Assessment of permafrost-related problems and hazards

(1) Breaching of moraine lake dams

Ground ice content in moraine dams plays an important role in the stability of moraine dams through its influence on hydraulic permeability, angle of repose, and resistance to erosion, e.g. during a lake outburst or piping.

Monitoring of elevation changes due to thaw settlement

Monitoring of displacements due to deforming ground ice

(2) Failure or overtopping of temporary dams

Permafrost-related sources of temporary dams: active layer detachments, thaw slumps, landslides, periglacial debris flows, periglacial rock avalanches, rock glacier advance and instabilities.

Detection of damming and dammed lakes depending on spatial resolution, temporal resolution and timing of remote sensing system; time series particularly useful

Monitoring of thickness changes and kinematics of long-lasting dams.

(3) Growth and breaching of thermokarst lakes

Progressive lake growth through thermal convection. Growth may destroy installations at the lake shore. Outburst causes similar to (1) and progressive melt of ice/permafrost dam.

Spectral detection of related lakes; time series particularly useful.

(4) Displacement waves into lakes

Displacement-waves impact on people, natural and artificial lake dams, and installations. Waves may trigger lake outbursts of types (1) and (2). Permafrost-related causes of waves: lake impacts of rock avalanches, landslides, debris flows.

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

(5) Enhanced runoff from permafrost

Permafrost is typically impermeable to surface water, resulting in runoff concentration at the 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). The enhanced runoff is a potential trigger of debris flows.

Not directly investigated by remote sensing.

(6) Adverse effects of permafrost creep

Permafrost creep forms (e.g. rock glaciers) can inundate land and destabilise or destroy constructions situated on or in it.

Monitoring of permafrost deformation by repeat high-resolution optical remote sensing, SAR interferometry and laser scanning.

(7) Periglacial debris flows

Thaw changes mechanical and hydrological properties of frozen ground and temporally increases its water content. As a consequence the susceptibility to periglacial debris flows may increase. Temporary runoff concentration (5) and ground saturation by water is, thereby, involved as trigger.

Only detectable using remote sensing when accompanied by changes in surface geometry. Cf. (1).

(8) Rockfall from rock glacier front

Continuous transport of surface debris over the rock glacier front may lead to local rockfall threatening people and mountain infrastructure.

Remote sensing see (6)

(9) Destabilisation of frozen debris slopes

In rare cases entire sections of rock glaciers or frozen debris slopes may destabilise. Can lead to (6), (7), and (8).

Slow movements detectable using high-resolution remote sensing. Methods of (6) and crevasse formation.

(10) 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 and can cause mass movements. Processes are also related to (insulating) snow and surface ice and their changes.

Detection of changes in snow and surface ice cover by optical sensors; increasing rockfall activity from repeat optical data, e.g. automatic cameras, or laser scanning; deformation of rockflank from laser scannig and ground-based SAR

(11) Active layer detachment

Changes in the thermal, hydrological and mechanical ground conditions can lead to detachment of the active layer. May lead to (2), (3), (4), (12)

Detection from (repeat) high-resolution optical and microwave data; elevation changes and volumes from repeat DTMs (optical, SAR, laser scanning)

(12) Retrogressive thaw slumps

Similar to (11) or a consequence of it. Progressive degradation of ground ice and erosion of ground.

See (11)

(13) Permafrost-related landslides

Similar to (11) and (12) or a consequence of it.

See (11);

Movements from matching of repeat images, SAR interferometry; loss of interferometric phase coherence

(14) Thaw settlement, subsidence and frost heave

Changes in permafrost surface elevation due to changes in ground ice content from ice-lens accumulation or thermokarst processes; often connected to increase or decrease of active layer thickness; affects construction and infrastructure; may lead to (1), (3), (5), (7), (9)-(13). Thaw and frost heave processes may be natural or anthropogenic in origin (e.g. changes in snow cover regime under constructions, basement heating, forest fires).

Monitoring of vertical changes from repeat high-precision DTMs (laser scanning) or DInSAR.

Detection of trigger processes, e.g. vegetation changes due to forest fire, storm, and pests.

(15) Erosion of river banks and sea coasts

Combined thermal and mechanical erosion; may lead to (11)-(14)

Spectral detection from repeat high-resolution optical and microwave data; detection from differences between repeat DTMs (airborne- and terrestrial photogrammetry, airborne SAR, airborne and terrestrial laser scanning)