Assessment of glacier and permafrost hazards

(1) 
Glacier- and perma-frost-related floods

(1.1) Breaching of moraine dams

Outburst of moraine-dammed lakes. Particularly far reaching glacier disasters (up to hundreds of km). Causes: enhanced runoff; impact waves (1.5); temporary damming / jamming at outlet.

Moraine-dammed lakes usually detectable by remote sensing, in particular optical techniques. Time series particularly useful for assessing lake dynamics and estimating future development. Assessment of moraine dam characteristics requires high-resolution and -precision techniques (dam geometry, deformation, settlement, surface material, etc.). Monitoring of associated glacier characteristics (geometry, surface type), changes and kinematics (thickness changes, velocity) may help assessing the evolution of proglacial lakes.

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(1.2) Failure or overtopping of ice-dams

Outburst of ice-dammed lakes. Particularly far reaching glacier disasters. Often repeating for permanent ice dams. Sources: ice-marginal or supraglacial lakes; temporary ice dams from ice avalanches (3.1) or glacier surges (2.1).

Detection of ice-dammed lakes depending on temporal resolution and timing of remote sensing system; detection of ice dams depending on spatial resolution and spectral characteristics. Time series particularly useful. Monitoring of thickness changes and kinematics of long-lasting ice dams supports assessment, e.g. of floatation level.

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(1.3) Glacier outbursts

Catastrophic water discharge from the en- or subglacial drainage system. Causes: geothermal or volcanic activity; temporary en- or subglacial water storage; catastrophic water release connected to surge termination (2.1).

Particularly difficult or impossible to assess due to sub-surface character.

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(1.4) Breaching of thermokarst and supraglacial lakes

On ice-rich permafrost or stagnant glacier ice. Progressive lake growth through thermal convection. Outburst causes: similar to (1.1), and progressive melt of ice/permafrost dam.

Detection of related lakes usually requires high image resolution due to the small lake size. Time series particularly useful. Disposition of lake development partially detectable through remote sensing of surface characteristics and kinematics.

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(1.5) Displacement waves

Displacement-wave impacts on people, natural and artificial lake dams, and other installations. Trigger for a number of lake outburst events of types (1.1) and (1.2). Causes: lake impact from snow-, ice-, rock-avalanches, landslides, debris flows, etc.; floatation of icebergs.

Assessment requires integrative remote sensing and modelling approaches of source processes.

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(1.6) Enhanced runoff from permafrost

Permafrost is for the most part impermeable for surface water, a fact that leads to runoff concentration at the permafrost table, in particular with enhanced surface runoff from snow-melt and intense rainfall; ice melt at permafrost table. Temporary water storage in or underneath permafrost is particularly difficult to investigate but suggested for rare cases (causes: taliks; ice-melt in permafrost; (temporary) water blockage in or under the permafrost?). Both phenomena, runoff concentration and water storage, may lead to unusually enhanced runoff. Potential trigger mechanisms of debris flows (4.3).

Can hardly be directly investigated by remote sensing.

(2) 
Glacier length and volume changes

(2.1) Glacier surge (unstable length change)

Temporary instability of large glacier parts with ice velocity increased by an order of magnitude (or more). Usually accompanied by drastic glacier advance. Besides the direct impact from glacier advance (overriding of structures, blockage of rivers, etc), glacier surges often trigger further hazards such as ice-dammed lakes (1.2). Enhanced englacial water storage, possibly released at surge end (1.3).

Surges can be tracked by high-frequency remote sensing. Former glacier surges, and thus surge-type glaciers, can often be recognised from deformed, so-called "looped" moraines. Geometry changes, if involved in the surge disposition and build-up, can be detected as glacier thickness changes.

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(2.2) Stable glacier advance

Advancing glaciers may inundate land, override installations, dam rivers and form lakes (1.2), cause ice break-offs (3.1), etc. Causes: positive mass balance, ice dynamics.

Can usually be monitored by remote sensing. Glacier area changes from repeat imagery, glacier mass changes from repeat DTMs. Forecast best done by a combination of remote sensing, glaciological field work and modelling.

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(2.3) Glacier retreat

Glacier retreat forms usually no direct hazard but is able to trigger a number of secondary hazards such as various slope instabilities (3). Causes and remote sensing see (2.2).

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(2.4) Changes in glacier runoff and seasonality

Glacier mass loss leads to reduction of water resources as stored in glaciers and to changes in dry-season river flows. Short-term perspective: increasing discharge due to enhanced melt; long-term perspective: decreasing discharge when glaciers become substantially smaller or disappear. Consequences for drinking water supply, irrigation, hydropower production, industrial water use, fishery, water quality, etc.

Best investigated through a combination of remote sensing, meteorology, and combined glaciological and hydrological modelling. Causes and remote sensing see (2.2).

