How do glaciers move?

In the northern hemisphere, glaciers typically form in north-facing hollows in upland areas. When snow falls in these areas during winter months, it can survive without melting in the summer months. Ice forms as layers of snow become compacted by the weight of subsequent snowfall, and the trapped air is squeezed out.

As ice accumulates, it begins to flow under gravity. It flows over the lip of the hollow and down the side of the mountain.

As the ice flows over the uneven mountainside, the glacier cracks, creating deep crevasses.

Crevasses in a glacier in the Swiss Alps

Due to the weight of the ice, pressure is created on the glacier’s base. This creates meltwater on the glacier’s base (squeeze an ice cube to see this process in action!). This lubricates the base of the glacier, helping it to flow. This process is known as basal flow.

The glacier also flows when temperatures are too cold for basal flow. When temperatures are very cold, the glacier moves like plastic. The speed is affected by the gradient of the slope. The steeper the slope, the faster the flow. This process is known as internal deformation.

Abrasion and plucking occur on the valley floor resulting in the valley floor being covered with rock fragments. This is called moraine.

The formation of a corrie

As the ice flows into lowland areas, the ice begins to melt as temperatures increase. Rock being transported by the glacier is deposited as moraine.

The snout is the end of the glacier. Meltwater flows from the glacier’s snout and can transport moraine away from the glacier. This is often deposited on the outwash plain of the glacier. Outwash plains are made up of outwash deposits and are characteristically flat and consist of layers of sand and other fine sediments. The image below shows an outwash plain in Iceland.