Periglacial landforms and processes Flashcards
Freeze thaw: process
Active layer freezes, causing soil to contract and crack
Melting in summer fills crack with meltwater and sediment. Refreezes in winter, widening and deepening crack
Repeated cycle between winter and summer
Permafrost: process
Concentrated in high latitudes but also lower latitudes with higher altitudes.
Below zero degrees for at least 2 years
Distribution is a good indicator of main periglaciated regions
Large areas of present temperate mid-latitudes experienced periglacial conditions due to ice sheet proximity during Pleistocene. 20-25% earth’s surface experienced permafrost and/or intense frost
Landform: ice wedge
Active layer refreezes causing soil to retract in winter.
Melting occurs in summer. The crack opens again and fills with meltwater including fine sediment
Winter/summer cycle repeats. Wedge gets deeper and wider
Landform: nivation hollows
Nivations are circular depressions in the ground
Freeze thaw and chemical weathering cause rock under snow to disintegrate.
Snow melts in spring. Weathered particles move downslope by meltwater and solifluction.
Over some period of time the hollow is formed. Snow can fall inside and become protected from the sun. It compacts into neve then firn
Erosion: meltwater washes sediments out of base of snow patch
Landform: solifluction lobes
In winter, freeze thaw loosens material whilst in the summer, the active layer thawing lubricates the slope allowing the material to move downhill. Slopes as shallow as 2 degrees can have parts of active layer move downslope. When the gradient changes again and flattens the material flow slows down and is deposited in a tongue shape. Frost heave and permafrost and solifluction causes gelifluction.
Landform: patterned ground
Geometric shapes formed by deformation of ground material in periglacial regions.
Active layer freezes->ice crystals develop. They increase volume of soil and cause upwards expansion of soil surface.
Frost heave causes fine grained soil to expand unevenly and form small domes on the surface.
Frost heave pushes coarser sediment up to the surface of the dome. The gradient of the dome forces gravity to act upon sediment and pull them down the camber slops and collect when ground plateaus.
Landforms: pingos
Dome shaped mound consisting of a layer of soil over a core of ice which is a product of a growing lens pushing up the ground.
Landforms: ognips
Thin surface layer above ice core collapses, leaving it exposed to atmo and sun. The ice melts, causing pingo to collapse. The ruptured pingo is left with depression in middle that can fill with water to form lake.
Solifluction prone-rampart
Landforms: closed pingo
Water comes from outside system
Found in low-lying areas with continuous permafrost on site of small lakes.
Frozen lake with sediment on floor insulates ground beneath ice, creating a talik.
As water freezes and expands, the frozen lake breaks up and slides away as ground heaves upwards into a dome shaped mound.
Lakes form in small depressions as meltwater cannot drain into frozen ground beneath it.
Landforms: open pingo
Water that forms ice lens comes from outside the system (Above ground).
Thin or discontinuous permafrost allows water to seep into upper layers of ground and freeze, forming lens
This expansion causes overlying sediment to heave upwards into dome shaped feature known as pingo.
Landform: loess
Glaciers grind rocks to fine powder
Derived from floodplains of glacial braided rivers that carried large volumes of glacial meltwater and sediments.
During autumn/winter sediment is susceptible to winnowing of silts and clays. Deposited downwards
Landform: ice lens
Moisture accumulates in soil and freezes.
As it expands it will push land above it.
Not many are exposed.
