Pacific Ocean

The Pacific Ocean is the body of all the salt water between Asia and Australasia in the west, the Americas in the east, the Southern Ocean to the south, and the Arctic Ocean to the north. It is the largest named ocean and it covers half the surface of the entire world. It joins the Atlantic Ocean at a line drawn due south from Cape Horn, Chile/Argentina to Antarctica, and joins the Indian Ocean at a line drawn due south from Tasmania, Australia to Antarctica.

A map of the Pacific Ocean. It is ringed by many volcanoes and oceanic trenches.

As the Atlantic slowly gets wider, the Pacific is slowly shrinking. It does this by folding the sea floor in towards the centre of the Earth - this is called subduction. This bumping and grinding is difficult so there are many earthquakes and volcanoes when the pressure builds up and is suddenly released when the rocks break. When an earthquake happens under the sea, the sudden violent jerk causes a tsunami. This is why tsunamis are more common around the rim of the Pacific than anywhere else. Many of the Earth's volcanos are either islands in the Pacific, or are on continents within a few hundred kilometres of the ocean's edge.