Defining permafrost:

Ground (soil/rock) remains remains at .
Permafrost has both a thermal component and a state, It is not permanently frozen ground, rather ground held at
Epigenetic Permafrost: normal ground subject to cooling and permafrost penetrates downwards.
Syngenetic Permafrost: Permafrost forms in concurrence with deposition of new ma

Moisture:

Peaty & Poorly drained soils are frost susceptible, conversely coarse and therefore well drained soils are Non-frost susceptible.
Often the ice in permafrost is more that the natural water in the soil, so thawing results in ground subsidence.
Subsequent consolidation following subsidence is called thaw consolidation.
It is worth noting that the geotechnical properties of soils when frozen is often very different to the frozen - potential Human issues (housing/industrial activity such as oil mining).
Often subsurface flows are restricted by permafrost, water is constrained to the active layer or unfrozen layers and taliks.

Properties of Permafrost:

Thermally, Ice is four time more conduction of heat that water therefore heat penetrates into permafrost faster than normal ground. Because of this, thermal regime is essential to the lapse rate in permafrost and the state of the active layer.
The Geothermal regime: For permafrost to form there needs to be cooling acting on the surface, alongside this the earth heats outwards. The basal cryopeg is an area of permafrost perennially cryotic, but not frozen.
If the geothermal gradient and ground surface temperature you can one dimensionlly calcluate the temperature at any depth: Tz = Ts + Gg X Z
Tz= Ground Temp, Ts= MAGST, Gg= Geothermal gradient, Z= Depth
Most relevant properties: 1) Moisture content 2) Density 3) Porosity.
Thermal Properties: Thermal conductivity (K), Mass & Volumetric heat capacity (Cm, Cv)Thermal diffusity (alpha) and latent heat of fusion (Qi).
Heat conduction theory: Presence of a water body can affect the permafrost, f sufficient enough the prescence of water can not only depress permafrost at the surface forming taliks, it can also affect the lower permafrost boundary or if big enough it can thaw all the ground beneath it. Most lakes >2m deep will form some talik.
Illisarvik lake draining experiment (West Canada): The lake bed was underlain with talik upto 30m deep, the lake was drained and the talik has been observed since. The removal of the water body resulted in freezing action both downwards from the air temperature but also upwards from the subsurface permafrost. In 1995 a small ice mound was recorded, indication prior ground water flow. 17 years after drainage the permafrost was 7m deep, and the talik continuing to shrink.

Permafrost Distribution:

High lat (artic), High Alt(alpine) or Plateau (tibet). Some sub-sea permafrost exists but it considered relict.

Continous (90-100%), Discontinuous (50-90%), Sporadic (10-50%) or isolated (0-10%).
Quaternary history of an region plays a big part in modern day distributions.

Alpine Permafrost;

Similar to arctic permafrost, immediately after the snow line there is continuous permafrost (or discontinuous at lower altitudes), to sporadic and then no permafrost as altitude it lost.
Furthermore in high latitude alpine areas the lower limit of permafrost (where sporadic would be found) exists at higher altitudes to low latitude areas. This relationship can be expressed by the gaussian type curve.
Generally limits can be estimated in this way, however in Alpine environments and especially at low latitudes t=many more factors can influence the lower permafrost boundary, e.g. the influence of continental weather.
BTS method is for estimating the boundary.

Relict Permafrost:

Permafrost defined as
Sub-sea permafrost occurs in Laptev and East Siberian seas as well as Beaufort and wast Canadian seas. It can be in thermal equilibrium or disequilibrium, is the sea bed temperature is

Relict Terrestrial Permafrost:

Mostly late Pleistocene in age, some has been estimated to be 40-125 thousand years old. Preserves Mammals have been found.

	Creado por samflint93 hace alrededor de 11 años

University finals (2 Drivers & Contrasts) GEOG3004 Apunte sobre French Ch. 5, creado por samflint93 el 05/10/2013.