Topic 2: Coastal Landscapes & Change (Edexcel A-Level Geography): Model Answers

Sea Level Change and Coastal Landscapes

Eustatic Sea Level Changes

A key contribution that changes in sea level makes to the formation of coastal landscapes is through eustatic changes. These occur on a global scale and are due to changes in the volume of water in the ocean. During the last glacial period, water was in a frozen state in ice caps and glaciers and so caused a fall in global sea levels. Subsequent melting of the ice has meant sea levels have risen by 120m. Recently there has been the thermal expansion of the oceans caused by global warming but this is on a far smaller scale – since 1900 it is estimated that sea levels have risen by 20cm. Eustatic changes therefore contribute to coastlines of emergence where sea levels fall and submergence where sea levels rise. In submerged coastlines such as South West England, the impact of rising sea levels creates what drowned river valleys called rias due to the process of marine transgression'. As sea levels rise the pre-existing drainage pattern becomes submerged and flooded with seawater. This creates broad but shallow inlets with often steep valley sides a winding profile which reflects the original route of the river and a fairly uniform depth such as the River Dart and Dartmouth. It is important to remember, however, that the coastal landscapes of SW England are not just the result of sea level change. Rather these changes are imposed upon other pre-existing influences such as lithology and topology. South West England can be thought of as a rocky coast with outcrops of resistant rock types such as granite and sandstones. As much as sea level change these also contribute to the resulting coastal landscape of rias but with rocky headlands and cliffs.

Similarly, the topology is a key factor in forming the Dalmatian coast in the Adriatic sea. This has a coastal landscape of long, narrow inlets with a chain of islands parallel to the coast. This is as a result of the fact that before sea level rise there was a longitudinal coast where mountains run parallel or concordant to the coast. The submergence of the coastline and the subsequent marine transgression created elongated islands which were the crests of the former ranges and the narrow sounds were the former longitudinal valleys.

Furthermore, it can also be the case that the impacts of sea level change are combined with other non-marine processes. In Norway, glaciation created long deep narrow U-shaped valleys. After the ice melted these became flooded due to sea level rise and long thin but deep (over 1000m) inlets called fjords are created. These are straighter than a ria glacial erosion has planned off the interlocking spurs found in the pre-glacial river valley. Overall it is clear that eustatic sea level changes can significantly contribute to the formation of coastal landscapes but often are imposed upon pre-existing coastline shaped by other factors such as by rock type and lithology or moulded by processes such as glaciation.

Isostatic Sea Level Changes

In comparison to eustatic changes which are global, isostatic are often regional and are the movement of the land relative to the sea. These can occur when during glaciation the extra weight of the ice on the land forces the earth to tilt down into the magma below. This is then corrected after the ice has melted. It is estimated that areas of Scotland are still rebounding by up to 7mm per year due to isostatic uplift. As a result of this rebounding coastlines of raised beaches and fossil cliffs are often found. At Dougarie on the Isle of Arran raised beaches were created when the sea level was much higher. As the sea level has dropped, it has left this beach as a raised beach. At the back of the beach are the fossil cliffs often with a wave-cut notch where the raised beach meets the fossil cliff caused by historic wave erosion as well as a cave and stack. Yet it is not only sea level change that has created these features. The raised beach is a product of deposition and so low energy conditions had to be prevalent. In addition both the wave cut notch, the fossil cliff and the stack were originally caused through the process of erosion and so sea level change appears to be only one process that has created this coastline. Overall it is clear that isostatic sea level changes can significantly contribute to the formation of coastal landscapes but are as dependent upon other contemporary processes such as low energy environments as well as erosional processes in creating these coastlines Sea level change need not be over such a long term as eustatic and isostatic appear to be. Short-term changes such as tides can also influence coastal landforms and so coastal landscapes. The changes between spring and neap tides can create a series of berms on shingle beaches that indicate the highest point of the breaking waves. Yet these berms are temporary and can be modified by the next spring tide depending upon the wave size and type which in turn is dependent upon the prevailing meteorological as opposed to climatological conditions. Overall it appears therefore that coastal the influence of sea level change on coastal landscapes is also dependent upon the temporal scale of the changes as much as the processes causing sea level change.

Conclusion

In conclusion, sea level change can be seen as a key influence on the formation of coastal landscapes but is not the only process nor factor that influences the development of coastal landscapes. Rather sea level change often imposes a variety of distinctive landforms such as rias and raised beaches on a pre-existing coastal landscape. In some cases such as the Dalmatian coast sea level change is the most significant influence on the resulting coastal landscape. On others such as the SW Devon coast or the Isle Arran, sea level change is only one of many factors that influence the formation of the coastal landscape highlighting the fact that in many coastal landscapes, the coastal landforms that create the resultant coastal landscape are in dynamic equilibrium with the processes and factors that create them.