Moraines

As I looked at erosion in my last post it seemed to make sense that I now look at what erosion leaves behind so this post specifically relates to moraines. It was only relatively recently that I first heard this term and even more recently that I researched it, so here goes. Hope I get it right.

In basic terms a moraine is material that a glacier has transported before later depositing. There are however 8 types of moraine split into two categories. 

The first 6 types of moraine are those that have been deposited by the glacier and become landforms. These are called:

1. Ground 
2. Lateral
3. Medial 
4. Push
5. Recessional 
6. Terminal

The following two types of moraine are those that only exist whilst the glacier is still active, compared to the previous six that form both during and after the glacier’s existence. These two types of moraine are:

1. Supraglacial 
2. Englacial

Ground Moraine: This is one of the most obvious types of moraine and forms when the material carried by the glacier (called till) is deposited on the valley floor after the glacier has melted. Ground moraine can either remain where deposited or become washed away by meltwater streams. When it remains in situ it is often found fairly regularly where the glacier would have once existed. 

Lateral Moraine: This is found along the sides of the glacier and forms when the glacier erodes the sides of the valleys that it passes. The material is carried along the edge of the glacier and is deposited there when the glacier melts, forming ridges which mark the edge of the former glacier.

  

Medial Moraine: Medial moraine is formed during the meeting of two glaciers which then merge. This happens when the lateral moraine on the inside edge of both glaciers merges and forms a new ridge along the centre of the now single large glacier. This can be seen when the glacier melts and the ridge is present between the two outer lateral moraine. This medial moraine acts as evidence that the current glacier had more than one source.

Push Moraine: This occurs when a glacier recedes, deposits debris across the valley floor and then expands again, each time pushing the current debris forward as it expands and depositing more on top as it recedes. This type of moraine provides evidence of a changing climate, with glaciers expanding during cool periods and receding during warm phases. Push moraines become obvious due to normally horizontal rocks having been ‘pushed’ into more vertical positions.

Recessional Moraine: Recessional moraine is similar to that of push moraine, except that the glacier recedes without re-expanding. Recessional moraine is formed when the glacier pauses for enough time to produce a large ridge whilst receding. Not to be confused with terminal moraine.

 

Terminal Moraine: Also known as end moraine, it is similar to recessional moraine except that it marks the maximum advance of the glacier, forming at its snout, across the valley floor.

Supraglacial Moraine: This is the collective name for all the types of moraine discussed whilst the debris lies on top of the glacier.

Englacial Moraine: This is similar to supraglacial moraine except that it consists of debris that has fell down lower into the glacier, therefore trapped in or under the ice as opposed to remaining on the top of the glacier. The term englacial moraine includes debris that is trapped within ice during thawing and refreezing.

(Once again please note that all of the photographs and diagrams above come from google images)