What are the effects of deglaciation on the landscape?
Changes in the landscape due to glacial melt water;
1) The impact of glacial melt water on pre existing drainage patterns
2) The impact of glacial melt water on sea level change and the effect of this on coastal landforms and inland river systems
3) The impact periglaciation and paraglaciation on slope processes in upland areas such as Snowdonia
4) The impact of periglacial and paraglacial processes on lowland areas of the UK
Paraglaciation- paraglacial landscape refers to an area that is changing from glacial to non glacial conditions but where surface features have not yet adjusted to the new post glacial environment.
· An area of subglacial meltout till that was stable when deposited beneath a glacier but may be prone to rapid erosion when exposed to surface processes once the glacier has gone
· A deposited lateral moraine that was stable when a valley glacier was present and supported it but is prone to rapid gravitational slope movement once the supporting ice has withdrawn
Deglaciation can cause instability and rapid change in a landscape until a new equilibrium is established between the surface materials and the new post glacial processes operating in the environment.
Periglaciation- periglacial areas are areas of permafrost conditions, intense freezing, freeze thaw on surface, surface layer melts briefly in the summer. Periglaciation occurs near mountain glaciers at margins, mountain peaks not covered by ice. At lower levels, it forms a U zone cold around continental glaciers in areas of high latitudes covering 20% earths land surface e.g. around periphery of ice sheets of Canada and Russia. ( forms range of landforms- ice wedge, casts, polygons and pingo slats)
· Periglacial areas in Britain- freeze thaw in mountainous areas such as the lake district, Scottish highlands experiencing periglacial processes
· Height of ice advance in the UK (Anglian glaciations)- from Severn Estuary to Thames, over whole of southern Britain
· Periglacial conditions extended as far as mid Europe and the whole of UK was covered
Impact of deglaciation on pre existing drainage patterns-
Drainage diversion and proglacial lakes- in land meltwater from the retreating Devensian ice sheet created large proglacial lakes such as Lake Lapworth, which formed in Shropshire. Drainage of these lakes changed river landforms by diverting course of rivers away from original path in case of river Severn and Lake Lapworth.
1) In periglacial times (before Devensian) river Severn was shorter that flowed into the Dee Estuary.
2) End of Devensian- Irish sea ice, which extended over North Shropshire and Cheshire plain retreated, large quantity of meltwater, was produced. Water could not drain northwards towards Dee Estuary due to location of ice sheet therefore Lake Lapworth formed as a result. Lake waters found an overflow outlet to the South and cut the gorge at Iron Bridge.
3) Post glacial- River Severn continued to flow southwards…