Glaciation key terms Flashcards
Meltwater (fluvioglacial)
carries material and deposits it as layered and stratified.
Erosion transportation (fluvioglacial)
meltwater channels cut through glaciers which adds to the volume of the moving water. It carries fine, light material along with minerals in the solution as well.
Deposition (fluvioglacial)
the material is always stratified and sorted. It is also smooth and round due to attrition.
Meltwater channels (fluvioglacial)
they form when meltwater from glaciers follows a pre-existing river channel.
Kames (fluvioglacial)
rocks and sediment accumulate on top of the glacier but when the weight is too much, a meltwater channel is formed which flows through the glacier carrying the accumulated material. Deglaciation of the crevasses results in the sediment being dumped as a mound when it reaches the valley bed.
e.g., the Carstairs Kames in Scotland
Eskers (fluvioglacial)
they form from a subglacial meltwater channel flowing at the bottom of a glacier. Sediment is then deposited within the channel at the bottom of the glacier, forming the long, sinuous ridge.
Outwash plains (fluvioglacial)
formed at the snout of the glacier as meltwater is released. Many of the meltwater channels join to form an outwash plain, a network of numerous meltwater channels.
Permafrost (periglacial)
frozen layer on or under the Earth’s surface consisting of soil, granite and sand usually bound by ice.
11% of the Earth’s surface is underlain by permafrost.
Active layer (periglacial)
the upper part of the permafrost soil which thaws every summer and then freezes again in the autumn - releases GHGs including CO2 and methane.
Mass movement (periglacial)
the downslope movement of soil, debris and material under the influence of gravity.
Solfluction and gelifluction (relating to mass movement) (periglacial)
- The gradual movement of wet soil or other material down a slope, especially where the frozen soil/permafrost acts as a barrier to percolation - this results in the top soil becoming oversaturated resulting in the flowage of water-saturated soil down a steep slope. The slow downslope flow of saturated soil often forms lobes of movement and terracettes.
- a periglacial category of solifluction where the downslope sliding movement of seasonally thawed and saturated soil material is facilitated by an impermeable layer of permafrost beneath.
Patterned ground (periglacial)
distinct and often symmetrical natural pattern of geometrical shapes formed by the deformation of ground material - related to frost heaving, the expansion that occurs when wet, fine-grained, and porous soils freeze.
Frost heave - the upward or outward movement of the ground surface (or objects on, or in, ground) caused by formation of ice in soil
Ice wedges (periglacial)
they are gaps in the permafrost made of ice that expands through freeze thaw - less than 10m vertically generally.
Pingos (periglacial)
Open-system pingo:
Formed in discontinuous permafrost, the groundwater in the soil in forced up due to the gaps in the permafrost. The ice then freezes together to form a conical core of ice which pushes the ground surface upwards forming a dome shaped hill up to 500m in diameter and 70m in height.
Closed-system pingo:
Formed in continuous permafrost where there is a lake at the surface which insulates the ground. As the lake dries up and forms a conical core of ice, the permafrost around it advances to the unfrozen ground where the conical core of ice lies. The core of ice forces the ground surface upwards forming a dome shaped hill up to 500m in diameter and 70m in height.
Blockfields (periglacial)
an area where the surface is covered by boulders or block-sized angular rocks, formed through regular freeze thaw activity, fragmenting and breaking up exposed rock.
Solifluction lobes (periglacial)
sheets of material that move when the saturated active layer of soil is thawed, usually during the summer months - a result of freeze thaw cycling in the active layer and solifluction.
Terracettes (periglacial)
a series of small ridges in the ground under vegetation, based on a usually small piece of land on a hillside - frost creep is integral to the formation process, as saturated soil expands and then contracts as it dries, prompting the downhill sliding of material.
Thermokarst (periglacial)
formed in a small depression in the land, filled with melted water from the thawed permafrost and ice wedges.
Corrie (erosional and depositional landforms of glaciated landscapes)
a deep hollow in a mountainside left behind by a glacier. It forms due to a build-up of snow that turns into glacial ice, steepening the back wall through plucking and abrasion. Material is constantly added by freeze thaw (adding moraine) as rotational slip ‘over-deepens the corrie, resulting in a rock lip forming at the head of the corrie. The glacier may spill over the rock lip and flow downslope. The corrie is left behind with whatever remains of the glacial ice, often leaving a tarn (or lake) in the corrie.
Arete (erosional and depositional landforms of glaciated landscapes)
a knife-edge ridge formed when two corries form back-to-back. The ridge becomes narrower as the corries erode each of the back walls to become steeper.
Glacial trough (erosional and depositional landforms of glaciated landscapes)
also known as a U-shaped valley, it is a flat-bottomed, steep-sided valley formed by glacial movement. The glacier erodes the V-shaped valley over an extensive period of time to become a U-shaped valley.
Hanging valley (erosional and depositional landforms of glaciated landscapes)
a smaller valley which is located high above the main U- shaped valley, formed due to a tributary glacier.
Roches moutonnees (erosional and depositional landforms of glaciated landscapes)
resistant crag of rock shaped by a glacier to have one smooth surface (stoss slope) and one rough, jagged surface (lee end).
Drumlin (erosional and depositional landforms of glaciated landscapes)
smooth, elongated, egg-shaped mounds on a U-shaped valley floor, parallel to the direction of ice movement. They can be over 1km in length, 300m in width and 40m in height. The smooth, long side is called the lee slope and the short craggy side is called the stoss end. The glacier makes contact with the stoss end first and then moves over the lee slope, smoothing the material.
Terminal moraine
at the end.
Medial moraine
in the middle.
Lateral moraine
at the side.
Truncated spurs (erosional and depositional landforms of glaciated landscapes)
When a valley fills with a glacier, any land which is in the way of the moving glacier will be eroded away. Truncated spurs have steep sides which show this erosion.
Till plains (fluvioglacial)
when a large section of ice detaches from the main body of the glacier and melts, the suspended debris will be deposited and form a large plain of unsorted till.
Basal sliding (fluvioglacial)
act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant - predominantly in warm-based glaciers.
Kettle hole (fluvioglacial)
forms when buried ice melts and overlying sediment collapses - ice wedges help form.
