Module 10 Flashcards
permafrost
permafrost – a thermal a thermal condition where ground temperatures remain below 0°C for two or more consecutive years
develops where the depth of frost penetration into the ground during the fall and winter is greater than the depth of ground thawing in the summer
pore water is frozen and acts to cement sediment particles, or fills a large proportion of the pore spaces in consolidated rock
periglacial
periglacial landscapes include landforms and locations characterized by intensive freeze–thaw action
describes areas where permafrost currently exists or has existed in the past, regardless of current or past glacial positions
includes both high latitude and high elevation regions
Permafrost Zones 4
continuous permafrost zone is the region in which permafrost conditions are generally (90–100 per cent) present beneath the seasonally thawed active layer
isolated patches of unfrozen terrain, called talik, are also present in the continuous permafrost zone
discontinuous permafrost zone is characterized by patchy distribution of permafrost, with frozen ground beneath the active layer representing 10–90 per cent of the area
alpine permafrost zone includes isolated patches where permafrost covers less than 10 per cent of the area and occurs in the lower parts of alpine and upland regions
subsea permafrost zone developed during the last glacial maximum period (25,000 years ago), when sea level was lower and parts of the sea floor were exposed to continuous cold temperatures
permafrost currently underlies __ per cent of Canada and is divided into zones
40
continuous permafrost means the regions has approximately __-__%
90-100
discontinuous permafrost means the regions has approximately __-__%
10-90
alpine permafrost means the regions has approximately __-__%
1-10%
3 types of discontinuous permafrost
discontinuous permafrost – mean annual air temperatures range from -0.5oC to -7oC
widespread: 50-90% underlain by permafrost
scattered: 30-50% underlain by permafrost
sporadic: 10-30% underlain by permafrost
- permafrost thickness increases poleward
_____(country) has the most permafrost
Russia
ground temperatures increase with depth in response to the …
geothermal heat flux
formation of segregated ice is favoured in materials with an average grain size finer than ___ mm diameter (i.e., silt and clay) – frost susceptible sediments
pore water expands upon freezing resulting in _______
0.01
frost heave
cryoturbation
repeated heaving and subsidence results in mixing of materials within the active layer, a process referred to as cryoturbation
contributes to the development of patterned ground
4 patterned ground examples of cryoturbation
sorted circles are small, circular features, tens of centimetres in diameter, with pebbles of uniform size
unsorted circles contain a wide range of clast sizes
stone stripes develop with increasing slope as circles become elongated in the downslope direction
felsenmeer develops where fractured bedrock is exposed on surface slopes, and frost heaving produces assemblages of angular cobbles and boulders covering the terrain
gelifluction
gelifluction is a slow downslope movement accentuated by frost heave and cryoturbation
It involves very slow (centimetres or millimetres per year) movement of saturated, non-frozen or partially frozen material over a frozen substrate
gelifluction should not be confused with frost creep
results in formation of small overlapping terraces, 1-10 m in width, forming a lobate pattern; gelifluction lobes
active-layer detachment slides (ALDS)
active-layer detachment slides (ALDS) are mass movements characterized by the sliding of a cohesive layer over the surface of a permafrost table or a seasonally developed frost table
ALDS can be triggered by a period of high temperatures under cloudless skies, resulting in enhanced input of solar insolation
melting of interstitial ice may generate high pore water pressures at base of slab facilitating motion; peak velocities may exceed 5 metres/hour
-slopeinstability initiated by the deepening of the active layer
Massive Ground Ice
massive ice bodies, often 10’s of metres thick, are widely reported in coastal lowlands bordering the Beaufort Sea
consists of intrusive ice formed by the movement of water under pressure into seasonally or perennially frozen materials
water is supplied by taliks, bodies of unfrozen materials within permafrost, that serve as aquifers
____ facilitate the flow of groundwater through permafrost towards stream channels and lake basins.
Talik
retrogressive thaw flows
occur where thawing of a disturbed area at the head or crown of the flow allows the bank to erode backward (retrogress), extending the disturbed area at the headward end
occur in silt or fine sand with a high interstitial ice content
motion similar to rotational slumps
velocities can reach 16 metres per year
thermokarst
thermokarst is the subsidence of the ground surface in permafrost regions due to differential melting of ice or ice-rich sediments and subsequent subsidence of the ground surface
primary cause is related to deepening of the active layer
melt water collects in subsiding basin; promotes further thawing and subsidence
thermokarst features can occur at any location where ice or ice-rich sediments are exposed to temperatures at or above 0°C
-human activities can also promote the development of thermokarst
global mean air temperature has increased by __°C over the past century
0.6
Air temperatures in the circumpolar North for past 100 years-
1900-1940
1940-1960
1970-present
Air Temperatures
circumpolar North has experienced both strong warming and cooling at various times over the past 50 to 100 years
warming through the 1900’s to the 1940’s
cooling through the 1940’s to the 1960’s
warming through the 1970’s to the present
currently, the Arctic is warming at more than _____ the rate of lower latitudes
twice
represents an increase of 2.3°C since the 1970s and 2.9°C since the beginning of the 20th century
Arctic Amplification mechanisms(4)
mechanisms for Arctic Amplification include:
reduced summer albedo due to sea ice and snow cover loss
decrease of total cloudiness in summer and increase in winter
additional heat generated by newly sea-ice free ocean areas that are maintained later into the autumn
lower rate of heat loss to space in the Arctic relative to the sub-tropics due to lowered mean temperatures
The Sea Ice _____ hasnt changed much in the last 3 decades but the Sea Ice _____ has declined markedly
maximum
minimum
Since 1970’s ice has been becoming annual ice instead of multi-year ice
