Drumlins. DRUMLIN An oval-shaped hill, largely composed of glacial drift, formed beneath a glacier or ice sheet and aligned in the direction of ice flow. Their formation remains controversial (see below) but in spite of this they are extremely useful for reconstructing former ice sheets.
They form near the margin of glacial systems, and within zones of fast flow deep within ice sheets, and are commonly found with other major glacially-formed features (including tunnel valleys, eskers, scours, and exposed bedrock erosion).
The Fonthill Kame in southern Ontario is in a densely populated area. Examples can also be found in Wisconsin and at the Sims Corner Eskers and Kames National Natural Landscape in Washington. They are also located in Mendon Ponds Park, SE of Rochester, NY.
An erratic is a piece of rock that has been eroded and transported by a glacier to a different area; it is left behind when the ice melts. Glacial erratics give us information about the direction of ice movement and distances of transport.
A crevasse is a deep crack, or fracture, found in an ice sheet or glacier, as opposed to a crevice that forms in rock. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement.
Unlike river deposits that are often sorted into different sizes, all glacial deposits are angular and mixed up (unsorted). Drumlins are elongated hills of glacial deposits. They can be 1 km long and 500 metres wide, often occurring in groups.
Most eskers are argued to have formed within ice-walled tunnels by streams which flowed within and under glaciers. They tended to form around the time of the glacial maximum when the glacier was slow and sluggish. After the retaining ice walls melted away, stream deposits remained as long winding ridges.
Each drumlin is a small hill, tending towards an egg shape, with its steepest slopes and summit at the up-ice end. Drumlins rarely occur singly, however, and are found in groups or swarms, with the tapered end of each hill pointing in the direction of glacier flow.
Drumlins are generally found in broad lowland regions, with their long axes roughly parallel to the path of glacial flow. Although they come in a variety of shapes, the glacier side is always high and steep, while the lee side is smooth and tapers gently in the direction of ice movement.
Arête, (French: “ridge”), in geology, a sharp-crested serrate ridge separating the heads of opposing valleys (cirques) that formerly were occupied by Alpine glaciers. It has steep sides formed by the collapse of unsupported rock, undercut by continual freezing and thawing (glacial sapping; see cirque).
A lateral moraine forms along the sides of a glacier. As the glacier scrapes along, it tears off rock and soil from both sides of its path. This material is deposited as lateral moraine at the top of the glacier's edges. Lateral moraines are usually found in matching ridges on either side of the glacier.
An outwash plain, also called a sandur (plural: sandurs), sandr or sandar, is a plain formed of glacial sediments deposited by meltwater outwash at the terminus of a glacier. As it flows, the glacier grinds the underlying rock surface and carries the debris along.
A terminal moraine, also called end moraine, is a type of moraine that forms at the snout (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, and has been pushed by the front edge of the ice, is driven no further and instead is dumped in a heap.
Definition: a tadpole-shaped landform developed by glacial erosion of rocks on unequal resistance. The crags are cliffs developed in near-cylindrical masses of strong rock. The tail is formed in softer rocks sheltered from erosion in its lee.
Frost also sorts the sediments in the ground. Once the mantle has been weathered, finer particles tend to migrate away from the freezing front, and larger particles migrate through the action of gravity. Patterned ground forms mostly within the active layer of permafrost.
A ribbon lake is a long and narrow, finger-shaped lake, usually found in a glacial trough. Its formation begins when a glacier moves over an area containing alternate bands of hard and soft bedrock.
U-shaped valleys, trough valleys or glacial troughs, are formed by the process of glaciation. They are characteristic of mountain glaciation in particular. Glaciated valleys are formed when a glacier travels across and down a slope, carving the valley by the action of scouring.
Explain the formation of a Corrie (Cirque). You may use diagrams to illustrate your answer. a) snow collects in hollows, b) snow compacts to ice, c) ice moves under gravity, lubricated by meltwater, d) ice rotates to lip, e) abrasion deepens corrie, f) plucking steepens back and sides, g) corrie lochan may fill hollow.
Till or glacial till is unsorted glacial sediment. Till is derived from the erosion and entrainment of material by the moving ice of a glacier. It is deposited some distance down-ice to form terminal, lateral, medial and ground moraines.
Some glacier caves are formed by geothermal heat from volcanic vents or hotsprings beneath the ice. An extreme example is the Kverkfjöll glacier cave in the Vatnajökull glacier in Iceland, measured in the 1980s at 2.8 kilometres (1.7 mi) long with a vertical range of 525 metres (1,722 ft).
Updated: 26th October 2019