Seismic activity increased on Mauna Loa's northwest flank on December 4, 2020, with M4.1 earthquake and clusters of small, shallow earthquakes occurring closely in time and location. The volcano is not erupting but the rates of deformation and seismicity have not changed significantly over the past week, remaining above long-term background levels. The last eruption of this volcano took place in 1984.
From December 4 to 10, 2020, the Hawaiian Volcano Observatory (HVO) seismometers recorded approximately 165 small-magnitude (below M2.5) earthquakes at Mauna Loa, mostly beneath the volcano's summit and upper flanks. The majority of these earthquakes occurred at shallow depths of less than 8 kilometers (~5 miles) below sea level.
Elevated seismicity in this region continued at the time of HVO's weekly update released 22:06 UTC on December 10, although events have occurred less frequently over the past 48 hours.
Clustering of shallow earthquakes in this region is not unprecedented, HVO said. Previous earthquake swarms at this location and depth occurred in October 2018, April 2017, July 2016, August 2015, and earlier.
These earthquakes remind us that Earth’s largest active volcano continues to show signs of unrest, HVO said on December 10.
They are located in an area where, over the past several years, persistent minor seismicity (generally smaller than magnitude-2) has occurred. Elevated seismic activity is one reason that Mauna Loa’s volcano alert-level has been ADVISORY - the volcano is exhibiting signs of elevated unrest above known background activity - since July 2019.
The last time an earthquake of similar magnitude and depth [M4.1] occurred in this area of Mauna Loa, approximately 5 km (3 miles) northwest of Moku‘āweoweo, was November 2011, when increased rates of minor seismicity were also occurring. In 2011, other monitoring data streams remained stable and an eruption did not occur. Current data streams on Mauna Loa also remain stable and do not indicate that an eruption is imminent.
Global Positioning System (GPS) measurements continue to show slow, long-term summit inflation, consistent with magma supply to the volcano's shallow storage system.
Gas concentrations and fumarole temperatures at both the summit and Sulphur Cone on the Southwest Rift Zone remain stable.
Webcam views have revealed no changes to the landscape over the past week.
Mauna Loa is the largest active volcano on our planet, rising gradually to 4 170 m (13 681 feet) above sea level. Its long submarine flanks descend an additional 5 km (3 miles) below sea level to the ocean floor.
The ocean floor directly beneath Mauna Loa is, in turn, depressed by the volcano's great mass another 8 km (5 miles). This places Mauna Loa's summit about 17 km (56 000 ft) above its base. The enormous volcano covers half of the Island of Hawaiʻi.
Mauna Loa last erupted 35 years ago, in 1984.
Eruptions typically start at the summit and, within minutes to months of eruption onset, about half of the eruptions migrate into either the Northeast or Southwest Rift Zones. Since 1843, the volcano has erupted 33 times with intervals between eruptions ranging from months to decades.
Eruption at Mauna Loa tend to produce voluminous, fast-moving lava flows that can impact communities on the east and west sides of the Island of Hawaiʻi. Since the mid-19th century, the city of Hilo in east Hawaiʻi has been threatened by seven Mauna Loa lava flows.
Mauna Loa lava flows have reached the south and west coasts of the island eight times: 1859, 1868, 1887, 1926, 1919, and three times in 1950.
Alert Level remains at Advisory, and Aviation Color Code at Yellow since July 2, 2019.
In VONA released on July 2, 2019, HVO said earthquake and ground deformation rates at Mauna Loa Volcano have exceeded long-term background levels over the past several months.
"An eruption is not imminent and current rates are not cause for alarm. However, they do indicate changes in the shallow magma storage system at Mauna Loa."
Featured image credit: USGS/HVO, April 2020
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