TOKYO, July 17 (UPI) -- Japan's Mount Fuji last erupted in 1707, but records suggest the average interval between events is 30 years -- and that is making scientists very nervous.
Volcano experts believe Fuji has erupted about 75 times during the past 2,200 years. But during the last 300 years there has not been one such event.
Mount Fuji is located 70 miles from Tokyo in a very heavily populated area in which the government estimates an eruption might cause more than $21 billion dollars in damage.
That makes Fuji one of the most closely watched volcanoes on Earth, with numerous global positioning system arrays and other equipment constantly monitoring its activity.
And that equipment has indicated deep low-frequency earthquakes continue to occur, believed by some experts to be caused by magma flowing into the roots of the volcanic system.
"A volcano can absorb quite a few (buildups) without erupting," Chris Newhall of the U.S. Geological Survey told NGN. "It's a bit like torquing a ratcheted spring: A little bit now, a little bit later, and eventually it's cocked."
But precisely when Fuji will be fully cocked, nobody knows.
