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Mt. Marsili, active volcano
-out of sight but not out of mind
In the general entry on the Geology of the Bay of Naples, you will find this paragraph:
Newspapers and recent comments on geology websites have been giving some attention to one of the “four undersea cousins” of Vesuvius; to wit, Mt. Marsili. No one has quite shouted “Thar she blows!” but comments include everything from the cautionary “This is active” to the alarmist “This thing could erupt at any time!”
Mt. Marsili (named for Italian naturalist Luigi F. Marsili [1658-1730] is a pretty good candidate for the best answer to the question, “What is the largest active European volcano?” depending, of course, on how you define “European” (mainland? islands? undersea?) and “active” (when was the last eruption?). Those are quiz-show quibbles, though. Even Etna is on an island (Sicily) as are the smaller still very active volcanoes of Stromboli, Vulcano, and Lipari in the Aeolian archipelago just above Sicily; Vesuvius is dormant (or just snoozing a bit) and the Solfatara sulphur pit in Pozzuoli is a volcano only to geologists, and what do they know? (I mean, these are the guys who tell you the world is older than 7,000 years!)
In any event, Marsili is a seamount volcano (that is, submerged) in the same Aeolian volcanic arc as the islands mentioned above. Marsili is right above those islands and 175 kilometers (109 miles) south of Naples (see map, above). Be glad you can’t see this thing; the seamount is 3,000 meters tall (almost 10,000 feet), about the same as Etna. The long axis of the volcanic structure (really two adjacent mounts) is NNE-SSW; the base is 70 km by 30 km ( 43 x 25 miles). The cone reaches to fewer than 500 meters from the surface of the water. Marsili is described as a fragile-walled structure, made of low-density and unstable rock, fed by an underlying shallow magma chamber. Although older reports said there had been no eruptions in historic times, the Italian National Institute of Geophysics and Volcanology announced in 2010 that Marsili could erupt "at any time," and might experience a catastrophic collapse. Vast amounts of magma would be released in an undersea eruption and a landslide that might trigger destructive tsunamis on the Italian coast. That report was a few years ago and made some headlines. Of course, "at any time" to a writer of headlines (motto: Scare the crap out of people today!) means tomorrow or the day after; anything beyond that is old dead junk. Thus, they have jumped on a more recent report from an oceanographic study by the National Interuniversity Consortium for Sea Sciences; the report says that studies of sediment and fossil remains show that the volcano has indeed been active in historic times—within the last 3,000-5,000 years. At least, says the report, Marsili should be moved “up” into the class of volcanoes such as the smaller ones in the Aeolians.
The good news is that while gloom-and-doom sayers see vast devastation, you are free to see a new island rising, roaring up Atlantis-like from the deep. No one will have to be evacuated, and think of all the new land available for time-share condos. Call me a dreamer.
update: January 18, 2014 - this note from good friend and geologist, Peter Humphrey:
And that reminds me of a precedent; this is from the long entry on the Geology of the Bay of Naples:
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