New Zealand sits at the boundary between the Australian and Pacific continental plates. When these two plates bumped into each other ('collided'), the Pacific plate moved under the Australian plate, north of the South Island. As a result, there has been lots of volcanic activity. South of the South Island, the Australian plate moves under the Pacific plate instead. The plates slide past each other in the South Island, where they have pushed up the Southern Alps. Because of these two colliding plates, New Zealand often has earthquakes. One of the best known is the 2010-2011 group of earthquakes that hit the Christchurch area. 