periglacial Flashcards
(19 cards)
active layer
saturated and possibly mobile seasonal layer, causedcby cycles of intense freezing and thawing meaning that surface sediments thaw in the summer
freeze thaw weathering
shattering of rock as result of water in its joints and pores freezing and expanding - especially active when temps flucatuate
frost heave
upward movement of rock or soil particles from pressures generated by the formation of ice segregations in the ground
frost action
when water seeps into cracks in a rock and when the temp below 0, ice forms and expands, cracking the rock untail chunks of rock break away
nivation
occurs when both weathering and erosion take place around and beneath a snow patch
- fluctuating temps and presence of meltwater promote frost shattering
-summer meltwater will carry away weathered rock debris to reveal an ever enlarging nivation hollow
-slumping may take place during summer as saturated debris collapses due to gravity
solifluction
mass movement of the active layer downslope
wind action
lack of vegetation cover due to low temp. plus prevailing aridity mean there are plenty opportunities fro
ice wedges
during summer, meltwater goes into cracks and freezes in winter to form ice wedges
-increase in size over cycles
-caused by frost heave
patterned ground
-repeated freezing, heaving, and thawing of the active layer produces the pattern
-frost heave pushes stones to the surface
-ground underneath filled back up with soil
- ponds of meltwater can form in hollows between ridges
closed system pingos
-form in areas of continous permafrost with a lake on the surface
-on small lakes, groundwater can be trapped by freezing from above and permafrost below
-freezing and expansion of trapped water pushed overlying sediment upwards and if the centre collapses it creates a lake
-the frozen lake with sediment on the floor insulates the ground beneath against the cold, allowing talik (year round unfrozen ground) to exist
open system pingos
-form in areas of discontinous permafrost
-temperatures drop and water freezes in the upper layers of soil
-ice expands in the soil, causing overlying sediment to heave upwards
-when the active layer starts the freeze from the surface down , water in the Talik trapped between the freezing active layer and permafrost begins to freeze aswell, creating an ice lens
-water migrates and rises to this ice lens (hydrostatic pressure) and freezes on contact, swelling the size of the lens, creating cracks where the surface ruptures
pingos
where frozen water layers expand, pushing sediment and land above into a dome
Loess
lack of vegetation and plentiful supply of fine, loose material in periglacial and glacial environments enable strong cold winds to pick up large amounts of material and redeposit far away from its source
-fine material created by glaciers grinding bedrock into a fine powder called rock flour, carried to end of glaciers by meltwater
blockfields
freeze thaw/frost shattering occurs, breaking off large chunks of rock and pile up as scree (collection of loose pieces of rock) at foot of slope
-frost shattering can create extensive areas of broken up angular fragments of rock called blockfields
solifluction lobes
solifluction is the downward movement of rock and soil under gravity, resulting in lobed shaped features called solifluction lobes
- in periglacial environments, active layer provides enough water to allow flow
-saturated soil slumps downhill during summer, forming lobes
braided rivers
meltwater can form these, as it flows across glacial outwash plains
nivation hollows
in summer, meltwater will carry away any weathered rock debris, to reveal an ever enlarging nivation hollow
-fluctuating temps and meltwater presence promote frost shattering
- Snow gathers in a small depression and eventually erodes into a hollow
types of permafrost
continous = 90% ground surface is permafrost
discontinous = 50-90% ground is permafrost
sporadic = 10-50% ground is permafrost
how much of world covered in permafrost
25%
