Tectonic Plate Model Hawaiian-Emperor Volcanic Chain
		Schematic block diagram of Hawaiian-Emperor Volcanic Chain. Volcanic mountain/islands are produced at the magmatic hot spot as partial melting of upper mantle rocks at 60-170 km (35-105 mi) depth produces molten magma which is in turn forced upward through the more rigid crust. The actual mechanism of magma formation is not well understood, but the 10-15% volume increase associated with the transformation of crystalline rock to molten magma and bouyancy of the less dense magma are the main forces driving the magma upward. As the Pacific Tectonic Plate moves across the hot spot a chain of oceanic volcanic mountains is produced. Eventually the mountain/islands subside and are eroded to produce, successively, low islands, reef shoals/atolls, and submerged seamounts. Such a process has been going on in the North Pacific for more than 70 million years. The numbers above the peaks indicate ages in millions of years. The oldest seamounts have already been subducted below the Aleutian Islands. (modified from Bradshaw and Weaver, 1993)