On the coast water
is hitting the land all the time which causes erosion.
The water also carries rocks and they hit the edge of the rock which grinds
away even more rock.
If there is softer rock or
a crack or fault at the bottom of a headland
or a cliff then the waves break into the rocks and this starts to make
a cave.
If the caves at the bottom
of a cliff get big enough, they will undermine the cliff and part of it
will collapse into the sea.
When the waves make caves
on both sides of a headland after a long time, the caves grow larger and
may eventually meet in the middle of the headland. This makes an
arch. An arch is where the rock has been eroded away and an arch
shape is left.
When the top of the rock
arch falls into the sea, a tall pillar of rock is separated from the headland.
This is called a stack.
Along the coast road
that runs from Victoria to South Australia there are lots of arches and
stacks. The Twelve Apostles are examples of stacks.
If the roof of a cave collapses
it might create a blowhole. The waves splash into the cave and the
pressure of the water makes it spurt up through the hole and into the air.
There is a well known blowhole at Kiama on the coast of NSW.
Click HERE
to see our model of a cave, an arch and a stack.
