Cryosphere/ Cold environments Flashcards
L4 - Periglacial environments & permafrost
What is permafrost?
Permafrost: soil or rock that remains at or below 0°C for at least two consecutive years.
L4 - P&P
define periglacial environments
Periglacial environment: cold but non-glacial, regardless of proximity to glaciers.
L4 - PP
Where is permafrost found?
*needs altering
high altitudes and latitudes
- Svalbard (potential threat=graveyard died from flu pandemic – this bacteria is locked up)
-Russian high arctic
Can impact rural an
L4 PP
What are permafrost properties and how is it distributed?
Active layer – freezes and thaws yearly, top layer. Depth varies,
Temps – well below freeze in winter, above freezing in summer. At surface has biggest swing in temp
Permafrost – frozen part of ground all year through or two as a minimum, depth varies substancially. This is based on 4 factors; mean annual temp, conductivity of ground, geothermal heat flux from below in earth, land cover (if more dense veg = insulates ground more than bare soil). Temp = never gets above 0oc
Talik – frost free soil. Temp = same throughtout doesn’t feel seasonal fluctuations. Unless near geothemal
Global distribution – high altitude or latitude. Eg tibettan plato. Polar permafrost: High
Latitude. Alpine permafrost: High altitude. Distirbution depends on four factors. Primar factor is temp on ground (further north=colder=more likely to have continuous permafrost)
Latitudinal and altitudenal
Can find permafrost in sea eg offshore alasa and russia and russian high arctic
L4 PP
what are the 3 types of permafrost?
Types of permafrost
Continuous permafrost: 90-100 % -6 to -8 °C
Discontinuous permafrost: 50-90%-1 °C
Sporadic permafrost: less than 50%, majority is unfrozen
L4 PP
what is the tecnique of finding where permafrost is?
How to find where permafrost is
Ground penetrating radar (GPR) - looks at electrical characterisitcs, frozen vs unfrozen material looks differet in the radar. Is useful to find lenses in the ice/ cores of ice in moraines. Usuaful to understad glaccial outburst lakes – links to hazard assessment.
L4 PP
what engineering challenges does permafrost cause?
Engineering challenges
Frost heave – crystals expand and push up grou d, pushes up unevenly
Thawing & subsidence – pushes up ground down unevely, causes problems to roads
Saturation – slides and sinks?
Freezing of buried pipes – pipes explode on small scale , or sewage pipes is large scale problem and oil and gas pipes.
L4 PP
what do we mean by passive and active disturbance to permafrost?
how do we deal with this?
Passive: minimise disturbance
Active: destroy permafrost, only works where smaller pockets of permafrost
example of how to deal with this?
Examples of dealing with it – buildings are built on stilts, minimise desturbance to permasfrost so heat doesn’t go into ground. Insulation stop heat going into ground.
L4 PP
case studies/ examples of passive engineering on permafrost
Examples Trans-Alaskan pipeline 1285 km long 1.2 m diameter Prudhoe Bay to Valdez, problem in arctic areas, oil producing areas are remote and permafrost. Oil flows best at 70oc, would thaw permafrost, so put pipes on pillars to not thaw permafrost. Have alarm systems on pipes to monitor.
Qinghai–Tibet railway, 1100 km long, Golmund to Lhasa – problem building across ground have
L4 PP
Periglacial environments have specific processes what are they? - key ones highlighted
Freeze-thaw – water freezes in winter and expands, in cracks in rocks, widens crack in rock, breaks up rock. Creates blockfield
Blockfield: mountain top covered by frost-shattered material – key indicator for this is angular rocks, if had been transported by river rocks would be rounded
Frost creep – permasfrost at bottom, active layer ontop. Rock pushed up at 90 degrees up and falls back down under gran=viety, particle creeps down slope. Movement of material downslope.
Gelifluction – permasfrost and active layer. Cant drain well, water doesn’t drain into permafrost. Top layer gets saturated and starts to flow downhill.
Braided rivers – could be process and landform, carries sediment, not defined in chanel. Individual streams, are seasonal, in summer more water and sediment travelling, look diff in winter. Form in periglacial and permafrost environments, important way to move sediment and water through evnironment.
Periglacial environments have specific landforms, what are they? - key ones highlighted
Key landforms (periglaical and permafrost)
Ice wedges (colder than -15°C) - form through freeze thaw, crack or weakness in ground fills with water and freezes and thaws, expanded crack makes individual ice wesge. Often form in polygon shapes = patterned ground
Ice wedges/ ice wedge polygons
Pingos – uplifted ground. Two types:
Hydrostatic/ closed systme/ mackenzie delta where they were discovered – depression on earth insultaes ground underneath, lake drains and unfrozen material is exposed to cold temps = freezing on top downwards. Migration of liquid water in talik up to freezing, water then freezes to cause a mound.
Hydraulic (open system / east Greenland) moving downslope, can lead to multiple pingos in area
Thermokarst (lakes) - formed in hollows, different bits form at different rates, large systems of depressions and ridges that fill up with water, important role in greengas fluces potentially provide a sink for gasses, important for wildlife source of water and habitia.would run into problems tryig to build a road over this landscape
L4 PP
is permafrost a major store of greenhouse gases?
Is it a major source of greenhouse gases?
Methane & carbon release
Gas hydrates – frozen within permafrost
Cycle - Increased air temperature
Increased permafrost temperature
and active layer thickening
Permafrost thaw
Decomposition of organic material
Emission of greenhouse gases