(3) 
Glacial and para-glacial mass move-ments

(3.1) Ice fall and ice avalanches

Ice break-offs and subsequent ice avalanches from steep glaciers. In rare cases detachment of complete glaciers. Particularly dangerous in winter with reduced basal friction, extended runout, and mass gain from snow. Glacier parts can fail due to a failure of the underlaying rock (3.2). Ice avalanches can be triggered by earthquakes. Ice avalanches can trigger lake outbursts (1.5), dam rivers (1.2), transform into mud/debris flows (3.5) (3.6).

Detection of steep glaciers through combination of spectral data with DTM. High-resolution, -precision, and -frequency remote sensing (e.g. terrestrial close range techniques) enables sometimes monitoring of mass changes and kinematics related to entire steep glaciers or unstable sections.

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(3.2) Rock fall, rock avalanche

Glacier retreat uncovers and debuttresses rock flanks. The related change in thermal, hydrologic, hydraulic and mechanic conditions can lead to rock fall and rock avalanches (fast mass movement). Rock avalanches can carry parts of overlaying glaciers. Rock avalanches can be of increased magnitude in glacial environments (extended runout on glaciers or when combined with ice, mass gain from ice, entrainment of glacier parts through impact, detachment of glaciers overlaying the rock mass breaking off). Rock avalanches can be triggered by earthquakes.

Mapping of rock faces and some boundary conditions (e.g. glacier retreat) possible through remote sensing.

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(3.3) Landslide / rock slide

Among other causes, glacier retreat (2.3) or slope undercutting by floods uncovers and debuttresses rock and debris flanks. The related change in hydrologic, hydraulic and mechanic conditions can lead to mass movements (slow mass movement). These can create secondary hazards such as river dams.

Landslide surface characteristics, geometry and kinematics can be monitored by repeat high-resolution and -precision remote sensing.

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(3.4) Destabili-sation of unconsolidated glacial deposits

Glacier retreat (2.3) leaves unprotected and unconsolidated moraine material that is prone to enhanced erosion and debris flows.

Related zones can be detected trough remote sensing combined with DTMs.

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(3.5) Debris flows from glacier floods

Glacier and permafrost floods (1) are often accompanied by debris flows when erodible material is available in steep parts of the flood path. Such debris flows can show a sequence of erosion and deposition. Debris flow deposits may dam tributaries or main rivers.

Remote sensing with sufficient spatial resolution supports estimating the availability of debris in a potential flood path and its slope (i.e. disposition to erosion or deposition).

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(3.6) Interaction between volcanic activity and glaciers

Potentially among the most devastating glacier disasters. Enhanced geothermal activity, geometric and mechanic changes, deposition of hot eruptive materials, or albedo change by volcanic ash can lead to drastic melt of ice or ice break-off on ice-clad volcanoes and to volcanic landslides or lahars. Ash layers thicker than some mm-cm insulate the underlying ice.

Ice cover on volcanoes and its changes (and partially also volcanic activity) can be monitored by remote sensing (see (2))

(4) 
Perma-frost- and ground ice-related mass move-ments

(4.1) Adverse effects of permafrost creep

Permafrost creep (often forming rockglaciers) can inundate land and destabilise or destroy constructions situated on or in it. Cause: gravity-driven deformation of ice-rich debris.

Monitoring of permafrost deformation by repeat high-resolution optical remote sensing and DInSAR.

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(4.2) Thaw settlement and frost heave

Changes in permafrost surface geometry due to changes in ground ice content from ice-lense accumulation or thermokarst processes. Affecting constructions; possibly triggering thermokarst lakes (1.4). Thaw and frost heave processes may be caused by constructions (e.g. changes in snow cover regime, basement heating).

Monitoring of geometry changes from repeat high-precision DTMs.

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(4.3) Debris flows from permafrost

Permafrost thaw changes mechanic and hydrological conditions in permafrost. As a consequence the disposition of periglacial debris flows may increase. Temporary runoff concentration (1.6) and ground saturation is, thereby, often involved as trigger.

Only detectable using remote sensing when accompanied by changes in surface geometry (4.2).

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(4.4) Rockfall from rockglacier front

Advance of rockglaciers involves continuous transport of surface debris over the rockglacier front. This may lead to local rockfall endangering people and mountain infrastructure.

Remote sensing see (4.1)

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(4.5) Destabilisation of frozen debris slopes

In rare cases entire sections of rockglaciers or frozen debris slopes might destabilise. Reasons largely unknown (dynamic, ground warming, ?). Can lead to (4.1), (4.3), and (4.4).

For slow movements detectable using high-resolution remote sensing ( (4.1) and crevasse formation).

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(4.6) Rockfall and rock avalanches from frozen rock faces

The thermal regime and ground ice in frozen rock faces have complex thermal, mechanical, hydraulic and hydrological effects on rock stability. Related changes can cause mass movements. Processes often also related to surface ice (3.2).

Remote sensing see (3.2).