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Two large-scale glacier detachments occurred at the peaks of the 2013 and 2015 CE melt seasons, releasing a cumulative 24.4–31.3 × 106 m3 of ice and lithic material from Flat Creek glacier, St. Elias Mountains, Alaska. Both events produced highly mobile and destructive flows with runout distances of more than 11 km. Our results suggest that four main factors led to the initial detachment in 2013: abnormally high meltwater input, an easily erodible glacier bed, inefficient subglacial drainage due to a cold-ice tongue, and increased driving stresses stemming from an internal redistribution of ice after 2011. Under a drastically altered stress regime, the stability of the glacier remained sensitive to water inputs thereafter, culminating in a second detachment in 2015. The similarities with two large detachments in the Aru mountains of Tibet suggest that these detachments were caused by a common mechanism, driven by unusually high meltwater inputs. As meltwater production increases with rising temperatures, the possible increase in frequency of glacier detachments has direct implications for risk management in glaciated regions.
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What drives large-scale glacier detachments? Insights from Flat
Creek Glacier, St. Elias Mountains, Alaska
Mylène Jacquemart1, Michael Loso2, Matthias Leopold3, Ethan Welty4, Etienne Berthier5, Jasmine
S. S. Hansen1, John Sykes6, Kristy Tiampo1
1 Department of Geological Sciences & CIRES, University of Colorado, Boulder, CO, 80309, USA
2 Wrangell-St. Elias National Park and Preserve, Copper Center, AK 99573
3 UWA-School of Agriculture and Environment, University of Western Australia, Perth, 6009, Australia
4 INSTAAR, University of Colorado, Boulder, CO, 80309, USA
5 LEGOS, Université de Toulouse, 31400 Toulouse, France
6 Department of Geography, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
Two large-scale glacier detachments occurred at the peaks of the 2013 and 2015 melt seasons, releasing a
cumulative 24.4 31.3 x 106 m3 of ice and lithic material from Flat Creek Glacier, St. Elias Mountains,
Alaska. Both events produced highly mobile and destructive flows with runout distances of more than 11
km. Our results suggest that four main factors led to the initial detachment in 2013: Abnormally high
meltwater input, an easily erodible glacier bed, inefficient subglacial drainage due to a cold-ice tongue,
and increased driving stresses stemming from an internal redistribution of ice after 2011. Under a
drastically altered stress regime, the stability of the glacier remained sensitive to water inputs thereafter,
culminating in a second detachment in 2015. The similarities with two large detachments in the Aru
mountains of Tibet suggest that these detachments were caused by a common mechanism, driven by
unusually high meltwater inputs. As meltwater production increases with rising temperatures, the possible
increase in frequency of glacier detachments has direct implications for risk management in glaciated
Large-scale glacier detachments occur when large portions of valley glaciers’ tongues decouple from the
glacier bed, resulting in catastrophic mass flows (Evans & Delaney, 2015). Recent observations from
around the world including the 2002 detachment of Kolka Glacier (100130 x 106 m3; Haeberli et al.,
2004; Evans et al., 2009), the twin 2016 detachments of the Aru glaciers in Tibet (68 x 106 m3 and 83 x
106 m3, respectively; Kääb et al., 2018), the 2007 detachment of Leñas Glacier in the Argentinian Andes
(4 x 106 m3, Falaschi et al., 2019), and repeated ice detachments from an unnamed glacier in central
China (unknown volume; Paul, 2019) raise the question whether anthropogenic climate change is not
only accelerating glacier retreat, but also introducing a previously unobserved yet catastrophic mechanism
of glacier destruction.
We extend the list above by documenting two large-scale detachments at Flat Creek Glacier,
Alaska, which occurred in 2013 and 2015. Understanding the cause of these hazardous events is critical to
predicting where else they are likely to occur. Although Gilbert et al. (2018) have proposed that the Aru
and Kolka detachments were ultimately caused by a failure of the subglacial till, the climatic and glacial
conditions leading up to these detachments differed significantly (Gilbert et al., 2018, Evans et al., 2009).
In this study, we used data from two field campaigns and a remote sensing analysis to characterize the
geologic, glacial, thermal, and meteorological conditions that led to the Flat Creek detachments. In an
attempt to identify common drivers of glacier detachments, we describe and quantify the Flat Creek
detachments and compare them to those of Aru and Kolka.
Prior to the 2013 detachment, informally-named Flat Creek Glacier covered 2.6 km2 (6.5%) of the Flat
Creek watershed (Fig. 1). It occupied a central trough at 2030 2650 m above sea level (asl) on the NNE-
facing headwall. Meltwater from the glacier drains into the White River at 1050 m asl. The glacier lies in
a subarctic climate in the rain shadow of the St. Elias Mountains. Over the last decade, the Chisana
weather station (50 km NW of Flat Creek, at 1012 m asl) recorded a mean annual air temperature of -4.5
°C and a mean annual precipitation of 335 mm. Regional and global maps (Jorgenson et al., 2008;
Gruber, 2012), electrical resistivity tomography, and ground temperature measurements (see methods
suppl.) indicate that permafrost is continuous in the upper part of the valley (above 1800 m asl) and
discontinuous-to-sparse on the alluvial fan (below 1600 m asl). Many glaciers in the area have a history of
surging (Post, 1969), and one glacier adjacent to Flat Creek surged between 2012 and 2015. Crosscutting
upper Flat Creek, the influence of the Totschunda Fault (Schwartz et al., 2012) is apparent in heavily
fractured, thin-bedded silt and sandstones of the Permian Hasen Creek Formation that underlie the
valley’s glaciers. Just downstream, the lithology changes to volcaniclastic sediments of the Nikolai
Greenstone Formation (MacKevett, 1979).
