Unit 5 Glaciated Landscapes

Periglacial landscapes

What is periglacial?

a landscape that undergoes summer melting and winter freezing, typically on the fringes of past and present glaciated regions

What is the active layer?

top layer of permafrost that thaws during the summer months.

What is the distribution of permafrost?

located at:

• higher latitudes

• higher altitudes

• surrounds nortj pole

What is sporadic permafrost?

occurs at the margins of periglacial environments and is highly fragmented and only a few metres thick

What is continuous permafrost?

forms in the coldest areas of the world where average annual temps are -6 degrees and can extend down hundreds of metres.

What is discontinuous permafrost?

like permafrost, just more fragmented and thinner

what impact does the permafrost have on climate changes?

1. climate change is causing more permafrost to melt

2. permafrost melts, dead organic matter decays

3. dead organic matter decay releases methane

4. methane is a potent greenhouse gas, contributing to climate change

Ground Ice Landforms: What is pore ice?

• develops in spaces between soil/sediment particles where liquid water can accumulate and freeze

What is needle ice?

• consists of narrow ice slivers that are up to several cm long

• normally form in moist soils when temperatures drop below freezing overnight

What is an ice lense?

bodies of ice formed when moisture, mixed within soil or rock, accumulates in a localised zone

How do ice wedges and ice wedge polygons form?

1st Winter

• contraction of the ground causes it to crack open as temps are below -20 degrees. Crack is usually a few mm wide.

1st Summer

• the ice from the active layer thaws and fills the crack.

2nd Winter:

• temps fall again and the water will refreeze expanding by 9%. This expansion puts pressure on the crack causing it to widen

• ice expansion also causes the spil layers adjacent to the developing ice wedge to be pushed upwards creating a slight bulge.

this process repeats each year, which causes the ice wedge to grow in size and depth. each winter new cracks form and old ones widen. Each summer, more and more water seeps into the crack and refreezing of this causes the surface mound to get bigger.

when viewed from above, these form patterns on the ground surface known as ice wedge polygons

How do stones move to the surface in periglacial environments and form stone sorted polygons?

1. the ground will freeze in periglacial environments and freeze downwards.

2. stones have are good conductors of heat and will therefore cool down quicker than the surrounding soil

3. consequently, when temps drop and the expanding ground begins to lift the stones, small amounts of moisture contained beneath the stone will freeze, expanding by 9%.

4. due to cryostatic pressure, the stones are raised up. this process is known as frost heave and will result in the doming of the overlying ground, forming a mound.

5. when the ice thaws, the ice contained beneath the snow will melt and wet soil will slump in the gap beneath the stone which will prevent it from dropping down back into place.

6. this process repeats until the stone is raised high enough to break through the surface of the ground.

7. once one the surface the stones will roll down the mound to the base of the mound, forming distinct stone sorted polygons.

8. if >6 degrees, stripes will form and if less, then stone polygons or circles will form.

What are pingos?

circular ice-cored hills with a height between 3-70m and a diameter of 30-300m

ice lense at the core of pingos will develop because of two reasons:

1. artesian groundwater flow(open system)

2. cryostatic pressure (closed system)

how does an open system pingo form?

1. liquid groundwater is confined below permafrost

2. as water rises through the permafrost it begins to cool and in some cases refreeze. If rising water reaches active layer in summer it may form a spring

3. during the winter months, the rising water will freeze before reaching the surface forming an ice lense

4. as more groundwater continues to rise, it will feed the ice lense causing it to grow bigger.

5. as it grows it displaces the overlying sediment formed a domed ice core hill known as an open system pingo.

how does a closed system pingo form?

1. in cold periglacial environments, permafrost will dominate however, in summer months, lakes will form within the active layer as winter approaches, the lake will begin to freeze from the top down

2. unfrozen lake water and sediment beneath the ice acts as an insulator for the underlying ground. this prevents the ground from freezing and results in talik which is unfrozen sediment.

3. during prolonged cold months, permafrost will advance and invade on the overlying talik. due to this water contained within the talik will freeze forming an ice lense.

4. as the ice lense grows, it exerts CRYOSTATIC PRESSURE and rises upwards, displacing the overlying lake. the sediment 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.

