USGS HVO Information Statement — Earthquake swarm on Mauna Loa Volcano's northwest flank

Release Date:

A swarm of earthquakes, that began on March 29, 2021, at 2:30 a.m. HST is occurring beneath the northwest flank of Mauna Loa. Mauna Loa is not erupting and other monitoring data streams currently show no signs of increased activity within the past day.

ACTIVITY SUMMARY

A swarm of earthquakes, that began on March 29, 2021, at 2:30 a.m. HST is occurring beneath the northwest flank of Mauna Loa. Mauna Loa is not erupting and other monitoring data streams currently show no signs of increased activity within the past day.

OBSERVATIONS

Beginning at 2:30 a.m. HST on March 29, 2021, the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) has recorded over 130 earthquakes beneath the northwest side of Mauna Loa’s summit, about 42 km (26 miles) WNW of Volcano. Most of these earthquakes are occurring in a cluster about 2 km (1 mile) wide and 6–8 km (3.5–5 miles) below the surface.

The largest event in the sequence, so far, was a magnitude-2.7 earthquake, with the bulk of the events being 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: https://earthquake.usgs.gov/earthquakes/eventpage/hv72405542/executive.

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 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. 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. HVO will issue additional messages and alert level changes as warranted by changing activity.

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: https://www.usgs.gov/center-news/volcano-watch-mauna-loa-a-stirring-giant

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

CONTACT INFORMATION:

askHVO@usgs.gov

The Hawaiian Volcano Observatory is one of five volcano observatories within the U.S. Geological Survey and is responsible for monitoring volcanoes and earthquakes in Hawaiʻi.