On 2013-08-05, the lowermost 500 m of Flat Creek Glacier (below 2270 m asl) detached and traveled 11
km downstream (Fig. 2). The remaining ice responded rapidly, advancing 3045 m in the days following
the detachment (measured with orthophotos from 2013-08-11 and 2013-09-05) and thinned by up to 28.1
± 0.7 m (Fig. 3). We estimated elevation changes by differencing two digital elevation models (DEMs)
from before and after the detachment (2012-08-26 and 2014-10-12). The total detachment volume was 6.8
± 0.2 x 106 m3 to 11.2 ± 0.7 x 106 m3 (Fig. 3, methods see suppl. data). The lower bound only considers
the elevation difference in the detachment zone. The upper bound further includes the thinning of the
upper glacier as an estimate of the volume that advanced into the detachment zone in response to the
Throughout summer 2013 to spring 2015, the remaining glacier advanced and crumbled at the
front, covering the original detachment zone with loose ice. Sometime between 2015-07-18 and 2015-07-
25, this loose ice detached and traveled 10 km down the valley (see suppl. data). On 2015-07-30, another
17.6 ± 0.2 x 106 m3 to 20.1 ± 0.3 x 106 m3 of ice and lithic material detached. This failure reached the
drainage divide at 2650 m asl (Fig. 2 & 3). The resulting mass flow spread debris over 8 km2 of the
alluvial fan, burying 3 km2 of mature forest (at least 4-centuries old; see suppl. data). The angle of the
exposed glacier bed presumably the failure plane was 21° above horizontal.
In both 2013 and 2015, the detached masses transformed into highly-mobile mass flows that
reached the White River (12 km downstream) in minutes and ran an average of 76 m up the back of West
Hill, a prominent bedrock knob adjacent to Flat Creek (Fig. 1). Using runup heights (Iverson et al., 2016;
Prochaska, 2008) and the duration of the detachment-induced quakes recorded at the Barnard Glacier
seismic station (60 km SW of Flat Creek), we derived peak velocities up to 50 m/s and mean velocities
around 30 m/s for both events (see suppl. data). Surveying the detachment deposits in 2018 and 2019, we
found fine-grained lithic material (3040 % clay, see suppl. data) mixed with interstitial ice and rounded
ice blocks. The lithic material was almost exclusively Hasen Creek mudstone from under the glacier.
Photographs of the detachment zone acquired with an unmanned aerial vehicle in 2018 show that the thin-
bedded mud and sandstones erode into thick layers of fine-grained, unconsolidated sediment. Despite the
proximity of the Totschunda Fault, we found no seismic triggers for the detachments in the US
Geological Survey (USGS) earthquake record.
One of Flat Creek Glacier’s remarkable features before the first detachment was thick, bulging
ice behind a thin, crevasse-free tongue (Fig. 2). From the length of the shadows cast by the bulge in a
2009-07-13 orthophoto, we constrained the maximum height of the bulge to 70.2 ± 9.4 m (see methods
suppl.). We rule out the possibility that the bulge was caused by a bedrock step because the post-
detachment DEM shows no such feature and it is unlikely that such a feature would have endured
centuries of glacial erosion, yet disintegrate during the detachment (Fig. 3). We found no change in the
horizontal position of the bulge between 2009 and 2011. However, between 2011 and 2013-06-22
(coincident with the surge of the glacier in the adjacent drainage), satellite images show that the bulge
advanced by as much as 100 m (Fig. 2; suppl. data), suggesting that a mass redistribution was underway.
In contrast, the glacier terminus did not advance during this time, supporting our inference of a cold-ice
tongue. The bulge and cold-ice tongue very closely resemble the geometry observed in 1980 on Trapridge
Glacier, 80 km SE (Clarke & Blake, 1991). Englacial temperature measurements on Trapridge Glacier
showed that a thin, cold-ice tongue served as a mechanical dam to temperate ice up-glacier, forming the
bulge. Given the morphological similarities to Trapridge Glacier, a mean annual air temperature of -
12.1°C at the pre-detachment terminus, and continuous permafrost in the headwall, we conclude that Flat
Creek Glacier was polythermal, with a thin cold-ice tongue slowing the advance of thicker, temperate ice
Based on Flat Creek Glacier’s thermal regime, we infer that subglacial drainage was restricted by
the cold-ice tongue. Glacier marginal-streams and deeply incised supraglacial streams on many of the
region’s small glaciers suggest that this mechanism is common in this area (Irvine-Fynn et al., 2011;
Ryser et al., 2013). Observations from Trapridge suggest that water likely drains through the subglacial
substrate to ice-marginal streams, and we suggest the same was true at Flat Creek Glacier. The limited
efficiency of this drainage mechanism causes water to accumulate if the input rate exceeds the output rate
(Clarke et al., 1984; Clarke & Blake, 1991). To identify where below Flat Creek Glacier water would
have accumulated, we applied a Rho8 flow routing analysis to the 2012-08-26 DEM (Fairfield &
Leymarie, 1991, see methods suppl.). Glacier surface topography is taken as an acceptable catchment-
level proxy for water drainage below the glacier (Igneczi et al., 2018). We find that the area immediately
upstream of the bulge received water from a larger catchment than any other point on the glacier. The
next highest flow concentrations were under the detachment zone. Given this large drainage area and the
crevassed surface of the glacier upstream of the bulge, meltwater likely reached the bed and increased the
subglacial water pressure.
