Volcanism for the Geological Dummy

eruption of melted rock (lava) from a volcano

From time to time we let the Antisocial Network's staff geologist out to see what dumbassery he can find about some of the most well-known events in the earth sciences. Many of the freelancers he catches are babbling incoherently about earthquakes, some blather about oil or mining, and quite a few think they can "educate" their readers about volcanoes. Landing squarely in group three, then, we find Catalogs.com "guru" George Garza and his monumentally doofus article, "What Makes a Volcano Erupt?" (now credited to "catalogs editorial staff").

Our geologist tells us that the answer to that question can be either shallow enough for first-graders or deep enough for a PhD volcanologist. Garza's answer, if you can call it that, lies at about the junior-high level. Unfortunately, George got off to a bad start, when he asked the rhetorical question, "What is a volcano?" His answer?

"It is a geologic formation which has fissures that lead to a deep part of the earth. "

At that point, our geologist hung his head in sorrow, in part because a volcano isn't a "formation," and in part because that's a really stupid answer. For what it's worth, a volcano might be called a "feature," but the word "formation" means something very specific to a geologist and a volcano ain't it. Whatever. Garza meandered on, providing a fragmentary and mostly incorrect explanation of the forces behind a volcanic eruption:

1. "The pressure under the earth is usually caused by tectonic plates which can come together or come apart, causing these fissures to appear."
2. "The magma pressure is from a heat source. It comes from natural radioactive decay within the Earth."
3. "This concentration of radioactive elements is not very high, but this is offset by the volume of the Earth. There is enough earth to add a significant amount of heat produced from the decay to cause the melting." 
4. "The material that melts, the magma, has a lower density and it migrates to the surface."
5. "The increasing pressure pushes the magma topside."

Here's what our geologist thinks George was trying to say, with corrections:

1. Ugh. That's a truly lousy description of volcanism at plate margins, making it appear as if there are only volcanoes at divergent margins. The entire "ring of fire" surrounding the Pacific plate comprises island arcs at convergent margins, George!
2. No, George, the heat of radioactive decay is (probably) the driving force behind plate movement, not the movement of magma.
3. Melting of what, George?
4. Guess what, George: you got something (sort of) right!
5. ...and then blew it: melted rock is less dense than solid rock, so magma is buoyant. Buoyancy is the force that causes magma to rise.

Some of Garza's other dumbassery includes the claim that, "Active volcanoes are the ones where there is still some activity present." Circular much, George? In fact, "active" means that the volcano has erupted with the past 10,000 years, not that it is bubbling and steaming.

And finally, Garza favored us with this fascinating pronouncement: "Volcanic eruptions are a thing of awe but can be deadly despite their appearance." Yeah, sure... as if there was any question remaining whether Garza deserves his Dumbass of the Day award, that certainly settles it!

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SI - VOLCANOES