Geosphere Lecture 4

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Three reasons for sea level change
Eustatic controls, Isostatic adjustments, tectonic controlss on ocean basin volume.
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What is Eustatic Controls?
(sea water & ice volumes, thermal expansion of water)
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What are Isostatic adjustments?
due to surface loading and unloading)
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The extent of the coastal zone corresponds to limits associated with
changes in sea level over the Quaternary (last 2.58Ma: glacial–interglacial cycle
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Water depth at edge of continental shelf is
100-200 m
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Waves are generated by
wind & seismic activity
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Deep water wave height is determined by
wind speed and duration
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As waves approach the shore they are influenced by the
frictional drag of the sea bed
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Waves steepen before
breaking
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Some of the wave’s energy is dissipated, providing energy to drive
sediment transport processes
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Tides are produced by the attraction of the
sun and moon
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Tides are influenced by
shape and size of ocean basins, and by the coriolis force
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Actual near-shore water levels can be increased by
storm-surge
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Tidal Range:
High - Low water level during tidal cycle
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Tidal Range is controlled by:
Bathymetry Width of continental shelf Coastal configuration Distance from amphidromic point
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Microtidal , Mesotidal , Macrotidal
under 2 metres, 2-4 metres , over 4 metres
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Erosional Coasts
High Energy systems with low sediment inputs
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List some Controls on coastal erosion
Wave environment (wave height, storm event frequency), Coastal lithology (susceptibility to weathering & erosion, structure, availability of erosional tools), Coastal morphology (planform configuration, cliff height and angle, bathymetry),
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List Erosional Landforms
Cliffs, Shore Platform
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Depositional coasts
Low energy systems or high sediment inputs
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Beach Gradient depends on
sediment size
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Beach form varies
seasonally
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Barrier Islands
Low gradient coasts with low tidal range , Linear, parallel to land & separated by a lagoon
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Estuaries are valley and lowland areas drowned by
post-glacial sea level rise,
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Estuaries are a zone of
salt and fresh water mixing
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Estuaries Sediment is derived from
local, fluvial and coastal sources
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Estuaries deposition is controlled by
sediment size, water energy & salinity
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Salt marshes occur on
upper parts of intertidal zone
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Salt Marshes are Dissected by
tidal creeks that supply/ remove water & sediment
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Controls on sediment supply to coast:
Catchment characteristics (size, relief, lithology, tectonics), Climate, soil and vegetation, Human Activity in catchment
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Delta growth reflects the balance between
Sedimentation (due to sediment supply) Subsidence and compaction Sediment reworking by waves, tides & currents Sea level change
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Impacts on deltas & mega-deltas by 2050
Coastal erosion Subsurface abstraction oil, water, gas Increased population pressure (500 people per km2 on average) Changing sediment input Precipitation change Sea level change Land & shelf subsidence
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Other cards in this set

Card 2

Front

What is Eustatic Controls?

Back

(sea water & ice volumes, thermal expansion of water)

Card 3

Front

What are Isostatic adjustments?

Back

Preview of the front of card 3

Card 4

Front

The extent of the coastal zone corresponds to limits associated with

Back

Preview of the front of card 4

Card 5

Front

Water depth at edge of continental shelf is

Back

Preview of the front of card 5
View more cards

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