HVO Reports Earthquake Swarm Under Mauna Loa

March 18, 2021, 4:51 PM HST
* Updated March 18, 5:01 PM
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More than 40 earthquakes occurred in an area under Mauna Loa Thursday, but the volcano is NOT erupting.

The US Geological Survey’s Hawaiian Volcano Observatory reported that the small swarm of shallow seismicity began at 1 am HST Thursday morning. It is occurring beneath the upper Ka‘ōiki seismic zone, under Mauna Loa’s southeast flank and northwest of Kīlauea’s summit. Other Mauna Loa monitoring data streams remain stable and show no signs of increased activity.


On March 18, 2021, (HVO) recorded more than 40 earthquakes beneath the upper Ka‘ōiki seismic zone, about 13 miles WNW of Volcano. These earthquakes are occurring in a cluster about one mile wide and 0.5–4 miles below the surface.

The largest event in the sequence, as of late Thursday afternoon, was a magnitude-3.5 earthquake. The bulk of the events have been less than magnitude-2 and not widely reported by residents. Reported felt events were described as weak shaking, with a maximum Intensity of II on the Modified Mercalli Intensity Scale.


Clustering of shallow earthquakes in this region does not mean an eruption is imminent. HVO has recorded shallow earthquakes in this area for many decades across several eruptive cycles at both Kīlauea and Mauna Loa. These earthquakes do not show any signs of magmatic involvement and are part of normal re-adjustments of the volcano due to changing stresses within it. Other monitoring data streams for Kīlauea and Mauna Loa, including ground deformation, gas, and imagery, show no signs of increased activity.


HVO continues to closely monitor geologic changes, seismicity, deformation, and gas emissions at Kīlauea and Mauna Loa Volcanoes. HVO will issue additional messages and alert level changes as warranted by changing activity.

For more information on earthquakes in the Kaʻōiki Pali area, see the Volcano Watch article titled, “Why do swarms of earthquakes occur around the Ka‘ōiki Pali?” published by HVO scientists on March 1, 2012:

For information on recent earthquakes in Hawai´i and eruption updates, visit the USGS Hawaiian Volcano Observatory website at


Mauna Loa activity summaries are available by phone: (808) 967-8866. Other Hawaiian volcano summaries are also available by phone: (808) 967-8877.

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