, northern Pakistan.

Rock avalanches onto glacier surfaces, involving volumes 1 Mm3 or more, are common in the glacier environments of NW North America. We analyse the Mount Munday rock avalanche (British Columbia) which occurred in July 1997. It involved the initial movement of 3.2 Mm3 of granitic gneiss that underwent a high degree of fragmentation as it was emplaced on Ice Valley Glacier as a thin 2.6-km2 debris sheet. The total height of the path was 850 m, and its length was 4,163 m yielding a fahrboschung of 10°, suggestive of a long runout in relation to volume. Potential energy expended in the movement was calculated as 4.33 × 1013 J and its specific energy was estimated at 5,204 J/kg. A simulation of the movement using 2D DAN-W and DAN 3D strongly supports the idea that debris sheet geometry (runout and thickness) and behaviour (velocity profile) resulted from movement on a low friction surface (glacier ice). Our analysis of the debris sheet geometry of 23 unconstrained rock avalanches on glacier surfaces in NW North America indicated that the debris sheets are distinct from those in non-glacial environments in that they are (a) longer in relation to volume and (b) more extensive in area in relation to volume. These two effects result in a very thin supra-glacial debris sheet. Using image analysis software, we found that ∼85 % of the initial source rock volume was fragmented to fragment sizes less than 4.7 m3 in volume during emplacement, and that within the debris sheet, the highest degree of fragmentation is associated with the thinnest debris. In the emplacement of rock avalanche debris sheets on glacier surfaces, the low friction glacier surface drives debris sheet thinning through spreading, which in turn results in the fragmentation of its entire thickness. We thus propose low friction surface-driven fragmentation as a process that contributes to long runout of rock avalanches on glacier surfaces and explains their distinctive debris sheet geometry.

A large rock avalanche occurred at 03:27:30 PDT, 6 August 2010, in the Mount Meager Volcanic Complex southwest British Columbia. The landslide initiated as a rock slide in Pleistocene rhyodacitic volcanic rock with the collapse of the secondary peak of Mount Meager. The detached rock mass impacted the volcano's weathered and saturated flanks, creating a visible seismic signature on nearby seismographs. Undrained loading of the sloping flank caused the immediate and extremely rapid evacuation of the entire flank with a strong horizontal force, as the rock slide transformed into a debris flow. The disintegrating mass travelled down Capricorn Creek at an average velocity of 64 m s−1, exhibiting dramatic super-elevation in bends to the intersection of Meager Creek, 7.8 km from the source. At Meager Creek the debris impacted the south side of Meager valley, causing a runup of 270 m above the valley floor and the deflection of the landslide debris both upstream (for 3.7 km) and downstream into the Lillooet River valley (for 4.9 km), where it blocked the Lillooet River river for a couple of hours, approximately 10 km from the landslide source. Deposition at the Capricorn–Meager confluence also dammed Meager Creek for about 19 h creating a lake 1.5 km long. The overtopping of the dam and the predicted outburst flood was the basis for a night time evacuation of 1500 residents in the town of Pemberton, 65 km downstream. High-resolution GeoEye satellite imagery obtained on 16 October 2010 was used to create a post-event digital elevation model. Comparing pre- and post-event topography we estimate the volume of the initial displaced mass from the flank of Mount Meager to be 48.5 × 106 m3, the height of the path (H) to be 2183 m and the total length of the path (L) to be 12.7 km. This yields H/L = 0.172 and a fahrböschung (travel angle) of 9.75°. The movement was recorded on seismographs in British Columbia and Washington State with the initial impact, the debris flow travelling through bends in Capricorn Creek, and the impact with Meager Creek are all evident on a number of seismograms. The landslide had a seismic trace equivalent to a M = 2.6 earthquake. Velocities and dynamics of the movement were simulated using DAN-W. The 2010 event is the third major landslide in the Capricorn Creek watershed since 1998 and the fifth large-scale mass flow in the Meager Creek watershed since 1930. No lives were lost in the event, but despite its relatively remote location direct costs of the 2010 landslide are estimated to be in the order of $10 M CAD.

Earthquake-triggered landslides are a major geological hazard in Central Asia. In July 1949, the M7.4 Khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the Tien Shan Mountains, central Tajikistan. These landslides involved widespread rock-slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region. In the Yasman valley hundreds of loess landslides coalesced to form a massive loess flow (est. vol. 245 Mm 3 ) that travelled up to 20 km on a slope of only 2°. In an adjacent valley, the Khait landslide involved transformation of an earthquake-triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement. It travelled 7.41 km over a vertical distance of 1421 m with an estimated average velocity of ~30 m/s. We estimate its volume as 75 Mm 3 , an order of magnitude less that previously published estimates. The Khait landslide was simulated using DAN. The number of casualties due to earthquake-triggered landslides in the epicentral region was considerable. Approximately 4000 people were killed in the Yasman valley loess flow as 20 villages ( kishlaks ) were overwhelmed. In the Khait landslide alone we estimate ca. 800 people lost their lives when the villages of Khait and Khisorak were overrun by rapidly moving debris. Our data indicates that a total of approximately 7200 people were killed by earthquake-triggered landslides in the epicentral region of the Khait earthquake and that, in terms of loss of life, the 1949 Yasman valley loess flow was one of the most destructive landslides in recent history.

