scholarly journals Enhanced rockwall retreat and modified rockfall magnitudes/frequencies in deglaciating cirques from a 6-year LiDAR monitoring

2020 ◽  
Author(s):  
Ingo Hartmeyer ◽  
Markus Keuschnig ◽  
Robert Delleske ◽  
Michael Krautblatter ◽  
Andreas Lang ◽  
...  
Keyword(s):  
Transient Signal ◽  
European Alps ◽  
Negative Power ◽  
Terrestrial Lidar ◽  
Frequency Distributions ◽  
Decadal Scale ◽  
Recent Climate ◽  
Glacial Environments ◽  
Lateral Erosion ◽  
Glacial Landforms

Abstract. Cirque erosion contributes significantly to mountain denudation and is a key element of glaciated mountain topography. Despite long-standing efforts, rates of rockwall retreat and the proportional contributions of low-, mid- and high magnitude rockfalls have remained poorly constrained. Here, a unique, terrestrial LiDAR-derived rockfall inventory (2011–2017) of two glaciated cirques in the Hohe Tauern Range, Central European Alps, Austria is analysed. The mean cirque wall retreat rate of 1.9 mm a−1 ranks in the top range of reported values and is mainly driven by enhanced rockfall from the lowermost, freshly deglaciated rockwall sections. Retreat rates are significantly elevated over decades subsequent to glacier downwasting. Elongated cirque morphology and recorded cirque wall retreat rates indicate headward erosion is clearly outpacing lateral erosion, most likely due to the cataclinal backwalls, which are prone to large dip-slope failures. The rockfall magnitude-frequency distribution – the first such distribution derived for deglaciating cirques – follows a distinct negative power law over four orders of magnitude. Magnitude-frequency distributions in glacier-proximal and glacier-distal rockwall sections differ significantly due to an increased occurrence of large rockfalls in recently deglaciated areas. In this paper we show how recent climate warming shapes glacial landforms, controls spatiotemporal rockfall variation in glacial environments and indicates a transient signal with decadal scale exhaustion of rockfall activity immediately following deglaciation crucial for future hazard assessments.

scholarly journals A 6-year lidar survey reveals enhanced rockwall retreat and modified rockfall magnitudes/frequencies in deglaciating cirques

2020 ◽  
Vol 8 (3) ◽  
pp. 753-768 ◽  
Author(s):  
Ingo Hartmeyer ◽  
Markus Keuschnig ◽  
Robert Delleske ◽  
Michael Krautblatter ◽  
Andreas Lang ◽  
...  
Keyword(s):  
Transient Signal ◽  
Negative Power ◽  
Terrestrial Lidar ◽  
Frequency Distributions ◽  
Decadal Scale ◽  
Recent Climate ◽  
Glacial Environments ◽  
The Mean ◽  
Lateral Erosion ◽  
Glacial Landforms

Abstract. Cirque erosion contributes significantly to mountain denudation and is a key element of glaciated mountain topography. Despite long-standing efforts, rates of rockwall retreat and the proportional contributions of low-, mid- and high-magnitude rockfalls have remained poorly constrained. Here, a unique, terrestrial-lidar-derived rockfall inventory (2011–2017) of two glaciated cirques in the Hohe Tauern range, Central Alps, Austria, is analysed. The mean cirque wall retreat rate of 1.9 mm a−1 ranks in the top range of reported values and is mainly driven by enhanced rockfall from the lowermost, freshly deglaciated rockwall sections. Retreat rates are significantly elevated over decades subsequent to glacier downwasting. Elongated cirque morphology and recorded cirque wall retreat rates indicate headward erosion is clearly outpacing lateral erosion, most likely due to the cataclinal backwalls, which are prone to large dip-slope failures. The rockfall magnitude–frequency distribution – the first such distribution derived for deglaciating cirques – follows a distinct negative power law over 4 orders of magnitude. Magnitude–frequency distributions in glacier-proximal and glacier-distal rockwall sections differ significantly due to an increased occurrence of large rockfalls in recently deglaciated areas. In this paper, the second of two companion pieces, we show how recent climate warming shapes glacial landforms, controls spatiotemporal rockfall variation in glacial environments and indicates a transient signal with decadal-scale exhaustion of rockfall activity immediately following deglaciation crucial for future hazard assessments.

