unit five Flashcards
what is a periglacial landscape?
a landscape that undergoes seasonal freezing and thawing, typically on the fringes of past and present glaciated regions
what is permafrost?
ground that remains frozen for 2 consecutive years and more
what does the mean annual ground temperature need to be for permafrost to occur?
-6 degrees for continuous permafrost
what percentage of the earth’s landscape contains permafrost?
25% of land in the northern hemisphere
how deep can permafrost be?
1500m
what is the active layer?
a thin layer of soil that thaws in summer and freezes in winter
what is the distribution of permafrost?
wide areas like russia, greenland, canada, scandanavia and china. mountainous areas and high latitude areas, some sporadic patches that are isolated, they become less dispersed moving outwards and 80% of alaska is covered in permafrost
what factors may help to explain the variations in permafrost globally?
different altitudes, latitudes and temperatures
what is continuous permafrost?
forms in the coldest areas of the world where average annual temperatures are below -6 degrees and can extend hundreds of meters
what is sporadic permafrost?
forms in the coldest areas of the world but more fragmented and thinner
what is discontinuous permafrost?
occurs at margins of periglacial environments and is highly fragmented and only a few meters thick
what impact does permafrost have on climate change?
contains remains of countless dead plants and animals, so when the ice thaws, these will be broken down and release huge amounts of greenhouse gases
what is the importance of permafrost on humans?
if it melts, buildings and important pipelines will collapse, causing a lot of damage and impacting peoples lives
how has ai been used to see the impact of permafrost melting?
developed mapping site to see the before and after
how much more is methane more potent than carbon dioxide?
25 times more
what is pore ice?
in pore spaces between soil/sediment particles where liquid water can accumulate and freeze
what is needle ice?
narrow ice slivers that are up to several cm long, normally forming in moist soils when temperatures drop below freezing overnight
what are ice lenses?
bodies of ice formed when moisture, mixed within soil or rock, accumulates in localised zones
what are ice wedges?
downward narrowing lens of ice that can grow up to 3m at the surface and extend below ground surface up to 10m
how do ice wedges form?
- a seasonal crack forms during winter season because temperatures are so low, the ground will contract and crack
- in the summer, temperatures warm up and the ice melts and liquid from the thawed active layer fills the cracks. as ice has a larger volume, meaning more water will fill the crack
- this repeats until the wedge is deep and wide
how do ice wedges cause ice wedge polygons?
the ice expansion causes soil layers adjacent to be pushed up and out, causing a slight bulge. many if these cause patterns in the ground
by what percentage does ice expand by?
9%
what are stone sorted polygons?
patterned ground
what are the different shapes that stone sorted polygons form?
stripes, circles and polygons
why do stone sorted polygons have different shapes?
due to gradient of the ground
what is frost heave?
the upward dislocation of soil and rocks by the freezing and expansion of soil water
what happens during frost heave?
- freezing progresses down from surface accompanied by upward expansion, lifts up stone by first freezing onto upper surface
- freezing front progresses down space created below as it is lifted
- ice crystals grow into space and push up stone
- thawing progresses down from the surface , contraction and lowering of surface level, but stone still supported by ice crystals
- thawed sediment collapses around stone supporting it
- stone held in thawed sediment while ice crystals melt and space filled by collapsing sediment
- this repeats
how do stone sorted polygons form?
when temperatures drop and the expanding ground begins to lift stones, the small amounts of moisture beneath the stone freeze and turn to ice, expanding. due to cryostatic pressure, the stones are raised up (frost heave), forming a dome of overlying ground. when the ice thaws, the wet material will slump into the gap beneath the stone, preventing it from dropping back in the same place. this process repeats until the stones slip, slide or roll to the base to form patterns
what type of gradients form stripes?
steeper gradients
what type of gradients form polygons or circles?
gradual gradients
what is cryostatic pressure?
the pressure exerted when ice expands
what is a pingo?
circular ice-cored hills with a height between 3-50m and a diameter between 30-300
why is the ice lens at the core of a pingo thought to develop?
artesian groundwater and cryostatic pressure
what are the 2 types of pingos?
open and closed system pingos
how do open system pingos form?
- liquid groundwater is confined below permafrost. if it finds a weakness in overlying permafrost, it will crack due to artesian pressure - as the water rises, it begins to cool and sometimes freezes. if the water reaches the active layer, in the summer it will form a spring
- during winter months, the rising water will freeze before reaching the surface and forming an ice lense
- more groundwater will feed the ice lense. as it grows, the ice lense displaces the overlying sediment, making a domed ice core hill
what is a talik?
unfrozen sediment found in an area of permafrost
how do closed system pingos form?