To evaluate the availability of liquid water prior to the detachments, we used a 36-year record of
dynamically-downscaled ERA-Interim temperature and precipitation data available for Alaska at 20 km
resolution (Bieniek et al., 2016; see methods suppl.), bias-corrected with ten years of weather station data
from Chisana. Since both failures happened during peak melt season, we calculated the cumulative
summer water availability for each year by summing rainfall and melt from April through July. Melt was
modeled at an hourly resolution using a degree-day approach with melt factors of 2.7 mm d-1 °C-1 for
snow and 4.87 mm d-1 °C-1 for ice (see methods suppl.; Hock, 2003). At Flat Creek, according to our
model, the cumulative summer water availability preceding the 2013 detachment exceeded the 36-year
mean cumulative summer water availability by 100 615 %, or 3.59 4.77 standard deviations (𝜎),
depending on elevation (Fig. 4). Water availability was lower than average (-0.49 0.03 𝜎) in 2014, but
again exceeded the mean by 0.08 0.91 𝜎 in 2015.
The apparent emergence of large-scale glacier detachments (Kääb et al., 2018; Falaschi et al., 2018; Paul,
2019; Jacquemart & Loso, 2019) raises the question of whether these events share common drivers, and
whether these will be exacerbated by current warming.
The 2013 detachment at Flat Creek Glacier coincided with unprecedented water availability
driven by record warm temperatures. Our modeled water availability is supported by Alaska-wide
measurements showing 2013 to be the year with the most negative mass balance since 2003 (Wouters,
2019). Due to the inefficient drainage mechanism identified at Flat Creek, the high melt rates allowed
water to accumulate under the glacier, increasing the water pressure in the subglacial till and weak
bedrock. The ultimate shear strength of subglacial till has been shown to increase linearly with effective
normal stress (Iverson et al., 1998). By reducing the effective pressure, increasing basal water pressure is
therefore likely to have weakened the subglacial till. Indeed, the high clay content of the deposits
indicates that the failure initiated within the glacier’s basal substrate. Meanwhile, the advancing bulge
upstream of the cold-ice tongue contributed to increased driving stresses. When meltwater input peaked in
July 2013, rising subglacial water pressures and increased driving stresses allowed the glacier tongue to
detach about 100 m upstream of the 2009 - 2011 location of the bulge.
In 2015, the geometry of the glacier was dramatically altered and we assume that all remaining
ice was temperate. However, the inverse correlation between water availability and glacier stability, and
the role of the weak basal substrate, continued. No detachment occurred in 2014, when water availability
was below average, while activity resumed with increasing water availability in 2015. The precursory
detachment of the loose ice accumulated in the detachment zone shows how easily the underlying lithic
material failed with increased water availability. Under the remaining glacier, the stability of the till may
have been compromised by two factors following the 2013 detachment: (1) reduction of the effective
normal stress due to thinning of the glacier (though this also reduces driving stresses), and (2) alignment
of clay particles by the glacier advance, an effect that has also been shown to reduce the shear strength of
glacial tills (Iverson, 1998). Combined, these factors likely contributed to the 2015 detachment, and also
highlight that a polythermal regime is not a mandatory prerequisite for a large-scale detachment.
Both the 2013 and 2015 mass flows impacted a large swath of 400 year old forest, indicating that
no event of comparable size has occurred here in the past 4 centuries. This suggests that large-scale
glacier detachments may indeed be a new hazard of our warming world.
A comparison with the Kolka and Aru detachments reveal that conditions at Flat Creek strongly
resemble those at Aru, but not those at Kolka. Kolka Glacier is temperate and the stress regime was likely
altered by an accumulation of debris from a series of ice and rock falls (Haeberli et al., 2004, Evans et al.,
2009). In contrast, the cold-ice margins of the Aru glaciers allowed water to accumulate in the subglacial
till over the 5 6 years preceding the detachments. Simultaneously, increasing flow velocities were
observed on bulging, temperate ice encroaching upon the tongues of both glaciers, increasing driving
stresses (Gilbert et al., 2018). Under this altered stress regime, the accumulation of water decreased the
effective normal stress on the till, inducing failure in 2016, the year with the highest recorded degree-day
sum (Kääb et al., 2018).
In conclusion, insights from this study suggest that remarkably similar glacial and climatic
conditions led to the Flat Creek and Aru detachments. At Flat Creek Glacier, these conditions led to two
detachments which both produced highly destructive mass flows with wide-reaching impacts, luckily
without human casualties or damage to infrastructure. Our work highlights the potential sensitivity of
soft-bedded polythermal glaciers to sudden detachments under warming conditions, and the need to refine
the criteria that distinguish collapse-prone glaciers from others in this broad category. Identifying which
glaciers are mostly likely to detach is critical to risk management in mountain environments.