Paraglacial responses in deglaciating cirque walls: Implications for rockfall magnitudes/frequencies and rockwall retreat

2020 ◽  
Author(s):  
Ingo Hartmeyer ◽  
Robert Delleske ◽  
Markus Keuschnig ◽  
Michael Krautblatter ◽  
Andreas Lang ◽  
...  
Keyword(s):  
European Alps ◽  
Atmospheric Conditions ◽  
Power Law Distribution ◽  
Glacier Surface ◽  
Negative Power ◽  
Terrestrial Lidar ◽  
Frequency Distributions ◽  
Ice Surface ◽  
Recent Climate ◽  
Glacial Landforms

<p>Over the past 150 years almost half of the glacier volume disappeared in the European Alps. Besides glacier retreat, ice surface lowering reflects much of the volume loss and uncovers the adjacent rockwalls. In steep glacial cirques, this process exposes rock to atmospheric conditions for the very first time in many millennia. Instability of rockwalls has long been identified as one of the direct consequences of deglaciation, but so far cirque-wide quantification of rockfall at high-resolution is missing and the proportional contributions of low-, mid- and high magnitude rockfalls have remained poorly constrained. <br>We use terrestrial LiDAR to establish a rockfall inventory for the permafrost-affected rockwalls of two rapidly deglaciating cirques in the Central Alps of Austria (Kitzsteinhorn). During six-year monitoring (2011-2017) 78 rockwall scans were acquired. Overall, we registered 632 rockfalls ranging from 0.003 to 879.4 m³, which concentrate along pre-existing structural weaknesses. 60 % of the rockfall volume detached from less than ten vertical meters above the glacier surface, indicating enhanced rockfall over tens of years following deglaciation. <br>Antecedent rockfall preparation is assumed to start when the rockwall is still ice-covered: Inside the Randkluft (gap between cirque wall and glacier) sustained freezing and sufficient water supply likely cause enhanced weathering and high plucking stresses. Following deglaciation, pronounced thermomechanical strain is induced and an active layer penetrates into perennially frozen bedrock, likely contributing to the observed paraglacial rockfall increase close to the glacier surface. <br>Observed mean cirque wall retreat of 1.9 mm a-1 ranks in the top range of reported values and is mainly driven by enhanced rockfall from the lowermost, freshly deglaciated sections of the investigated rockwalls. Rockfall magnitude-frequency distribution, which has never been quantified before for deglaciating cirques, follows a distinct negative power law distribution over four orders of magnitude. Magnitude-frequency distributions in glacier-proximal and glacier-distal rockwall sections differ significantly due to an increased occurrence of large rockfalls in recently deglaciated areas. The present study thus demonstrates how recent climate warming shapes glacial landforms, controls spatiotemporal rockfall variation in glacial environments and indicates an exhaustion law over decades for rockfall activity immediately following deglaciation crucial for future hazard assessments.</p>

scholarly journals Current glacier recession causes significant rockfall increase: The immediate paraglacial response of deglaciating cirque walls

2020 ◽  
Author(s):  
Ingo Hartmeyer ◽  
Robert Delleske ◽  
Markus Keuschnig ◽  
Michael Krautblatter ◽  
Andreas Lang ◽  
...  
Keyword(s):  
Minor Effect ◽  
European Alps ◽  
Atmospheric Conditions ◽  
Glacier Surface ◽  
Terrestrial Lidar ◽  
Physical Weathering ◽  
Ice Surface ◽  
Recent Climate ◽  
Ample Supply ◽  
A Minor

Abstract. In the European Alps almost half the glacier volume disappeared over the past 150 years. The loss is reflected in glacier retreat and ice surface lowering even at high altitude. In steep glacial cirques surface lowering exposes rock to atmospheric conditions for the very first time in many millennia. Instability of rockwalls has long been identified as one of the direct consequences of deglaciation, but so far cirque-wide quantification of rockfall at high-resolution is missing. Based on terrestrial LiDAR a rockfall inventory for the permafrost-affected rockwalls of two rapidly deglaciating cirques in the Central Alps of Austria (Kitzsteinhorn) is established. Over six-years (2011–2017) 78 rockwall scans were acquired to generate data of high spatial and temporal resolution. 632 rockfalls were registered ranging from 0.003 to 879.4 m³, mainly originating from pre-existing structural rock weaknesses. 60 % of the rockfall volume detached from less than ten vertical meters above the glacier surface, indicating enhanced rockfall activity over tens of years following deglaciation. Debuttressing seems to play a minor effect only. Rather, preconditioning is assumed to start inside the Randkluft (gap between cirque wall and glacier) where sustained freezing and ample supply of liquid water likely cause enhanced physical weathering and high plucking stresses. Following deglaciation, pronounced thermomechanical strain is induced and an active layer penetrates into the formerly perennially frozen bedrock. These factors likely cause the observed paraglacial rockfall increase close to the glacier surface. This paper presents the most extensive dataset of high-alpine rockfall to date and the first systematic documentation of a cirque-wide erosion response of glaciated rockwalls to recent climate warming.

