Recent Earthquake Activity on Mauna Loa Addressed by USGS-HVO

Over the last couple of weeks there has been some elevated seismic activity beneath Mauna Loa, and naturally we have been getting more questions about the possibility of eruption. We know Mauna Loa will erupt again one day, but we also know that there have been flurries of earthquakes that did not lead to an eruption. This week's update on Mauna Loa has a little bit extra information provided as a result: HAWAIIAN VOLCANO OBSERVATORY WEEKLY UPDATE USGS-HVO - Mauna Loa Volcano is not erupting. Rates of seismicity remain elevated above long-term background levels. Other Mauna Loa monitoring data streams—ground deformation, gas concentrations, visual appearance in webcams—show no significant changes. Observations: During the past week, HVO seismometers recorded over 400 small-magnitude (below M3.0) earthquakes below the summit and upper-elevation flanks of Mauna Loa. Most earthquakes occurred beneath Moku‘āweoweo, Mauna Loa’s summit caldera, at depths of 1-2 mi (2-3 km) below the surface. This increase in seismicity does not mean that an eruption is imminent nor that progression to an eruption is certain. Elevated earthquake activity under Mauna Loa began in mid-2022 but intensified at approximately 2 a.m. HST on September 23, 2022. Earthquakes have continued at rates of about 50 per day. This represents an increase compared to an average of 15 earthquakes per day prior to this swarm. Most earthquakes have been smaller than magnitude-2 and are unlikely to be felt or cause damage; the largest event in the swarm so far was a magnitude-2.8 on September 23 (https://earthquake.usgs.gov/earthqu.../eventpage/hv73149937/). A minor ground tilt signal was recorded coincident with this swarm. Ongoing tilt changes are difficult to separate from ground motions due to daily heating/cooling cycles and strong seasonal signals. This tilt excursion is smaller than one that accompanied an earthquake swarm in August 2022, and both are smaller than one that occurred in March 2021 that was the subject of a Volcano Watch: https://www.usgs.gov/.../volcano-watch-mauna-loa-sleeping.... Global Positioning System (GPS) measurements show low rates of deformation in the volcano's summit region continuing through the past week. Concentrations of sulfur dioxide (SO2), hydrogen sulfide (H2S), and carbon dioxide (CO2), as well as fumarole temperatures, remain stable at both the summit and at Sulphur Cone on the upper Southwest Rift Zone. Webcam views have shown no changes to the volcanic landscape on Mauna Loa over the past week. Increases in seismic activity have been detected previously at Mauna Loa with no subsequent eruptions. We expect additional shallow seismicity and other signs of unrest to precede any future eruption, if one were to occur. HVO will continue to closely monitor Mauna Loa for changes.