Story: Geology – overview

Spectacular pillow lavas are exposed in coastal cliffs near Ōamaru, in a sequence of limestones deposited in the Eocene and Oligocene periods. They are formed when molten lava is gently erupted on the sea floor and suddenly chilled. Each pillow has a dark skin of volcanic glass and a centre of grey basalt. The pale limestone between the pillows originated as lime mud on the sea floor.