Submergent coastline

(Redirected from Drowned coastline)

Submergent coastlines or drowned coastlines are stretches along the coast that have been inundated by the sea by a relative rise in sea levels from either isostacy or eustacy.

A submergent landform: the drowned river valley (ria) of Georges River in the greater Sydney area, Australia

Submergent coastline are the opposite of emergent coastlines, which have experienced a relative fall in sea levels.

Many submergent coastlines were formed by the end of the Last Glacial Period (LGP), when glacial retreat caused both global sea level rise and also localised changes to land height.[1]

Formation edit

Submergent coastlines form either when sea level rises or the land level fall. This can be caused by isostatic or eustatic change.[2] Both isostatic and eustatic change can be caused by a variety of reasons.

Isostatic change could be due to post-glacial adjustment.[2] Another common cause of isostatic change that can result in a submergent coastline is tectonic action.[2] Events such as earthquakes or volcanic eruptions may cause land subsidence therefore causing isostatic sea level increases.[2]

Eustatic sea level rise can also be caused by many reasons. One common reason is thermal expansion.[2] Thermal expansion occurs when water gets warmer and so the volume of water increases, this therefore causes global sea level rise forming submergent coastlines.[2]

Common Features edit

Features of a submergent coastline include:

Rias edit

 
Sydney Harbour is one example of a ria.

Rias, are a drowned river valley.[1] They are a section of a river valley flooded by the sea, making much wider than would be expected based on the river flowing into it.[1] Many rias were formed by the rise in sea level after the melting of the vast continental glaciers.[3] Rias commonly have a widening funnel shape and gradually increasing depth as they move towards the coast. The widening and deepening of the ria towards the sea usually causes an exaggerated tidal effect within the estuary.[3]

Fjords edit

Fjords, which are drowned glaciated valleys (Also known as U-shaped valleys). A section of a glacially eroded valley is flooded by the sea when a fjord is formed.[1]

Dalmatian Coasts edit

 
Map showing the Dalmatian coast of the Dalmatia region of Croatia. The narrow islands running parallel to the coast can be clearly seen.

Dalmatian coasts composed of long narrow islands running parallel to the coastline and separated from the coast by narrow sea channels called sounds.[1] Dalmatian coasts are named after the Dalmatia region of Croatia which displays the common features of a dalmatian coast.

Examples edit

Notable and illustrative examples of submergent coastlines include:

References edit

  1. ^ a b c d e f g h "7B Emergent and Submergent Coastlines".
  2. ^ a b c d e f "https://www.physicsandmathstutor.com/pdf-pages/?pdf=https://pmt.physicsandmathstutor.com/download/Geography/A-level/Notes/Edexcel/2B-Coastal-Landscapes-and-Change/Detailed Notes - Coastal Landscapes and Change - Edexcel Geography A-level.pdf". www.physicsandmathstutor.com. 2021-06-03. Retrieved 2023-04-01. {{cite web}}: External link in |title= (help)
  3. ^ a b "Ria | geology | Britannica". www.britannica.com. Retrieved 2023-04-01.