GREEN
05/20/2014 05:06 pm ET | Updated May 20, 2014

What Happens When The World's Largest Volcano Erupts Again?

Joe Carini via Getty Images

Imagine living in the shadow of the world's largest -- and still active -- volcano.

For residents on Hawaii's Big Island, a threat has long rumbled within the Mauna Loa volcano, which takes up almost half of the island. Not only is it more than 1,000 feet taller than Mount Everest from seafloor to summit, Mauna Loa seems primed -- some might even say overdue -- for an eruption.

Of the five active volcanoes in Hawaii, only the Kilauea and Loihi volcanoes have been quietly erupting consistently for decades. But Mauna Loa is seen as the big threat there. What Kilauea erupts in one day, Mauna Loa has erupted in 20 minutes, as it did in 1984. It came way too close to destroying Hilo, where more than 35,000 people lived at the time.

“The eruption rates on Mauna Loa are scary in comparison to Kilauea. The amount of lava coming out per unit is actually life threatening,” Frank Trusdell, a leading Mauna Loa scientist for the United States Geological Survey at the Hawaii Volcano Observatory, told Hawaii News Now.

Over recorded history, Mauna Loa has erupted an average of every six years -- 39 times since 1832. But its last eruption was in 1984, and scientists say there is a 100 percent chance that Mauna Loa will erupt again.

Perhaps scariest is that researchers don't know where the next eruption will take place, making it really hard to plan for, in terms of both time and danger zone. John Drummond, of the Hawaii County Civil Defense Agency, told The Huffington Post that their first response will be to set up an evacuation center, then, depending on wind direction and flow of the lava, get people out of harm’s way.

"We look at the situation as it happens and react accordingly," he said. "Everything is situational.”

Big Island volcanoes aren’t typically explosive in the Mount St. Helens or Eyjafjallajökull way, so there’s no huge threat of debris or ash clouds. But, according to the civil defense's mitigation plan, the Big Island's lava is exceptionally fluid and voluminous, making lava flowing down the volcano the greatest threat.

Scientists at the Hawaii Volcano Observatory monitor earthquakes and chart possible lava flows based on theoretical vent maps. When earthquakes cluster at high rates, it can mean that the magma (or underground lava) is on the move, rearranging rock and other earth. When Hawaii sees 500 to 600 earthquakes-per-day, “we’re on high alert,” Trusdell told Hawaii News Now.

Ten years ago, for example, a cluster of earthquakes signaled something big might happen at Mauna Loa. Instead, half the mountain shifted south, giving the magma more room to stay beneath the surface. That bank of extra magma is still underground.

Does that mean Hawaii is in for an even bigger eruption? Nobody really knows, Trusdell said, but he’s confident that scientists will forecast the next eruption.

You can stay updated by keeping an eye on all the Hawaiian volcanoes for yourself.

ALSO ON HUFFPOST:

Fascinating Volcanoes

CONVERSATIONS