The USGS Hawaiian Volcano Observatory raised the alert on the world’s largest active volcano this week, putting Mauna Loa in Hawaii at “advisory” level and raising the aviation color code from green to yellow.
For the past several months, earthquake and ground deformation rates at Mauna Loa Volcano have exceeded long term background levels. An eruption is not imminent and current rates are not cause for alarm. However, they do indicate changes in the shallow magma storage system at Mauna Loa.
Following a significant earthquake swarm in October 2018, HVO seismic stations have recorded an average of at least 50 shallow, small-magnitude earthquakes per week beneath Mauna Loa’s summit, upper Southwest Rift Zone, and upper west flank. This compares to a rate of fewer than 20 per week in the first half of 2018. Shallow earthquakes are occurring in locations similar to those that preceded Mauna Loa’s most recent eruptions in 1975 and 1984.
During this same time period, GPS instrumentation and satellite radar have measured ground deformation consistent with renewed recharge of the volcano’s shallow magma storage system. The current rate and pattern of ground deformation is similar to that measured during inflation of Mauna Loa in 2005 and again from 2014 – 2018.
Together, these observations indicate the volcano is no longer at a background level of activity. Accordingly, HVO is elevating the Mauna Loa alert level to ADVISORY and the aviation color code to YELLOW.
Alert levels and aviation color codes are explained here: https://volcanoes.usgs.gov/vhp/about_alerts.html
This increase in alert level does not mean that an eruption is imminent nor that progression to an eruption is certain. A similar increase in activity occurred between 2014 and 2018 and no eruption occurred.