GL17 Landforms of glacial deposition Flashcards
Why might a glacier deposit material?
Deposition takes place when there is a drop in velocity, a rise in ablation, a rise in pressure (may lead to more debris lodged into the bedrock) and rock carrying capacity. When the glacier mass balance reaches equilibrium and the glacier becomes static and deposition takes place.
What is a terminal moraine?
A terminal moraine is formed when a glacier deposits material at the end of its snout. It is a ridge of till extending across a glacial trough, marking the position of the maximum advance of the ice. Terminal moraines form when the glacier mass balance reaches equilibrium and the glacier becomes static, and their size depends on the length of time the glacier remains in equilibrium.
What is a lateral moraine?
A lateral moraine is formed from material weathered from the exposed valley sides and deposited along the edges of a glacial valley as the glacier melts or retreats. It is a ridge of till running along the edge of a glacial valley.
What is a recessional moraine?
A recessional moraine is formed during a temporary still-stand in retreat, further up the valley than the terminal moraine. They are a series of ridges running transversely across glacial troughs and are broadly parallel to each other and to the terminal moraine. Their height seldom exceeds 100m as these temporary pauses are rarely prolonged.
What is an erratic?
An erratic is an individual piece of rock, varying in size from a small pebble to a large boulder, that is composed of a different geology from that of the area in which they have been deposited. Erratics were eroded or added to the supraglacial debris and transported and deposited into an area of differing rock type.
What are till sheets?
Till sheets are large expanses of thick unsorted glacial till deposited by an ice sheet as it retreats. They are formed from the deposition of material carried by the glacier, and their composition is determined by the area over which the ice sheet flowed. Analysing them can help to reconstruct past ice sheets.
What is a drumlin?
A drumlin is a mound of glacial debris that has been streamlined into an elongated hill, often pear-shaped and aligned in the direction of ice flow. The formation of drumlins is not fully understood, but they may be formed by lodgement of subglacial debris, reshaping of previously deposited material, accumulation of material around a bedrock obstruction, or thinning of ice. Drumlin swarms or fields can be from 100m to 1km in length and from 5 to 25m tall.
What are some examples of distinctive landforms influenced by deposition?
Distinctive landforms influenced by deposition include terminal, lateral, and recessional moraines, erratics, drumlins, and till sheets. These landforms are formed from the deposition of material carried by the glacier, and their characteristics depend on the processes that caused the deposition and the conditions under which they were formed.
