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5 Big Questions About Hawaii's Volcanoes

The Mauna Loa (MOW-nah LOH-uh) volcano erupted last fall. Here’s what you need to know about Hawaii’s volcanoes. 

1. What happened at Mauna Loa?

Erik Kabik Photography/MediaPunch/IPX/AP Images

Mauna Loa

On November 27, lava began spewing from the volcano on what is known as the Big Island of Hawaii. The fiery liquid gave the sky an eerie red glow. For about two weeks, streams of lava as hot as 2,000 degrees Fahrenheit oozed from the volcano. 

Mauna Loa is the world’s biggest active volcano. It covers more than half of the Big Island. The volcano has erupted 34 times since 1843, most recently in 1984. 

Mauna Loa isn’t the only volcano on the Big Island. The nearby Kilauea (kee-lah-WAY-ah) volcano has erupted on and off for decades. 

2. Why are there so many eruptions in Hawaii?

Hawaii’s eight main islands are the tops of giant undersea volcanoes. Tens of millions of years ago, magma began to burst through an area on the ocean floor called a hot spot. As the lava cooled, it hardened into rock. The eruptions continued, creating mountains that rose above the ocean’s surface to form the Hawaiian Islands. 

Jim McMahon/Mapman®

Hawaii is the name of both the state and the biggest of the state’s eight main islands.

3. What do Hawaii’s volcanoes look like? 

When you think about volcanoes, you might picture cone-shaped mountains that shoot huge clouds of ash and lava high into the sky. But Hawaii’s volcanoes are different. They’re wider and flatter, with gentle slopes that formed as lava built up and spread out over time. They’re called shield volcanoes because they look like a warrior’s shield lying flat on the ground. When shield volcanoes erupt, lava tends to flow out slowly. Last fall, for example, lava from Mauna Loa crawled at a rate of about 20 to 40 feet per hour.

Inside Mauna Loa

Diagram illustration by Kate Francis

Clockwise from top-left

Caldera: a large hole at the summit, or top, of a volcano that forms when land collapses after an eruption 

Fissure: a crack at the surface from which lava erupts

Lava flow

Side vent 

Magma chamber: an area filled with magma that rises from a hot spot 

Central vent: the main path through which magma flows

Hardened lava from past eruptions

4. Does that mean Hawaii’s volcanoes aren’t dangerous? 

Not necessarily. Lava from Mauna Loa’s recent eruption wasn’t a threat to any of the Big Island’s 200,000 residents. But some past eruptions have caused major damage. In 2018, lava flows from Kilauea destroyed more than 700 homes. The volcano spewed enough lava to fill about 320,000 Olympic-sized swimming pools.

In addition, eruptions often blanket nearby communities in a haze of volcanic smog—called “vog” for short. Vog can cause headaches and sore throats and make it hard for some people to breathe. 

USGS

A scientist monitors the Kilauea eruption in 2021. 

5. How can scientists keep Hawaiians safe?

Scientists constantly study Hawaii’s active volcanoes, looking for any signs that they might roar back to life. For example, experts expected Mauna Loa to erupt last fall. For months, they had noticed more earthquakes within the volcano. That was a sign that magma underground was rising toward the surface. 

Wendy Stovall is a volcanologist at the U.S. Geological Survey. She says it’s important for scientists to get up close to volcanoes. “That can help us understand more about how volcanoes behave,” she explains, “so we can forecast eruptions in a better way in the future.”

  1. What are shield volcanoes, and why did they get this name?
  2. Did the fall 2022 eruption of Mauna Loa surprise scientists? Explain.
  3. What dangers can Hawaii’s volcanoes present?
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