The U.S. Geological Survey’s (USGS) Hawaiian Volcano Observatory (HVO) recorded a magnitude-4.3 earthquake located beneath Mauna Loa’s south flank on Saturday, April 3, at 11:15 am HT (5:15pm ET) , making it the strongest earthquake yet to strike the world’s largest active volcano this week. This earthquake was preceded by a magnitude-3.9 at approximately the same location on 11:02 am HT (5:02 pm ET). More than 150 earthquakes have rattled the area around the massive volcano, putting some residents on edge. However, the USGS is clear to point out that an eruption isn’t imminent -yet.
The magnitude-4.3 earthquake epicenter was 3 miles northwest of Pāhala, near Wood Valley, with a depth of approximately 5 miles below sea level. Weak to light shaking, with maximum Intensity of IV on the Modified Mercalli Intensity Scale, has been reported across the Island of Hawai‘i. According to the USGS, at this intensity, significant damage to structures is not expected. More than 130 people reported feeling the earthquake, including one report as far away as the island of Kaua’i.
According to HVO Scientist-in-Charge Ken Hon, the earthquake had no apparent effect on Mauna Loa or Kīlauea volcanoes. “At this time, we have not observed any changes in activity at Mauna Loa or Kīlauea as a result of this earthquake. Please be aware that aftershocks are possible and may be felt. HVO continues to monitor Kīlauea and other Hawaiian volcanoes for any changes.”
According to the USGS, both the magnitude-4.3 and magnitude-3.9 earthquakes appear to be slip along vertical faults caused by southeast motion of Mauna Loa’s south flank. Today’s earthquakes are significantly shallower and west of the location of the ongoing seismic swarm under the Pāhala area that began in August 2019. In a statement released today, HVO said, “This does not represent a significant departure from the seismic activity observed over the past year and the Volcano Alert Level for Mauna Loa remains at ADVISORY. Other Mauna Loa monitoring data streams show no significant change in deformation rates or patterns that would indicate increased volcanic hazard at this time.”
For now, the alert level for Mauna Loa is “ADVISORY” while the color code for the volcano is “YELLOW.”
Aviation Codes are green, yellow, orange, or red. When ground-based instrumentation is insufficient to establish that a volcano is at a typical background level of activity, it is simply “unassigned.” While green means typical activity associated with a non-eruptive state, yellow means a volcano is exhibiting signs of elevated unrest above known background levels. When a volcano exhibits heightened or escalating unrest with the increased potential of eruption, it jumps to orange. Finally, when an eruption is imminent with significant emission of volcanic ash expected in the atmosphere or an eruption is underway with significant emission of volcanic ash into the atmosphere, the code becomes red.
Volcanic Activity Alert levels are normal, advisory, watch, or warning. As with aviation codes, if data is insufficient, it is simply labeled as “unassigned.” When the volcano is at typical background activity in a non-eruptive state, it is considered normal. If the volcano exhibits signs of elevated unrest above background level, an advisory like the one now in effect for Cleveland is issued. If a volcano exhibits heightened or escalating unrest, a watch is issued while a warning is issued when a hazardous eruption is imminent.
While there are no signs of an imminent eruption, USGS wants people prepared for the possibility of an eruption here. Earlier this month USGS cautioned, “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.”
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.”
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.”
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.
After being quiet for nearly 2 years, Kilauea began erupting again in December. While lava is erupting on the surface at this volcano, it is contained within a lava lake deep inside Kilauea’s caldera. Lava is not threatening any community at this time; other than its glow reflected in the night sky, lava is not visible from viewing areas within Hawaii Volcanoes National Park at this time.
One place getting attention for lava flows on the surface now is in Iceland, where a new volcano started to erupt there in March. There is no known link to volcanic activity around the world; scientists say the fresh volcanic activity in Iceland is not indicative of something related brewing in the U.S.. This includes the Cleveland Volcano, which is also being monitored for possible eruption by the USGS in Alaska.