Seismic unrest is building at the world’s largest active volcano in Hawaii, where officials are urging people on the Big Island of Hawaii to pack “go bags” and prepare for the inevitable eruption of the giant Mauna Loa volcano. Yesterday, the Hawaiian Volcano Observatory (HVO) said that they detected 65 small-magnitude earthquakes 2-3 miles below the Mokuāʻweoweo caldera beneath the upper-elevation northwest flank of Mauna Loa, an increase in activity from the ongoing period of unrest. Global Positioning System (GPS) instrumentation on Mauna Loa continue to measure inflation at rates elevated since mid-September, indicating that magma is building inside the volcano.
While Mauna Loa is not erupting and there are no signs of an imminent eruption at this moment, scientists are concerned that the inevitable eruption of the giant volcano may arrive sooner than wanted.
“Mauna Loa continues to be in a state of heightened unrest as indicated by increased earthquake activity and inflation of the summit,” HVO said in a statement. “The current unrest is most likely being driven by renewed input of magma 2-5 miles beneath Mauna Loa’s summit.”
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 first two weeks of the month. Peak numbers of over 100 earthquakes per day occurred on September 23rd and 29th. While 65 quakes hit in the 24 hours ending yesterday, there were 53 similar earthquakes in the 24 hours ending today.
For now, other signs indicative of an imminent eruption have yet to present themselves. Tiltmeters at the summit are not showing significant surface deformation over the past week and concentrations of sulfur dioxide (SO2), hydrogen sulfide (H2S), and carbon dioxide (CO2), as well as fumarole temperatures, remain stable at the summit and at Sulphur Cone on the upper Southwest Rift Zone.
“The current increase in activity does not suggest that a progression to an eruption is certain, and there are no indications that an eruption is imminent,” added HVO in their October 12 statement.
Nevertheless, officials urge people in Hawaii be prepared for the moment Mauna Loa erupts.
“This uptick in activity is a good reminder to be prepared for a volcanic eruption, whether you live on the flanks of Mauna Loa or anywhere else on the Island of Hawaiʻi,” said USGS in a new update.
“The steps to be prepared for a volcanic eruption are the same as for many other hazards and is part of “All Hazards” preparedness. It includes putting together a “go bag” with essentials in the case of quick evacuation, as well as a communication plan among your family members, and knowing how to get updated emergency information.”
About 50% of the Hawaii Island population lives on the slopes of Mauna Loa. There’s also a considerable vacationing population potentially in harm’s way; major resorts, including the Waikoloa Beach Resort complex which is home to the Waikoloa Marriott and the Hilton Waikoloa Village, and the Mauna Lani Beach Resort complex which is home to the Fairmont Orchid and the Auberge Mauna Lani Resort, is built on previous Mauna Loa flows and could find themselves in front of a lava flow front once again in the future.
Talmadge Magno, Administrator of the Hawaii County Civil Defense, is one official urging that people prepare for the threats volcanoes pose people on the island. In an interview with Honolulu KHON2-TV this week, Magno said, “All the people that live on its slopes, you know, some portion of that 50%, those people could be affected,” Magno said. “I live on the slopes of Mauna Loa. I have to be aware of that potential for my where I live, where I work.”
Hawaii County Civil Defense has developed an Emergency Preparedness web page with information on how to prepare a family, a home, and/or a business for potential disasters that could strike –a volcano being one of them.
“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.”
Public access to the summit was closed on October 6 in response to increased seismic activity on the volcano.
“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.
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 gases and a volcanic haze known as vog, as well as fall-out of volcanic debris such as ash or volcanic glass.
Scientists today are looking for clues similar to those that came before Mauna Loa last erupted in the 1980s.
Early in the morning of March 25, 1984, swarms of earthquakes underneath Mauna Loa began to swell. The tremors soon became so constant that nearby telescopes on Mauna Kea could not be stabilized due to continuous vibrations. By 1:30 am, satellites picked up indications of an eruption and people around the island reported seeing a glow above the volcano. By late afternoon on that first day, the fissure that would become the eruption’s main vent opened up at 9,350 feet in elevation. Within hours, it expanded both towards the ocean and the mountain, creating a curtain of fire, a solid line of lava fountains over a mile long. Lava pouring out of that curtain of fire flowed in the general direction of Hilo on the Big Island’s eastern side. The eruption eventually ended on April 15, with lava stopping its forward movement only 4 miles from Hilo.
According to USGS and HVO, the immediate precursors to the 1984 eruption consisted of an abrupt increase in small earthquakes and volcanic tremor recorded on seismic stations located near Moku‘āweoweo. At 10:55 pm on March 24, small earthquakes began at a rate of 2-3 per minute. By 11:30 pm, the seismic background increased, marking the onset of tremor.
The gap between the intense earthquake activity and the actual eruption in 1984 was less than 3 hours. Fast moving lava flows could reach the coast along portions of Hawaii’s west coast in as little as 3 hours too, which means people may only have 6 hours of advance warning to escape when Mauna Loa erupts the next time too.