scholarly journals Current glacier recession causes significant rockfall increase: the immediate paraglacial response of deglaciating cirque walls

2020 ◽  
Vol 8 (3) ◽  
pp. 729-751 ◽  
Author(s):  
Ingo Hartmeyer ◽  
Robert Delleske ◽  
Markus Keuschnig ◽  
Michael Krautblatter ◽  
Andreas Lang ◽  
...  
Keyword(s):  
Minor Effect ◽  
European Alps ◽  
Atmospheric Conditions ◽  
Glacier Surface ◽  
Terrestrial Lidar ◽  
Physical Weathering ◽  
Ice Surface ◽  
Recent Climate ◽  
Ample Supply ◽  
A Minor

Abstract. In the European Alps, almost half the glacier volume has disappeared over the past 150 years. The loss is reflected in glacier retreat and ice surface lowering even at high altitude. In steep glacial cirques, surface lowering exposes rock to atmospheric conditions probably for the very first time in several millennia. Instability of rockwalls has long been identified as one of the direct consequences of deglaciation, but so far cirque-wide quantification of rockfall at high resolution is missing. Based on terrestrial lidar, a rockfall inventory for the permafrost-affected rockwalls of two rapidly deglaciating cirques in the Central Alps of Austria (Kitzsteinhorn) is established. Over 6 years (2011–2017), 78 rockwall scans were acquired to generate data of high spatial and temporal resolution. Overall, 632 rockfalls were registered, ranging from 0.003 to 879.4 m3, mainly originating from pre-existing structural rock weaknesses. A total of 60 % of the rockfall volume detached from less than 10 vertical metres above the glacier surface, indicating enhanced rockfall activity over tens of years following deglaciation. Debuttressing seems to play a minor effect only. Rather, preconditioning is assumed to start inside the randkluft (void between cirque wall and glacier) where measured sustained freezing and ample supply of liquid water likely cause enhanced physical weathering and high quarrying stresses. Following deglaciation, pronounced thermomechanical strain is induced and an active layer penetrates into the formerly perennially frozen bedrock. These factors likely cause the observed paraglacial rockfall increase close to the glacier surface. This paper, the first of two companion pieces, presents the most extensive dataset of high-alpine rockfall to date and the first systematic documentation of a cirque-wide erosion response of glaciated rockwalls to recent climate warming.

scholarly journals Range dynamics of mountain plants decrease with elevation

2018 ◽  
Vol 115 (8) ◽  
pp. 1848-1853 ◽  
Author(s):  
Sabine B. Rumpf ◽  
Karl Hülber ◽  
Günther Klonner ◽  
Dietmar Moser ◽  
Martin Schütz ◽  
...  
Keyword(s):  
Plant Species ◽  
Species Abundance ◽  
Elevational Gradient ◽  
High Elevation ◽  
Range Limits ◽  
European Alps ◽  
Cold Adapted ◽  
Recent Climate ◽  
Range Dynamics ◽  
Mountain Plant

Many studies report that mountain plant species are shifting upward in elevation. However, the majority of these reports focus on shifts of upper limits. Here, we expand the focus and simultaneously analyze changes of both range limits, optima, and abundances of 183 mountain plant species. We therefore resurveyed 1,576 vegetation plots first recorded before 1970 in the European Alps. We found that both range limits and optima shifted upward in elevation, but the most pronounced trend was a mean increase in species abundance. Despite huge species-specific variation, range dynamics showed a consistent trend along the elevational gradient: Both range limits and optima shifted upslope faster the lower they were situated historically, and species’ abundance increased more for species from lower elevations. Traits affecting the species’ dispersal and persistence capacity were not related to their range dynamics. Using indicator values to stratify species by their thermal and nutrient demands revealed that elevational ranges of thermophilic species tended to expand, while those of cold-adapted species tended to contract. Abundance increases were strongest for nutriphilous species. These results suggest that recent climate warming interacted with airborne nitrogen deposition in driving the observed dynamics. So far, the majority of species appear as “winners” of recent changes, yet “losers” are overrepresented among high-elevation, cold-adapted species with low nutrient demands. In the decades to come, high-alpine species may hence face the double pressure of climatic changes and novel, superior competitors that move up faster than they themselves can escape to even higher elevations.

