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On Earth, there are only two different ways to create major volcanoes.

One way is subduction. It occurs when older/heavier rock sinks beneath younger/lighter rock. As the rock descends, it liquefies into magma, climbing up to the surface as a mountain concealing a deadly magma chamber. This is why the Pacific Ring of Fire ranks highly among the most dangerous of all the volcanoes.

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The other way is rarer and more stationary. The volcanoes of Hawaii, Iceland, the Galapagos and Yellowstone form from plumes of mantle beneath the surface, making them "hotspot volcanoes". When a plate moves, the plume stays put.

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Let's say someone thought up of a mantle plume near or even in a subduction point. Is this geomechanically possible? If yes, then how deadly would a subductive hotspot volcano be?

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  • $\begingroup$ 1) Your images are broken - I get pictures of D-Link Router login screens when I click on the links. 2) You should try earthscience.stackexchange.com $\endgroup$ – Aify Jul 3 '16 at 5:04
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    $\begingroup$ Earth Science looks down on speculative scenarios. And since we don't have mantle plumes in or near subduction zones, this counts as WB. $\endgroup$ – JohnWDailey Jul 3 '16 at 5:31
  • $\begingroup$ It would be like Iceland. $\endgroup$ – JDługosz Jul 3 '16 at 6:08
  • $\begingroup$ @JDługosz how would it be like iceland when Iceland is not a subduction zone? Subduction happens in convergent boundaries not divergent ones. $\endgroup$ – Martine Votvik Jul 3 '16 at 12:27
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I'd go with not impossible, but unlikely.

A mantle plume is generally a spot where hotter magma flows flows upward to replace cooler magma sinking somewhere else. So they would generally be located in areas where the mantle is hottest. Which would be same as the areas where the magma that sunk somewhere else has had most time to warm up. Which is the same as the spots farthest away from areas where cooler magma sinks.

And the the areas where magma cools and sinks are the subduction zones. The melting of the plate absorbs energy, which cools the magma and makes it sink. This sucks magma below the plates toward the subduction zones so that it is cooler the closer the subduction zone it is. At the lower level the magma flows away from the subduction zone and gets warmer as it goes, so it is hotter the farther away from subduction zones it is.

So normally the hotspots would be roughly in the middle of the subduction zones. But we are talking about 3D flows in curved space, so I am not going to say it is impossible to have hotspot "cross" a subduction zone, if the geometry is complex enough. Still, I'd recommend just having a super volcano without coupling it with a hot spot. It will spectacular enough...

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One way I could imagine this to happen is if there was a shift in plate tectonics where one plate that had previously just slid alongside another begun to submerge beneath it instead. The submerging plate might then jam into a hot spot underneath the other plate and wreck some unpredictable effects on magma chambers positioned above it.

To my imagination it seems possible that this could contribute to a powerful eruption from the magma chambers.

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