By Victoria Cavaliere
SEATTLE (Reuters) - A series of explosions set off by a team of scientists were expected to rattle Washington state's Mount St. Helens on Wednesday as researchers map the interior of the volcano, whose 1980 eruption was the deadliest in U.S. history.
Mount St. Helens, about 95 miles (150 km) south of Seattle and 50 miles (80 km) north of Portland, erupted in an explosion of hot ash in May 1980, spewing debris over a wide area, killing 57 people and causing more than a billion dollars in damage.
Scientists from across the United States are trying to get a better handle on the magma stores and internal workings of the 8,300-foot (2,530-meter) volcano to improve warning systems prior to eruption.
"Mount St. Helens and other volcanoes in the Cascade Range threaten urban centers from Vancouver to Portland," lead scientist Alan Levander of Rice University in Houston said in a statement.
"We'd like to better understand their inner workings in order to better predict when they may erupt and how severe those eruptions are likely to be," he said.
On Wednesday, geophysicists from across the United States were to begin running seismic waves through the volcano's interior by firing "shots" at the mountain to install mapping instruments deep underground.
The instruments will help create a sort of CAT scan on the interior and will "illuminate the architecture of the greater Mount St. Helens magmatic system from slab to surface," according to researchers from the project, called Imaging Magma Under St. Helens, or iMUSH (http://imush.org/)
A total of 23 boreholes 80 feet (24 meters) deep were to be installed by July 31, said researcher Steve Malone.
"These shots are done at night to give the best chance of recording good signals without other vibrations being present such as from wind or vehicle traffic," Malone said.
Residents living near Mount St. Helens were unlikely to feel the shots because of their depth, but their insertion approximates a magnitude 2 earthquake, scientists said.
In May, the U.S. Geological Survey said that magma levels were slowly rebuilding inside Mount St. Helens, but there was no sign of an impending eruption.
(Reporting by Victoria Cavaliere; Editing by Cynthia Johnston and Sandra Maler)