submergent and emergent coastlines Flashcards
(25 cards)
what is a submergent coastline?
coastline formed by a rising sea level (marine transgression)
what are the three examples of submergent coastlines?
Fjords, Rias, and dalmation coastlines.
what is a Fjord?
Drowned U shaped glacial valley
how do Fjords form?
1) During a colder glacial stage the input of snow is larger than the output via melting or sublimation
2) the snows builds up and becomes compressed ice, eventually growing into a glacier
3) the glacier flows downslope under gravity (basal slippage)
4) as galcier moves it grinds subglacial sediment into the rock below it. this intense abrasion causes vertical erosion.
5) continous erosion from the galcier creates a U shaped valley
6) warmer interglacial stage causes glacier to melt and leave behind the U shaped valley
7) warmer conditions, thermal expansion of water floods the valley, forming a Fjord
8) shallower water at the entrance to the Fjord as snout of glacier was less able to move/erode (known as Threshold)
what is the example of a Fjord and what are its dimensions?
SognefJorden, Norway
195 km long, 1300m deep
it is symetrical
how much more erosive is ice than water
10x more erosive
what is a Ria?
a drowned river valley
what shape is a Ria?
dendritic
how does a Ria form?
1) water moves faster around outside of a meander bend, this causes lateral erosion through abrasion and h. action (etc) this will attack valley sides and push back bluff lines. this will eventually create a wide valley.
2) when heavy rain, river floods load of river deposited across valley to form a layer of alluvium, creating a flat floodplain.
3) climate change - glacio eustatic sea level rise. rising water floods the river valley. flocculation forms mudflats which are visible at low tide
what is our example of a Ria and what are its dimensions?
Kingsbridge Estury , South Devon
7km long
typically less than 10m deep
it is asymetrical
what is a Dalmation coastline?
A series of elongated islands that sit parallel to the coastline. They are the result of sea level rise.
how are Dalmation coastlines formed?
1) concordant coastline where alternating bands of relatively harder and softer rock types run parrallel to the coastline.
2) differential erosion has caused soft rock to become valleys and hard rock to become highlands. this leaves a sequence of parralel valleys and mountians.
3) global warming has led to glacio-eustatic sea level rise and the thermal expansion of water. this eustatic sea level rise has caused a marine transgression. the river valleys have flooded and left highland as islands.
what is an example of a Dalmation coastline?
Croatian Coastline.
what is an emergent coastline?
when the sea level falls or the land rises and new land is exposed (marine regression)
what is isostatic rebound?
when ground rises up due to the dissapearing of depressing glacial ice.
what are raised beaches?
a deposit of former beach material including sea shells which can be found further inland of the present day beach at a higher relief
what is an example of a raised beach
Cock of Arran. lower beach at 8m and one at 30m above sea level
how do raised beaches form?
sediment e.g sea shells are deposited and then isostatic rebound lifts the beach up. the origional coastline has been emerged
what are relict cliffs?
an old cliff found further inland at a higher relief, displaying features such as caves, arches and stacks
how are relict cliffs formed?
abrasion and hydralic action occur at a high energy coastline and erode a sea cave. isostatic rebound has shifted the caves up to a higher relief
what is an example of a relict cliff?
kings cave in arran, consists of several large caves, approximately 10m high and 15m wide
what is a marine platform?
they are a sequence of terraces that slope towards the sea.
how does a marine platform form?
end of devensian period, sea levels rose due to glaciers melting which produced a new cliff higher up. Then isostatic rebound occurs due to the regression of the depressing ice, so a new cliff forms at the bottom. this creates a sequence of terraces.
what are some of the effects of climate change?
many villages lost to the sea since the domesday book (1086)
10,000 years ago England was joined to mainland europe
75% of the scottish coastline unaffected due to isostatic rebound
