2. Ice formation and movement - Ice movement Flashcards
Ice movement can be due to Compressional Flow and Extensional Flow. Describe and explain how ice moves by Compressional and Extensional Flow.
Ice movement is complex and several types of movement can be identified. The main types are:
Compressional Flow - Compressional flow occurs where there is a reduction in the gradient of the valley floor leading to ice deceleration (where velocity falls) and a thickening of the ice mass. At such points ice erosion is at its maxium. Compressional flow occurs in zone of ablation.
Extensional Flow - Extensional Flow occurs when the valley gradient becomes steeper. The ice accelerates (velocity increases) and becomes thinner, leading to reduced erosion. Extensional flow occurs in zone of accumulation.
Ice movement can be due to Basal Sliding/Slipping. Describe and explain how ice moves by Basal Sliding/Slipping.
Ice movement is complex and several types of movement can be identified. The main types are:
Basal Sliding/Slipping - as the glacier moves over the bedrock, there is friction. The lower ice is also under a great deal of pressure (due to the weight of overlying ice) and this, combined with the friction, results in some melting (even though temperatures are not above freezing). The resulting meltwater acts as a lubricant, enabling the ice to flow more rapidly.
Obstacles to the ice flow (especially small ones under a metre) create added pressure on the ice as it begins to move over them; this causes melting which aids the passage of the ice over the obstacle – this is known as a regelation slip. (Regelation refers to the layer of ice where the process occurs at the base.)
Ice movement can be due to Internal Deformation. Describe and explain how ice moves by Internal Deformation.
Ice movement is complex and several types of movement can be identified. The main types are:
Internal Deformation - Internal Deformation occurs when ice crystals orientate themselves in the direction of the glacier’s movement and slide past each other. As surface ice moves faster, crevasses develop. Internal Deformation is the main feature of the flow of polar glaciers as, without the presence of meltwater, they tend to be frozen on their beds.
This movement is slow and occurs especially in cold based glaciers. This links to compressional and extensional flow also.
Ice movement can be due to Rotational Flow. Describe and explain how ice moves by Rotational Flow.
Ice movement is complex and several types of movement can be identified. The main types are:
Rotational Flow - Rotational Flow occurs within the corrie (cirque), the birthplace of many glaciers. Here ice moving downhill can pivot about a point, producing a rotational movement. This, combined with increased pressure within the rock hollow, leads to greater erosion and an over-deepening of the corrie floor.
