7B - Emergent and Submergent Coastlines

Sea level change has produced emergent coastlines (raised beaches with fossil cliffs) and submergent coastlines (rias, fjords and Dalmatian)
​

Emergent Coastlines

• During the Devensian Glacial eustatic changes lowered sea levels by 120 m.
• At the start of the Holocene Interglacial (10,000 years BP) led to a rapid 100 m eustatic rise in global sea levels, as 3,000 years of ice sheets and glaciers shrank. This happened over about 1000 years, (very rapid) and submerged coastlines.
• However, the post-glacial adjustment of ice-covered land (and adjacent areas) was much slower. 
• Previously ice-covered land gradually rose out of the sea, such as northern Britain and Scandinavia. 
• The Ford and Clyde valleys in the border region of Scotland are currently rising 2 mm p.a. (though initial adjustment was faster) 
• Areas of Northern Europe and North America that were covered by the thickest ice are rebounding fastest. Some areas rose isostatically by 300 m. 

Emergent coastlines are being produced by post-glacial adjustment. These are parts of the littoral zone where a fall in sea level exposed land once part of the sea bed. They have landforms reflecting the previous sea levels. 

1. Raised beach
   1. A relict beach now above high tide level
   2. A flat surface covered by sand or rounded pebbles/boulders. 
   3. Usually vegetated by plant succession (though further succession prevented due to grazing)
2. Fossil cliff
   1. a steep slope found at the back of a raised beach exhibiting evidence of formation through marine erosion but now above high tide level. 
   2. they may contain wave-cut notches, caves and arches providing evidence of formation by marine erosion
   3. episodic nature of isostatic recovery allows marine processes to erode cliffs and deposit beaches when sea levels are stable. Relatively rapid drop in sea level then leaves relict coastline abandoned above high tide and some distance inland. 
   4. E.g. the Isle of Arran has a raised beach 5 m above current sea level north of Drumadoon. Arran has three levels of raised beaches produced at different stages of post-glacial adjustment. 
   5. E.g. at Lendalfoot in Ayrshire, western Scotland, a flat raised beach surface is used as a route for the A77 main road. 40 m raised cliff at the back of the now now 200 m inland from the present-day beach.
3. Also raised stumps, etc.

Submergent Coastlines

Submergent coastlines are sections of the littoral zone where sea level rise inundated areas that were previously part of terrestrial land. They are found in southern England and the east coast of America. 

• Areas of land adjacent to ice covered regions experience isostatic uplift during the Devensian due to the see-saw effect. These are now subsiding due to post-glacial adjustment - producing marine transgression and emerging coastlines. 

A ria is a drowned river valley - a section of river valley flooded by the sea, making it much wider than would be expected based on the river flowing into it.

• ​Rias are the most common coastal landform.  
• They are common in periglacial areas that were adjacent to land covered by ice during the Devensian, e.g. Southern England. 
• Rivers eroded steep-sided V-shaped valleys into the frozen landscape giving the ria a V-shaped cross section when the valley flooded. 
• Rias have a sinuous plan profile reflecting the meandering river course. The plan view is dendritic as tributies are flooded by the rising sea. 
• Rias are a type of estuarine coastline. 
• E.g. Kingsbury Estuary on the south Devon coast is a 6 m long ria. Main channel is 1 m wide near its mouth at Salcombe. Two large drowned tributaries extend from the east side of the ria, with Frogmore Creek 2 km long and 500 m wide. 

​​

Fjord
Fjords are drowned glacial valleys - a section of a glacially eroded valley flooded by the sea. They are common in glaciated areas that were covered during the Devensian, e.g. western Norway. Many Scottish sea lochs are fjords. 

• Fjords often have a relatively straight profile as glaciers truncate spurs to produce a direct downslope route. 
• Glacier erosion is often cut deep into the landscape, often tens of metres lower than the adjacent unglaciated land - meaning that fjords are often deeper than the adjacent sea. 
• Fjords often have a shallow entrance where there is a submerged 'lip' formed by the ridge of a terminal moraine. 
• Many fjords are shallowing by a few milimetres per year due to isostatic adjustment. 
• Sognefjord in western Norway is 205 km long, 1.3 deep and the main branch is 4.5 km wide. 

Dalmatian Coast
This is composed of long, narrow islands running parallel to the coastline and separated from the coast by narrow sea channels called sounds. 

• They are produced by sea level rise flooding the coastline with the geological structure of folds aligned parallel to the coast. 
• Sea level rise at the end of the Devensian Glacial floods synclines to form sounds. 
• Sea overtops low points forming straits linking straits linking sounds and separating sections of anticline ridge into narrow islands parallel to the coast. 
  
• The Dalmatian region of Croatia has a  limestone coastline stretching 520 km NW-SE with 1,240 islands running parallel to the coast. 

Other

• Isostatic rebound is episodic - long periods of little change followed by short bursts of marine regression. 

• Rias are economically important as they provide sheltered ports. 

Barrier islands? (from revision guide)
The east coast of the USA has barrier island landforms

• these may have formed as lines of coastal sand dunes attached to the shore
• later sea level rise flooded the land behind the dunes forming a lagoon, but the dunes themselves were not eroded and formed islands
• as sea levels continued to rise, the dune systems slowly migrated landwards 
• rivers and tidal flows maintain open water between islands
• barrier islands supplied with sediment from longshore drift