Sea level Flashcards
1
Q
Why is sea level important?
A
- Enough ice sheets to raise sea level by 70m
- 200 million people live in coastal floodplains.
- Indian Ocean tsunami 2004, Hurricane Katrina, Thames Barrage etc
2
Q
What are some key concepts in sea level change?
A
- Eustasy
- Isostasy
- Relative sea level changes
3
Q
What is Eustasy?
A
- A change in global sea level that may reflect a change in water quantity or a change in the actual shape of ocean basins.
4
Q
What is isostasy?
A
- Describes conditions where Earth’s surface and mantle try to find a balance or a gravitational equilibrium- isostatic uplift.
- Occurs because the crust floats on the mantle.
5
Q
What is glacioistosasy?
A
- If ice load is removed: 3 stages of glacioisostatic ulift
1) Restrained rebound
2) Postglacial rebound
3) Residual rebound
6
Q
What is a relative sea level change?
A
- Cannot refer to absolute sea level as it is effectively meaningless
- Relative sea level rise is a rise in sea level relative to the land.
- It may occur due to Eustasy, isostasy or a combination of the two.
7
Q
What are the controls on Eustasy?
A
- Volume of ocean basins- spreading rate, ocean trenches, sediment, plate tectonics
- Volume of water- glaciations, hydrosphere, volcanism, ocean temps, amount of water vapour
8
Q
What is the geoid?
A
- If the earth was uniform in mass distribution, it would be an absolute sphere.
- The ‘geoid’ is the shape that the sea surface would have if the ocean were not in motion and was only influenced by gravity.
9
Q
What happens if an EQ grows or shrinks?
A
- This not only affects Eustasy and isostasy but also gravitational attraction of water to ice.
- When an ice sheet shrinks, the gravitational attraction decreases between the ice and the water- not what you’d expect.
- If Antarctica and Greenland ice sheets melted the same amount, there would still be huge variations in spatial sea level rise.
10
Q
What else might cause a change in sea level?
A
- tidal or natural variability
- tectonic
11
Q
What is sea level change closely linked to?
A
- Tectonics
12
Q
What happened in 1953?
A
- North Sea flood
- One of the worst disasters in the UK
13
Q
What caused the events of 1953?
A
- Intense depression moved from Scotland to Denmark. Low pressure results in a higher sea level and in this case a rise of about 43cm
- As the low pressure system moved east, very strong winds funnelled water towards the southern part of the North sea.
- The surge then moved down the east coast.
- When this surge coincided with high tide the results were catastrophic, especially as high winds combined to form large waves.
14
Q
How can we calculate storm water level?
A
- Predicted tide level + surge + wave height
15
Q
What were the consequences of the North Sea Flood in 1953?
A
- East coast of England: over 300 people died
- 24,000 houses flooded
- 40,000 people evacuated from their homes
