Thermokarst Failures on Surface Processes in Arctic Landscapes
This large, NSF-funded research project is a collaborative, interdisciplinary effort to study the responses of Arctic landscapes to permafrost degradation known as thermokarst - landscape features caused by structural failure following the melting of ground ice. As the arctic climate warms, there is increasing report of thermokarst incidence.
Trouble In The TundraLisa Jarvis, Chemical & Engineering News | August 17, 2009
Features formed by melting permafrost provide clues to a changing Arctic landscape and climate
Alaska's biggest tundra fire sparks climate warningTracey Logan, The New Scientist | 30 July 2009 Thermokarsts are areas of collapsed terrain where structurally important permafrost has thawed – a process that can damage the foundations of homes, roads, and pipelines. Permafrost melt will also increase the amount of greenhouse gases (such as methane) entering the atmosphere.
Glossary of Arctic Transportation, Permafrost, Snow and Hydrology Terms
Most of the definitions given below were taken from the Multi-Language Glossary of Permafrost and Related Ground-Ice Terms
(van Everdingen, 1998). For a full list of permafrost-related terms, visit the US Permafrost Association website.
The layer of ground subject to annual thawing and freezing in areas underlain by permafrost
Active-layer Detachment Slide
Shallow landslides that develop in permafrost areas, involving
reduction in effective stress and strength at the contact between a
thawing overburden and underlying frozen material. Active-layer
detachment slides can occur in response to high seasonal air
temperature, summer rainfall events, rapid melting of snowcover, or
surface disturbances See Lewkowicz (1992).
The thickness of the layer of ground subject to annual thawing and
freezing in areas underlain by permafrost (cf. thaw depth) See Nelson
and Hinkel (2003).
A large depression of the ground surface produced by thawing of a large
area (e.g., > 1 ha) of very thick and exceedingly ice-rich
A collective term used to describe all soil movements due to frost action.
Irregular structures formed in earth materials by frost
penetration and frost action processes, and characterized by folded,
broken, and dislocated beds and lenses of unconsolidated deposits,
included organic horizons, or bedrock.
A derived unit of measurement used to express the departure of the mean
temperature for a day from a given reference temperature. Also see
freezing index and thawing index.
Depth Of Zero Annual Amplitude
The distance from the ground surface downward to the level beneath
which there is practically no annual fluctuation in ground temperature.
The volume of ice in the ground that exceeds the total pore volume that
the ground would have under natural unfrozen conditions.
Freezing of material, followed by thawing. The two fundamental frequencies involved are diurnal and annual.
The cumulative number of degree-days below 0°C for a given time period (usually seasonal).
The process of alternate freezing and thawing of moisture in soil,
rock, and other materials, and the resulting effects on materials and
on structures placed on or in the ground.
The net downslope displacement that occurs when a soil, during a
freeze-thaw cycle, expands perpendicular to the ground surface and
settles in a nearly vertical direction.
The upward or outward movement of the ground surface (or objects on or
in the ground) caused by the formation of ice in the soil.
Any mound-shaped landform produced by ground freezing, combined with
accumulation of ground ice due to groundwater movement or migration of
soil moisture. Also see Nelson et al. (1992).
The movement of a freezing front into the ground during freezing.
Frost Susceptible Soil
Subsurface earth materials in which segregated ice will form (causing
frost heave) under the required conditions of moisture supply and
Soil or rock in which part or all of the pore water has turned into ice.
A special form of solid clathrate compound in which crystal lattice
cages or chambers, consisting of host molecules, enclose guest
The slow downslope flow of unfrozen earth materials over a frozen substrate. Also see solifluction.
The study of earth materials and processes involving temperatures of 0°C or below.
The rate of temperature increase with depth below the ground surface.
A general term referring to all types of ice contained in freezing and frozen ground.
An ice-wedge polygon in which melting of the surrounding ice wedges has
left the central area in a relatively elevated position.
A dominantly horizontal, lens-shaped body of ice of any dimension.
The formation of discrete layers or lenses of segregated ice in
freezing mineral or organic soils, as a result of the migration and
subsequent freezing of pore water.
A massive, generally wedge-shaped body with its apex pointing downward,
composed of foliated or vertically banded, commonly white, ice.
A network of ice wedges defining the boundaries of a geometric polygon in plan view.
