What causes hawaii to have volcanoes?

Hawaiian plumes and the hotspot activity.

Explanation:

As volcanoes are created by the collision of the two plate boundary the Hawaiian volcano is a result of the Hotspots created by the sudden shift and movements in the Pacific plates.  The presence of the magma chambers induces this hotspot activity and as this slowly increases over time make the volcanoes active and these are formed by the convective cells that originate from the mantel of the earth.