What are the processes of glacial transport and deposition and what are the resultant landforms?
· Erosion occurs at higher altitudes and is transported at lower altitudes when glaciers melt
· It is important to note that erosion is essential to occur for material to be transported then deposited
· Effective glacial erosion can only continue if eroded material is entrained and transported by flowing ice. The deposition of this entrained material at a larger stage produces distinctive landforms and landscapes.
· To understand the origin of depositional features, an understanding of glacial transportation is essential
Glacial transportation- glaciers transport a wide range of debris from clay/silt sized particles to huge boulders several metres in diameter. This debris is transported through the glacial system in the direction of ice movement.
· According to its position within the ice body, the debris can be classified into; supraglacial debris which is transported on the surface of the ice body, englacial debris which is transported within the ice body and subglacial debris which is transported at the base of the ice body.
1) Supraglacial transportation-
· most common on confined valley glaciers, in valley glaciers this debris is concentrated in bands either at the sides of the glacier (lateral moraine) or in the middle of the glacier (medial moraine)
· lateral moraine is derived from freeze thaw
- medial moraine is created due to a confluence of 2 lateral moraines therefore also created by freeze thaw
2) Englacial transportation-
· englacial debris can enter an ice body in various ways
· supraglacial debris that becomes buried by snowfall in the zone of accumulation will therefore create englacial debris
· when two separate valley glaciers converge they will erode the separating body of rock creating a vertical section of englacial and supraglacial debris known as a medial moraine
3) Subglacial debris-
- This debris is mainly derived from the processes of abrasion and plucking, it creates subglacial armoury which aids further abrasion.
Transportation and the role of extending and compressing flow-
· From the point of weathering/erosion a piece of debris may as it is transported, take the role of supraglacial, englacial and subglacial debris.
· extending and compressing flow is a further mechanism by which debris can change its path of transportation, when the glacier experiences internal stress applied by a change in the underlying gradient over which the ice is flowing, the ice may fracture and internally flow along slip planes;
· ice that flows over an increasingly steep gradient will experience internal stress resulting in extending flow, this can result in supraglacial debris falling down crevasses and becoming englacial
· ice that flows over a decreasing gradient will experience internal stress resulting in compressing flow which can result in compressing flow which can result in sub or englacial material being moved towards the surface
Glacial deposits (referred to as drift) can be broadly categorised into…