Emergent and Submergent Coasts PDF

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Emergent and Submergent Coasts Emergent Isostatic and eustatic scale changes largely during and after the last glacial period. In North America and Northern Europe, the post-glacial isostatic adjustment has been more than 300m. The two changes are linked but happen at very different rates: -

Post-glacial sea level rise was very rapid and would have drowned many coastlines. Isostatic adjustment was very slow, meaning that in previously icecovered areas newly drowned coastlines slowly emerged from the sea (and are still emerging today).

Submergent Coastlines are not affected by glacial ice cover; the post-glacial sea level rise has created Submergent (drowned) coastlines. E.g. South coast of England and East coast of America. Ria- A drowned river valley in an unglaciated area caused by sea level rises flooding the river valley, making it much wider than would be expected based on the river flowing into it. Barrier Island- Offshore sediment bars, usually sand dune covered but, unlike spits, they are not attached to the coast. They are found between 500m and 30km offshore and can be tens of kilometres long.

Landform Raised Beach

Fossil Cliffs

Emergent or Submerg ent? Emergent

Emergent

How is it formed?

Example

When sea levels fall, more of the coastline is revealed. Beaches are no longer combed by waves, so are left stranded and exposed above the new sea level. The lower part will often show signs of marine erosion, and a smaller cliff may be formed. After a raised beach is formed, the cliffs are

Fife, Scotland.

Ayrshire, Scotland.

Ria

Submerge nt

Fjord

Submerge nt

Barrier Island

Submerge nt

exposed to only sub-aerial erosion and are now called fossil cliffs. As time goes on, a new beach is formed and the old beach forms the new cliff line which is exposed to marine and sub aerial erosion. The fossil cliffs become weathered and vegetated and are prone to mass movement Small streams run into different arms of estuary (creeks). These streams could not have eroded the wide valleys that form the creeks. The sea level rise has pushed the sea inland, drowning valleys that were eroded by rivers millennia ago. Fjords are too drowned valleys, yet they are different to rias: is always U-shaped in a glacially eroded valley, it’s deeper than the adjacent sea, there is a submerged ‘lip’ at the end of the fjord representing the former extent of the glacier. Most explanations focus on coastal submergence as a key process. They may have been formed as lines of coastal sand dunes attached to the shore. Sea level rises flooded the land behind the dunes forming a lagoon, but the lagoons themselves were not eroded and so became islands. Sea level continues to rise and dune systems move landward.

The Kingsbridge Estuary near Salcombe in Devon.

Norway, Canada, New Zealand and Chile.

East Coast of USA, from Florida to Connecticut....