Glaciation Pack K Flashcards
1
Q
What are the characteristics of periglacial areas?
A
- Daily temperatures are below 0 for at least 9 months and below -10 for at least 6 months per year
- Low precipitation, typically less than 600mm per year
- Fluctuating temperatures causing cycles of freezing and thawing
- Soil that has permafrost (permanently frozen ground)
2
Q
What are the processes that cause distinctive landscapes?
A
- Freeze-thaw weathering
- Ground ice formation
- Mass movement of the active layer
- Wind and fluvial action
3
Q
How does ground ice formation happen?
A
- Continuous, discontinuous or sporadic permafrost
- In summer, daily input of radiation of solar energy exceeds the output from terrestrial radiation
- Active layer deepens and there is less ground ice
- Active layer may become waterlogged (as water can’t seep down)
- In autumn, the energy balance becomes negative so the ground water freezes again
- Amount of ground ice depends on water and texture of active layer materials
- Sand is a poor water retainer but will freeze at 0 and clay retains water (due to being fine grained) but will only freeze at temperatures below 0
- This leads to uneven active layer
4
Q
What causes ice lenses to form?
A
- It is an area of ice under the surface caused by water from the surrounding area migrating to a frozen area
- May form under stones as stones lost heat faster than the soil around the
- Soil under stones gets colder and water freezes
- Moisture accumulates around ice and freezes
- As ice expands/grows, it pushes the surface up into higher land (frost heaving)
5
Q
What causes a thermokast landscape?
A
- As a result of melting permafrost
- Domes caused by frost heave and ice lenses may collapse
- This leaves depressions which can fill with water
6
Q
What causes ice wedge polygons?
A
- When temperatures get very low in winter, the ground contracts and cracks form in the permafrost (frost contraction)
- In spring, temperatures rise so the active layer thaws and meltwater seeps into the cracks
- Permafrost layer is still frozen so the water freezes in the cracks
- The frozen water is known as an ice wedge
- Frost contraction in following years re-opens cracks and more water seeps in
- Each time the ice wedge gets larger
- As the ice expands, it pushes up the soil above to form ridges, which look like polygons from above
7
Q
What causes patterned ground?
A
- Landform that looks like circles, polygons or stripes made up of stones on the surface
- Formed by frost heave or frost contraction
- Water underneath stones freezes and expands so the stones are pushed upwards until they reach the surface
- Smaller particle replace them so they can’t fall back down
- Upon reaching the surface, they may roll down to the edges of the mounds to form circles
- If mounds are close together, circles will join to form polygons
- If the mounds are on a slop, they will form lines
E.g. Tuktoyatuk, Canada
8
Q
What causes pingos?
A
- Pingos are conical hills with a core of ice
- 3-80m high and 30-1000m in diameter
Open system:
- Formed where there is discontinuous permafrost
- Groundwater is forced upwards from unfrozen areas lower down
- It collects together and freezes
- Forms a core of ice that expands pushes the ground above it upwards into a dome
Closed system:
- Formed in areas of continuous permafrost where there is a lake at the surface
- Ground under it is insulated so remains unfrozen
- When the lake dries up, the insulation effect stops and water in the ground freezes
- Forms a core of ice that pushes the ground above upwards into a dome
9
Q
What causes asymmetric valleys?
A
- When one valley side becomes steeper than the other
- Due to some slopes getting more insolation (S facing in the N hemisphere)
- There is more melting and more mass movement, which leads to less steep slopes
10
Q
What causes nivation hollows?
A
- Form where snow gathers in sheltered areas
- Freeze-thaw weathering weakens the rock underneath
- Meltwater takes the material area leaving a hollow/depression
- Can be the start of a corrie
- More common on N facing slopes which get less direct sunlight
11
Q
What causes blockfields?
A
- Expanses of loose rocks
- Formed from frost shattering of bedrock due to repeated freeze-thaw action
- Angular rocks and no transportation has taken place
- Located on flat land
12
Q
What causes tors, scree slopes and rock glaciers?
A
- A tor is an exposed rock mass of jointed and broken blocks usually at the top of a hill
- Loose rocks from freeze-thaw are moved by gravity to the base of hills and form large scree slopes
-Rock glaciers occur when there are large areas of angular rocks, ice, snow, mud and water that move down a slope very slowly due to gravity
13
Q
What causes head deposits?
A
- Head deposits are the fragmented weathered material deposited often in the furthest parts of valley bottoms
14
Q
What causes protalus ramparts?
A
- These are areas of rock that have moved down the hillside
- An area of snow acts as a buffer to stop further movement
- Snow then melts to leave long small wall
15
Q
What causes solifluction lobes and terraces?
A
- In summer, the active layer melts to form a saturated layer that slowly moves down a slope, creating lobes
- Lobes only form on slopes with a gradient of 10-20 degrees
- When the gradient changes and flattens out, the material flow slows and is deposited in a tongue shape
- Terraces are when the soil slumps under vegetation or on more gentle slopes