Ice formed from water injected into soils or rocks.
Latent Heat Of Fusion
The amount of heat required to melt all ice (or freeze all pore water)
in a unit mass of soil or rock. For pure water this quantity is 334 J
An ice-wedge polygon in which thawing of ice-rich permafrost has left the central area in a relatively depressed position.
Mass Wasting (mass Movement)
Downslope movement of soil or rock on or near the earth's surface under the influence of gravity.
A comprehensive term used to describe large masses of ground ice,
including ice wedges, pingo ice, buried ice, and large ice lenses.
Mean Annual Air Temperature (MAAT)
Mean annual temperature of the air, measured at standard screen height above the ground surface.
Mean Annual Ground -surface Temperature (MAGST)
Mean annual temperature at the surface of the ground.
Mean Annual Ground Temperature (MAGT)
Mean annual temperature of the ground at a specified depth.
The ratio of the freezing or thawing index at the ground surface to that derived from air temperature records.
Permafrost mounds ranging from about 0.5 to about 10 m in height and
exceeding about 2 m in average diameter, comprising (1) aggradation
forms and (2) degradation forms. The term "palsa" is a descriptive term
to which an adjectival modifier prefix can be attached to indicate
formative processes. See Washburn (1983) and Nelson et al. (1992).
A general term for any ground surface exhibiting a discernibly ordered,
more or less symmetrical, morphological pattern of ground and, where
The conditions, processes, and landforms associated with cold,
nonglacial environments, regardless of proximity to past or present
Earth materials that remains continuously at or below 0°C for at least two consecutive years.
Regions in which permafrost occurs nearly everywhere beneath the
exposed land surface. At the circumpolar scale the term continuous
permafrost zone refers to a broad area, crudely conformable with
latitude, in which permafrost is laterally continuous. See Nelson and
Regions in which permafrost is laterally discontinuous owing to
heterogeneity of material properties, subsurface water, and surface
Permafrost containing neither free water nor ice.
Permafrost containing excess ice.
A perennial frost mound consisting of a core of massive ice produced
primarily by injection of water, and covered with soil and vegetation.
Retrogressive Thaw Slump
A slope failure resulting from thawing of ice-rich permafrost.
Seasonally Frozen Ground
Ground that freezes and thaws annually.
Is a particular location where an established protocol is carried out to collect snow depths and snow densities.
Is a field campaign designed to visit multiple snow measurement sites with the intent being to characterize snow conditions (in terms of snow depth and snow density) over a given study domain.
Is where snow depths (quantity dependent on length of transect) are collected along a linear route. This is often done in an east-west and north-south direction covering an entire watershed, or along a road.
A pit dug in snowpack to ground surface. On the vertical profile of the snowpack wall, snow layers are identified. A density snow pit involves taking density samples along the entire vertical profile of the snow wall.
A general term referring to the slow downslope flow of saturated unfrozen earth materials over an impermeable substrate (cf. gelifluction).
Time-dependent compression resulting from thawing of ice-rich frozen ground and subsequent draining of excess water.
The instantaneous depth below the ground surface to which seasonal thaw has penetrated (cf. active-layer thickness). See Nelson and Hinkel (2003).
A lake whose basin was formed or enlarged by thawing of frozen ground. Hopkins (1949), Washburn (1980, 271).
Compression of the ground due to loss of excess ground ice and attendant thaw consolidation.
Thawing Index (DDT)
The cumulative number of degree-days above 0°C for given time period (usually seasonal).
The quantity of heat that will flow through a unit area of a substance
in unit time under a unit temperature gradient. In permafrost
investigations thermal conductivity is usually expressed in W m-1 oC-1
Erosion of ice-bearing permafrost by the combined thermal and mechanical action of moving water.
Temperature depression in the upper layer of permafrost, resulting from
the combined effects of seasonal differences of thermal conductivity
and the operation of nonconductive processes in the active layer. See
Williams and Smith (1989) and Nelson et al. (1985). See Goodrich
Irregular topography resulting from the melting of excess ground ice and subsequent thaw settlement.
Zero Curtain Effect
Persistence of a nearly constant temperature very close to the freezing
point of water during annual freezing (and occasionally thawing) of the
active layer. See Outcalt et al. (1990).