Coastal
Landscapes
and Change
Enquiry Question 3: How do coastal erosion and sea level
change alter the physical characteristics of coastlines and
increase risks?
, 2B.7 Sea level change influences coasts on different timescales.
Sea level change on a day-to-day basis is a result of tides, changes in atmospheric air
pressure and winds. Such changes are very short term. However, over long time scale, sea
level changes are more permanent and the outcome of complex factors. Part of the
complexity is that a change in sea level can be brought about by a change either in land
level (Isostatic change) or in the volume of the sea (eustatic change).
Eustatic Change Isostatic Change
Weight of ice depresses the land, so
lands level falls.
Sea level rises when land ice melts.
Ice Melting Melting of ice causes weight to be
Sea level falls when it freezes ice caps.
removed, so land rises/rebounds =
Isostatic rebound.
As oceans warm, they expand (thermal
Thermal
expansion) causing a rise in sea level.
Changes (Sea ---
As oceans cool, they contract (thermal
Temperatures)
contraction), causing a fall in sea level.
Sediment transported by rivers into Sediment deposited when rivers
the sea deposits it on the seafloor, meets the sea = delta. Over time, it
Subsidence
causing a rise in sea level, as there's sinks under weight of more
less capacity to hold water. deposition = rise in sea level.
Sediment transported by rivers into Sediment deposited when rivers
Accretion
the sea deposits it on the seafloor, meets the sea = delta. Over time, it
(Sediment
causing a rise in sea level, as there's sinks under weight of more
Accumulation)
less capacity to hold water. deposition = rise in sea level.
Volcanic islands form in oceans,
displaces the water, so there's a rise in
Uplift of land at plate boundaries
Tectonics sea level.
(subduction) = a fall in sea level.
Plate movement could reduce size of
an ocean basin.
Emergent and Submergent Coast
Marine transgression is a rise in relative sea level, so sea will flow over land, produces a
submergent coast, eg: rias, fjords and Dalmatian coasts.
Marine regression is a fall in relative sea level, exposes sea floor, producing an emergent
coast, eg: raised beaches with fossil cliffs.
A marine transgression results from a eustatic rise in sea level (at the end of a glacial
period) and an Isostatic rise in sea level (when land sinks under the weight of accumulated
snow and ice). In both cases, large areas of land are submerged beneath the sea, producing
a submergent coast. The ria coastline is one of the best examples of such a coast.
Landscapes
and Change
Enquiry Question 3: How do coastal erosion and sea level
change alter the physical characteristics of coastlines and
increase risks?
, 2B.7 Sea level change influences coasts on different timescales.
Sea level change on a day-to-day basis is a result of tides, changes in atmospheric air
pressure and winds. Such changes are very short term. However, over long time scale, sea
level changes are more permanent and the outcome of complex factors. Part of the
complexity is that a change in sea level can be brought about by a change either in land
level (Isostatic change) or in the volume of the sea (eustatic change).
Eustatic Change Isostatic Change
Weight of ice depresses the land, so
lands level falls.
Sea level rises when land ice melts.
Ice Melting Melting of ice causes weight to be
Sea level falls when it freezes ice caps.
removed, so land rises/rebounds =
Isostatic rebound.
As oceans warm, they expand (thermal
Thermal
expansion) causing a rise in sea level.
Changes (Sea ---
As oceans cool, they contract (thermal
Temperatures)
contraction), causing a fall in sea level.
Sediment transported by rivers into Sediment deposited when rivers
the sea deposits it on the seafloor, meets the sea = delta. Over time, it
Subsidence
causing a rise in sea level, as there's sinks under weight of more
less capacity to hold water. deposition = rise in sea level.
Sediment transported by rivers into Sediment deposited when rivers
Accretion
the sea deposits it on the seafloor, meets the sea = delta. Over time, it
(Sediment
causing a rise in sea level, as there's sinks under weight of more
Accumulation)
less capacity to hold water. deposition = rise in sea level.
Volcanic islands form in oceans,
displaces the water, so there's a rise in
Uplift of land at plate boundaries
Tectonics sea level.
(subduction) = a fall in sea level.
Plate movement could reduce size of
an ocean basin.
Emergent and Submergent Coast
Marine transgression is a rise in relative sea level, so sea will flow over land, produces a
submergent coast, eg: rias, fjords and Dalmatian coasts.
Marine regression is a fall in relative sea level, exposes sea floor, producing an emergent
coast, eg: raised beaches with fossil cliffs.
A marine transgression results from a eustatic rise in sea level (at the end of a glacial
period) and an Isostatic rise in sea level (when land sinks under the weight of accumulated
snow and ice). In both cases, large areas of land are submerged beneath the sea, producing
a submergent coast. The ria coastline is one of the best examples of such a coast.