- in summer months, lakes will form within the active layer. when winter approaches, the lake will freeze from top down
- the unfrozen lake water and sediment beneath the ice acts as an insulator, which prevents the ground from freezing and results in talik
- during long periods of cold, the permafrost will encroach on the overlying talik causing the liquid water contained within the talik will freeze, forming an ice lense
- as the ice lense grows, it will exert cryostatic pressure and rise upward, displacing the overlying lake. the sediment that was once at the bottom of the lake covers the raised lense. the resistant ice core hill is a pingo
what is a thermokarst?
a land surface characterised by irregular surfaces of marshy hollows and depressions formed as permafrost thaws due to a warming climate
what is solifluction?
mass movement of wet saturated active layer under the influence of gravity
how does a thaw lake form?
- active layers will thaw and solifluction will occur due to the saturation of the soil
- continued solifluction will mean that the active layer will decrease
- depression will slowly form and it will fill with water, forming a lake
- the permafrost layer will increase while the active layer decreases
what is an example of an extreme thermokarst?
the batagay mega slump crater in russia
what proportion of russia has permafrost?
over half (more than anywhere in the world)
what caused the batagay mega slump to form?
the melting of permafrost. longer and hotter summers means rapidly melting. the active layer will increase in size meaning there is more permafrost melting
what is mass movement?
process by which the soil, sand and rocks move downslope typically as a solid continuous mass under the force of gravity
what is frost weathering?
temperature fluctuates around 0 degrees, causing repeated freezing and thawing. expands by 9% causing pieces of rock to eventually break down
how does a nivation hollow form?
- north facing slopes receive limited insolation
- cold temperatures enables snow to remain in the hollow all year resulting in formation of firn
- freeze-thaw weathering due to temperature fluctuation around 0 degrees, provides a supply of weather material
- snowmelt in summer produces meltwater
- weathered rock removed by meltwater and solifluction
what is another name for blockfields?and what does it mean?
felsenmeer meaning rock sea
what is a blockfield?
a surface covered by large, angular rocks
how do blockfields form?
are a product of freeze thaw weathering on flat plateau surfaces
what is an example of a blockfield?
in snowdonia, on the glyder plateau around the pyramidal peak of glyder fawr?
why are the rocks on blockfields angular?
it is more resistant rock against freeze thaw weathering
what are scree slopes?
an accumulation of freeze thaw weathered rock fragments at the base of a cliff
how do scree slopes form?
- freeze thaw frost shattering occurs at the top of a cliff
- this provides the scree that builds up at the base of the cliff (mass movement)
- as more scree accumulates, this reduces the slope’s angle and creates a scree slope
what is a protalus rampart?
a ramp shaped mound of scree that forms in a similar way to a scree slope
how does a protalus rampart differ from a scree slope?
involves ice or snow being present on a valley slope
what is an example of a scree slope?
the lake district have has a lot of vast water scree slopes
what is an example of a protalus rampart?
cwm idwal
what is solifluction?
saturated soil that flows under the influence of gravity
where do solifluction lobes occur?
on slopes with a gradient as gentle as 1 degree but is more pronounced on steeper slopes between 10-20 degrees
how do solifluction lobes form?
during the summer, the active layer thaws whilst the underlying layer remains frozen and impermeable. the surface layer becomes waterlogged and active as a result
what is soil creep?
when mass movement occurs in periglacial areas due to repeated freezing and thawing of the active layer
what is frost heaving?
the expansion of soil
how do terracettes form?
- in summer, the active layer thaws
- in winter, the active layer freezes and expands outwards parallel to the surface
- in summer, the active layer thaws, soil particle drops vertically downwards causing a downslope movement of particles
what is infiltration?
when water moves into the ground/seeping in
what is percolation?
moving through the rock, heading down towards the groundwater store
why is there no infiltration or percolation in permafrost areas?
it is impermeable meaning nothing can go through it
what are dry valleys?
relict periglacial landforms showing evidence that the landscape was previously influenced by flowing water
where do dry valleys form and why?
regions of permeable rock, like chalk and limestone, which usually allow water to infiltrate and percolate the ground
how do dry valleys form?
- meltwater pools on and runs over the ground surface
- as the ice masses retreat and warmer conditions develop, higher levels of runoff occur, eroding and deepening the valley
- once permafrost has melted, water from the surface will infiltrate and percolate, reducing runoff and leaving the river dry
what are loess deposits?
fine rock debris transported and deposited by glacial winds
how do loess deposits occur?
transported by meltwater rivers during spring and summer months onto sandurs. during autumn and winter the flow these rivers is reduced, therefore large parts of the sandur will dry out and are exposed to strong katabatic winds off the ice therefore fine rock particles are picked and transported, eventually depositing it as a thick sediment, creating a flat plateau landscape
what are katabatic winds?
winds that flow downhill
what are some examples of where loess can be found?
extensive regions in europe particularly in ukraine
