8.2. Sea level change on Coastal Landforms

Question 1

Sea level changes

Answer 1

• On a human timescale, sea level appears to be constant
• However, the global timescale shows alarming fluctuations
• During the one million years, sea level has fluctuated from just above current levels in the water interglacial periods to almost 120m below present levels during the cold glacial periods
• These changes have had a significant impact on the coastline and on coastal features

Question 2

Main types of Sea Level Change

Answer 2

1) Eustatic (world-wide)

2) Isostatic

Question 3

Eustatic Sea Level Change

Answer 3

• Produced by climate change
• Could be a future effect of global warming
• A related factor is the thermal expansion and contraction of the oceans
• When the climate is warmer, the oceans are warmer; they expand and take up more room - global sea level rises
• The opposite is true during a time of global cooling

Question 4

Isostatic Sea Level Change

Answer 4

• Produced by the melting of local ice cap, the deposition of delta sediments or by tectonic changes
• All of these processes lead to the depression or elevation of Earth’s crust in one particular place. If crust moves vertically, sea level will change in that place

Question 5

Coastal landforms produced by a rising sea level

Answer 5

• A rise in sea level drowns the lowlands near the old coastline and drowns the lower parts of valleys
• This is mostly due to the rapid eustatic rise in sea level at the end of the last glacial period

These would besubmergent landforms

1) Rias
2) Fjords
3) Dalmation Coast

Question 6

Rias

Answer 6

• Drowned river valleys
• In cross-section, rias are V-shaped and have a smooth, concave long section
• Form deep, sheltered harbours with many branching arms

Question 7

Fjords

Answer 7

• Drowned glaciated valleys
• Typical U-shaped cross section and fjords get deeper as you move further from the sea
• Very long and narrow

Question 8

Dalmation Coast

Answer 8

• When sea level rose at the end of the last glacial period, the valleys were flooded and the ridges became long, narrow islands
• Drowned coastlines with long narrow islands

Question 9

Coastal landforms produced by a falling sea level

Answer 9

• Fall in sea level leads to coastal features being left high and dry, often some way from the new coastline
• This has been mostly due to the steady fall in sea level over the last 10 million years but also to higher sea levels during more recent interglacial periods

1) Raised Beaches
2) Emerged Coastal Plains

Question 10

Raised beaches, with relict beach features

Answer 10

• Relict features such as wave-cut platforms, cliffs, caves, arches, stacks
• These features are a result of an initial rise in sea level at the end of the last glacial period, followed by a rise in the land due to isostatic rebound

Question 11

Emerged coastal plains

Answer 11

• In a part of the world with a wide, shallow continental shelf, a fall in sea level can produce a wide coastal plain, backed by a relict line of cliffs which represent the old coastline

Question 12

Future change in sea levels

Answer 12

• Measurements show that sea level is rising
• It may be because we are still coming out of our last ice age
• Most people think that it is mainly because the planet is getting hotter (human-induced climate change), melting ice at the poles and thermally expanding seawater