MORAINE

(Redirected from Ground moraine)

'Moraine' refers to any glacially formed accumulation of unconsolidated debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past ice age. This debris may have been plucked off the valley floor as a glacier advanced or fallen off the valley walls as a result of frost wedging. Moraines may be composed of silt like glacial flour to large boulders. The debris is typically angular. Moraines may be on the glacier’s surface or deposited as piles or sheets of debris where the glacier has melted. Moraines may also occur when glacier or iceberg transported rocks fall into the sea as the ice melts.

Contents

Types of moraines

Lateral moraines

Medial moraines

Ground moraines

End or terminal moraines

See also

References

Types of moraines

Lateral moraines

Lateral moraines are parallel ridges of till deposited along the sides of an alpine glacier. The unconsolidated debris is deposited on top of the glacier by frost shattering of the valley walls and from tributary streams flowing into the valley. The till is carried along the glacial margin until the glacier melts. Because lateral moraines are deposited on top of the glacier, they do not experience the postglacial erosion of the valley floor and therefore, as the glacier melts, lateral moraines are usually preserved as high ridges. Lateral moraines stand high because they protect the ice under them from the elements, which causes it to melt or sublime less than the uncovered parts of the glacier. Multiple lateral moraines may develop as the glacier advances and retreats.

Medial moraines

Medial moraines are formed when the inside lateral moraines of two glaciers merge together. They form a ridge down the center of the combined glaciers. Like lateral moraines, medial moraines form on top of the glacier. However, medial moraines do not have a constant source of debris, like the valley walls of lateral moraines, so they usually result in relatively smaller landforms when the glacier melts.

Ground moraines

Ground moraines are till covered areas with irregular topography and no ridges often forming gently rolling hills or plains. It is accumulated under the ice by lodgement, but may also be deposited as the glacier retreats.

End or terminal moraines

End moraines or terminal moraines are ridges of unconsolidated debris deposited at the snout or end of the glacier. They usually reflect the shape of the glacier's terminus. Glaciers act much like a conveyor belt carrying debris from the top of the glacier to the bottom where it deposits it in end moraines. End moraine size and shape is determined by whether the glacier is advancing, receding or at equilibrium. The longer the terminus of the glacier stays in one place the more accumulation there will be. There are two types of end moraines, terminal and recession moraines. Terminal moraines mark the maximum advance of the glacier. Recessional moraines are small ridges left as a glacier pauses during its retreat. After a glacier retreats the end moraine may be destroyed by postglacial erosion.

See also

★ Glacial landforms

★ List of landforms

★ Drumlin

★ Esker

★ Gettlinge

★ Tarn

★ Moraine-dammed lake

★ Geomorphology

References

{{Commons|Category:Moraine|

★ Easterbrook, D. J. (1999) ''Surface processes and landforms.'' (Second Ed). Prentice Hall, Upper Saddle River, New Jersey.