The characteristics of glacial deposits

Question 1

How is glacial till usually classified?

Answer 1

Glacial till is usually classified as a diamicton, being poorly sorted and non-stratified.

Question 2

Define the term diamicton?

Answer 2

Diamicton - A terrigenous sediment (sediment resulting form terrestrial erosion) that is unsorted to poorly sorted and contains particles ranging in size from clay to boulders, suspended in a matrix of mud or sand.

Question 3

What are the characteristics of glacial deposits?

Answer 3

• They are angular or sub-angular in shape because they have been embedded in the ice during transport and were therefore not subjected to rounding or smoothing
• They are unsorted, containing particles of a range of sizes in a matrix of finer material
• They are dropped in mounds and ridges rather than in layers, so deposits are unstratified
• They may contain elongated particles which are mostly all orientated in a particular direction
• They are composed of a variety of rock types that are mainly unweathered

Question 4

Give three ways in which glacial till deposits vary?

Answer 4

• Rock debris associated with supraglacial ablation till is more angular and less spherical because it is largely unaltered compared with subglacial ablation till
• Rock debris associated with lodgement is more rounded and less angular due to attrition at the ice/rock interface, with pronounced orientation of rock debris in the direction of ice flow
• Subglacial clasts often have striations on their surface.

Question 5

What can be inferred by studying the characteristics of till deposits?

Answer 5

The characteristics of till deposits may vary in more subtle ways which provide further information about the environment and processes of deposition.