Extreme Environments Flashcards
Whats permafrost?
Impermeable permanently frozen ground for at least 2 consecutive years
What’s thermokast?
Depressions caused by subsidence due to the melting of permafrost - leads to waterlogged soil
What is thermokast caused by? (4)
- change in vegetation affects albedo affect
- shifting of stream channels
- fire which destroys permafrost
- disruption of vegetation
What are the 3 different types of permafrost?
- continuous (-5/-50)
- discontinuous (-1.5/-5)
- sporadic (0/1.5)
What is plucking?
Occurs at the base of the glacier
Water seeps into joints of rock, freezes onto the rock and is ripped out by the moving glacier
What is abrasion?
Debris carried by glacier scratches sides of rocks leaving striations
What does the rate of erosion depend on?
- local geology
- the amount of load carried by glacier
- weight and thickness of glacier
How do Cirques form?
1) periglacial hollow is enlarged by freeze-thaw
2) Ice accumulates in the hollow
3) After reaching a certain height, ice moves out in a rotational way which erodes rock around it by abrasion and plucking
4) Cirques keeps enlarging due to freeze-thaw and sometimes forms a lake
How are arretes and pyramidal peaks formed?
Due to headward recession (cutting back of 2 or more cirques)
How are hanging valleys formed?
Formed by tributary glaciers, which are left suspended over
What is drift?
Refers to all fluvioglacial and glacial deposits left after ice has melted
What is till and what are its two types?
Till refers to deposit that is angular and unsorted
Lodgement till - from a moving glacier
Ablation till - from a stagnant glacier
What are the characteristics of till? (5)
- poor sorting/stratification
- mixture of rock type
- many particles of striations
- compaction of deposits
- sub-angular particles
What are erratics?
Large boulders that don’t belong with the local geology
What is moraine? What are the 3 types of moraine?
Lines of loose rocks, weathered by the valley side and carried by the glacier
- terminal moraine
- lateral moraine
- medial
What is medial moraine?
When two glaciers merge and two lateral moraines form in between the enlarged glacier
What is froze heave?
When water freezes in soil lifting up individual soil particles to the surface
What is solifluction?
Water freezes rocks and soil under. This melts and flows downhill. It doesn’t infiltrate the soil because of the impermeable permafrost. When it’s deposited it forms solifluction lobe.
What is frost creep?
Movement of sediments from frost heave, moving downhill due to gravity
What is patterned ground?
Patterns in ground such as circles, stripes that are found in soil coming from intense frost action
What are pingos?
Isolated, conical hills only found in periglacial areas formed by freezing water under pressure- expansion of permafrost
What are the two types of pingos?
Open system pingos
Closed system pingos
What is salt crystallisation?
Causes the deposition of rocks by solutions of salt
What are the two main types of salt growth?
- areas of temp. change, where sodium sulphate expands creating pressure of joints
- water evaporates and leave salt crystals (salt expands when heated)
What is disintegration?
Rock heats up during the day and expands, then contracts at night which causes stress in outer layer- exfoliation occurs
What do flash floods do?
Carry sediments which have large erosive force, flowing through canyons which leads to deposition
What is an exotic/ exogenous river?
Comes from a wetter environment but flows through a desert
What is an endoheic river?
Those that drain inland lake or sea
What is an ephemeral river?
Those that flow seasonally or after storms
Dunes shape and size depends on what factors? (4)
- supply of sand
- direction of wind
- nature of the ground surface
- presence of vegetation
What is deflation?
Progressive removal of small material leaving behind larger materials forming stony deserts
What is abrasion (wind)?
Erosion carried out by wind-borne particles (acting like sandpaper) Usually within 1 metre of the ground where the largest, heaviest, most erosive particles are carried
