Scientists set up a GPS station to measure the height of the old shoreline of Laguna del Maule in Chile. Credit: Brad Singer
The Laguna del Maule, an area of the volcanoes in the Andes, is restless.
The surface of the Earth in the region is increased, and not slowly. Satellite photos taken in the past 10 years have shown that the surface has risen by about 8 inches (20 cm) a year — much faster than any other volcanic area in the world.
Because this region is traditionally known for its explosive eruptions, geologists try to figure out what is happening under the surface to better predict when and how such catastrophic events can occur.
In a new study published June 27 in the journal Science Progress, a group of geologists used traces of an ancient coastline to understand why the ground is rising today.
“The anxiety expressed today is pretty amazing,” said Bradley Singer, a professor of geology at the University of Wisconsin-Madison and the lead author of the study, with reference to the rising ground. But “we do not believe that the current amazing state of restlessness, is something new.” These events have probably happened around 16 times in the last 10,000 years, he added. [The 11 Largest Volcanic Eruptions in History]
The use of traces of an ancient shoreline and sediments left over from past explosions, the researchers created models to recreate how the field is distorted by the underground movement boiling from the Earth’s mantle over thousands of years.
This research arose from a head-scratcher.
The middle of the volcanic region is filled by a lake, but the lake used to be much larger for a section of a lava dam collapsed, leading to a flood event that drained part of the about 9,400 years ago, Singer said. When the water level dropped, it left behind a mark like a bathtub ring. Singer and his team that there is something odd about this old coastline mark — it was much higher on the south side of the edge of the lake than on the north side.
When they measured it, they found a difference of approximately 200 feet (60 meters) between the sides, and they predicted that this shift was the result of the earth’s mantle pumping of large quantities of magma in magma reservoirs that are 3.1 to 4.3 km (5 to 7 km) underground. When the pool of magma was puffing in the ground that is not directly under the lake.
That same type of hot magma injection is likely to occur today, although this time is, amongst others, the Singer said.
“It is not just a balloon of magma that is filled in a poignant event,” Singer said. It is not only “an injection of magma, the taking of many small injections of hot magma from deeper layers in the crust and the mantle to hatch this reservoir,” Singer said.
Most of the magma that reaches these reservoirs, cooling and crystallizes in a rock formation known as a pluton, such as the Half Dome rock structure in Yosemite (but below ground), Singer said. But some of it remains liquid and can erupt, ” he said.
Explosions happen every few hundred to a few thousand years, Singer said. If an explosion occurred in this region, it would be much better than the recent explosive eruptions, such as those at Hawaii’s Kilauea and Guatemala, the Fuego volcano, which killed dozens, ” he said.
That’s because the region’s volcanoes erupt rhyolite — a type of magmathat is very explosive, due to the high water and carbon dioxide content. Magma rises from the mantle is usually a nonexplosive basaltictype, Singer said. Some volcanoes such as Hawaii’s Kilauea, directly spew this type of molten rock.
But in Laguna del Maule, the jacket keeps pumping basaltic magma in subsurface reservoirs, where it cools and crystallizes, the formation of rhyolite. As more and more magma pumps in these underground pools, the magma can heat up, creating the right conditions for explosive eruptions.
“This current episode of inflation may or may not be able to produce a modest eruption,” Singer said. But it is really hard to predict, he added. “Even a modest or small eruption like that would be quite devastating for this part of Chile and Argentina.”
Originally published on Live Science.