The 1962 and 1970 Huascaran mass movements, originated as rock/ice falls from the mountain's North Peak, transformed into higher-volume high-velocity mud-rich debris flows by incorporation of snow from the surface of a glacier below Huascaran and the substantial entrainment of morainic and colluvial material from slopes below the glacier terminus. Water for fluidization of the entrained material originated in the melting of incorporated snow and the liberation of soil moisture contained within the entrained materials. Eyewitness reports indicate very high mean velocities for the events; 17–35 m/s (1962) and 50–85 m/s (1970). The runout distances and velocity profiles of both events were simulated using DAN/W. Both mass movements continued downstream in the Rio Santa as debris floods (aluviones) that in 1970 reached the Pacific at a distance of 180 km. In strong contrast to publications in the geosciences literature, 1961 Peru Census data indicates that the death toll of the 1970 event is ca. 6000 and that total life loss in the two events did not exceed 7000 people.

A large rock and ice avalanche occurred on the north face of Mount Steele, southwest Yukon Territory, Canada, on July 24, 2007. In the days and weeks preceding the landslide, several smaller avalanches initiated from the same slope. The ice and rock debris traveled a maximum horizontal distance 5.76 km with a maximum vertical descent of 2,160 m, leaving a deposit 3.66 km2 in area on Steele Glacier. The seismic magnitude estimated from long-period surface waves (M s) is 5.2. Modeling of the waveforms suggests an estimated duration of approximately 100 s and an average velocity of between 35 and 65 m/s. This landslide is one of 18 large rock avalanches known to have occurred since 1899 on slopes adjacent to glaciers in western Canada. We describe the setting, reconstruct the event chronology and present a preliminary characterization of the Mount Steele ice and rock avalanches based on field reconnaissance, analysis of seismic records and an airborne LiDAR survey. We also present the results of a successful dynamic simulation for the July 24 event.

Catastrophic mass flows (CMFs) in the glacial environment are an important geomorphic process that may pose significant hazard to communities and infrastructure in glacierized mountains. CMFs form a broad range of glacial hazards and include mass movements of glacial ice, rock avalanches, ice–rock avalanches, glacial debris flows, and outburst-generated flows. Broadly, CMFs in the glacial environment are characterized by a sudden onset, high mean velocity (≥5 m/s), high mobility (i.e., long runout in relation to volume), and generally involve a mixture of earth materials, water, snow, and ice. In some cases, CMF runout may exceed 100 km from source. CMFs commonly undergo dramatic process transformation during movement in response to melting of entrained ice and snow, entrainment of additional materials along its path, river-damming effects, and incorporation or displacement of water in the periglacial environment; process complexity thus represents a challenge to quantitative hazard assessment. CMFs initiate in uninhabited glacial environments and frequently descend into denser populated areas where they have an impact on mountain communities and infrastructure. CMFs have been responsible for several notable mountain disasters since 1940, resulting in the death of >15,000 people worldwide. Our focus on an examination of process illuminates an assessment of CMF hazard in glacierized mountain regions and forms the basis for the development of mitigation strategies based on detection, warning, engineering techniques in source and run-out areas, and land-use controls. The precise relationship between the magnitude/frequency of CMFs and cryospheric change in the mountain glacial environment since ca. 1900 remains uncertain.

The formation and behaviour of natural and artificial rockslide dams are reviewed to update the well-known work of Costa and Schuster [1]. Rockslide dams block surface drainage to form upstream lakes. They may occur naturally due to landslides or as a result of engineered rock slope failure. As evidenced by the 2010 Hunza event (Pakistan), the stability of rockslide dams is a major consideration in landslide risk assessment in mountain terrain, particularly with respect to the possibility of a destructive downstream flood resulting from a breach of the dam. The damming of a river by a rockslide may require immediate engineering response to mitigate the hazard. However, failure by breaching is less frequent than long-term stability. These issues are examined with reference to nine case histories of rockslide dams and rockslide-dammed lakes; Gohna (1894), Rio Barrancas (1914), Condor-Sencca (1945), Mayunmarca (1974), La Josefina (1993), Tsao-Ling (1999), Yigong (2000), Tangjiashan (2008), and the Hunza (2010). The case histories also illustrate the utility of digital terrain data (especially the SRTM-3 data set obtained in February 2000) and remote sensing imagery to obtain accurate estimates of the impoundment volumes and other geomorphic data on rockslide-dammed lakes. Methods of estimating peak breach discharge and downstream flood effects exist but are still largely empirical in nature. Measures to mitigate hazard associated with rockslide-dammed lakes include the construction of a spillway over the rockslide debris, a by-pass tunnels through the abutments of the debris dam, the implementation of dam and lake-level monitoring and failure warning systems to mitigate downstream damage. A review of some well-documented examples show that these measures have had been applied with mixed success in the past. Natural rockslide dams are commonly used for foundations for conventional constructed dams. Artificial rockslide dams are created by rock slope failure induced by large-scale explosion (blast-fill dams). The largest blast-fill dam yet constructed is the Medeo Dam, a debris flow retention structure near Alma-Ata, Kazakhstan. Rockslide dams and their geomorphic effects may create an important legacy in the landscape through massive accumulations of lake sediments, impact on river channels, and effects on river long-profiles.

