Australia, which sits at the leading edge of the giant Indo-Australian Plate, moves in a northeasterly [right] direction. In so doing it collides with the western edge of the Philippine Plate. This collision pushes up the ocean floor above sea level, creating island chains, island arcs, and a twisted, tumultuous sea floor .

The Pacific Plate, moving northwest, subducts under the eastern edge of the Philippine Plate. This area of subduction is a hotbed of volcanic and earthquake activity and part of the infamous "Ring of Fire." You can see a mid-ocean ridge to the south of Australia, the site of sea-floor spreading. New Zealand, to the southeast, exists along this complex tectonic boundary.
   
Thanks to Bruce Heezen and Marie Tharpe.

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