So there are more bubbles breaking because of more water, and when the bubbles finally do break, they do so with greater force. How do pyroclastic flows form after the eruption of a volcano like Fuego in Guatemala? Mahood : These can form directly from an explosive eruption, or they can form by lava that comes out and cools a little bit, gets stuck and fills the vent. Those continue to effervesce and produce ash.
People around Fuego are largely being killed by pyroclastic flows. Lowe: In , debris flows following the eruption of Nevado del Ruiz volcano in Colombia killed about 20, people in a town called Armero, 60 kilometers 37 miles downslope. These flows originated when hot ash, like the stuff coming out of Fuego, landed on a glacier around the summit.
A minor puff of ash melted just a small part of that glacier and sent huge volumes of water cascading down canyons. We learned by looking at older deposits in roadcuts around this town that this had been a common process in the past. All the elements were there that should have made a planner recognize that this was not a good place for a town. Better geological studies would have shown that the area had suffered many similar catastrophes in the past.
In fact, hazard maps created in the months before the eruption showed Armero would be in the path of any mudflows a type of debris flow triggered by the volcano. But those maps were not widely distributed. One promising theory is that water gets sucked under the main flow like hydroplaning on your tires. Another theory centers on how particles interact in the flow. Do they just kind of carry along passively in the fluid? Maybe particles in a debris flow behave like gas molecules in a balloon — they collide with one another, exert pressures and help keep themselves suspended.
These details are important to understanding how far debris flows can go, how much stuff they can carry, how quickly they form — all of which are relevant to whether you build towns around volcanoes, deciding how far away they need to be and evaluating the danger of settlements and villages that are already there.
How does this compare to some of the biggest eruptions in history? Mahood: This is not a big eruption by any stretch of the imagination. One of the big problems in Guatemala and many other places — in Indonesia and the Philippines, for example — is the large population packed on and around volcanoes of this type.
Moderately small eruptions can kill a lot of people. Fuego is a very active volcano. Is it possible to anticipate whether and when a given eruption will produce this type of hazard?
In fact, most scientists don't even upload the information to their computers. Larson was working with colleagues from the University of Alaska Fairbanks, who set up GPS antennae at Alaska's Mount Redoubt to measure how terrain shifted during an eruption. Those measurements come from an array of satellites beaming down signals that indicate the exact position of a GPS antenna on earth.
Equipment on the ground automatically stores GPS data on the strength of the signals coming from those orbiting satellites. But Larson is the first to use the information to measure volcanic plumes. Think of your cell phone, said Larson. She found that the plume, which was loaded with bits of volcanic ash, somehow blocked the GPS signal coming from satellites in space.
Knowing this, Larson could then track the plume in real time by observing the strength of the GPS signal in a certain area. Once the plume passed, the signal bumped back up to its normal level.
This once-overlooked information may help track plumes when other methods like radar or pictures taken from satellites fall short. Images taken from space can monitor plumes but "if it's cloudy you can't see anything," said Larson. Since the GPS signal strength beamed down from orbiting satellites is largely unaffected by clouds and water vapor, Larson can detect only the dangerous ash within a plume.
Radar can spot plumes but the equipment is expensive. Many scientists already have GPS antennae dispatched at volcanoes all over the world that automatically collect signal strength data. The ocean-entry plume can also cause acid rain that has a pH between 1.
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