Glacial Systems - Processes Operating in a Fluvioglacial Landscape

This study note outlines the main erosional and depositional processes operating in a fluvioglacial landscape.

Erosional processes operating in a fluvioglacial landscape

During times when glacial ablation is greater than accumulation, meltwater streams flow from the snout of a glacier across the land in front of it. High discharge provides the meltwater output with volume and velocity which gives substantial energy. This means it can both erode the landscape and transport much material from both glacial deposition and from its own erosive activity.

There are four main types of erosion:

• Hydraulic Action - the sheer force of the water erodes the bed and banks of the meltwater channel. The meltwater will force air into fissures in the bed and banks of the channel resulting in pressure cavitation, causing material to be loosened. This material will then be carried away by the stream in times of high discharge to be deposited in an outwash plain.
• Abrasion - stones in transport within the water are thrown at the bed and the banks of the meltwater channel, eroding them. Where the bed and banks of channels are formed from soft rock or sediment, this process will occur rapidly. This process can over-deepen and widen the meltwater channel.
• Corrosion - where weak acids within the water react with the rocks, bed and banks of the channel. This erosional process will only take place when the rock type is affected by acids, such as limestone.
• Attrition - rock fragments in transport are thrown into one another during channel turbulence. This will reduce the size and smooth the shape of material. Material will change from angular glacial material to rounder, smoother material; evidence of fluvial erosion and subsequent deposition.

Depositional processes operating in a fluvioglacial landscape

Deposition occurs when glacial ablation periodically reduces so meltwater streams have a smaller discharge.

It also takes place with increasing distance from the ice front as meltwater load increases while energy input is dispersed.

When discharge decreases, so does velocity and the stream’s energy will be reduced. Lower energy results in the meltwater stream depositing its load. Fluvial deposition is sorted, with the larger, heavier materials being deposited first and smaller materials further away, and fine materials at the furthest extent.

Changes in discharge in a fluvioglacial landscape

Discharge can change quickly so has a significant impact upon both erosion and deposition. Erosion and deposition balances can change quickly over the short term or over longer periods of climate change. Summer discharge is likely to be higher than winter, therefore increasing erosion in summer. However, changes can also occur on a daily basis whereby daytime discharge increases and it reduces at night due to a fall in temperature and less meltwater being released from the glacier.