French Ch. 5

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.

Permafrost Hydrology: Although perennially frozen ground restricts groundwater movement, talik and unfrozen ground within permafrost does exist allowing groundwater flow. Taliks exist as: 1) Supra-permafrost talik, essentially when the freeze doesnot penetrate the active layer enough so a layer of talki forms between the active layer and uppermost permafrost boundary. RARE. 2)Intra-permafrost talik is confined within permafrost. 3) sub-permafrost talik is unfrozen zones beneath permafrost. in discontinuous permafrost through talik can form linking the sub and supra permafrost layers. Rivers ice over at the height of winter, just before the spring melt. Chemically at low temperatures the solubility of CO2 decreases as the solubility of dolomites, gypsum and calcites are increased. Groundwater icings ussually form in the winter months, and the larger ones will include sub/intra permafrost waters.

Hydrochemistry: Low ground temperatures result in reduced reaction times and dissolution rates, as well as increased solubility of CO2 => increased solubility of calcite's, dolomite and Gypsum. chemical composition of water bodies depends on residence time in sub surface and the mineral composition of the aquifer.  Low Temperature generally results in low solubility of CO2 and so 'purer; water suitable for drinking. Flowing spring s in heavily permafrosted areas are few but noteworthy( and crucial for surrounding villages/population. Groundwater icings, occur in winter 

Terrain Factors: Relief and aspect: Relief affects the amount of solar radiation received by the ground and therefore affects snow coverage. Aspect and orientation also influences the solar radiation received by the surface. Particularly evident in the Yukon territory where permfrost occur on north facing slopes but not adjacent south facing slopes. Rock Type/Geology: Varying solar/thermal conductivity values.In areas of continuous permafrost rock type has a bigger effect on the active layer (thickness and other parameters). Fresh Snow and organice material are good insulators of the ground. Vegetation: Primarily shields the permafrost from solar radiation (both by tree coverage and organic soil layer. trees shade ground (insolation) and intercept snowfall, therefore permafrost tends to extend deeper in areas with tree cover.Siberian veg primarily pine, North America is spruce. Spruce's denser canopy causes a thinner active layer. Snow Cover: Snow is a god insulator, heavy snow reduced the frost action on the ground due to insulation. Although north of the tree line there is not as much snow, snow that accumulates in lee slopes and gullies will cause differential effects on the ground surface. Fire: Wild fires in tundra and cold environments result due to the aridity of the environment, lightening is a common starter. Fires are more common in the boreal forests rather that tundra simply due to the lack of wood. The speed at which the fire moves across the landscape determines that damage done to the permafrost, slow moving fires (due to damp veg) cause more damage than quick moving ones. Usually a region will exhibit and  thicket active layer post fire.

The Active Layer: Layer of ground above permafrost that thaws annually (during summer). Generally thicker in polar and thinner in sub-arctic regions Some of the variance in the controls on permafrost formation are reflected in the annual change in the active layer. To calculate the thickness of the active layer stefans equation can be used if ground surface temperature, soil thermal conductivity and volumetric latent heat of fusion are known.

The Transient Layer: Near surface ice rich layer between the active and upper permafrost boundary. During warm summers, the active layer deepens further than normal (into transient layer) and causes increases process action including; Slope instability, rapid mass movement and soliufluction.

Active/thermal regime:Freeze/thaw of the active layer can be diurnal (low lats) or seasonal (high lats) thawing is one dimensional (thaws downwards), whereas freezing acts both from above and below the active layer.

General

Hydrology

Terrain

The Active Layer