Reading magma, predicting giant eruptions
Running short of worries? Then ponder the super-volcanoes — earth-bombs that can vomit 10 or 100 or 1,000 cubic kilometers of molten rock. Super-volcanoes can change history by creating rivers of red-hot ash moving at highway speed, spreading dust across hundreds of kilometers and spewing vapors that block the sun, destroy crops and start famines.
A volcano may go dormant for thousands of years after such a huge eruption, so they may be even harder to predict than smaller ones — which are also unpredictable at this point…
But this week, Nature published a new analysis of Santorini, a Mediterranean monster, that shows the movement of molten rock that preceded the eruption.
Santorini’s sudden release of 40 to 60 cubic kilometers of rock and ash was followed by a giant collapse that left a characteristic ring of hills called a caldera. Thousands may have died in the eruption, which laid down a 60-meter layer of ash and rock.
Eruptions of this general size happen about every 300 years, says Timothy Druitt, a volcanologist at the Université Blaise Pascal in France, who lead the current study. The most recent was in 1815 at Tambora, in Indonesia.
Druitt’s new analysis of crystals within the frozen magma offers a rough schedule for the entry of molten magma into a holding tank — the magma chamber — below the volcano, which is a precursor to eruption.
Caldera-forming eruptions rival earthquakes and tsunamis as the deadliest natural disasters. “People who work in the field know these volcanoes are not rare, even on a human time scale,” says Druitt, but “we have never been able to monitor one of these big eruptions during the long buildup phase, so we are not really sure how that happens.”
The crystal analysis detects microscopic changes in chemical composition, offering a unique, after-the-fact picture of the gestation of eruption.
In the crystals
As crystals grow in the cooling magma, atoms of trace elements diffuse within them, and both growth and diffusion are affected by condi