2.7 Flashcards
(12 cards)
What is the difference between ecstatic and isostatic sea level rise
Eustatic - global scale sea level rise causing change caused by a change in the volume of water in the ocean store
Isostatic - local scale sea level change caused by a change in the level of land relative to the sea
Causes of eustatic sea level change
Thermal expansion
- as more heat is absorbed ocean temperatures rise
- causes water to expand by 0.05% for ever degree Celsius
Storage of water as ice on land (glaciers)
- as temperatures riseglaciers melt
- melt water runs off into the sea
- causes sea levels to rise
Tectonic activity
- Change in rate of sea floor spreading: changes in the rate alters the volume of the ocean basins
- Emission of geothermal heat into oceans by underwater volcanic activity can cause thermal expansion of ocean water
Causes of isostatic sea level rise
- when the weight of an ice sheet on land causes it to sink (isostatic subsidence)
- gives the appearance that the sea has risen
- when the ice melts th reduces weight causes the land to readjust and rise (isostatic rebound/recovery)
- this gives the appearance that the sea level is falling
What is an emergent coastline
Coastlines that are risking relative to sea level, typically due to isostatic uplift (Scotland/north of England)
Emergent coast landforms - raised beaches
- beaches which are above high tide level
- flat surface covered by sand or round pebbles
- usually vegetated by plant succession
- formed by falling sea levels or land uplift due to isostatic rebound
- often backed by fossil cliffs
- Isle of Arran Scotland
Emergent coast landforms - fossil cliffs
- a steep slope found at the back of a raised beach
- they show evidence of formation through marine erosion but now they are above high tide level so no longer vulnerable to this
- formed when sea retreats/land rises leaving cliffs stranded
- Isle of Arran Scotland
What is a submergent coastline
Coastlines that are sinking or where sea level is rising relative to the land (south of England)
Submergent coastline landform - ria
- A drowned river valley (a section of a river valley flooded by the sea)
- formed when sea level rises
South Devon has a 6m long ria
Submergent coastline landform - fjord
- a flooded glaciated valley formed when a glacier erodes vertically created a u shaped valley
- formed when sea level rises and floods a u shaped valley
- sognefjord Norway
Submergent coastline landform - fjard
- drowned glacial low land (less dramatic than fjords)
- formed in areas of low relief
- western Finland coast
Submergent coastline landform - Dalmatian coast
- long narrow islands running parallel to the coast separated by narrow sea channels
- formed by sea level rise flooding the coastline with the geological structure of folds aligned parallel to the coast
- Croatia
Historical sea level rise
- During the ice ages (approximately 20,000 years ago) sea levels were 120m lower
- During the post ice age period of warming (about 120,00 years ago) temperatures rose therefore glaciers melted so sea levels rose rapidly
- For about 6000 years before 1850 sea levels were relatively stable during the pre industrial phase
- From 1850 to present the burning of fossil fuels since the industrial era have accelerated global warming resulting in a sea level rise of
o 1.4 mm a year (1900-1990)
o 3.3 mm a year since 1993
