Mauna Loa Erupts! What’s Next?
After a long period of unrest, Mauna Loa volcano began erupting near midnight on November 27th. Is this eruption a big frigging deal? Is it going to destroy major Hawaiian cities? How did we get here? Let’s delve!
First, you’ve gotta watch the first moments of the eruption though the USGS thermal camera at the summit. Watching a fissure split Moku’āweoweo caldera and fresh lava spill across the caldera floor is absolutely riveting:
Isn’t that gorgeous? I was mesmerized in the wee hours of the morning, refreshing the summit webcams and watching the eruption evolve. There’s something incredibly beautiful about fresh lava fountaining and flowing where it has absolutely zero chance of seriously ruining anyone’s day.
After resurfacing most of the caldera floor (which is a lot- the floor is nearly 15km² in area!), lava flows overtopped the crater rim to the southwest on the morning of November 28th. You could see lava from the coast!
2022 Mauna Loa eruption seen from Waikoloa, HI. Credit: USGS
Thankfully, that was just Mauna Loa psyching us out. It would have been a very hairy time if the Southwest Rift Zone had gotten involved – lava flows from there have the potential of overcoming cities in mere hours.
Instead, the eruption migrated quickly to the Northeast Rift Zone. Three fissures opened right near the base of Dewey Cone, feeding new lava flows above NOAA’s Mauna Loa Weather Observatory, while activity ceased within Moku’āweoweo. For a while, lava flows remained active within the low slopes of the “saddle” between Mauna Loa and Mauna Kea. Fountain heights reached 30-60 meters (100-200 feet), and flows were within 18 kilometers of Saddle Road. But by 1:30 PM HST, two of the fissures had shut down and most lava flows stalled. Fountain heights were down to a few meters. Fissure Three’s lava flows are so far remaining above 10,000 feet elevation, and were a good 16 kilometers from Saddle Road at last report.
Fissures and lava flows in the Northeast Rift Zone. Credit: USGS
The early days of a Mauna Loa eruption are dynamic, though, and new fissures could open near the current location of the eruption at any time.
Let’s take questions now, eh?
Is this eruption a big frigging deal?
I’d say yes! It’s the first eruption of Mauna Loa in nearly forty years. And that was the longest it’s gone without erupting since we began keeping records in the 19th Century.Many of us were but we bairns the last time it put on a show. So this is pretty exciting.
That doesn’t mean we’ll have an exceptionally large eruption this time, though. So far, it’s looking about average for Mauna Loa. More on that in a bit.
Is Hilo gonna die?
Almost certainly not. As the USGS staff pointed out in their Facebook comments, the current lava flows in the Northeast Rift Zone are very small, not extending much past their fissures. The eruption is very high elevation, whereas populations are located far down the slopes closer to sea level. And it’s rare for Mauna Loa eruptions to last long enough to reach Hilo anyway. Take 1984, when flows reached within 6.5 kilometers of the outskirts of Hilo within just a few days. Once they hit those really shallow angles, they slowed significantly. Also, the eruption began to wane. Levees broke, draining lava from the main channel. Blockages formed. Things stalled out, and then within a couple of weeks the eruption ended. So there’s virtually no worries there.
Will Mauna Loa blow up?
Yeah, nah, it’s not that kind of volcano. While there have been occasional explosions at Mauna Loa, the chances of this eruption being one are infinitesimal, and even if there is a ba-boom, it won’t be anything like a stratovolcano. You don’t gotta worry about big bangs here.
Isn’t it possible that Kona is still in danger?
Nope. Mauna Loa has very predictable patterns: once an eruption migrates from the summit and localizes to a rift zone, it tends to stay there. Since this eruption has chosen the Northeast Rift Zone, it’s almost certain it will stay there. It would take “a major and unexpected shift in activity” for it to swap to the Southwest Rift Zone. I had a bigger chance of winning that billion-dollar Powerball, and I didn’t even play.
Well, why not erupt out of both rifts?
Physics, my love. There’s not enough overpressure for that to happen. We’ve been monitoring Mauna Loa’s eruptions for centuries now, and never on over 30 of ’em has it erupted out both zones. I’m pretty sure if the current intrusion of magma was of unprecedented size, we’d have known by now. So far, everything looks business as usual.
What about Kilauea? Will this affect its eruption? Has it already?
Not so far. Keep in mind that the volcanoes don’t actually share a magma chamber. They’re fed by the same hotspot, but different source regions. Per the USGS: “There do seem to be occasional sympathetic, and sometimes even opposite, behaviors at times, but those are believed to be controlled through stress and pressure effects that might be transmitted through the entire hotspot system.”
I just checked the webcams (midnight PST), and Kilauea is plugging along much as it has been for the last several months. No major effects so far.
Fun fact: While their lavas have a very different source and chemistry, they have about the same viscosity. It’s just that Mauna Loa tends to erupt more lava and faster, so its flows travel further and faster (with the exception of 2018, when Kilauea proved it can sometimes match pace with its bigger sibling).
Was it weird that the eruption happened so suddenly?
I know it seems really weird that the morning of the 27th, you were seeing a volcano activity update that said there were no signs of an imminent eruption, no significant changes in the last 24 hours, and no indications from earthquakes, gas emissions, or inflation rates that we were going to see lava by midnight. But that’s Mauna Loa’s MO. It starts slow and builds gradually. Then, when it’s ready to erupt, you get maybe an hour or so of vigorous seismicity and inflation as magma moves from the reservoir to the surface. It’s very hard to anticipate when that final crescendo will happen, but the years of increasing activity you see before it let you know to keep a close watch, so it’s not an entire surprise.
The buildup to this eruption actually started back in late 2014. We saw an increase in seismicity and summit inflation, indicating magma on the move. There was a brief pause in 2017 and 2018, but then everything picked up again and kept steady on. We had tilt and swarm events, where seismicity jumped and tiltmeters registered ground surface tilt, in January to mid-April of 2021 and again in August 2022, which left us in no doubt that magma was on its way to the summit. Then in late September of 2022, seismicity increased from around 20 earthquakes per day to 40-50, and stayed there. A couple of days registered over one hundred quakes. It was enough activity to tell us we’d better shut down access to the summit and let the folks living at the base of the volcano know to make their get-the-F-out plans now.
If you want historical comparisons: The eruptions in 1975 and 1984 were very similar to the sequence we saw here. Dead normal Mauna Loa behavior, this.
How long will this eruption last?
The USGS predicts it will continue anywhere from hours to weeks. Months are unlikely. Years are almost right out. So enjoy it while we’ve got it!
I’ll let you know if there are any significant changes to the eruption. Let’s hope both Mauna Loa and Kilauea give us good holiday shows with no property damage or casualties!
Here are the first 24 hours of the eruption from the summit webcams for ye:
First 24 hours of the eruption from the summit webcam
HVO crews monitoring the eruption at Mauna Loa summit. Credit: USGS
References:
Hawaii Volcano Observatory Activity Notices
USGS Volcanoes Facebook Posts
Featured Image: Mauna Loa Eruption from Saddle Road. Credit: Janice Wei/NPS
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