Headlands and bays are features of coasts that are formed by erosion. Waves
wear down different types of rocks at different rates. Softer rocks wear away
more quickly than harder rocks.
Bays form where the waves erode soft rocks, but headlands are left as land that
juts out into the water.
Sea caves and blowholes
sea cave, cave formed in a cliff by wave action of an ocean or lake. Sea caves
occur on almost every cliffed headland or coast where the waves break directly
on a rock cliff and are formed by mechanical erosion rather than the chemical
solution process that is responsible for the majority of inland caves.
Zones of weakness in the cliff give way under the force of the waves and are
eroded out; these cavities are enlarged by the hydraulic pressure built up by
each wave.
Holes, commonly known as blowholes, may eventually be forced through the
roof of the cave to allow the pressure created by each wave to be released as a
jet of spray.
Collapsed sea cave, Santa Rosa Island, California.
CAVES, ARCHES, STACKS
Erosion can create caves, arches, stacks and stumps along a headland.
Caves occur when waves force their way into cracks in the cliff face.
The stack will be attacked at the base in the same way that a wave-cut notch is formed.
This weakens the structure, and it will eventually collapse to form a stump.
Caves occur when waves force their way into cracks in the cliff face. The water
contains sand and other materials that grind away at the rock until the cracks
become a cave. Hydraulic action is the predominant process.
If the cave is formed in a headland, it may eventually break through to the other
side forming an arch.
The arch will gradually become bigger until it can no longer support the top of the
arch.
When the arch collapses, it leaves the headland on one side and a stack (a tall
column of rock) on the other.
The stack will be attacked at the base in the same way that a wave-cut notch is
formed. This weakens the structure and it will eventually collapse to form a stump.