Landscapes of glacial deposition

Around 10,000 years ago as the ice age advance began to melt, glacial deposits or drift were left behind. These glacial deposits were of two kinds:

  • Till - mixed or unstratified materials directly deposited by ice. Examples of till deposits include drumlins, moraines and erratics.
  • Fluvio-glacial - layered or stratified materials deposited in layers by meltwater. When ice is melting, materials are sorted in the water. Examples of fluvioglacial deposits include eskers, kames or kame terraces.

Till deposits

A bird's eye view of drumlins in a landscape, as well as a profile view. It shows that the tapered lee slope side faces the direction of previous ice flowThe formation of drumlins

Drumlins are oval hills which form in groups called swarms. The unsorted till appears moulded by ice to form a blunt end with a more streamlined, gentler lee slope.

Moraines are mounds of poorly sorted till where rock debris has been dumped by melting ice or pushed by moving ice.

Rock

The different types of moraine include terminal moraine, which marks the end of an ice sheet or valley glacier, and lateral moraine, which forms at the edge of a glacier at the valley side.

Erratics are boulders carried by ice, often for many kilometres, and deposited in areas of completely different rock type.

Fluvio-glacial deposits

Outwash plains are areas of sorted sand and gravel deposited at the mouth of meltwater rivers which were often braided.

Kettle holes may be found if a block of 'dead ice' is partially buried by fluvio-glacial deposits. When the ice melts a hole is left which may fill with water to form a kettle hole lake.

A 3D representation of an esker alongside a picture of the same landscape during previous glaciation when water runs under ice, depositing fluvioglacial sediment along the wayThe formation of eskers

Eskers are long, winding ridges of layered sand and gravel similar to railway embankments. They are formed inside the ice, in tunnels in which meltwater streams flowed.

Kame terraces are gentler slopes of layered sand and gravel at the side of valleys. They were formed at the edge of the glacier and valley side where meltwater forms on the surface.

A depiction of a terminal moraine made up of unsorted rocks that are left behind after glaciationThe formation of terminal moraines

Terminal moraines or end moraines as they are often referred to are ridges of unsorted material at the snout of the glacier. They mark the furthest point reached by the ice sheet or glacier.

Terminal moraines form when the ice melts and deposits all the moraine it was transporting at the front of the glacier. Glaciers can transport huge amounts of material including rocks, stones and smaller particles. It takes great force for a glacier to be able to transport this material.

When a glacier begins to lose its strength, for example when it begins to melt or retreat, it deposits some of this material. At this point the ice is still moving, so material is constantly being added to the terminal moraine. The longer the ice continues to melt at the same place, the higher the terminal moraine.

Glaciers carry moraine at the sides of the glacier, called lateral moraine, in the middle of the glacier called medial moraine, and at the base of the ice called ground moraine. Therefore, terminal moraines are completely unsorted, and may extend for many kilometers.

Diagram of a moraine

The video below discusses evidence of glaciation in Scotland

Move on to Test
next