Fig. 1: Study area: Glacier and alluvial fan changes (orange & purple box) are shown in detail in Fig. 2.
Yellow dots indicate the locations of electrical resistivity tomography surveys, ground temperatures were
measured at ERT-1. Cyan lines are from the Randolph Glacier Inventory 6.0 (RGI Consortium, 2017).
Flat Creek Glacier is labeled FCG. Note that the background image shows the watershed prior to the
detachments (© Planet, 2018).
Fig. 2: Changes of Flat Creek Glacier and the alluvial fan (orange & purple box in Fig. 1). Panel a) Image
from 2013-08-11. The orange star indicates the accumulation point of water based on the flow
accumulation analysis. Panel b) Image from 2015-08-13. All images © Planet
Panel c) Crevasse-free tongue of Flat Creek Glacier and thicker, crevassed ice upstream. Ikonos image
from 2009-07-13. The shadow used to estimate bulge height is indicated with a white arrow. Yellow and
magenta lines are the edge of the bulge in 2009 and 2013, respectively. © Maxar
Fig. 3: Top left: Surface elevation change between 2012-08-26 (AK IfSAR DEM) and 2014-10-12. Top
right: Surface elevation change between 2014-10-12 and 2016-03-13 (both ArcticDEM, Porter et al.,
2018). The inset maps resolve more detail over the detachments (dashed outlines), the black line is the
original glacier outline. Note the ongoing surge of the glacier west of Flat Creek.
Bottom: Longitudinal profiles from 2012, 2014, and 2016. Below the 2013 detachment line, loose ice
(area shaded green) masked the full surface change.
Fig. 4: Total summer (April - July) water availability at Flat Creek depending on elevation and mean
decadal water availability for an elevation of 2100 m asl.
We acknowledge a NASA Earth and Space Science Fellowship for M. Jacquemart and funding from the
NPS Inventory and Monitoring Program. E. Berthier acknowledges funding CNES funding. Field work
Pre-detachment total liquid water availability
1980 1985 1990 1995 2000 2005 2010 2015
Water availability (mm)
Elevation (m asl)
decadal mean
was partially funded under NASA IDS award 80NSSC17K0017, as was K. Tiampo. We thank J. Trop, T.
Vaden, P. Claus, and L. Wassink for early field observations. Valuable input was received from A. Kääb,
M. Dokukin, K. Allstadt, D. Farinotti, A. Vieli, W. Haeberli, and G. Wolken. We thank R. Hooke and A.
Gilbert as well as one anonymous reviewer for their valuable comments.
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... The Aru 2016 twin glacier detachments, which killed nine people and hundreds of other animals, likely were triggered by basal failure linked to increasing water pore pressure due to increases in surface melting and rainfall . Other detachment events have been recorded from the Caucasus (Tielidze et al., 2019), the Andes (Falaschi et al., 2019), the Alps (Bodin et al., 2017), Alaska (Jacquemart et al., 2020) and the Pamir . ...
... Previous studies have shown that a soft glacial bed appears to be a common attribute of large low-angle glacier detachments. For example, the failures of the Aru twin glaciers Kääb et al., 2018), Kolka glacier (Evans et al., 2009), Bérard Rock Glacier (Bodin et al., 2017), and Flat Creek glacier (Jacquemart et al., 2020), all involved water acting on soft glacier beds. When the subglacial till is saturated with water, the shear strength can decrease significantly to trigger the failure, as a result of increasing pore water pressure, lubrication, and softening (Evans et al., 2009;Gilbert et al., 2018;Iverson et al., 1998). ...
... Many crevasses created during a surge potentially extend to the bed (Rea and Evans, 2011;Sharp, 1985) and allow surface water to reach the soft glacier bed (Clason et al., 2012), leading to faster basal sliding Jacquemart et al., 2020). The glacier detachments of 2007, 2016 and 2019 occurred in warm season and likely were influenced by weather conditions . ...
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... Namcha Barwa (Peng et al., 2022;Hu et al., 2020;Montgomery et al., 2004;Zhang, 1992) showed high disaster risks in this high mountain region. Based on previous glacier-related disaster studies, some precursors of abnormal glacier dynamics, such as accelerated surface velocity, widening surface crevasse and glacier thickening at the glacier terminus, could be captured prior to glacier collapse using repeated high-resolution remote sensing data (Kä ä b et al., 2018;Jacquemart et al., 2020;An et al., 2022;Shugar et al., 290 2021), thus providing first-order discrimination of glaciers at risk. ...
