The active volcano’s in Hawaii are situated on top of a ‘hot spot’ in the earth’s crust. The earths crust has been moving for millions of years which allowed this hot spot to create a long line of islands in the Pacific Ocean. If you follow the line of these islands they are in a straight line heading northwest. At around the island of Midway  the submerged sea mounts which are also part of this chain turn northward. The current theory is that 45 million years ago when the Indian continent crashed into Asia all the earths plates were disrupted causing the radical shift in the direction of the Pacific plate.

(The Great Courses – The Nature of Earth: An Introduction to Geology)