Describe and explain the cause and effects of sea level change on coastal landforms
The main effect of rising and lowering of sea level is the movement of the position of the coast.As sea level rises, the coastline is moved toward the land.Geologists refer to this movement as a transgression.
Conversely, if the sea level drops, the coastline moves out toward the sea, or a regression. The effect of transgressions is most readily seen as the sea floods, river or glacial valleys, forming drowned valleys or fjords, respectively.
Although not prominent on our coasts, this is a common feature on the East Coast of the United States. There are two classes of sea level movement, localized or eustatic. Localized sea level changes only affect a limited area of coastline and can be caused by tectonic movements or rapid influx (or removal) of sediment. Eustatic changes refer to the removal or addition of water to the entire global ocean system, thus lowering or raising sea levels worldwide.
Eustatic changes are brought on by the removal and locking up of ocean water in glaciers, or by major plate tectonic movements causing changes in the volume of the ocean basins. One example of the latter is that during time of rapid sea-floor spreading, the spreading centers become warmer and rise, thus lowering the volume of the oceans. The reasons for sea levels change usually come after an ice age, as the temperature rises, snow and ice begin to melt globally.
This affects different areas differently, as the melting of the ice can cause either transgression or regression. In Scotland where the ice during the ice age produced a lot of pressure and pushed the land down, the land was now free to move back up, causing landforms such as raised beaches. The south of England during this time will sink slightly, due to Scotland rising. This coupled with the sea level rising means that features such as dalmatian coasts and rias, in other countries such as Norway, this can cause Fjords.
Raised beaches, as the land rose, former wave cut platforms and their beaches were moved out of reach from the beach. Raised beaches can be found on the west coast of Scotland and are characterised by a line of cliffs behind a formally wave cut platform. Along these cliffs you may find old landforms such as wave cut notches, caves and arches, the fact that these landforms exist show that isostatic uplift could not have been constant, and so the land raised and there was a pause between the first uplift and a second uplift.
During the ice age some rivers continued to flow, and these cut their valleys downwards to the lower base level, as the ice melted the sea level rose, this caused the flooding of the lower parts of the valley and its tributaries to produce sheltered, winding inlets called rias. Dalmatian coasts are found when the drowned tributaries and valleys ran parallel to the coast rather than at a right angle like rias. Fjords are formed when glaciers cut below the sea level and when the ice melted they flooded to form long, deep, narrow inlets with precipitous sides and hanging valleys (fjords are drowned glacial troughs).