What are the different types of Moraines?

Moraine is the name of specific landforms formed by the deposition of glacial debris. There are several types of moraines which are given below:

(i) Lateral Moraines:

Lateral moraines form along each side of a valley glacier. It is a ridge of glacial load by the side of a glacier or lying along the side of a valley which was formerly occupied by a glacier.

In the presence of a glacier this types of moraine overlies the glacier’s margin as a result of which the glacial debris may act as a protective covering of the ice which does not allow it to melt.

In such a case the lateral moraine may become ice-cored. As the valley glacier moves downhill and wastes, a series of lateral moraines may be formed at different lower levels down the valley sides.

The slopes towards the valley are smooth and uniform. When well- developed lateral moraines meet a terminal moraine, a huge horse shoe-shaped ridge is formed.

The lateral moraines comprise a mixture of glacial drift – a mixture of dirt, rock-flour and sub- angular boulders of varying sizes. In Alaska lateral moraines as high as 350 meters show the thickness of the glacier that formed them.

(ii) Medial Moraines:

When two glaciers flow side by side, they do not unite. The result is that two lateral moraines of these glaciers mingle together, giving rise to a medial moraine.

Such moraines exist in large numbers in present day glaciers, but they become non-existent after a glacier retreats and stream erosion dominates. Medial moraines vary in width from a narrow ridge to a broader spread of morainic material.

(iii) Ground Moraines:

If the lower part of a glacier is heavily charged with debris which it cannot transport, the excess load is deposited as ground moraine. It consists of an irregular sheet of glacial drift over the valley floor.

Ground moraines vary in thickness and in surface topography. The more or less horizontal sheets of drift have small depressions and knolls, boulders as well as alluvium deposited by glacial streams as their topographical features.

These moraines are then overridden by the more active ice above. Near the Snout of the retreating glacier, melting is greatest and ice becomes thinner, so the load capacity is naturally reduced. Hence the glacial till is deposited is the form of ground moraine.

(iv) Terminal Moraines:

End moraines that mark the farthest advance of the glacier’s snout are called terminal moraines. When the snout remains stationary for a long period of several years, an arcuate ridge comprising glacial debris is built up.

These moraines are characterised by the presence of kettle and hummocks. Lakes and marshes in the depressions are another characteristic feature. There are irregular belts of knolls and basins known as knob and basin topography.

(v) Recessional Moraines:

Moraines deposited because of a halt in the snout’s retreat, followed by a stabilization of the ice front prior to further retreat are called recessional moraines. In other words, recessional moraines are a kind of terminal moraines which form during the various halts of the glacier during its retreat.

(vi) Englacial Moraines:

Sometimes weathered material and debris present in the body of the ice-mass move downward and deposited as and when conditions are favourable.

These moraines are embedded within the ice. Remember that the debris is derived either by downward movement from the glacier surface or by movement upwards from the bed of the glacier.

Besides the major types of moraines, there are great varieties of linear moraines some of which show sorting by melt-water on their outer slopes where glacio-fluvial processes have been active. The minor forms of linear moraines compraise the following:

De Geer moraines push moraines, Rogen moraines Thule-Baffin moraines and washboard moraines.