2B.7 Sea Level Change

Question 1

give 3 reasons why sea levels can change in the short term

Answer 1

-high and low tides altering twice a day
-atmospheric air pressure
-winds pushing water towards a coast

Question 2

long term sea level changes

Answer 2

-occur over thousands of years
-due to eustatic and isostatic factors, and tectonics

Question 3

what is eustatic change?

Answer 3

a rise or fall in water level caused by a change in the volume in water (thermal expansion)

Question 4

how may eustatic change occur?

Answer 4

-ice sheets melt, increasing the volume of water in oceans, raising global sea levels
-thermal expansion occurs (marine transgression)- flooding low land areas

-colder, glacial periods lead to the formation of ice sheets, a decrease in the volume of water in the oceans produces a global fall in sea level
-sea bed is exposed (marina regression)

Question 5

what is isostatic change?

Answer 5

a local rise or fall in land level in relation to sea

Question 6

what can an isostatic rise be due to?

Answer 6

-post glacial adjustment
-accretion (sediment builds lands up)
-tectonics

Question 7

what can an isostatic fall be due to?

Answer 7

-post glacial adjustment
-subsidence (deposition of sediment adds weight to land)
-tectonics

Question 8

marine regression

Answer 8

where the sea bed is exposed and the sea level drops
-emergent coasts

Question 9

how can marine regression occur?

Answer 9

-eustatic fall (glacial periods form ice sheets, global fall in sea level)
-isostatic fall (ice builds up, causing Earth’s crust to sag as it melts the land rebounds upwards out of the sea)

Question 10

marine transgression

Answer 10

land is flooded and the coastline is drowned
-submergent coastlines

Question 11

how can marine transgression occur?

Answer 11

-eustatic rise in sea level (melting ice returns to water, rise in global sea level, temp and vol of water increase)

-isostatic rise in sea level (land sinks due to deposition of sediment)- subsidence

Question 12

can isostatic and eustatic changes occur at the same time?

Answer 12

yes

Question 13

give an example of a location that is sinking

Answer 13

south england
-isostatic subsidence is accelerating a rise in sea level produced by global warming

Question 14

give an example of a location that is rising

Answer 14

north england
sea levels are falling as isostatic rebound exceeds eustatic rise in global sea levels

Question 15

post-glacial adjustment

Answer 15

as the weight of ice decreases as it melts, the previously ice-covered crust slowly rebounds upwards whilst other areas subside

Question 16

why may the earth’s surface move?

Answer 16

sediment or tectonic activity

Question 17

give examples of marine regression on emergent coasts

Answer 17

Fife, Eastern Scottish Coastline
-it has rebounded, leaving cliff lines and beach platforms above the current sea level
-raised beach and fossil cliffs

Isle of Arran, Scotland
-experiencing isostatic rise of land, with raised beaches

Question 18

give examples of marine transgression on submergent coasts

Answer 18

Kingsbridge Estuary, Salcombe, Devon
-example of a ria (drowned river valley from sea level rise)
-provides a natural harbour with deep water at its mouth)

Dalmatian coastlines
-composed of long, narrow islands running parallel to the coastline and separated from the coast by narrow sea channels
-sea levels rise, leaving elongated islands offshore

Question 19

the haff coastline

Answer 19

emergent coastlines
(land is rising)
in the Baltic Sea
constructive low energy waves moved sediment landwards as sea levels rose, the long term effect of relative sea level change in this sea is caused by glacial isostatic adjustment and the global rise in mean sea level

Question 20

what is a raised beach?
(emergent coastlines)

Answer 20

relic beach now above high tide level, a flat surface covered by sand or rounded pebbles and boulders
-usually vegetated by plant succession

Question 21

what is a fossil cliff?
(emergent coastlines)

Answer 21

a steep slope found at the back of a raised beach, showing evidence of formation through marine erosion
-can contain erosional landforms e.g. notches, caves and arches
e.g. Isle of Arran has a raised beach 5m above current sea level

Question 22

Fjords

Answer 22

drowned glacial valleys- flooded by the sea
-common in glaciated areas
-have a relatively straight profile, often deeper than the adjacent sea

e.g. Sognefjord in Western Norway
-205 km long, 1.3 km deep
-main branch is 4.5 km wide

Question 23

what has climatic warming led to?

Answer 23

eustatic sea level rise
-the melting of mountain glaciers and polar ice sheets, increasing volume of water in ocean

thermal expansion of existing ocean water as temperature rises

Question 24

what has tectonic activity caused?

Answer 24

caused 10% of sea level rise
-geothermal heat into oceans by underwater volcanic activity can cause thermal expansion

Question 25

past tectonic activity

Answer 25

Heracleion- Egyptian city is now submerged as a result of local tilting of land around 1500 years ago

Question 26

present tectonic activity

Answer 26

the Indonesian tsunami and Earthquake, boxing day 2004 causes parts of the sea bed to rise by 0.1mm in Band Aceh
-earthquake caused the crust to sink, permanently flooding some parts of the city

Question 27

what are proxy records?

Answer 27

-used by Scientists to study past climates and reconstruct past climatic conditions
-proxy data is preserved physical characteristics of the environment that can stand in for direct measurements

Question 28

what coastlines are at risk?

Answer 28

-low lying ones (marine transgression causing coastal flooding)
-low lying volcanic islands- risk of complete disappearance e.g. Maldives in Indian Ocean
-volcanic islands are at risk from both global warming and tectonic activity