Last month, Sicily’s Mount Etna erupted for two weeks, providing television viewers with spectacular pictures but really doing very little damage.
But that’s not always the case with volcanoes. After all, the most violent explosion on Earth in modern times wasn’t a nuclear blast–it was the eruption of Krakatoa, which blew apart in 1883. The explosion, heard in the Indian Ocean, 4,800 kilometres away, ejected 21 cubic kilometres of dust into the atmosphere, caused 12-story waves and killed 36,000 people.
Beneath the relatively thin crust of the Earth lies a vast expanse of molten rock called magma, kept hot by the decay of naturally occurring radioactive material and possibly by heat left over from the planet’s formation. Volcanoes occur where a fissure in the crust allows this magma (called lava once it’s above ground) to leak out.
Generally, these fissures occur where the various moving plates of the Earth’s crust are either running into each other or pulling apart. The greatest volcanic activity occurs at the latter locations, but they’re mostly on the ocean floor. As well, the lava flow there tends to be a nice quiet oozing.
By contrast, volcanoes that arise where two plates are crashing into each other (if you can call something happening at five centimetres a year “crashing”) tend toward violent explosions. The Andes Mountains and the Aleutian Islands are examples.
Finally, there are volcanoes that arise well away from the edges of the plates, over “hot spots,” such as the Hawaiian Islands and the Yellowstone volcanic field.
The lava that erupts from hot-spot volcanoes usually (though not always) emerges quietly and flows gently away. (It’s still nothing to mess with: at 850 to 1,250 degrees, it will burn practically anything.)
Mt. Etna has always acted like a hot spot volcano, but now scientists say it is starting to display features more like the volcanoes that appear where two continental plates are crashing into each other–which is worrisome, because that could mean Etna’s eruptions may soon become more explosive.
Pierre Schiano of Blaise Pascal University and fellow researchers studied minute amounts of magma ejected by Etna over thousands of years and preserved in minerals to chart the volcano’s change in personality. They note that Etna, although it’s acted like a hotspot volcano, is situated between the European and African continental plates, and they suspect a slab north of Mount Etna is migrating south into another slab, causing the change in the volcano. The most recent eruption of Etna supports their theory; it was a mixture of lava flow and explosions.
Etna wasn’t the only volcano erupting last month; at any given time, about 20 volcanoes are erupting somewhere (many are underwater). And yes, Canada has volcanoes–Natural Resources Canada lists more than 250. While none are erupting, several are considered potentially active.
Of course, most of Canada’s volcanoes are in the Rockies, so Canadians living on the East Coast might feel safe. But they should think again. An article in the September 1 issue of Geophysical Research Letters says that an eruption of Cumbre Vieja, a volcano in the Canary Islands, could conceivable generate massive waves that would inundate the East Coast of North America hours later.
The threat exists because of an existing rift across the volcanoes side. If a new eruption caused it to split open, a huge landslide could crash into the ocean. In a worst-case scenario, a wave more than 20 metres high–the height of a seven-story building–could strike parts of the East Coast nine hours later. (That’s not so bad when you consider that islands near the eruption would be wiped away by waves hundreds of metres high, and 100-metre waves could strike Africa.) Smaller landslides are also possible, which would produce waves one-fourth to one-half that height.
Such giant waves are called tsunamis, and they’re not usually considered a threat in the Atlantic–but it’s worth remembering that the last East Coast tsunami, in 1929, caused by a landslide off Newfoundland, killed 30 people in Nova Scotia.
Geophysicists Steven N. Ward of the University of California at Santa Cruz and Simon Day of University College, London, say the likelihood of such a catastrophe low; the volcano in question hasn’t erupted since 1949 and it might take many eruptions to weaken the rift to the point of collapse. And yet…the possibility is there.
And, I confess, the possibility of such a disaster adds to the mystique of volcanoes. As much as I like humans (I’m one myself), I have to say that as a species we can be a tad overconfident about our place on this planet and our ability to wrestle its forces into submission.
Nobody, but nobody, wrestles with a volcano.
