Two moderate quakes jolted the area around Mauna Loa volcano this morning on the Big Island of Hawaii, prompting the USGS to issue a statement about the stronger seismic activity observed today on the area known to be the world’s largest active volcano. USGS’s Hawaiian Volcano Observatory (HVO) recorded a magnitude 4.3 earthquake on Friday, April 15, 2022 at 1:58 am followed 8 seconds later by a magnitude 4.6 earthquake.
According to HVO, strong shaking, with a maximum intensity of VI on the Modified Mercalli Intensity Scale, had been reported across parts of the Big Island of Hawaii. According to USGS, at that intensity, significant damage to buildings or structures isn’t expected. However, an earthquake of these intensities can rattle objects and nerves. According to USGS, “many objects fall from shelves” in a quake of this magnitude while it can “frighten many.” While structural damage is unlikely, fallen plaster, broken windows, and damaged chimneys can occur near the epicenter of such an earthquake. Outside, this type of earthquake can shake and drop tree limbs and tops, while isolated rockfalls and landslides could be possible too.
According to HVO geophysicist, Jefferson Chang, these earthquakes had no apparent effect on Kīlauea or Mauna Loa volcanoes. “This earthquake appears to be part of the seismic swarm under the Pāhala area, which has been going on since 2019. Earthquakes in this region have been observed at least as far back as the 1960s. We see no detectable changes in activity at the summits or along the rift zones of Mauna Loa or Kīlauea as a result of these earthquakes. Please be advised that aftershocks are occurring and some of these may be large enough to be felt.” USGS said that HVO continues to monitor Hawaiian volcanoes for any changes.
In addition to no life-threatening volcanic eruption threat, there is also no threat of tsunami. The National Weather Service’s Pacific Tsunami Warning Center in Honolulu, Hawaii issued their own bulletin about the double quake saying no tsunami is expected despite the shaking felt from the earthquakes.
Today’s earthquake was centered near the town of Pahala on Hawaii Island’s southeast coast. Scientists believe that magma that supplies Mauna Loa and Kilauea Volcanoes travels deep beneath the seismically active town.
Nearby Kilauea volcano continues to erupt. However, lava from that eruption is completely contained within its caldera crater. Currently a tourist attraction inside Hawaii Volcanoes National Park, the eruption at Kilauea doesn’t pose any immediate lava threat to residential areas.
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, 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.