Rocky Coasts and Coastlines
75% of the world’s coasts are rocky.
Most along active geologic margins (not all)
Many are the result of erosional processes
Morphology of coasts is a function of:
Structure and composotin of bedrock
Physical, chemical, and biological processes operating on the coast
Coasts are rocky because they don’t accumulate sediment
Also occur where the sediment has been turned into rock through cementation
Locally: Volcanoes!
ACTIVE MARGINS tend to produce rocky coasts
Rivers in these areas are typically short and provide coarse material (with some exceptions)
California example: deep submarine canyons enar the coast result from narrow continental
shelf-much sediment transported down the canyons.
Glaciated coastlines-erosional-fjords (Scandanavia, BC Canada), scouring of sediment leaving
bedrock (Acadia NP Maine)
Rocky carbonate islands formed when sea level was higher-Bahamas, Australia, Caribbean,
Bermuda
BEACHROCK-lithified sands by carbonate sediment-common in tropical locations
Physical Processes of Erosion
Wave-induced erosion-wave action of breaking waves with cool names like: wave
hammer, air compression, quarrying, and abrasion
Northern Latitudes also have Freeze-Thaw cycles affecting the rock (9% expansion by water
when it freezes)
Some biological erosion (boring into sediment)
Factors affecting erosion:
Rock Type
Degree of fracturing
Wave Energy
Tidal Range (time and height over which waves act)
Climate
Relative sea level
Sea Cliffs can form from undercutting
High cliffs tend to form in mid-latitudes where wave energy is high
Low latitudes-more chemical weathering, lower wave height
Benches or Platforms: often result from differential weathering, also can be wave cut (10 m
deep platform in So. California where waves don’t really affect anymore-rising sea level has
drowned it.
Marine Terraces: uplifted or downdropped benches. Examples from New Zealand where uplift
has left the benches separated by steep cliffs reflecting rate of uplift.
Sea stacks, arches and erosional features