The volcanic rock at the base of the cliff is formed mainly of basalt (black) and scoria (purple). Scoria is eroded more readily by the sea than basalt, causing channels and tunnels to form. This process of erosion not only creates blowholes, but in time destroys them.

Before the turn of the century there was a blowhole on the Cape which roared so loudly, that when conditions were favourable it could be heard in Portland. Sometime around 1900 it collapsed, but new ones are forming and when a good swell is running, spectacular spouts of sea spray are pushed high into the air.

This coastal area is so intriguing, that it is possible to sit and watch for hours. Local Aboriginal communities attached many legends and myths to the Blowholes and remainders of middens (scatterings of shells) can be seen along the cliff-tops.