The apostles were formed by erosion: the harsh weather conditions from the Southern Ocean gradually eroded the soft limestone to form caves in the cliffs, which then became arches, which in turn collapsed; leaving rock stacks up to 45#160;metres high.br/br/The Great Ocean Road hugs the south-eastern coastline, providing visibility of Bass Strait and the Southern Ocean. The road traverses rainforests, as well as beaches and cliffs composed of limestone and sandstone.