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Locations of Volcanoes
Image of a diagram showing a 'hotspot' volcano (e.g., Hawaii).  This image links to a more detailed image.We currently think that hot spots are caused by plumes that rise from the lower mantle. Remember that not all of the Earth's internal heat is transported by mantle convection, but that part is transported by plumes of very hot rock. Experimental and computer models suggest that when a plume reaches the lithosphere, the plume flattens out against the bottom of the lithosphere, heats it, and causes it to bulge and fracture. Decompression melting converts some of the plume material to lava that rises through cracks to the surface to form a huge flood basalt volcano. Later, as the plate continues to move over the hot spot, the "head" of the plume is sheared off, leaving the narrower hot "tail." Lava rising up the tail and through the plate over a long period of time leaves a trail of shield volcanoes leading away from the huge flood basalt deposit. Since the lavas come from the mantle, the plumes are basaltic in composition and low in dissolved gases. Plumes come in all different sizes and can occur anywhere.

All of this should sound familiar. Virtually all of these model predictions match features seen in hotspot volcanism, which is why the plume model is the leading hypothesis for hotspot volcanoes.

Image of a paricutin that links to a more detailed image.An interesting consequence of hotspot volcanism is that a hotspot volcano can occur anywhere, even in your own backyard! In fact, a volcano did occur recently in one farmer's backyard. In 1943 Dionisio Pulido found a crack spewing out red hot rocks and lava in his cornfield. Within a year the crack grew into a volcano--Paricutin--that covered his field, his farm, his local village, and everything else within five miles. Paricutin is still active in southwestern Mexico. Of course, a glance at the map will show that Paricutin is in a zone of many active volcanoes caused by plate subduction under Mexico; therefore, its location was not exactly a complete surprise. On the other hand, it is estimated that hotspot volcanism will affect every part of the Earth's surface on an average of every 500 million to 800 million years. So even if you live in Lafayette, Indiana, you might wake up some morning to find a brand new hotspot volcano in your own backyard! Photo: Courtesy of NGDC/NOAA.

(Now all you have to do is figure out the probability of that actually happening in your lifetime!)

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