Geomorphic diversity and complexity of the inner shelf, Canadian Arctic Archipelago, based on LiDAR and multibeam sonar surveys

2020 ◽  
Vol 57 (1) ◽  
pp. 123-132
Author(s):  
John Shaw ◽  
D. Patrick Potter ◽  
Yongsheng Wu
Keyword(s):  
Sea Level ◽  
Gas Hydrate ◽  
Canadian Arctic ◽  
Slight Modification ◽  
The Arctic ◽  
Canadian Arctic Archipelago ◽  
Beach Ridge ◽  
Terrestrial Lidar ◽  
Sea Levels ◽  
Glacial Landforms

Data from two surveys by multi-beam sonar and two by marine/terrestrial LiDAR are used to evaluate the geomorphology of the seafloor in littoral areas of the Canadian Arctic Channels, near King William Island, Nunavut. Submarine terrains show well-preserved glacial landforms (drumlins, mega-scale glacial lineations, iceberg-turbated terrain, recessional moraines, and glaciofluvial landforms) with only slight modification by modern processes (wave action and sea-ice activity). At Gjoa Haven the seafloor is imprinted by fields of pits 2 m wide and 0.15 m deep. They may result from gas hydrate dissolution triggered by falling relative sea levels. The Arctic Archipelago displays what might be termed inverted terrains: marine terrains, chiefly beach ridge complexes, exist above modern sea level and well-preserved glacial terrains are present below modern sea level. This is the inverse of the submerging regimes of Atlantic Canada, where glacial terrains exist on land, but below sea level they have been effaced and modified by marine processes down to the lowstand depth.

scholarly journals Recent patterns of discharge and sediment output of the Gorner Glacier, Switzerland

2020 ◽  
Author(s):  
Günther Prasicek ◽  
François Mettra ◽  
Stuart Lane ◽  
Frédéric Herman
Keyword(s):  
Organic Carbon ◽  
Water Samples ◽  
Water Pressure ◽  
Seasonal Pattern ◽  
Monitoring Program ◽  
Early Summer ◽  
Organic Carbon Content ◽  
European Alps ◽  
Glacier Terminus ◽  
Recent Climate

<p>Recent climate change is causing rapid retreat of alpine glaciers around the globe. As ice melts and glaciers thin, glacier motion and subglacial processes will change. One of the most relevant aspects for down-valley environments, settlements and infrastructure is the potential change in flow discharge and sediment output.</p><p>Here we present the results of an ongoing monitoring program at the Gorner Glacier, Switzerland, the second-largest glacier system in the European Alps.  During the melt season of 2018 and 2019, stage and turbidity were monitored with a 5 minute frequency along a turbulent section of the glacial river, located approximately 1 km downstream of the glacier terminus. For calibration of the turbidity measurements, daily water samples were obtained with an automated pump sampler, supported by additional intermittent manual sampling. The data is complemented by a discharge time series that also contains information on the flushing of a bedload trap at the hydro power weir located about 2 km downstream of the glacier terminus. The discharge and flushing data have a resolution of 15 minutes.  Turbidity and discharge allow estimation of the output of suspended load, while the flushing data inform about bedload. We further measured total organic carbon content of the water samples to infer the water and sediment source.</p><p>Data suggest a clear seasonal pattern, not only in discharge and sediment output, but also in suspended sediment concentration (SSC). While SSC is high during snow melt and in early summer, it decreases rapidly in July and stays at similar levels until September. This may indicate exhaustion of sediment storage beneath the glacier, but could also result from a change in subglacial regime, e.g. from a decrease in subglacial water pressure due to the progressive opening of subglacial cavities during the melt season. High fractions of organic carbon, presumably due to lateral sediment input from hillslopes, occur during storms throughout the entire season.</p>

scholarly journals Carbon dioxide sources from Alaska driven by increasing early winter respiration from Arctic tundra

2017 ◽  
Vol 114 (21) ◽  
pp. 5361-5366 ◽  
Author(s):  
Róisín Commane ◽  
Jakob Lindaas ◽  
Joshua Benmergui ◽  
Kristina A. Luus ◽  
Rachel Y.-W. Chang ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Remote Sensing Data ◽  
The Arctic ◽  
Emission Rates ◽  
Early Winter ◽  
Spatially Resolved ◽  
Arctic Soils ◽  
Decadal Scale ◽  
Recent Climate ◽  
Carbon Release