In April 2000 a large-scale rock avalanche dammed the Yigong Zangbo River, forming an extensive rockslide-dammed lake. The impoundment lasted for 62 days before a catastrophic breaching caused a massive outburst flood in the Yarlung Zangbo (Tibet) and the Dihang Rivers (India) that travelled about 500 km downstream to the floodplain of the Brahmaputra in northeastern India. In response to discrepancies in the published literature on the event, a review and re-evaluation of the characteristics of the rock avalanche and associated landslide-dammed lake has been undertaken using remote sensing data. The data included SRTM-3 digital terrain data and LANDSAT-7 imagery obtained before, during and after the impoundment. Analysis of satellite imagery and SRTM-3 terrain data indicates that the volume of the damming rockslide was ca. 105 Mm3 and the outburst volume of the rockslide-dammed lake was ca. 2 Mm3 at a maximum pool elevation of 2,264 m a.s.l (rounded to 2,265 m a.s.l.). These figures differ from those previously published but are believed to be well-constrained credible estimates of the volumes of the 2000 Yigong events. In terms of historical outburst volumes from rockslide-dammed lakes, the volume of the 2000 Yigong event is only exceeded by that of the 1841 outburst flood from the Indus River rockslide-dammed lake, northern Pakistan.

The remains of rockslide dams are widespread in the river valleys of the northwest Himalayas (Pakistan and India) and the adjacent Pamir Mountains of Afghanistan and Tajikistan, Central Asia. The region contains in excess of two hundred known rockslide deposits of, as yet, unknown age that have interrupted surface drainage and previously dammed major rivers in the region in prehistoric time. In addition, the region contains (1) the highest rockslide dam (the 1911 Usoi rockslide, Tajikistan) in the world that dams the largest rockslide-dammed lake (Lake Sarez) on Earth, (2) the largest documented outburst flood associated with a historical rockslide dam outburst (the 1841 Indus Flood, Pakistan), and (3) the world’s most recent (2010) rockslide-dammed lake emergency, the Attabad rockslide dam on the Hunza River, in the Upper Indus basin of northern Pakistan. We show that some prehistoric rockslide dams in the northwest Himalayas impounded lakes with volumes in excess of 20 Gm3, significantly larger than present-day Lake Sarez. We use SRTM-3 digital terrain data and satellite imagery to analyse four major historical rockslide damming events (1) our analysis of the 1841 Indus rockslide-damming event indicates that the volume of the impoundment and subsequent outburst was 6.5 Gm3, the largest outburst from a rockslide-dammed lake in historical time, (2) the 1858 Hunza Valley rockslide dam impounded about 805 Mm3 before catastrophic outburst in August 1858, (3) the development of the 2010 Hunza rockslide-dammed lake is described in detail for the first time. It reached a maximum volume of 430 Mm3 before stable overflow of the rockslide debris began on May 29, 2010. This remains the situation as of July 25, 2010 (200 days after impoundment), (4) the filling of Lake Sarez was conditioned by excessive outflow seepage through the debris as the lake filled to the extent that a freeboard of ca. 50 m is still naturally maintained without engineering intervention. The emplacement of rockslide dams and the behaviour of their impounded lakes are critical hazards to communities and the development of infrastructure, including hydroelectric facilities, in this region of Central Asia.

On 4 January 2010, a rockslide 1200 meters long, 350 meters wide, and 125 meters high dammed the Hunza River in Attabad, northern Pakistan, and formed Lake Gojal. The initial mass movement of rock killed 20 people and submerged several villages and 22 kilometers of the strategic Karakoram Highway linking Pakistan and China. Tens of thousands of people were displaced or cut off from overland connection with the rest of the country. On 29 May, the lake overflow began to pour through a spillway excavated by Pakistani authorities. On approximately 20 July, the lake attained a maximum depth of 119 meters and a torrent at least 9 meters deep issued over the spillway, according to Pakistan's National Disaster Management Authority (NDMA). To date, the natural dam is holding and eroding slowly. However, the threat of a catastrophic outburst flood remains.