What is a thermokarst landscape?

characterised by irregular surfaces of marshy hollows and depressions formed as permafrost thaws due to warming climate.

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

What do thermokarst areas often contain?

often contain thermokarst lakes that form in depression by meltwater from thawing permafrost.

e.g. BAGATAY, Russia

What mechanism leads to thermokart landscapes?

pingo collapse

What is the process of thermokarst landscapes?

1. ice lense is melting and beginning of a depression sarts to form. water from ice saturates soil so it becomes more runny and solifluction increases. (water cannot percolate downwards as permafrost is impermeable so water is kept in soil)

2. ice lense has melted and depression has started to form= sediment starts to collapse

3. ice has completely melted leading to depression filling with water forming a thermokarst landscape

periglacial action of water: dry valleys formation process?

these landscapes show evidence that the landscape previously was influenced by flowing water

1. develops in regions of permeable rock e.g. chalk, limestone. These rocks will usually allow water to infiltrate and percolate the ground

2. when permafrost in present in such regions, no percolation can occur and meltwater pools on surface and runs over ground surface

3. as ice masses retreat and warm conditions develop, high levels of river run off will occur eroding and deepning river valleys

4. once warm conditions fully set in, and the permafrost has melted, water from the surface will infiltrate and percolate reducing run off leaving the valley dry.

periglacial action of wind- loess deposits process?

loess is fine rock debris transported and deposited by glacial winds

1. derived from glacial abrasion and transported by meltwater rivers during spring and summer months onto sandurs

2. during the autumn and winter, when melting is reduced, the flow of rivers is greatly reduced

3. as a consequence, large parts of the sandur will dry out and are exposed to strong kabbatic winds(cool, high density winds) off the ice

4. fine rock particles picked up and transported by wind in a process called deflation

5. by the process of deflation, winds will pick up and transport the loess many miles eventually deposting it as a thick sediment creating a flat plateau landscape

FROST SHATTERING/FREEZE THAW WEATHERING: what is freeze thaw weathering?

where rockis subjected to repeated cycles of freezing and thawing. Water infiltrates cracks in the rock; when it freezes, it expands, causing the rock to fracture and gradually break apart.

How is frost shattering included in the process of nivation hollows?

frost shattering provides a supply of loose material.

rock debris removed by meltwater streams or solifluction in summer (mass movement)

how are blockfields formed?

• surface covered by large angular rocks

• product of freeze thaw weathering on flat plateau surfaces

EXAMPLE: Snowdownia, on the Gylder Plateau

Frost shattering/freeze thaw weathering process: how do scree slopes form?

• accumulation of freeze thaw weathered rock fragments. At slope one, before weathering occurs, slopes will have steep gradients

  At slope TWO:

• reduction of slope angle, overtime the angle of slope is reduced as material from the top accumulates at the bottom resulting in a more gradual incline.

AT Slope THREE:

• debris transported through mass movement

• the profile of the slope will develop towards a more horizontal surface

What is mass movement?

process by which sediment move downslope as a solid, continouous/discontinuous mass largely under the force of gravity.

frost shattering and mass movement: how do protalus ramparts form?

It involves ice or snow being present on a valley slope where frost shattering occurs, creating a build-up of debris that tumbles down.

material builds up at the base of the cliff and when the ice melts, an accumulation of scree is left forming a protalus rampart

EXAMPLE: Cwm Idwal

mass movement: solifluction lobes

saturated soil that flows under the influence of gravity:

• solifluction is a type of mass movement. can take place on gentle slopes but is more effective on steeper slopes

in periglacial conditions during summer, the active layer thaws whilst the underlying ground remains frozen due to permafrost. the surface layer becomes waterlogged and active as a result. solifluction sheets and lobes can be formed which flow under the force of gravity.

mass movement: frost creep and terracettes formation?

mass movement can also occur in periglacial environments due to repeated freezing and thawing of the active layer resulting in a process called soil creep

over a large area the frost heaving process (expansion of soil) can produce feautures called terracettes.

1. soil particle in the active layer thaws.

2. when active layer freezes it expands outwards parallel to the surface.

3. when the active layer THAWS, soil particle drops vertically downwards, resulting in downslope movement of particles