High-latitude ecosystems have the capacity to release large amounts of carbon dioxide (CO2) to the atmosphere in response to increasing temperatures, representing a potentially significant positive feedback within the climate system. Here, we combine aircraft and tower observations of atmospheric CO2 with remote sensing data and meteorological products to derive temporally and spatially resolved year-round CO2 fluxes across Alaska during 2012–2014. We find that tundra ecosystems were a net source of CO2 to the atmosphere annually, with especially high rates of respiration during early winter (October through December). Long-term records at Barrow, AK, suggest that CO2 emission rates from North Slope tundra have increased during the October through December period by 73% ± 11% since 1975, and are correlated with rising summer temperatures. Together, these results imply increasing early winter respiration and net annual emission of CO2 in Alaska, in response to climate warming. Our results provide evidence that the decadal-scale increase in the amplitude of the CO2 seasonal cycle may be linked with increasing biogenic emissions in the Arctic, following the growing season. Early winter respiration was not well simulated by the Earth System Models used to forecast future carbon fluxes in recent climate assessments. Therefore, these assessments may underestimate the carbon release from Arctic soils in response to a warming climate.

scholarly journals Future retreat of Great Aletsch Glacier

2019 ◽  
Vol 65 (253) ◽  
pp. 869-872 ◽  
Author(s):  
Guillaume Jouvet ◽  
Matthias Huss
Keyword(s):  
Emission Scenario ◽  
Climate Projections ◽  
European Alps ◽  
Climate Data ◽  
Three Dimensional Model ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Climate Conditions ◽  
Future Evolution ◽  
Recent Climate

AbstractWe model the future evolution of the largest glacier of the European Alps – Great Aletsch Glacier, Switzerland – during the 21st century. For that purpose we use a detailed three-dimensional model, which combines full Stokes ice dynamics and surface mass balance forced with the most recent climate projections (CH2018), as well as with climate data of the last decades. As a result, all CH2018 climate scenarios yield a major glacier retreat: Results range from a loss of 60% of today's ice volume by 2100 for a moderate CO2 emission scenario (RCP2.6) being in line with the Paris agreement to an almost complete wastage of the ice for the most extreme emission scenario (RCP8.5). Our model results also provide evidence that half of the mass loss is already committed under the climate conditions of the last decade.

scholarly journals Recent and future warm extreme events and high-mountain slope stability

2010 ◽  
Vol 368 (1919) ◽  
pp. 2435-2459 ◽  
Author(s):  
C. Huggel ◽  
N. Salzmann ◽  
S. Allen ◽  
J. Caplan-Auerbach ◽  
L. Fischer ◽  
...  
Keyword(s):  
Slope Stability ◽  
Climate Models ◽  
Swiss Alps ◽  
High Mountain ◽  
Temperature Pattern ◽  
European Alps ◽  
High Mountains ◽  
Slope Failures ◽  
Recent Climate ◽  
The Future

The number of large slope failures in some high-mountain regions such as the European Alps has increased during the past two to three decades. There is concern that recent climate change is driving this increase in slope failures, thus possibly further exacerbating the hazard in the future. Although the effects of a gradual temperature rise on glaciers and permafrost have been extensively studied, the impacts of short-term, unusually warm temperature increases on slope stability in high mountains remain largely unexplored. We describe several large slope failures in rock and ice in recent years in Alaska, New Zealand and the European Alps, and analyse weather patterns in the days and weeks before the failures. Although we did not find one general temperature pattern, all the failures were preceded by unusually warm periods; some happened immediately after temperatures suddenly dropped to freezing. We assessed the frequency of warm extremes in the future by analysing eight regional climate models from the recently completed European Union programme ENSEMBLES for the central Swiss Alps. The models show an increase in the higher frequency of high-temperature events for the period 2001–2050 compared with a 1951–2000 reference period. Warm events lasting 5, 10 and 30 days are projected to increase by about 1.5–4 times by 2050 and in some models by up to 10 times. Warm extremes can trigger large landslides in temperature-sensitive high mountains by enhancing the production of water by melt of snow and ice, and by rapid thaw. Although these processes reduce slope strength, they must be considered within the local geological, glaciological and topographic context of a slope.

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