Transcript 103-27bCoastalErosionalLandforms

COASTAL EROSIONAL
LANDFORMS
GEOL 1053
LIST OF MAJOR COASTAL EROSIONAL
LANDFORMS
(involving consolidated rocks)
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Sea cliffs
Wave-cut platform
Sea arches
Sea stacks
Sea caves
Coastal waterfalls
WAVE-CUT PLATFORMS
• Erosion of a sea cliff leaves
a gently sloping rock
platform that is visible at
low tide. It may be partly
covered by a veneer of
coarse-grained sediments,
even cobbles and boulders.
wave-cut notch
wave-cut platform
Wave-cut platform: Headland and beach cut on
Oligocene Amuri Limestone. (south of Kaikoura,
South Island, New Zealand)
Wave-cut platform
SEA ARCHES:
• Differential weathering at tide level along a narrow promontory.
• Natural bridge (sea arch) in Plio/Pleistocene limestone (North
coast of Aruba).
SEA STACKS
• More resistant rock remains as a promontory because of compositional or
structural differences which lead to differential weathering & collapse of
arches.
• Sea stacks and sea arches in cyclically bedded Upper Cretaceous
chalks (French Channel coast).
SEA STACKS
(CONT.)
Sea stacks along a cliffed, rocky coastline (Victoria coast,
Australia). Large waves from the Southern Ocean have eroded
fractured sandstones into a series of headlands and isolated
stacks (remnants of headlands). Although clearly vulnerable to
wave erosion, such stacks survive for tens to hundreds of years.
SEA CAVES
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Deep erosion locally in a sea cliff
Of weaker rocks
At tide level
“Blowholes” may
develop where roof
collapses
COASTAL WATERFALLS
• when horizontal cliff erosional retreat is
faster than stream bed erosion downward
• produces a “hanging valley”
Evolution of a drowned coastline
(ria coast):
- erosion occurs
- sediments form
- shoals develop
- depositional
landforms (beaches,
spits, etc.) develop
There is a tendency for the coast to
straighten - all other factors being equal
(more resistant rocks will form headlands
while the less resistant rocks will form
embayments). Bays fill with sediments.
Large erosional talus blocks of Pleistocene limestone that have
tumbled down the erosional escarpment that exposes the Scotland
Fm. in the background. Note the wave-cut notches at the base of
the talus blocks. Such notches, cut by physical and biological
processes, are excellent indicators of sea level and can be
preserved in some circumstances. Human bathers. (Bathsheba,
Barbados)
END OF FILE
Rocky, tectonically active, immature coastline with
numerous small offshore sea stacks and islands(San
Francisco-Mendocino area, California).