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The Tibetan Plateau and its surroundings have recently experienced several catastrophic glacier-related disasters. It is of great scientific and practical significance to establish ground-based early warning systems (EWS) to understand the processes and mechanisms of glacial disasters and warn against potential threats to downstream settlements and infrastructure. However, there are few sophisticated EWSs on the Tibetan Plateau. With the support of the Second Tibetan Plateau Scientific Expedition and Research Program, an EWS was developed and implemented in the Sedongpu Valley, southeastern Tibetan Plateau, where repeated river blockages have occurred due to ice/rock collapse debris flow. The EWS collected datasets of optical/thermal videos/photos, geophone waveforms, water levels, and meteorological variables in this sparsely populated zone. It has successfully warned against three ice-rock collapse-debris flow - river blockage chain events and seven small-scale ice-rock collapse-debris flow events. Meanwhile, it was found that the low-cost geophone can effectively indicate the occurrence and magnitude of ice/rock collapses by local thresholds, and water level observation is an efficient way to warn of river blockages. Our observations showed that several factors, such as the volume and location of the collapses and the percentage of ice content involved, influence the velocities of debris flows and the magnitude of river blockages. There are still two possible glaciers in the study area that are at risk of ice collapse. It is worth monitoring their dynamic changes using high-resolution satellite data and the ground-based EWS to safeguard the surrounding hydrological projects and infrastructure in this transboundary region.
... In fact, the snow in the basin melted dramatically in the summer, providing hardly any areas for ice accumulation in rock glaciers under the effects of climate warming [10]. Subsequent glacier thinning and retreat have exposed the steep rock walls below the glacier, separating the glacier from the rock and leading to the formation of fissures [11][12][13]. A powerful 6.9-magnitude earthquake struck near the Sedongpu Basin on 18 November 2017, causing significant ground motion within the basin, which affects the stability of the rock slopes and promotes the occurrence of large ice avalanches [13]. ...
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Drastic climate change has led to glacier retreat in southeastern Tibet, and the increased frequency and magnitude of heavy rainfall and intense snow melting have intensified the risk of ice avalanche-induced debris flows in this region. To prevent and mitigate such hazards, it is important to derive the pre-disaster evolutionary characteristics of glacial debris flows and understand their triggering mechanisms. However, ice avalanche-induced debris flows mostly occur in remote alpine mountainous areas that are hard for humans to reach, which makes it extremely difficult to conduct continuous ground surveys and optical remote sensing monitoring. To this end, synthetic aperture radar (SAR) images were used in this study to detect and analyze the pre-disaster deformation characteristics and spatial evolution in the Sedongpu Basin and to detect changes in the snowmelt in the basin in order to improve our understanding of the triggering mechanism of the ice avalanche-induced debris flows in this region. The results revealed that the maximum average deformation rate in the basin reached 57.3 mm/year during the monitoring period from January 2016 to October 2018. The deformation displacement in the gully where the ice avalanche source area was located was intimately correlated with the summer snowmelt and rainfall and was characterized by seasonal accumulation. Clear acceleration of the deformation was detected after both the most recent earthquake and the strong rainfall and snowmelt processes in the summer of 2018. This suggests that earthquakes, snowmelt, and rainfall were significant triggers of the Sedongpu ice avalanche-induced debris flows. The results of this study provide new insights into the genesis of the Sedongpu ice avalanche-induced debris flows, which could assist in disaster warning and prevention in alpine mountain regions.
Glacier-related geohazards threaten societies in mountain regions. Massive rock-ice avalanches/rockslides/glacier debris flows frequently occurred and triggered secondary geohazard chains in the Yarlung Zangbo River downstream, which pose a serious threat to nearly residents and engineering facilities and can be linked to climate change as glaciers generally retreated after 2000. This paper provides an interdisciplinary and insight analysis for geohazard modes, monitoring and evolutions, deposits features and dynamic process of glacier geohazards by combining satellite images, field investigation, InSAR, UAVs, and simulation. It is revealed that more and more ice crevasses of various size, which may expand and further decrease the integrity of rock mass due to meltwater, earthquakes, and rainfall infiltration, appear on avalanche sources through cases analysis. The temperature rise accelerates glacier retreat and results in glacier movement. Hereafter, the slope gradually becomes unstable and starts to fail. It also analyzes historic events and long-runout process of rock-ice avalanches in the Sedongpu gully. Geomorphology plays an important role in high mobility and volume amplification, such as terrain gradient, valley twist, and moraines. The volume amplification is not only connected with the substrate entrainment, but also the riverbanks failure. This work mainly provides a scientific basis for disaster risk assessment and government policy formulation in this region.
Under the effect of global warming, the Sedongpu Basin, located in the lower reaches of the Yarlung Zangbo River on the Tibetan Plateau, has experienced frequent ice and rock avalanche disasters, which were particularly prominent after the 2017 Ms6.9 Milin earthquake, resulting in significant topographic geomorphological changes. The current geomorphology of the Sedongpu Basin, as well as the moraine volume and geomorphological changes since 2017, was interpreted in detail by unmanned aerial vehicle (UAV) and InSAR technology. Sedongpu Basin can be divided into the ice and rock area and moraine area and dam area according to the material and disaster characteristics. There are large structural planes and wide cracks in the ice and rock area, which provide the material basis for ice and rock avalanches. Moraines in the moraine area are widely distributed and very thick; the maximum change in moraine height since 2017 reaches 335 m; the moraine volume has decreased by more than 420 million m3, and strong erosion and geomorphic changes have occurred. The dam in the dam area has a thickness of ~ 37–40 m, and now, the residual dam area is 9.2 km long, with an impact area of more than 8.1 km. The InSAR interpretation shows two large deformation areas; the maximum cumulative deformation reaches 130.7 m, and there is still a possibility of disaster in the future. In addition, it is discussed that the different material properties of different areas make the Sedongpu Basin show obvious vertical zonation characteristics, resulting in disaster chain effects. Such effects not only play a role in modifying the geomorphology of the Sedongpu Basin and the Yarlung Zangbo River channel but also amplify the ice and rock avalanche disasters in the alpine area.
