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Current global period, where only one tenth of the landmasses are covered in ice.
A series of advances and retreats of the icecaps. Last one (Pleistocene) lasted from 1.7 million years to 10,000 years BP. Most of Britain (far south as Severn Thames line) and Northern Europe were glaciated as well as the high mountain regions of the south of the continent. Some places it was over a thousand meters thick.
Areas of permanent snow where glaciers form. They occur at high altitudes, latitudes nearer the poles, and often on the colder, north-facing slopes.
As more snow falls, the pressure makes the earlier flakes melt. Repeated melting and refreezing forms granules called firn or neve. Further compression forms larger crystals of glacial ice. It can take 30-40 years for snow to form dense glacial ice, and start moving downslope.
The difference between a glaciers accumulation and ablation (sublimation and melting). A glacier with a sustained negative balance (loss > gain) is out of equilibrium and will retreat, while one with a sustained positive balance (gain > loss) is out of equilibrium and will advance.
Different parts of a glacier move at different speeds due to different degrees of friction. The top part is brittle and cracks as it moves over obstacles to form crevasses. They vary in speed of movement, from 3 meters to 300 meters per year. Flow due to internal deformation or basal sliding.
A large mass of moving ice formed when winter snow accumulation exceeds summer melting. They carve out u-shaped valleys and can be Alpine or Continental.
Alpine (valley) glaciers
Glaciers that form in high mountains. They are the fastest moving glaciers and are made when snow accumulates and is compressed and recrystallized into ice. Valley walls restrict the glacier's flow. Start in cirques and extend down-valley.
(ice sheets) Glaciers that spread over a wide geographic area and often extend out over the ocean.
Irregular, hilly, unsorted sediments (till) deposited for at the end of an advancing glacier.
An accumulation of till at the terminus or snout of a glacier. Tend to form ridges, generally stretch across the valley (from one side to the other side), and may curve slightly downhill in the center due to the faster ice flow in the center of the glacier. Two different types are terminal moraines and recessional moraines. The terminal moraine marks the farthest extent of glacial advance and thus is located at the lowest elevation. Recessional moraines form when glaciers are temporarily stationary during periods of overall glacial retreat and thus are located at higher elevations than the terminal moraine.
Till deposited directly beneath a glacier, between the glacial ice and underlying bedrock. Located between end moraines. Gently rolling hills and plains.
Accumulation of glacial sediments that form on side of a glacier. Freeze-thaw weathering of alpine valley walls results in rock debris falling on the surface of valley glaciers. This rock debris constitutes lateral moraines, thus lateral moraines form ridges of rock debris on top of existing alpine glaciers parallel to the valley walls.
Moraines that form when 2 or more lateral moraines merge due to the convergence of intersecting glaciers. The ridge is formed on top of and in the middle of an existing glacier. Can be created downstream from rock outcrops extending up through the surface of alpine glaciers.
A long, oval (tear shaped) hill that is usually found in groups called "drumlin fields." Deposited and shaped by an advancing glacial ice composed of poorly sorted glacial till.
A long winding ridge formed when sand and gravel fill meltwater tunnels beneath a glacier. Composed of stratified, sorted glacial deposits since it was deposited by water, not ice.
A small cone-shaped hill of stratified sand and gravel formed at a glacial front by meltwater carrying sediment off the glacier's surface.
A bowl-like hollow found in deposits of glacial outwash, formed when a large block of ice left behind by a glacier melted (kettle lake when filled with water).
Glaciers scratch and polish underlying bedrock, leaving lines (grooves) that indicate the direction in which the glacier was moving. Happens because of debris embedded in base of glacier.
(cirque) Snow collects in hollows (especially on the north and east facing slopes), turns to glacial ice, and moves downwards under the force of gravity/ meltwater. The ice rotates to lip, abrasion deepens corrie, plucking steepens back and sides, and circular corrie lochan (tarn) may fill hollow with water. It is deep and rounded (armchair shaped), with a steep head or back wall. Low spot is a col.
A narrow, sharp-edged (knife shaped) ridge with forms the side walls of cirques and separates different glacial valleys.
Sharp, pointed hilltop. Three or more corries form around a peak, where their sidewalls meet they form an arete, and where the aretes meet they form the horn.
Long, narrow lake occupying an area of the trough floor which has been over deepened (soft rock basin) and filled with melt water. Can also be made when glacial deposits build a natural barrier across a glacial trough. Ex: English Lake.
Vertical erosion in the main valley is far greater than in the smaller tributary glaciers. Valleys are not the same depth and after the glacier has retreated, rivers flowing down the tributary join the main through waterfalls. At the base, alluvial fans are sometimes found as a result of deposition (silt).
U-shaped. Steep sided valley with flat floors, formed when glacier abrades the sides and floor of a V- shaped river valley to deepen, widen, and straighten it. Any later rivers are called 'misfit streams' because they are far to small to have cut the valley.
Steep, rocky section of the side of a trough where the tips of pre-glacier interlocking spurs have been removed by glacial erosion.
Resistant rock outcrop with gentle sloping smooth up-valley side, and jagged lee-ward side.
(frost shattering). Water in cracks in the rock freezes and expands. After many cycles of freezing and thawing lumps of rock are broken off. Sharp, angular pieces of rock formed are called scree. Weathering.
When glaciers physically weather underlying bedrock. Glacier ice melts due to friction as it goes over a rock mass, instantly refreezes into cracks in rocks due to overlying pressure of ice, and when the glacier moves it pulls out chunks, transports them, and deposits them. Leaves a jagged surface. Erosion.
Rock debris embedded in the ice grind away the bedrock under the glacier. The rock is scratched, polished, smoothed, and eventually worn away by the scoring action. The pieces of rock also become smaller. Erosion.
When a glaciated valley is submerged or drowned by a rise in sea level. Ex: sea lochs of western Scotland.
A chain of lakes in a glacial valley. They may form when end moraines, particularly a series of recessional moraines, dam meltwater flowing out from a glacier, or due to differential glacial erosion of more- and less-resistant bedrock layers. The less-resistant bedrock layers become low spots where water can accumulate while the more-resistant bedrock layers form natural dams that allow significant amounts of water to accumulate in the low spot.
A small glacier that does not extend beyond the edge of the cirque it is located in. Could also be the part of a valley glacier that lies in the cirque at the head of the glacier.
A crack in the upper 30 meters (100 feet) of a glacier. Ice up here tends to be brittle and as the glacier flows, cracks develop. Rarely extend much deeper than 30 meters because below this depth the ice is too plastic and any surficial cracks close.
The ice equivalent of a waterfall. As ice flows over a drop-off, the glacier breaks apart often forming transverse crevasses and then reforms at the base of the drop-off.
Alternating bands of light and dark ice that form a series of ridges and swales at the base of some ice falls. The arcuate bands bend down-glacier due to the faster flow in the center of the glacier than along the sides of the valley walls. The dark bands represent ice that moved over the fall during the summer season when more melting occurs and form swales. The light bands represent ice that moved over the fall during the winter season when little or no melting occurs and form ridges.
Nonglacial processes and landforms associated with cold climates, particularly with various aspects of frozen ground. "Almost Glacial."
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