I would like to know about magma plumes. I was also told that Hawaii is actually a set of sea mounds which were once active volcanoes that moved way from a magma plume and have cooled. Is the plume stationary and the plate moves over it causing the island arc chain?

rocky Jackie Kitzler

Dear Jackie,

About 95% of the world's volcanoes are located near the boundaries of tectonic plates. The other 5% are thought to be associated with mantle plumes and hot spots. Mantle plumes are areas where heat and/or rocks in the mantle are rising towards the surface. A hot spot is the surface expression of the mantle plume. Geologists think the hot spots are stationary and the tectonic plates are mobile. The hot spot provides magma which supplies volcanoes. The movement of the plate carries the volcano off the hot spot and it gradually becomes extinct and usually subsides below sea level. A new volcano begins to form on the sea floor and grow towards the surface. Some of these volcanoes rise above sea level to make islands. The classic example is the Hawaii-Emperor volcanic chain, a line of volcanoes and seamounts that extends from Hawaii to Daikakuji, 2,200 miles (3,500 km) to the northwest. Suiko seamount is 65 million years old, the oldest seamount associated with the Hawaiian hot spot. The hot spot is probably older but any volcanoes it produced have been destroyed by subduction.

At first glance the shape and topography of the Hawaii-Emperor volcanic chain might remind you of an island arc. However, volcanoes of the Hawaii-Emperor volcanic chain are progressively younger towards Hawaii and made of basalt. Island arc are produced at convergent plate boundaries where an ocean plate is subducted beneath an adjacent ocean plate. The Aleutians of Alaska is an example. There is no age progression and andesite is the most common rock.

Steve Mattox, University of North Dakota 

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