moraines

till

glacial erratics

glacial stratigraphy

eskers

glacial lakes

kame terrace

outwash terraces

kettle holes

Outwash terraces at the confluence of the Avon and Spey at Bridge of Avon

Braided channel pattern, with gravel bars and branching channels

 

 

 

 

 

 

 

 

 

 

 

 

 

Imbrication of flat pebbles: a property perhaps first recognised in 1860 by T F Jamieson

Outwash terraces

Definition: outwash is the meltwater that flows from the glacier. It is often highly charged with sediment and this may accumulates down valley. River incision shapes this stratified sand and gravel into sequences of terraces.

Many of the Cairngorm glens contain stepped sequences of outwash and river terraces. The best known are in Glen Feshie (Young, 1975; 1976). Here the terraces are related to the retreat of ice into upper Glen Feshie and Glen Tromie. The progressive development of soils on late-glacial outwash and younger river terraces has been traced here (Robertson-Rintoul, 1986).

A good example of an outwash terrace can be seen transected by the gravel pit at Inverdruie. Here a valley sandur or outwash plain existed just as the last ice was melting in Glenmore. The quarry sections show horizontally bedded gravels and sands - and the braid bars of the original floodplain can be seen.

In the lower photo, the flow direction towards the left can be judged from the imbrication of the gravel. Clasts tend to be stacked like bricks in the direction of former flow.