Mauna Loa, the world’s largest active volcano located on the Big Island of Hawaii, is experiencing potentially troubling signs: the volume of earthquakes is increasing while the ground near the volcano’s summit appears to be swelling. While the volcano is not erupting right now, out of an abundance of caution, the National Park Service announced the closure of the summit area of Mauna Loa within Hawaii Volcanoes National Park.
USGS says that while Mauna Loa is not erupting and there are no signs of an imminent eruption at this time, they will update the public on the volcano’s status on a daily basis starting today due to increased activity there. Prior to today, USGS simply shared updates on a weekly basis.
USGS is monitoring earthquake activity, ground swelling, and gas emissions coming from the giant volcano. While monitoring data show no significant changes in the past day, earthquake rates are elevated indicating Mauna Loa is currently experiencing heightened unrest. Global Positioning System (GPS) measurements show continued surface deformation related to inflation of a magma chamber beneath the summit. As magma accumulates in an underground reservoir before an eruption, the ground surface typically swells. Concentrations of sulfur dioxide (SO2), hydrogen sulfide (H2S), and carbon dioxide (CO2), as well as fumarole temperatures, remain stable at both the summit and at the Sulphur Cone on the upper Southwest Rift Zone.
“While an eruption of Mauna Loa is not imminent, now is the time to revisit personal eruption plans. Similar to preparing for hurricane season, having an eruption plan in advance helps during an emergency,” said HVO in an earlier statement.
“Due to elevated seismic activity on Mauna Loa and as a precautionary measure, Hawai‘i Volcanoes National Park is closing the Mauna Loa summit backcountry until further notice,” cautioned the National Park Service in a press release announcing the closure of the summit area. “Mauna Loa Road and the Mauna Loa Lookout at 6,662 feet elevation remain open to the public.”
The park closure at Mauna Loa has no impact on roads and trails around Kilauea, an active volcano currently erupting within its summit caldera elsewhere in the national park.
Mauna Loa eruptions tend to produce voluminous, fast-moving lava flows that can impact communities on the east and west sides of the Big Island from Kona to Hilo. Since the 1850s, Hilo in eastern Hawaii has been threatened by 7 Mauna Loa lava flows. On the south and west sides of the island, Mauna Loa lava flows have reached the coast there 8 times: in 1859, 1868, 1887, 1926, 1919, and three times in 1950.
Earthquake activity has been increasing from 5-10 earthquakes per day since June 2022, to 10-20 earthquakes per day in July and August, and reaching approximately 40-50 earthquakes per day over the past two weeks. Peak numbers of over 100 earthquakes per day occurred on September 23rd and 29th.
With another eruption on Mauna Loa inevitable, although the timing is not yet defined, the USGS is urging people on Hawaii to have a personal response plan, prepare a “go bag”, and determine what one would do in the event of an eruption at different times of the day or week.
“The most important thing you can do is to have a personal response plan,” says the USGS. Document what you’d do when a volcano erupts and make sure your family and friends are aware of what that plan is.
USGS suggests getting a “go bag” in order. “Nowadays, people pack “go” bags containing essential items in case you have to leave your house under an evacuation order. You may want to include important documents, like your birth certificate, deeds, legal papers, and medications.”
USGS says people in Hawaii should develop plans that factor in different types of days and time of day: if family members are at work or school at specific times, the plan should address what people should do and how they should communicate if an eruption occurs when people aren’t home. USGS says, “It is useful to also have a communication plan, so you can be in touch with those you care about.”
Mauna Loa is one of 5 volcanoes that make up Hawaii’s Big Island. The oldest volcano on Hawaii Island is Kohala, which is more than one million years old. Kilauea is the youngest, at an estimated 300,000-600,000 years old. Mauna Loa is the second youngest volcano on the island, estimated to be about 700,000 years old.
Mauna Loa is a shield volcano with long, broad slopes that fall off into the ocean. Lava eruptions from Mauna Loa are very fluid and are typically non-explosive. Magma for Mauna Loa and Kilauea, the latter which has been erupting since December, is sourced from a hot spot in the middle of the Pacific Plate. Because the plate is slowly drifting, Mauna Loa will eventually move away from the hotspot, become an extinct volcano in the next 500,000-1,000,000 years.
Mauna Loa’s most recent eruption occured from March 24 to April 15 in 1984. Lava from the 1984 flow spilled over near the summit while additional fissures drove flows in the general direction of Hilo. The flows stopped roughly 4 miles outside of Hilo’s city limits. No lava has flowed from Mauna Loa since.
While scientists are certain Mauna Loa will erupt, they aren’t exactly sure when yet or where lava will flow from the next eruption. Previous flows impacted the communities of Puako and Waikoloa Beach on the northwest coast, Kailua-Kona and Captain Cook on the west coast, Milolii and Ocean View on the southwest coast, and Hilo on the east coast. Because of the wide range of impacts in past eruption events, the USGS is encouraging people island-wide to prepare for the possibility of volcanic activity. Beyond the hazards of fast moving lava flows, there could be toxic volcanic gasses and a volcanic haze known as vog, as well as fall-out of volcanic debris such as ash or volcanic glass.
Hawaii also doesn’t have a monopoly on volcanic threats in the United States. While USGS rated Kilauea as the biggest volcanic threat in the U.S. in its updated 2018 list of volcanic dangers, Mauna Loa is only 16 on the list. Washington’s Mount St. Helens and Mount Rainer, Alaska’s Redoubt, California’s Mount Shasta, and Oregon’s Mount Hood and Three Sisters are considered to be even more dangerous.