The Three Sisters area — which contains five volcanoes — is only about 170 miles (274 km) from Mount St. Helens, which erupted in 1980. Both are part of the Cascades Range, a line of 27 volcanoes stretching from British Columbia in Canada to northern California. This perspective view was created by draping a simulated natural color ASTER image over digital topography from the U.S. Geological Survey National Elevation Dataset. CREDIT: NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

Volcanic activity is causing the earth to rise in Oregon, scientists have found.

Though whether such uplift is a sign of an imminent eruption remains uncertain.

As early as the summer of 1996, a 230-square-mile (600-square-kilometer) patch of ground in Oregon began to rise. The area lies just west of the South Sister Volcano, which with the North and Middle Sisters form the Three Sisters volcanoes, the most prominent peaks in the central Oregon stretch of the Cascade Mountains.

Although this region has not seen an eruption in at least 1,200 years, the scattered hints of volcanic activity here have been a cause of concern, leading to continuous satellite-based monitoring. Now 14 years of data is revealing just how the Earth is changing there and the likely cause of the uplift — a reservoir of magma invading the crust 3-to-4 miles (5-to-7 km) underground.

Uplifting ground

The European Space Agency’s European Remote Sensing and Envisat radar satellites revealed that the terrain deformed in three distinct phases since this uplift began. From 1996 to 1998, the ground rose by 0.4 inches (1 cm) per year. Then, from 1998 to 2004, uplift grew to 1.2-to-1.6 inches (3-to-4 cm) annually. However, for the rest of the decade, uplift declined to only a few millimeters per year, for a total of 9.8 inches (25 cm) of uplift so far.

“The most important implication of our research is that the ground appears to still be uplifting,” said researcher Susan Riddick, a geodesist at the University of Oregon. “Previous researchers believed that the ground uplift, a result of the input of magma deep in the Earth’s crust, had stopped at around 2006. We found that the ground is still uplifting as of late 2010 and may still be uplifting, but at a slow rate.”

By analyzing precisely how the landscape was changing, the researchers suggest the magma pocket behind this uplift has a volume of 1.76-billion-to-2.47-billion cubic feet (50-million-to-70-million cubic meters), enough to fill 20,000-to-28,000 Olympic-size swimming pools.

Eruption monitoring

Since the ground is still rising, “magma may still be accumulating, and as a result, this area needs to be continually monitored to determine whether or not there will be an eruption,” Riddick told OurAmazingPlanet.

“If there were to be an eruption, it would probably not be from a pre-existing volcano that we can see because the uplifting ground area is several kilometers from historically active volcanoes,” Riddick added. “A new volcanic vent would likely form. Lava would be ejected from a vent and fall to the ground to create a cinder cone, which is a steep conical volcano made of lava fragments. We believe it would be a small eruption, because we calculated that only a relatively small amount of magma has accumulated in the earth’s crust so far.”

If the researchers are correct, ” if an eruption were to take place, it would produce a small cinder cone, then the eruption would be localized within the Three Sisters wilderness area and would not pose a great hazard to the public in neighboring towns,” Riddick said. “However, this can change if more magma accumulates at depth, which is why continual monitoring of this area is crucial.”

Riddick and her colleague David Schmidt detailed their findings online Dec. 17 in the journal Geochemistry, Geophysics, Geosystems.

from:    http://www.livescience.com/17727-magma-causing-oregon-uplift.html