On 11th July 2018, a destructive rock-ice avalanche and subsequent glacier debris flow occurred in the Tianmo Gully in the southeastern Tibetan Plateau (SETP). However, the source area and triggering factors of this cascading geohazard event remained unclear. In this study, we combined satellite remote sensing, meteorological observations, numerical modeling, and post-event field investigation to comprehensively analyze its evolution processes and potential triggers. The remote sensing observations of terrain and landform changes suggest that the initial avalanche occurred on the southeastern flank of the glacier, releasing approximately 2.77 × 106 m3 of lithic and ice material. From our analysis, we suggest that the complex evolution process of this cascading geohazard event could be manifested as earthquake and hydrological triggers → an initial rock-ice avalanche → glacial debris flow → triggered landslides → landslide dam → dammed lake. Our results suggest that the 2017 Ms. 6.9 Nyingchi earthquake, the unusually high meltwater from snow and ice during the abnormally warm and dry summer in 2018, and the short-duration intense rainfall (22 mm on 10 July) recorded one day before the event are the three main factors for the catastrophic event. These factors caused the rock-ice avalanche in the source zone and subsequently cascaded glacial debris flow and shallow landslides. This study highlights the urgent need for regular monitoring of high-risk glaciers, including anomalous changes in temperature and precipitation, and accelerated movements of glaciers due to earthquakes, especially in the SETP, where climate warming will be expected to intensify occurrences of such cascading geohazard events in the future.
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Using global Sentinel-1 radar backscatter data, we systematically map the locations of glaciers with surge-type activity during 2017–22. Patterns of pronounced increases or decreases in the strongest backscatter between two winter seasons often indicate large changes in glacier crevassing, which we treat here as a sign of surge-type activity. Validations against velocity time series, terminus advances and crevassing found in optical satellite images confirm the robustness of this approach. We find 115 surge-type events globally between 2017 and 2022, around 100 of which on glaciers already know as surge-type. Our data reveal a pronounced spatial clustering in three regions, (i) Karakoram, Pamirs and Western Kunlun Shan (~50 surges), (ii) Svalbard (~25) and (iii) Yukon/Alaska (~9), with only a few other scattered surges elsewhere. This spatial clustering is significantly more pronounced than the overall global clustering of known surge-type glaciers. The 2017–22 clustering may point to climatic forcing of surge initiation.
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The Chilean Central Andes have been under severe hydrological stress due to the uninterrupted megadrought for the last 13 years. The region is known for being the denser populated zone of the country and it hosts a wide variety of glaciers along with the largest ice masses outside Patagonia. This work presents a susceptibility assessment for glacier hazards in the Rio Volcan basin (-32.82°/-70.00°), located 40 km east of Santiago city. The region is characterized for elevation ranges from 3380 to over 6000 m a.s.l. at the active and glacier-covered San José Volcanic Complex. Its closeness to the capital favours outdoor activities, tourism, urban and hydroelectric power development. Nowadays, there are accounted 195 glaciers in the area, including 47 glaciarets, 15 mountain glaciers and 8 valley glaciers. The susceptibility of 5 different phenomena is evaluated based on an analytical hierarchic process method through the determination of a susceptibility index. The multiple processes evaluated include ice avalanches, surges, low-angle glacier detachments, GLOFs and eruption-triggered lahars. The results show that within the Rio Volcan basin 4 glaciers are highly susceptible for ice avalanches, 1 for surges, 2 for sudden low-angle detachments, 2 for GLOFs whereas 19 glaciers, mainly glaciarets (68 %), are highly susceptible for eruption-triggered lahars. Only the 7 km-long Loma Larga glacier is highly susceptible for 3 out of 5 assessed processes excluding lahars. It is concluded that the proposed method can be used in other regions after adjustments regarding the work scale and conditioning factor’s weight are applied.
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Collapsing valley glaciers leaving their bed to rush down a flat hill slope at the speed of a racing car are so far rare events. They have only been reported for the Kolkaglacier (Caucasus) in 2002 and the two glaciers in the Aru mountain range (Tibet) that failed in 2016. Both events have been studied in detail using satellite data and modeling to learn more about the reasons for and processes related to such events. This study reports about a series of so far undocumented glacier collapses that occurred in the Amney Machen mountain range (eastern Tibet) in 2004, 2007, and 2016. All three collapses were associated with a glacier surge, but from 1987 to 1995, the glacier surged without collapsing. The later surges and collapses were likely triggered by a progressing slope instability that released large amounts of ice and rock to the lower glacier tongue, distorting its dynamic stability. The surges and collapses might continue in the future as more ice and rock is available to fall on the glacier. It has been speculated that the development is a direct response to regional temperature increase that destabilized the surrounding hanging glaciers. However, the specific properties of the steep rock slopes and the glacier bed might also have played a role.
