USGS HVO Information Statement — Small earthquake swarm on Mauna Loa Volcano's southeast flank

Release Date:

Mauna Loa Volcano is not erupting. A small swarm of shallow seismicity, that began at 1:00 a.m. HST this morning, 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.

ACTIVITY SUMMARY

Mauna Loa Volcano is not erupting. A small swarm of shallow seismicity, that began at 1:00 a.m. HST this morning, 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.

OBSERVATIONS

On March 18, 2021, the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) has recorded over 40 earthquakes beneath the upper Ka‘ōiki seismic zone, about 21 km (13 mi) WNW of Volcano. These earthquakes are occurring in a cluster about 2 km (1 mi) wide and 0.5–6 km (0.5–4 mi) below the surface.

The largest event in the sequence, so far, was a magnitude-3.5 earthquake, with the bulk of the events being 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 Volcano’s. HVO will issue additional messages and alert level changes as warranted by changing activity.

For more information on earthquakes in the Kaʻōiki Pali area, please 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: https://www.usgs.gov/center-news/volcano-watch-why-do-swarms-earthquakes....

For information on recent earthquakes in Hawaii and eruption updates, visit the USGS Hawaiian Volcano Observatory website at https://www.usgs.gov/observatories/hawaiian-volcano-observatory.

MORE INFORMATION:

Mauna Loa activity summary also available by phone: (808) 967-8866

Other Hawaiian volcanoes summary also available by phone: (808) 967-8877

Subscribe to these messages: https://volcanoes.usgs.gov/vns2/

Mauna Loa webcam images: https://www.usgs.gov/volcanoes/mauna-loa/webcams

Mauna Loa photos/video: https://www.usgs.gov/volcanoes/mauna-loa/photo-video-chronology

Mauna Loa FAQs: https://www.usgs.gov/observatories/hawaiian-volcano-observatory/faqs-mau...

Summary of volcanic hazards from eruptions: https://www.usgs.gov/observatories/hawaiian-volcano-observatory/hazards

Recent earthquakes in Hawaiʻi (map and list): https://www.usgs.gov/observatories/hawaiian-volcano-observatory/earthquakes

Explanation of Volcano Alert Levels and Aviation Color Codes: https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels