Sea Level Change

Question 1

Why are sea levels rising?

Answer 1

Global warming - polar ice sheets and glaciers are melting, and thermal expansion.

Question 2

What is thermal expansion?

Answer 2

Sea water expands as it warms.

Question 3

How have temperature and sea levels risen?

Answer 3

Average global temps - 0.85°C from 1880-2012.

Average sea levels - 21cm from 1870-2010

Question 4

What are the types of long term sea level change?

Answer 4

Eustatic

Isostatic

Question 5

What is eustatic change?

Answer 5

When the sea level itself rises or falls

Question 6

What is isostatic change?

Answer 6

When the land rises or falls, relative to the sea

Question 7

Why does eustatic change occur?

Answer 7

In cold, glacial periods, precipitation falls as snow and forms huge ice sheets that store water normally held in the oceans. As a result sea levels fall.

At the end of glacial periods, as temperatures rise, the ice sheets begin to melt and retreat.
Their stored water then flows into the rivers and the sea again, and sea levels rise.

Question 8

Where does isostatic change occur?

Answer 8

Locally

Question 9

Why does isostatic change occur?

Answer 9

During glacial periods, the enormous weight of the ice sheets makes the land sink (isostatic subsidence).

As the ice begins to melt at the end of a glacial period, the reduced weight of the ice causes the land to readjust and rise (isostatic recovery).

Question 10

What change occurs quicker?

Answer 10

Eustatic - glacial meltwater caused a relatively rapid rise is sea level, which led to the formation of the English Channel and the North Sea.

However, the land only started to rise very slowly, and is still rising now.

Question 11

What are types of isostatic change that occur in the UK?

Answer 11

Land in the north and west which was covered by ice sheets during the last ice age, is still rising as a result of isostatic recovery.

Land in the south and east (which the ice sheets never covered) is sinking. Rivers pour water and sediment into the Thames estuary, and the weight causes the crust to sink and relative sea levels to rise.
Also the land is rebounding from the ice age now the ice sheets have melted.

Question 12

What landforms are caused by changing sea level?

Answer 12

Emergent coastlines -
Raised beaches
Relic cliffs

Submergent coastlines -
Rias
Dalmatian coasts
Fjords

Question 13

What are emergent coastlines?

Answer 13

A fall in sea level exposes land previously covered by the sea

Question 14

What are submergent coastlines?

Answer 14

A rise in sea level that floods the coast.

Question 15

What are emergent coastline landforms?

Answer 15

Raised beaches

Relic cliffs

Question 16

How are emergent coastline landforms created?

Answer 16

As the land rose as a result of isostatic recovery, former shoreline platforms and their beaches were raised above the present sea level.

Raised beaches are common on the west coast of Scotland, where often the remains of eroded cliffs (called relic cliffs) can be found behind the raised beach, with wave-cut notches and caves as evidence of past marine erosion.

Question 17

What are rias?

Answer 17

Sheltered winding inlets with irregular shorelines.

Question 18

How do rias form?

Answer 18

When valleys in a dissected upland area are flooded.

Question 19

What are Dalmatian coasts?

Answer 19

Similar to rias.

The rivers flow almost parallel to the coast - rather than at right angles to it.

Question 20

What are fjords?

Answer 20

Formed when deep glacial troughs are flooded by a rise in sea level.

They are long and step sided, with a U shaped cross-section and hanging valleys.
Unlike rias, fjords are much deeper inland than they are at the coast. The shallower entrance marks where the glacier left the valley.