Two separate eruptions from Mt. Hood – 220 years ago and about 1,500 years ago – have revealed that many volcanoes prefer cold storage of magma, as opposed to the traditional visual we have had of these monumental inferno towers resting atop a giant pool of –
The crystals analyzed in Mt. Hood’s lava reveal a chronological and temperate history of wonders. These crystals have been trapped beneath the volcano for nearly 100,000 years at temperatures so cold, the lava was compared to that of “a jar of old honey from the fridge”, too sticky and slow to erupt. The research suggests that the liquid cut-off is around 50% crystals. Beyond this ratio, the magma becomes too thick to push through the fractures leading to the surface.
From the MNN article:
“This tells us that the standard state of magma for this system is that it can’t be erupted,” said Kari Cooper, a geochemist at the University of California, Davis. “That means that having a magma that can erupt is a special condition. Our expectation is that there’s a lot of volcanoes that behave this way.”The results suggest that monitoring volcanoes for liquid magma could warn of coming eruptions. Not all kinds of volcanoes behave like Mount Hood — Hawaii, for instance, is built differently, atop a giant hot spot — but most of the world’s most active volcanoes are in similar settings.
“If you can see a body of magma that has a high amount of liquid, perhaps this magma is getting ready to erupt or at least has some potential to erupt,” said study co-author Adam Kent, a geologist at Oregon State University. “It wouldn’t be a slam-dunk guarantee.”
The reason why Mt. Hood is set up this way is due to it being a subduction zone volcano, or, a volcano formed due to tectonic plates converging (slowwwwwly) with another. One plate is forced upward toward the surface, the other, downward toward the mantle, causing boundary known as a subduction zone, whereby the fluids (released by the plate being forced toward the mantle) melt the rocks above, pushing them to the surface to form volcanoes.
Learn about “subduction zones” HERE. [image source]
Looking at the “Ring of Fire” around the Pacific Ocean reveals the link between subduction zones and volcanoes. Inland of each subduction zone lies a chain of spouting volcanoes called a volcanic arc, such as Oregon’s Cascades, Alaska’s Aleutian Islands and Indonesia’s 130 active volcanoes.“We have partial data sets for other systems, and they all seem to behave remarkably similarly, where they spend most of the time cold,” Cooper said.
An almost identical process to Mount Hood’s recent eruptions occurred in the early 1990s at Mount Pinatubo, Kent added. “People could see the arrival of this hotter magma from below, and it eventually initiated an eruption,” he said.
Mount Hood’s chilly magma reservoir sits about 2.5 to 3 miles (4 to 5 kilometers) beneath the surface. Its temperature is usually 1,380 degrees Fahrenheit (750 degrees Celsius), according to an analysis of the crystals.
You can read the rest of the article via MNN.
