Swarm of 130 Small Earthquakes Detected at Mauna Loa

An earthquake swarm that began at 2:30 a.m. on March 29, 2021 beneath the northwest flank of Mauna Loa is being monitored by the US Geological Survey’s Hawaiian Volcano Observatory. The HVO reports that Mauna Loa is not erupting and other monitoring data streams currently show no signs of increased activity within the past day.

The HVO has recorded more than 130 earthquakes beneath the northwest side of Mauna Loa’s summit, about 26 miles WNW of Volcano. Most of these earthquakes are occurring in a cluster about 1 mile wide and 3.5–5 miles below the surface, according to the HVO.

The largest event in the sequence, so far, was a magnitude-2.7 earthquake. The bulk of the events were less than magnitude-2. Only one event was reported “felt” by a resident and was 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,” the HVO reports.

According to the HVO, scientists have recorded shallow earthquakes in this area for many decades across several eruptive cycles at both Kīlauea and Mauna Loa. “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,” the HVO reports.

Other monitoring data streams for Mauna Loa and Kīlauea, including ground deformation, gas, and imagery, show no significant changes in activity. 

HVO continues to closely monitor geologic changes, seismicity, deformation, and gas emissions at Mauna Loa and Kīlauea volcanoes.

For more information on earthquakes in this area, please see the Volcano Watch article titled, “Mauna Loa—A Stirring Giant?” published by HVO scientists on June 12, 2014.