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What if the 1926 Mauna Loa eruption happened today, what would happen?

3:19 AM · Nov 22, 2022

There is a wide range of possibilities when it comes to eruptions on Mauna Loa, ranging from a relatively benign summit eruption that stays confined to the summit caldera to a fast-moving Southwest Rift Zone eruption that enters residential communities and cuts off the highway within hours. This write-up is meant to give one possible eruption scenario where lava enters an inhabited area from Mauna Loa based on historical records, but there are many more likely scenarios. Inspiration is taken from USGS records of the 1926 eruption of Mauna Loa and combines experiences from the 2018 Kilauea eruption in Lower Puna to paint an eruption scenario that could be plausible. I will leave the decision on how realistic this scenario is to those that lived through the 2018 eruption of Kilauea. As the old saying by Mark Twain goes, “History Doesn't Repeat Itself, but It Often Rhymes”. Again, this scenario does NOT represent the most likely scenario for the next Mauna Loa eruption. So what’s different now and a century ago? First, the number of people living on the slopes of Mauna Loa has grown drastically. Hawaii Island’s population greatly exceeds that of a hundred years ago but the main difference between now and then is technology. Technology has changed much, and today the expectation is with modern technology and monitoring by USGS-HVO the eruptive sequence used for this scenario would be identified ahead of the eruption and warnings issued in a timely fashion. This series of write-ups assumes early indications of a Mauna Loa eruption are missed by the story’s main character and communications by USGS for months before the event was ignored. They are thrown into the eruption with little knowledge or experience about Hawaiian volcanoes. The story progresses day by day through the eruption and provides a first-person perspective of a person living in the path of lava. Disclaimer: There have been significant efforts to improve eruption response following the 2018 eruption made by emergency managers, hopefully, some of the events portrayed here are handled better than I’ve represented them. Day 0 (The Day Prior) - The day begins like any other, nothing unusual. You commute to work every Wednesday from Milolii to Kailua-Kona. Traffic getting to work was its usual congestion, and after working a few hours you’re looking forward to lunch. Just before noon, you feel the ground start to move, it’s an earthquake, but not a very strong one. After a second of shaking the movement ends, there is no damage and you go back to what you were doing. Earthquakes are common on the Big Island, and you’re used to it. You return home after a long day at work. Later that night you hear through coconut wireless that Mauna Loa is acting up. You find a television and check the news to see that the USGS Hawaiian Volcano Observatory is raising the Volcano Alert Level from Yellow/ADVISORY to Orange/WATCH. Checking Facebook, you see people talking about an imminent eruption, and people are noticeably scared of what may come. You have heard people say an eruption was imminent on Mauna Loa before though. Your phone rings, it’s friends from the mainland worried about your safety. You tell them you’re fine and that the news regularly exaggerates with Mauna Loa, but you are going to play it safe anyways. When you go to bed that night you have felt no earthquakes since the one earlier. The sky is dark, and you can see the stars. Day 1 (The Eruption Starts) - At 3:35 am, you’re awoken by your cell phone ringing. Half asleep, you roll over and notice a red tint to the sky outside your window. Upon checking your phone you see a dozen missed calls and several text messages telling you that Mauna Loa is erupting. Unsure in the heat of the moment what to do, you log onto Facebook looking for something official on the eruption. You feel another earthquake. You need more information. No evacuation notices have been issued as activity is currently confined to the summit region, but authorities are warning that activity could migrate further down to one of the rift zones. You feel another earthquake. You see a post saying USGS upgraded the Volcano Alert Level on Mauna Loa from Orange/WATCH to Red/WARNING. They say that the volcano only gave them a couple of hours of warning to work with before erupting. You feel another earthquake. Social media is full of pictures of the red glow and speculation as to what comes next. You see one of your friends from the mainland suggests that all of Hawaii Island should evacuate immediately and something about a megatsunami... That is enough internet for now. Someone in the household can’t sleep due to the frequent earthquakes, but after an hour the earthquakes reside, but the red glow in the sky remains. You don’t even try to get any more sleep, Mauna Loa is actually erupting! When the sun finally rises, the news is full of videos of lava fountains from the summit eruption that woke you in the night. A fissure well over a mile long was putting down multiple lava flows extending down from the caldera. An official morning update on the volcano’s status is posted online, they say that the lava extends down from the summit 3 miles to the south but lava flows haven’t left the rift zone. They say that current activity is confined to the summit region. By 9 am activity at the eruptive vents has slowed some but continues to erupt, a pillar of volcanic gas can be seen from your house over Mauna Loa. Their worry currently is about the rift zones, particularly the Southwest Rift Zone which has been showing signs of magma moving into it. The Department of Education announces that all schools on the south slopes of Mauna Loa stretching from Konawaena to Pahala will not open today. You feel another earthquake. You decide it’s best to play it safe today and stay home in case the call comes to evacuate, maybe prepare a few things so you call out of work. Most everyone else at work had the same reaction as you did, they also called out of work with many needing to watch their kids with the sudden cancellation of school, your employer will not be opening at all today. You watch and wait at home, tied to the latest news wondering if you’ll need to evacuate. The eruption is the talk of the town and online throughout the day, it even makes national and international news. You talk to a friend in Waikoloa Village that invites you to stay with them if you would like to. You decline politely for the time being. You see that by 5 pm the eruption has ceased, yet the pillar of gas remains towering over Mauna Loa’s summit. You see friends online talk about dodging a bullet from the volcano, while others suggest the eruption is not over yet and is moving downslope into the rift zones underground, and others are stocking up on supplies in Kona… somehow Costco is already out of toilet paper. You check the news again before bed. You feel another earthquake. Authorities start by urging residents to remain on high alert, the eruption could resume at any time. Monitoring is ongoing they say, decisions to issue evacuation orders may come at any time anywhere on the southside of Mauna Loa. You look out the window to see the sky is dark minus some stars, and you think about how the sky is clearer when the volcanoes are not erupting. You find it hard to sleep. You feel another earthquake. ---- Day 2 and the days following will be posted over the coming days and weeks. Image: April 10, 1926 taken around 4 am at the outbreak of the eruption on Mauna Loa, taken from Kilauea by Dr. Thomas Jaggar. Colorized by Dane DuPont with References: Bevins, D., Takahashi, T. J. & Wright, T. L. (1988). The early serial publications of the Hawaiian Volcano Observatory: Volume 3, Monthly Bulletin of the Hawaiian Volcano Observatory (1821-1929). Finch RH (1926) The April 10, 1926 outbreak of Mauna Loa. In: Fiske RS, Simkin T, Nielsen EA (eds) (1987) The Volcano Letter 68.

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