An earthquake swarm continues at the world’s most active volcano on the Big Island of Hawaii, prompting USGS to issue an update about the Mauna Loa Volcano there. In the last 24 hours, 63 earthquakes have struck in and around Hawaii, with most earthquakes centered in two areas: the first is near the summit area of Mauna Loa volcano, the other is located near the town of Pahala near the southeast coast of Hawaii Island. In the last 7 days there were 322 earthquakes recorded by USGS here; in the last 30 days, the count is up to 739. The overall trend is for an increase in seismic activity in Hawaii, especially near the summit of Mauna Loa, where 38 earthquakes hit yesterday morning alone.
“Seismic activity beneath Mauna Loa has been gradually increasing over the past two months,” said USGS Hawaiian Volcano Observatory (HVO) Scientist-in-Charge Ken Hon. “Small earthquake swarms are considered a normal part of this increase in activity. Currently there are no indications that magma is moving toward the surface and other monitoring systems are displaying normal behavior. Levels of seismicity and deformation remain below those recorded during the winter of 2021. HVO will continue to closely monitor this activity and report any significant changes.”
Scientists continue to evaluate what is creating this most recent seismic swarm on Mauna Loa. In a statement, USGS said, “These earthquakes may result from changes in the magma storage system and/or may be part of normal re-adjustments of the volcano due to changing stresses within it. HVO continues to monitor Hawaiian volcanoes for any changes.”
According to USGS, a swarm is a sequence of mostly small earthquakes with no identifiable mainshock. “Swarms are usually short-lived, but they can continue for days, weeks, or sometimes even months,” USGS adds.
The swarm began at about 2 am Hawaii time on Friday and continues today. The first 38 earthquakes of the swarm were located beneath the summit caldera region with most earthquakes in a cluster about 3.1 mi wide and -1.2 to 0.6 mi below the surface.
Mauna Loa isn’t the only volcano behaving a little bit differently this week. On September 20, increased seismicity, ground deformation, and surface lava flows at Kilauea Volcano’s summit occured between 3 pm and 6 pm that day. Beginning at 3 pm, earthquake activity beneath the summit began to increase, followed by summit inflation beginning around 4:20 pm. New breakouts of lava began occurring on Halema’uma’u crater floor inside Kilauea’s caldera at 4:30 pm.
At the same time, there were about 50 earthquakes detected beneath the Kilauea summit, with most striking roughly 1 mile beneath Halema’uma’u. The strongest earthquake in that swarm was a magnitude 2.9 event, with most others recorded below 2.0.
During this activity, a lake of lava dramatically fell by 23 feet while the crater floor surrounding the lava lake also subsided by several yards.
While Kilauea is actively erupting, all of the lava flows are contained to inside the deep Kilauea Summit caldera. Tourists can drive up to and walk around large parts of the Caldera and peer into the volcano from Hawaii Volcanoes National Park. Unlike the incident that unfolded in 2018 during the Kilauea Lower East Rift Zone eruption, the volcanic activity there is confined to the volcano summit and doesn’t pose an immediate threat to nearby neighborhoods at this time.
While Kilauea is erupting, Mauna Loa isn’t –and hasn’t for many years. The last eruption was in 1984.
Mauna Loa is considered the largest active volcano on Earth, rising to 13,681 feet above sea level. Mauna Loa rises up from the ocean floor of the Central Pacific at a depth of about 3 miles. Because of the volcano’s significant mass, the ocean floor directly beneath Mauna Loa is depressed by another 5 miles. According to USGS, this places Mauna Loa’s summit about 56,000 feet above its base; the enormous volcano covers half of the island of Hawaii, also known simply as the “Big Island of Hawaii.”
HVO scientists with USGS continue to urge caution and preparation for the eventual day Mauna Loa will erupt again. “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.
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.
According to USGS, while Mauna Loa is not erupting right now , rates of deformation and seismicity remain elevated above long-term background levels. GPS measurements continue to show slow, long-term summit inflation consistent with magma supply to the volcano’s shallow storage system. A slight increase in the rate of inflation that began in January 2021 continues.
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, 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.