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Glaciers outside of the ice sheets are known to be important contributors to sea level rise. In this work, we provide an overview of changes in the mass of the world's glaciers, excluding those in Greenland and Antarctica, between 2002 and 2016, based on satellite gravimetry observations of the Gravity Recovery and Climate Experiment (GRACE). Glaciers lost mass at a rate of 199 ± 32 Gt yr−1 during this 14-yr period, equivalent to a cumulative sea level contribution of 8 mm. We present annual mass balances for 17 glacier regions, that show a qualitatively good agreement with published estimates from in situ observations. We find that annual mass balance varies considerably from year to year, which can in part be attributed to changes in the large-scale circulation of the atmosphere. These variations, combined with the relatively short observational record, hamper the detection of acceleration of glacier mass loss. Our study highlights the need for continued observations of the Earth's glacierized regions.
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Among glacier instabilities, collapses of large parts of low-angle glaciers are a striking, exceptional phenomenon. So far, merely the 2002 collapse of Kolka Glacier in the Caucasus Mountains and the 2016 twin detachments of the Aru glaciers in western Tibet have been well documented. Here we report on the previously unnoticed collapse of an unnamed cirque glacier in the Central Andes of Argentina in March 2007. Although of much smaller ice volume, this 4.2±0.6×106 m3 collapse in the Andes is similar to the Caucasus and Tibet ones in that the resulting ice avalanche travelled a total distance of ∼2 km over a surprisingly low angle of reach (∼5∘).
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In north-western Tibet (34.0° N, 82.2° E) near lake Aru Co, the entire ablation areas of two glaciers (Aru-1 and Aru-2) suddenly collapsed on 17 July and 21 September 2016. The masses transformed into ice avalanches with volumes of 68 and 83×106 m3 and ran out up to 7 km in horizontal distance, killing nine people. The only similar event currently documented is the 130×106 m3 Kolka Glacier rock and ice avalanche of 2002 (Caucasus Mountains). Using climatic reanalysis, remote sensing, and three-dimensional thermo-mechanical modelling, we reconstructed the Aru glaciers' thermal regimes, thicknesses, velocities, basal shear stresses, and ice damage prior to the collapse in detail. Thereby, we highlight the potential of using emergence velocities to constrain basal friction in mountain glacier models. We show that the frictional change leading to the Aru collapses occurred in the temperate areas of the polythermal glaciers and is not related to a rapid thawing of cold-based ice. The two glaciers experienced a similar stress transfer from predominant basal drag towards predominant lateral shearing in the detachment areas and during the 5–6 years before the collapses. A high-friction patch is found under the Aru-2 glacier tongue, but not under the Aru-1 glacier. This difference led to disparate behaviour of both glaciers, making the development of the instability more visible for the Aru-1 glacier through enhanced crevassing and terminus advance over a longer period. In comparison, these signs were observable only over a few days to weeks (crevasses) or were absent (advance) for the Aru-2 glacier. Field investigations reveal that those two glaciers were underlain by soft, highly erodible, and fine-grained sedimentary lithologies. We propose that the specific bedrock lithology played a key role in the two Tibet and the Caucasus Mountains giant glacier collapses documented to date by producing low bed roughness and large amounts of till, rich in clay and silt with a low friction angle. The twin 2016 Aru collapses would thus have been driven by a failing basal substrate linked to increasing pore water pressure in the subglacial drainage system in response to increases in surface melting and rain during the 5–6 years preceding the collapse dates.
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Ice flow can transfer variations in basal topography and basal slipperiness to the ice surface. Recent developments in this theory have made it possible to conduct numerical experiments to predict mesoscale surface topographical undulations and surface relief on an ice sheet-scale. Focussing here on the contemporary Greenland Ice Sheet (GrIS), we demonstrate that the theory can be used to predict the surface relief of the ice sheet from bed topography, ice thickness and basal slip ratio datasets. In certain regions of the GrIS our approach overestimates, while in others underestimates, the observed surface relief. The magnitude and spatial pattern of these mismatches correspond with the theory's limitations and known uncertainties in the bed topography and basal slip ratio datasets. Our prediction experiment establishes that the first-order control on GrIS surface relief is basal topography modulated by ice thickness, surface slope and basal slip ratio. Additional analyses show that the surface relief, which is controlled by the bed-to-surface transfer of basal topography, preconditions the large scale spatial structure of surface drainage, with other factors such as surface runoff modulating the actual drainage system through influencing the temporal evolution of meltwater features. It follows that the spatial structure of surface drainage depends strongly on the transfer of basal topography to the ice surface. These findings represent an important step toward investigating and understanding the net long-term (>102 years) effect of surface drainage on ice sheet mass balance and dynamics during deglaciation events.
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Surges and glacier avalanches are expressions of glacier instability, and among the most dramatic phenomena in the mountain cryosphere. Until now, the catastrophic collapse of a glacier, combining the large volume of surges and mobility of ice avalanches, has been reported only for the 2002 130 × 10^6 m3 detachment of Kolka Glacier (Caucasus Mountains), which has been considered a globally singular event. Here, we report on the similar detachment of the entire lower parts of two adjacent glaciers in western Tibet in July and September 2016, leading to an unprecedented pair of giant low-angle ice avalanches with volumes of 68 ± 2 × 10^6 m3 and 83 ± 2 × 10^6 m3. On the basis of satellite remote sensing, numerical modelling and field investigations, we find that the twin collapses were caused by climate- and weather-driven external forcing, acting on specific polythermal and soft-bed glacier properties. These factors converged to produce surge-like enhancement of driving stresses and massively reduced basal friction connected to subglacial water and fine-grained bed lithology, to eventually exceed collapse thresholds in resisting forces of the tongues frozen to their bed. Our findings show that large catastrophic instabilities of low-angle glaciers can happen under rare circumstances without historical precedent.
