Unit 5 glaciation periglacial landforms

Question 1

What does periglacial mean?

Answer 1

periglacial describes a landscape that undergoes seasonal freezing and thawing, typically on the fringes of past and present glaciated regions.

Question 2

What is permafrost?

Answer 2

Ground that remains frozen for 2 consecutive years - periglacial environments often contain permafrost.

Question 3

What percentage of the earths landscape contains permafrost?

Answer 3

25% - exposed land surface in the northern hemisphere

Question 4

What does the mean annual ground temperature need to be for permafrost to occur?

Answer 4

between -6 and -4 degrees

Question 5

What is the active layer?

Answer 5

The surface layer of grounds that thaws in summer and refreezes in winter.

Question 6

How deep can permafrost be?

Answer 6

Up to 1500m

Question 7

What’s the distribution of permafrost?

Answer 7

There is more permafrost in high altitude areas such as the poles and latitude areas such as the Rockies, alps and the Himalayas. It surrounds artic regions. Examples include Scandinavia, China, Alaska, Russia, Canada and coastal Greenland areas.

Question 8

What is continuous permafrost?

Answer 8

It forms in the coldest areas of the world where average annual temperatures are below -6 degrees and can extend down hundreds of meters.

Question 9

What is discontinuous permafrost?

Answer 9

It forms in the coldest areas of the world where average annual temperatures are below -6 degrees and can extend down hundreds of meters but it is more fragmented and often thinner.

Question 10

What is sporadic permafrost?

Answer 10

It occurs at the margins of periglacial environments and is highly fragmented and only a few meters thick.

Question 11

What is Talik?

Answer 11

Unfrozen ground between permafrost.

Question 12

How is the melting of permafrost leading to climate change?

Answer 12

As permafrost melts, dead, organic matter is unfrozen meaning it decays, this releases methane which is a pottant greenhouse gas contributing to climate change. However climate change causes the permafrost to melt in the first place so it’s a vicious circle - a negative feedback loop.

Question 13

Where does pore ice develop? - GROUND ICE LANDFORMS

Answer 13

In pore spaces between soil/sediment particles where liquid water can accumulate and freeze

Question 14

What is needle ice? - GROUND ICE FORMATION

Answer 14

Needle ice consists of narrow ice slivers that are up to several centimetres long. They normally form in moist soils when temperatures drop below freezing overnight.

Question 15

What are ice lenses? - GROUND ICE LANDFORMS

Answer 15

Ice lenses are bodies of ice formed when moisture, mixed soil or rock, accumulates in a localised zone.

Question 16

What are ice wedges? - GROUND ICE LANDFORM

Answer 16

Ice wedges are downward narrowing lens of ice that can grow up to 3 meters wide at the surface and extend below the ground surface up to 10 meters. These lens of ground-ice can lead to the formation of ice wedge polygons (pattern)

Question 17

How do ice wedges form?

Answer 17

1st winter- the temperature is around 10 degrees, the ground contacts due to cold temp, creating a fracture just over 1m in the ground. Rainwater fill the fracture/crack which freezes due to the cold temp - when water freezes it expands by 9 % enlarging the crack.
1st summer - The temperature increases so the ice in the enlarged crack melts.
2nd winter- the water refreezes, enlarging the crack again as when water freezes it expands by 9%.
100th winter - an ice wedge is formed through this repeating process. Ice wedge is now over 2m.

Question 18

What is patterned ground?

Answer 18

The surface of periglacial areas is often characterized by the presence of stones arranged in symmetrical, geometric shapes. These features collectively known as patterned ground. Shapes can include stripes, circles and polygons.

Question 19

What is frost heave?

Answer 19

The upward dislocation of soil and rocks by the freezing and expansion of soil water.

Question 20

What happens during frost heave?

Answer 20

1. Freezing progresses down from surface accompained by upward expansion, lifts stone by first freezing onto upper surface.
   2.Freezing front progresses down space created below stone as it is lifted.
   3.Ice crystals grow into space and push up stone.
   4.Thawing progresses down from surface, contraction and lowering of surface level, but stone still supported by ice crystals.
2. Thawed sediment collapses around stone supporting it.
3. Stone held in thawed sediment while ice crystals melt and space filled by collapsing sediment.

Question 21

What are pingos?

Answer 21

Pingos are circular ice-cored hills with a height between 3 to 50 meters and a diameter between 30 to 300 meters. The ice lens at the core of pingos develops because of artesian groundwater flow (open system) and cytostatic pressure (closed system)

Question 22

What happens in an open system pingo formation?

Answer 22

Liquid groundwater is confined below the impermeable permafrost. If it finds a weakness in the overlying permafrost it will rise into the crack due to artesian pressure. As the water rises through the permafrost it begins to cool and in some cases freeze. If the rising water reaches the active layer in summer it may form a spring. During winter months or prolonged periods of cold temps, the rising water will freeze before reaching the surface forming an ice lense. As more groundwater continues to rise from below the permafrost, it feeds the ice lens, causing it to grow. As it grows, the lense displaces the overlying sediment forming a domed ice-core hill known as an open-system pingo.

Question 23

What happens in a closed system pingo formation?

Answer 23

In cold periglacial enviroments, permafrost will dominate. However, in summer months lakes will form within the active surface layer. As winter approaches, the lake will begin to freeze from the top down. The unfrozen lake water and lake sediment beneath the ice acts as a insulator for the underlying ground. This prevents the ground from freezing and results in Talik. During prolonged periods of cold, the permafrost will advance and encroach (invade) on the overlying Talik. Consequently, liquid water contained within the Talik will freeze, forming an ice lense. As this ice lense grows it will exert cytostatic pressure and rise upwards displacing the overlying lake. The sediment that was once at the bottom of the lake now covers the raised ice lense. The resultant ice-core hill is known as a closed system pingo.

