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Fluvioglacial Landforms

A variety of landforms are associated with meltwater from glaciers, including Outwash plains or Sandur, Varves, Braided Streams, Eskers, Kames and Kame terraces, Kettle holes and proglacial lakes. The aim of the exercise below is for you to research all of these landforms.

You will first need to read this PDF file about fluvioglacial landforms (for the original source click here).

Then you need to complete this whole booklet so that you understand the main features of fluvioglacial landforms and how they are created.

Fluvioglacial landforms are those that are created by the work of meltwater streams in front of an often retreating glacier.  Glacial deposits tend to be unstratified (have no layers), unsorted and angular.  Meltwater changes these glacial sediments or tills by sorting them by size, stratifying them into layers and rounding the sediments.  This gives fluvioglacial landforms a very distinct look or set of characteristics. Melt water can create landforms through both erosion and deposition, and the environment is highly dynamic and in constant flux. The key point here is that melt water streams are highly dynamic and highly VARIABLE both in terms of their discharge and sediment load. Discharge can vary wildly over time;

In summer discharges will be very high, as melt water arrives from many melt water streams from all over the glacier.  In winter, melt water discharge may even stop, as temperature may never rise above the pressure melting point.  Discharges also vary on a DAILY basis; with greatest discharges coinciding with the greatest daily temperatures (albeit with a LAGTIME to allow the water to reach melt water channels.

 

Fluvioglacial landforms include melt water channels, kames, eskers, varves, braided streams and outwash plains. The major erosion landform created by melt water are Melt water channels also known as glacial overflow channels. These form as the original course followed by a river before glaciation may be blocked by ice, or as an overflow from a proglacial lake (one that results from melt water from glaciers). These huge releases of water had much energy to erode and carve out deep gorges using processes such as abrasion and hydraulic action, which today are occupied by streams too small to have created the valleys they flow in. Examples are well documented Newtondale and Lake Pickering, Lake Lapworth and Ironbridge Gorge.

 

A fluvioglacial landform created by both erosion and deposition by melt water is a Sandur or outwash plain that often has braided streams. Outwash plains are areas that may have been glaciated by ice sheets and then affected by melt water or they may be areas in front of the snout. When melt water emerges from the snout, it loses its energy as it is no longer flowing under hydrostatic pressure. Consequently, the material it is carrying is deposited the largest first often forming an alluvial fan at the end of the glacier. When a number of these merge an outwash plain is formed. The finest material is carried furthest, sorting the sediment by size.  In addition these outwash plains are often stratified, because the sediment is laid down in layers during annual flood events and during periods of higher discharge (in summer when there is more melting).  Braided streams are often found in these outwash plain, because the highly variable discharge of the melt water streams and deposition cause the river to split into smaller streams.  Lateral erosion from these streams also helps to create this flat layered feature.  Outwash plains can be huge, many 10s of kilometres long and wide.

 

The rest of the landforms created by melt water are depositional in nature.  Eskers are winding/sinuous ridges of often coarse sands and gravels that are deposited by melt water as it flowed in a channel beneath is under pressure and much material is carried, to be dropped when melt water reduces in winter and exposed when the glacier melts. Material is rounded due to water erosion. They vary in height 5-20m for small eskers and length from a km to 400km (e.g. Munro esker in Canada is 250km long!).

The next depositional feature is a Kame, which are rounded mounds/hills of fluvioglacial deposits. These are found near the end of the former glacier as it began to retreat. Melt water held back by terminal moraine led to formation of lakes and material was deposited where the melt water left the glaciers to flow into lakes creating delta-like landforms. When the ice supporting the up-valley side melted, the material collapsed back to form the kame. There is the suggestion that hollows on the surface of a melting glacier would fill up with sediment and then gradually go down to lower levels as the ice melted ultimately forming a mound on the ground surface. Kame terraces are found where meltwater runs between the glacier and the sidewall and material is deposited (sorted) when flow is reduced.     

Fluvioglacial environments during glaciation  

Fluvioglacial environments after glaciation  

Within proglacial lakes the sediment is often sorted into varves stratified annual layers of sediment.  Coarse material is deposited when the discharge is high in summer (because of lots of melting), and fine material is deposited when flows slow in winter.  This leaves an annual layer of alternating coarse and fine sediment.

The final depositional landform is Kettle lakes.  These small round features are found in zones where dead ice was left on an outwash plain by a retreating glacier.  As melt water streams emanated from the ice they buried these blocks of dead ice under deposits of sorted and stratified sediments.  The ice melted and this left a depression in the outwash plain known as a Kettle hole.

 In conclusion, it is clear that melt water plays a vital role in the shaping of fluvioglacial landforms and environments.  Both erosional processes and to a greater extent depositional processes serve to sort, stratify and round sediment, creating a unique set of landforms.

  Think about it   

Visit the Geography pages to read more.

Good document from OUCanada - includes a self test quiz

Good document outlining various fluvioglacial landforms

Watch the presentation below(This isn't one of mine - many thanks to RCha!)

 
Fluvioglaciation