Mauna Loa, Hawaii: Alert level raised for the world’s largest active volcano

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For the past several months, earthquake and ground deformation rates at Mauna Loa Volcano have exceeded long term background levels.

Accordingly, HVO is elevating the Mauna Loa alert level to ADVISORY and the aviation color code to YELLOW. 

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Amazing picture from 1984 Mauna Loa eruption in Hawaii. Picture via Twitter

According to latest investigations, 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.

Seismic Unrest

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. 

Ground Deformation Rates

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. 

Prognosis

As has happened before, it is possible that current low-level unrest will continue and vary in intensity for many months, or even years without an eruption. It is also possible that the current unrest is an early precursor to an eventual eruption. At this time, we cannot determine which of these possibilities is more likely.

HVO expects that days or weeks prior to an eruption, monitoring instruments will detect signs of an increased potential for eruption such as:

  • further increases in rates of earthquakes and ground deformation
  • increases in the sizes of earthquakes
  • increase in surface temperatures
  • increase in visible steam plumes or sulfur dioxide emissions 

However, it is also possible that the timeframe to eruption could be shorter – hours to days. All communities on the flanks of the volcano should be prepared. 

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. But again be prepared!

[HVO]

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