Periglacial landforms

tundra environment features x4

very cold so permafrost forms

short summers

consistently low temps

120-1400mm rainfall

active layer

layer that thaws- varies greatly and releases lots of CO2

permafrost layer

permanently frozen ice where temps below 0 for 2 years + 20-25% land surface

talik layer

ground below active layer that remains unfrozen

continuous permafrost

coldest, reaching 1500m deep active layer, hardly any melting

discontinuous permafrost

slightly warmer, active layer can reach 45m, gaps in pf as water forms

sporadic permafrost

mean temps around/ below 0, pf only in isolated areas where local climate prevents thawing

3 mass movement processes and collective name for them

congelifluction

solifluction/ gelifluction

frost creep

rock falls

solifluction/gelifluction process

upper layers of pf melt

ground underneath frozen and impermeable so water cannot drain through

water remains and reduces friction between soil particles

little evaporation so saturated layer becomes mobile and moves downslope at 2 degree angle

frost heave and when does it become frost creep

water underneath rocks or ground freezes expands and forces mass upwards

becomes frost creep when on slope

rock falls

freeze thaw action produces material that falls onto glacier

scree slopes are accumulation of talus (material) at bottom of slope from frost shattering

blockfields

large angular boulders left on flat areas

temporal changes to blockfields

last long time- only displaced by weathering

patterned ground

larger material in soil heat up and cool down quicker than surrounding material

material underneath rock freezes and expands by 9% pushing rocks up

rocks cannot fall back to original position as finer material replaces it

cycle repeats until rocks on surface and pattern emerges

what patterned ground do flat areas create

polygons

steep make stripes

temporal changes to patterned ground

medium amount of time- disrupts formation of ice lenses

ice wedges formation

narrow cracks in upper layer fill with ice

refreezing of active layer causes soil to crack open at surface

melt and repeat to form larger wedges

characteristics of ice wedges

polygons on flat ground

ice wedge cast if melt and fill with fine sediment

temporal changes to ice wedges

last medium amount of time- need temps to stay low enough for ice wedge to grow

pingos (general) formation and characteristics

dome shaped ice cored mound

variable in size

temporal changes to pingos

last medium amount of time- water from cracks and higher temps can melt ice lens

closed pingos formation

deep lakes unfrozen

permafrost layer insulated (by lake) and thaws

unfrozen waterlogged ground now sandwiched between permafrost and lake

lake drains and waterlogged area freezes

localised differences in pressure between lake, lakebed and permafrost means freezing water gathers to form ice lens

lens expands and pushes lakebed sediments up into some shape

continues to grow as still unfrozen ground as source of pressurised water

where are closed pingos found

beneath lake beds and water originates from in situ

open pingus formation

water able to sleep into upper layers of ground from talik and flows from higher surrounding areas under artesian pressure

water accumulates in flat low lying areas between upper layers and permafrost or frozen ground beneath water then freezes

freezing ice core expands and domes the upper layers (surface cracks)

grow as pressurised water continues to flow from surroundings

where are open pingos found

discontinuous permafrost areas

valley bottoms and water originates from outside area (eg talik)

solifluction lobes and sheets formation

sheets formed when on slope 1-20 degrees

lobes formed when on 10-20 degrees

appearance of solifluction lobes and sheets

sheets have smooth surface and extend over 100m

lobes have tongue like appearance extending downslope

temporal changes to solifluction lobes

last short amount of time:

soil cannot hold stretched structure for long

temp rise= soil moisture dec

terracettes formation and characteristics

narrow paths running horizontally along side of slope

frost heave pushes soil particles up but cannot fall downhill through creep due to vegetation intervention

temporal changes to terracettes

last short time- thawing can interrupt frost heave

thermokarsts formation

ice melting within permafrost

karsts= limestone formation

causes localised subsidence giving ground surface of hollows and depressions

result from temp changes

thermokarsts characteristics

depressions in ground surface

strong links to human influence

temporal changes to thermokasts

short amount of time- dry up with temp Inc or permafrost retreat

temporal/spatial change

length of freeze thaw cycles eg in Scotland daily but in polar regions occur over millennia

where can patterned ground be found

mount kenya

where can ice wedges be found

canada- beaufort sea coast

where can pingos be found

Canada- Ibyuk (largest in Canada)

increasing a few cm per year

where can solifluction lobes be found

alaska- eagle summit

where can thermokarst be found

Siberia