Mauna Loa - A Look Back At The 2022 Mauna Loa Eruption (pt 1)

An honest look back and review of what happened with the Mauna Loa eruption, this series will overview the eruption sequence, the night one response, discuss nuances of Mauna Loa eruptions, the communication efforts, and then give a run-down on things that could be improved. What went well? What could be improved? What went off the rails? We’re going to be looking back at the 2022 eruption of Mauna Loa in more detail in this multipart series. PREGAMING BEFORE THE ERUPTION Months prior to the eruption occurring on Mauna Loa, the USGS had raised awareness levels on Mauna Loa and began outreach with the communities most exposed to the volcano’s hazardous Southwest Rift where fast moving lava flows in residential areas are a real consideration. Timing of these meetings in Oceanview, Pahala, and Konaweana ended up being well attended and helped with general preparation. ERUPTION OVERVIEW While the USGS and Civil Defense community outreach was ongoing for months, the night of November 27th had elements that made it difficult to give precise forewarnings of eruption onset. As of 9:30pm, the inflationary trends of Mauna Loa were holding and seismic activity was not raising any alarm bells. Around 10:30pm, a very shallow swarm of rather large earthquakes up to M4.2 began on the Mauna Loa Summit. Only one hour later, around 11:30pm, lava could be clearly seen on the USGS thermal cam looking into the summit caldera. USGS-HVO preceded to raise the volcanic alert level to RED/ WARNING to represent to start of the eruption, and posted a Volcano Alert Notice. No evacuation order was made by Civil Defense as the eruption had not entered the Southwest Rift Zone, so no alerting text messages were sent out. The eruption began a half hour before midnight on November 27th, starting at the summit as all Mauna Loa eruptions do. The fissure inside the caldera began to grow rapidly to the north, but more so initially towards the south. Not long after the eruption began, fissures had expanded miles across the Moku'āweoweo caldera floor and outside of the caldera to the south. Lava descended out of the summit region in the direction of Kona and west Hawaii, a lava flow visible for all to see from Oceanview to Kailua-Kona. Within six hours of the eruption starting, a fissure opened outside of the summit region on the Northeast Rift Zone of the volcano at a height around 11,000ft. The eruption proceeded in a manner best described as text-book for Mauna Loa, with more fissures opening on the Northeast Rift Zone downslope from the first. The primary concerns transitioned from the SWRZ and rapidly moving lava flows going into residential areas and focused on the NERZ and the potential for the fissures to propagate further down-rift nearer to Hilo, or the vent staying at the active fissures and perhaps challenging Saddle Rd with a long lava flow like in 1935. The eruption maintained it’s vigor for over the first week, producing an over 10-mile-long 'a'ā lava flow with supporting lava channels to feed a flow front over a mile wide that slowly advanced through the flats and towards Saddle Road. The ‘definitely not a viewing area’ was established, deemed the Traffic Hazard Mitigation Route by Hawaii County, was an effort to allow people safe viewing and reduce traffic hazards on Saddle Road. The Old Saddle Road route was opened in collaboration with Pōhakuloa Training Area and the State, allowing the public a safe area to see the eruption for themselves from the no longer in use Old Saddle Road. Inhabited areas were at no near-term risk from this eruption while Fissure 3 remained the primary vent for activity, and every day that passed suggested activity would remain at Fissure 3 - a stark difference from Kīlauea in the 2018 eruption where a total of 23 fissures erupted. For a rift zone eruption of Mauna Loa, the location of Fissure 3 was advantageous for those that live on her slopes as it kept the flow in the flat areas on the Saddle between Mauna Loa and Mauna Kea. The initial lava flows were fast-moving and created multiple lava channels running in parallel to each other before later merging further downslope and feeding a larger A’a flow front once the topography of the land flattened out. The giant mass of a flow front would eventually be compromised further and further upslope until on Day 10, the entirety of it’s supporting lava channel feeding the front would drain of lava. The front would then slowly come to a halt like an overloaded train taking a long time to completely come to a stop and Saddle road was spared. Over the next few days the eruptive activity would further reduce, gas emissions dropped, and volcanic tremor associated with the passage of magma underground ceased. Since then, Mauna Loa has been quiet as Kilauea’s activity inside it’s summit caldera has resumed. Nothing really unexpected occurred during the 2022 Mauna Loa eruption volcanically, the eruption was pretty standard as far a Mauna Loa rift zone eruptions go. However, what was your impression of the preparation and response to the eruption? The response to the eruption will be further discussed in part 2. Questions for You What was your experience during the Mauna Loa eruption? Did you go and see the eruption in person? When did you hear that Mauna Loa was erupting? What actions did you take when you heard of the eruption? What do you think could be done better in term of response and preparation for the next Mauna Loa eruption? The next part of this series will look at the night one response and some of the complexities and challenges the first several hours presented in responding to the eruption. Image credit to Andrew Hara