EXPLAINER – Where is Hawaii’s largest volcano going to erupt?

EXPLAINER: Where will Hawaii’s biggest volcano erupt from?

HONOLULU — The ground is shaking and swelling at Mauna Loa, the largest active volcano in the world, indicating that it could erupt. Scientists say they don’t expect that to happen right away but officials on the Big Island of Hawaii are telling residents to be prepared in case it does erupt soon. These are some facts about the volcano.


Mauna Loa, one of the five volcanic cones that make up Hawaii’s Big Island is located in Hawaii. It is also the most southernmost Hawaiian island. Although it isn’t the highest (that honor goes to Mauna Kea), the volcano makes up half the island’s total land mass.

It sits immediately north of Kilauea volcano, which is currently erupting from its summit crater. Kilauea is well-known for a 2018 eruption that destroyed 700 homes and sent rivers of lava spreading across farms and into the ocean.

Mauna Loa last erupted 38 years ago. In written history, dating to 1843, it’s erupted 33 times.

The Big Island is mainly rural, and home to coffee farms, cattle ranches and resorts. It’s about 200 miles (320 kilometers) south of Hawaii’s most populous island, Oahu, where the state capital Honolulu and beach resort Waikiki are both located.


Mauna Loa has more powerful eruptions than Kilauea. It’s greater height gives it steeper slopes, which allow lava to rush down its hillsides faster than Kilauea’s.

It’s enormous size may allow it to store more magma, leading to larger lava flows when an eruption occurs.

Frank Trusdell, research geologist at the Hawaiian Volcano Observatory, which is part of the U.S. Geological Survey, said data indicates that Mauna Loa has a much larger magma reservoir than Kilauea, which may allow it to hold more lava and rest longer between eruptions than Kilauea.


Scientists won’t know until the eruption begins. Each eruption since 1843 started at the summit. Half the time, the volcano later also began erupting from vents at lower elevations. The other half of the time it only erupted in the summit caldera.

Scientists can’t tell far in advance when and where Mauna Loa will open new vents and erupt.

Vents generally form along the volcano’s rift zone. This is where the volcano’s rift zone is formed. The rock is fractured and weaker, making it easier for magma and other elements to form.

An eruption from vents on the southwest rift zone could hit residential communities, coffee farms or coastal villages on the west side of the island. In a matter of hours or days, lava could be delivered to homes.

The presence of an active volcano on the west side would protect it from any Mauna Loa volcanic eruption. Hualalai’s broad flanks, which are located between Mauna Loa’s southwest rift zones and Kailua-Kona, would prevent any lava from reaching the coast community.

An explosion from the northeastern rift zone might send lava towards Hilo and other East Hawaii towns. This side of the mountain could be occupied for weeks to months.

Scott Rowland, a geologist at the University of Hawaii at Manoa, said there’s no pattern when it comes to where an eruption will occur.

“Just because the last one was on the northeast rift zone does not mean the next one will be down the southwest rift zone,” he said.


Fifty-seven people died when Washington state’s Mount St. Helens erupted in 1980 and blasted more than 1,300 feet (400 meters) off the top of the mountain. Steam, rocks and volcanic gas burst upward and outward. A plume of volcanic ash rose over 80,000 feet (24,384 meters) and rained down as far as 250 miles (400 kilometers) away.

Hawaii volcanoes like Mauna Loa tend not to have explosion eruptions like this.

That’s because their magma is hotter, drier and more fluid, said Hannah Dietterich, a research geophysicist at the U.S. Geological Survey’s Alaska Volcano Observatory.

The magma at Mount St. Helens is more sticky and traps more gases, which makes it more likely that it will explode as it rises.

The gas in the magma of Hawaii’s volcanoes tends to escape, and so lava flows down the side of their mountains when they erupt.

Hawaii’s volcanoes are called shield volcanoes because successive lava flows over hundreds of thousands of years build broad mountains that resemble the shape of a warrior’s shield.

Shield volcanos are also found in California and Idaho as well as Iceland and the Galapagos Islands. Alaska’s Wrangell-St. Elias National Park has eight shield volcanoes including Mount Wrangell.

Volcanoes like Mount St. Helens are called composite or stratovolcanoes. The eruption of viscous volcanic flows, rock, ash, and gas creates steep slopes that are conical in shape. Another example is Mount Fuji in Japan.


The Hawaiian Volcano Observatory has more than 60 GPS stations on Mauna Loa taking measurements to estimate the location and the amount of magma accumulating beneath the surface.

Scientists use tiltmeters to track long-term changes in the tilting of the ground, helping them identify when the ground is swelling or deflating. An eruption can be identified by a rapid shift in tilt.

There’s also a thermal webcam at Mauna Loa’s summit that will identify the presence of heat. Satellite radar is also able to track ground swelling and deflation.


Associated Press Writer Mark Thiessen contributed to this report from Anchorage, Alaska.

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