World's largest active volcano shows signs of life in Hawaii

Mauna Loa, the world's largest active volcano, has rumbled back to life in Hawaii over the past 13 months with more seismic activity than at any time since its last eruption, scientists say, while calling it too soon to predict another blast.

The volcano, which last erupted in 1975 and 1984, has been rattled since March 2013 by earthquakes of the same type and in the same location as the temblors that preceded those explosions, said Wes Thelen, a seismologist for the US Geological Survey's Hawaiian Volcano Observatory.

"The earthquakes we are seeing at Mauna Loa lead us to believe that some of the same things that happened before the 1975 and 1984 eruptions are happening right now," Thelen told Reuters. "We don't see this kind of activity outside of pre-eruptive earthquake sequences," he said.

The USGS posted a photo of Mauna Loa on Instagram on Wednesday with the caption: "After a 30-year repose, this sleeping giant may be stirring slowly to life."

Thelen said the earthquakes so far had not been regular or sustained enough to lead the observatory to forecast an eruption or raise the color-coded volcano warning system. But seismologists were keeping a close eye on the volcano.

Mauna Loa, which covers half of the island of Hawaii, is a popular destination for hikers despite being one of Earth's most active volcanoes. "We're not closing down the summit or doing anything drastic," he said. "This is of interest because it may be the very first sign that something's up deep underneath the volcano, but we'll wait until either the earthquakes get larger or we see more inflation in the volcano to raise the color code."

Mauna Loa's last eruption in 1984 sent hot magma flowing toward several populated areas, close enough to the city of Hilo that residents could see it glowing on hillsides.

Thelen said Mauna Loa, which has erupted 33 times since 1843, had been unusually quiet since 1984, although it inflated between 2002 and 2005, which seismologists interpreted as magma filling the magma chamber.

"Volcanos are very irregular beasts but certainly the historical eruptive history at Mauna Loa is much more active than what we've seen in the last 30 years," he said. "There aren't a lot of cases in the historical record where we've seen Mauna Loa have such a long gap between eruptions."

(Reporting by Dan Whitcomb; Editing by Peter Cooney)