Question 24

What is a thermokarst landscape?

Answer 24

Thermokast is a land surface characterised by irregular surfaces of marshy hollows and depressions formed as permafrost thaws due to a warming climate.

Question 25

What happens to the active layer as permafrost thaws?

Answer 25

As permafrost thaws the wet saturated active layer soil lows under the influence of gravity a process known as solifluction.

Question 26

What is solifluction?

Answer 26

Mass movement results in downward slope of wet saturated soil - occurs during thawing of active layer.

Question 27

Thermokarst areas contain thermokarst lakes, that form in a depression by meltwater from thawing permafrost. What’s one mechanism which leads to these lakes forming?

Answer 27

Pingo collapse

Question 28

What happens during a pingo collapse?

Answer 28

During summer, the active layer begins to thaw and become saturated with water. This makes the soil begin to flow in a process known as solifluction.
Ice lense begins to melt and forms a depression in the pingo, decreasing viscosity, increasing solifluction. Sediment collapses inwards on the melted ice lense forming a larger depression.
As the permafrost layer is impermeable, meltwater cannot percolate into the layer. This causes the water to pool in the depression, forming a thermokarst lake.

Question 29

What’s an example of melting permafrost and solifluction on a slope?

Answer 29

Northern Alaska

Question 30

What proportion of Russia has permafrost?

Answer 30

50%

Question 31

What problems is melting permafrost causing for towns such as Batagay in Russia?

Answer 31

Infrastructure collapsing as firm ground is melted.

Question 32

What caused the Batagay mega slump crater to develop?

Answer 32

Permafrost melting rapidly on a wide scale - 2x as fast. Active layer increasing in depth.

Question 33

Why is a largescale melting of permafrost a concern?

Answer 33

It releases tonnes of methane gas into the atmosphere which is 25x as potent as CO2.

Question 34

What is mass movement?

Answer 34

The movemnt of material down a slope under the force of gravity such as soil, sand, regolith rock.

Question 35

Where rock outcrops in periglacial environment’s, large quantities of angular fractured rock develop due to repeated cycles of what?

Answer 35

Freeze thaw weathering - temp fluctuating around zero repeatedly.

Question 36

Explain the formation of a nivation hollow due to freeze thaw/frost weathering.

Answer 36

• north facing
• plucking - cracks in the rock surface fill with moisture - freeze and expand by 9% freeze thaw breaks off and is plucked by ice.
• ice movement down slope
• abrasion of sediment - sediment helped move by meltwater and solifluction - meltwater.

Question 37

What is a blockfield?

Answer 37

A blockfield is a surface covered by large, angular rocks. They are a product of freeze thaw weathering on flat plateau surfaces. An example can be found in Snowdonia, on the Glyder Plateau around the pyrimidal peak of Glyder Fawr in Nant Francan valley.

Question 38

What is a scree slope?

Answer 38

A scree slope is an accumulation of freeze-thaw weathered rock fragments at the base of a cliff. - mass movement and more gradual angle - reduction. Lake district.

Question 39

What is protalus Ramparts?

Answer 39

A protalus rampart is a ramp shaped mound of scree that forms in a similar way to a scree slope. It differs in formation from a scree slope as it involves ice or snow being present on a valley slope. Scree accumulates at the base of the snow/ice and melted sediment slumps and marks edge of where ice/snow was. - Cwm Idwal

Question 40

What is a solifluction lobe?

Answer 40

Solifluction can take place on slopes with a gradient as gentle as just 1 degrees but is more pronounced on steeper slopes of between 10 and 20 degrees. Solifluction is slow with movement rarley exceeding 10cm per year, usually being between 0.5 and 5cm per year. In periglacial conditions during summer, the surface active layer thaws whilst the underlying layer remains frozen and impermeable. The surface layer becomes waterlogged and active as a result. Solifluction sheets and lobes can be formed.

Question 41

Mass movement can also occur in periglacial areas due to repeated freezing and thawing of the active layer resulting in a process called what?.

Answer 41

Soil creep

Question 42

Over a large area the frost heaving process - soil expansion - can produce what?

Answer 42

Terracettes

Question 43

In summer the permafrost beneath the thawed surface remains frozen where very little or no infiltration or percolation can occur which makes the ground what?

Answer 43

Impermeable

Question 44

Explain the formation of a dry valley?

Answer 44

Dry valleys are relict periglacial landforms showing evidence that the landscape previously was influenced by flowing meltwater. Dry valleys develop in regions of permeable rock, such as chalk or limestone, which would usually allow water to infiltrate and percolate the ground. When permafrost is presnt in such regions the frozen ground prevents percolation meaning that meltwater pools on and runs over the ground surface. As the ice masses retreat and warmer conditions develop, high levels of river run off occur eroding and deepening river valleys. Once warm interglacial conditions have developed and the permafrost has melted, water from the surface will infiltrate and percolate, reducing surface runoff and leaving the river valley dry.

Question 45

What is loess deposits?

Answer 45

Loess pronounced lers is fine rock debris snad silt and clay, transported and deposited by glacial winds. Loess is derived from glacial abrasion and transported by meltwater rivers during spring and summer months onto sandurs. During the autumn and winter, when melting is reduced the flow of these rivers is greatly reduced. As a consequence, large parts of the sandur will dry out and are exposed to the strong katabatic winds off the ice. By the process of deflation winds will pick up and transport the loess many miles, eventually depositing it as thick sediment, creating a flat plateau landscape. Loess deposits can be found across extensive regions of Europe, particularly in regions such as present day Ukraine, where good quality agricultural soils are found today. They are also found in Romania.