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Run-up of debris flows against obstacles in their paths is a complex process that involves profound flow deceleration and redirection. We investigate the dynamics and predictability of run-up by comparing results from large-scale laboratory experiments, four simple analytical models, and a depth-integrated numerical model (D-Claw). The experiments and numerical simulations reveal the important influence of unsteady, multidimensional flow on run-up, and the analytical models highlight key aspects of the underlying physics. Run-up against a vertical barrier normal to the flow path is dominated by rapid development of a shock, or jump in flow height, associated with abrupt deceleration of the flow front. By contrast, run-up on sloping obstacles is initially dominated by a smooth flux of mass and momentum from the flow body to the flow front, which precedes shock development and commonly increases the run-up height. D-Claw simulations that account for the emergence of shocks show that predicted run-up heights vary systematically with the adverse slope angle and also with the Froude number and degree of liquefaction (or effective basal friction) of incoming flows. They additionally clarify the strengths and limitations of simplified analytical models. Numerical simulations based on a priori knowledge of the evolving dynamics of incoming flows yield quite accurate run-up predictions. Less predictive accuracy is attained in ab initio simulations that compute run-up based solely on knowledge of static debris properties in a distant debris-flow source area. Nevertheless, the paucity of inputs required in ab initio simulations enhances their prospective value in run-up forecasting.
A ring-shear device was used to study the factors that control the ultimate(steady) strength of till at high shear strains.Tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26.3° and 18.6° for tills containing 4% and 30% clay-sized particles, respectively Other tests at steady normal stresses and variable shear-strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate. This weakening may be due to small increases in till porosity. These results provide no evidence of viscous behavior and suggest that a Coulomb-plastic idealization is reasonable for till deformation. However, viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till. We hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure. During a deformation event, transient dilation of discrete shear zones should cause a reduction in internal pore-water pressure that should strengthen these zones relative to the surrounding till, a process called dilatant hardening. Consequent changes in shear-zone position, when integrated over time, may yield the observed distributed strain.
Trapridge Glacier, Yukon Territory, Canada is a subpolar surge-type glacier. It last surged in the 1940s and is now in the late stages of quiescence. Since 1969, when the glacier was first surveyed, a large wave-like bulge has formed near the glacier terminus. Our surveys from 1969–89 show the profile evolution that has accompanied the formation and downflow propagation of this feature. Ice-temperature measurements taken in 1980–81 established that the bulge was forming at the boundary between thick warm-based ice lying up-glacier from the bulge, and thin cold-based ice lying down-glacier from it. The bulge is propagating at roughly 30 m a−1 and thick ice has now completely overridden the region once covered by thin cold-based ice that we instrumented in 1980–81. In 1987, and again in 1988, the geographical positions of the 1980 measurement sites were redrilled and instrumented with new thermistor cables. Comparison of the 1980–81 data with that from 1987–88 shows that this region of the glacier has undergone a dramatic change in geometry and thermal regime. Water penetration into surface crevasses has warmed the 15-m ice temperature by roughly 2°C. The zone of transition from warm- to cold-based ice is migrating down-glacier but at a slower rate than that of the bulge feature. The transition from warm-based to cold-based ice appears to cause a discontinuity in the flow that resembles a transition from flow over a sliding boundary to flow over an adhering boundary. The discontinuity in the flow field is associated with anomalies in the temperature field and appears to be the source region for an englacial structure formed from subglacial sediment. This structure was not present in 1980–81 and is thought to have the geometry of a thrust fault or recumbent fold.
In western North America 204 surging glaciers have been identified by aerial photographic observations. These glaciers exhibit either intense crevassing and rapid ice displacements during surges or distinctive surface features which have resulted from past surges. Distribution of these unusual glaciers is not random throughout the glacierized areas, as they occur only in the Alaska Range, eastern Wrangell Mountains, eastern Chugach Mountains, Icefield Ranges, and the St Elias Mountains near Yakutat and Glacier Bay. No surging glaciers have been identified in the Brooks Range, Kenai Mountains, west and central Chugach Mountains, west and central Wrangell Mountains, Coast Mountains, Rocky Mountains, Cascade Range, Olympic Mountains, or Sierra Nevada. No definite reason for this restricted distribution is apparent. Surging glaciers are found in maritime to continental and temperate to subpolar environments. Practically all physical forms of glaciers are represented. The restricted distribution does not relate to topography, bedrock type, altitude, orientation, or size of glacier. Some surging glaciers are associated with fault-related valleys, but neither recent faulting nor earthquakes have initiated surge activity. Possible causes for the limited distribution of surges are unusual bedrock roughness or permeability in certain areas, anomalously high ground-water temperatures, and/or abnormal geothermal heat flow.