Kīlauea starts new eruptive cycle with a lava show

Kīlauea Volcano on the Big Island of Hawaii reawakened on Dec. 20 with a flourish, fountaining lava in its summit crater. Temblor talks with volcanologist Michael Poland about what the eruption means.
 

By Megan Sever, science writer and editor (@megansever4)
 

Citation: Sever, M., 2020, Kīlauea starts new eruptive cycle with a lava show, Temblor, http://doi.org/10.32858/temblor.147
 

 

At 9:30 p.m. local time on Dec. 20, Kīlauea Volcano erupted for the first time since 2018. After seismicity ramped up about starting at approximately 8:30 p.m., lava broke out of the walls of Kīlauea’s summit crater, Halema’uma’u. The fresh lava vaporized the crater’s water lake, swapping it for a new lava lake on the crater floor. Fountains initially flowed out of three vents in the crater wall, filling the crater at a rate of several meters per hour. Don’t worry: Rates have slowed to about 1 meter, or approximately 3 feet, per hour and as of the morning of Dec. 22, the lava lake was still more than 480 meters, or approximately 1,600 feet below the crater rim. And even if the lava lake does eventually overflow, it will flow onto the summit caldera floor.

The volcano’s last eruption ended in 2018, after consistently erupting for 35 years. While much of that lengthy eruption had been fairly safe, with effusive lava flows at the ocean front and bubbling lava lakes in the Pu’u ‘Ō’ō cone and the summit, the increased activity in 2018 spectacularly disrupted life on the Big Island. From May through August 2018, Kīlauea erupted as much lava as it normally produces in 10 to 20 years. It opened up a couple of dozen new fissures, shot lava fountains more than 80 meters (260 feet) into the air, buried roads and destroyed some 700 homes. Then, it stopped.

At the end of the 2018 eruption, scientists thought that the magma reservoir that had been feeding the eruption had emptied like a deflated balloon, explaining why the eruption stopped. “We had speculated that the volume of magma that was in that reservoir was actually about what was erupted,” says volcanologist Michael Poland of the U.S. Geological Survey. But subsequent studies have suggested the massive eruption actually only drained a small fraction of the total volume of the reservoir, he says.

Kīlauea is one of the most active volcanoes on Earth and also one of the best instrumented. As such, scientists — and the world, thanks to the Hawaiian Volcano Observatory webcams — can see what’s happening at the volcano in real time.
 

 

On Dec. 21, Megan Sever spoke with Poland for Temblor Earthquake News about what Kīlauea’s latest rumblings mean for the volcano.
 

MS: Is this a continuation of 2018 eruption — was it not really finished? Or is this new?

MP: This is a new phase of activity. It’s clear that [after the 2018 eruption], we entered a different style of eruptive activity.

It’s quite exciting, because we’re seeing the volcano come back to life. And all of the datasets we can collect are going to tell us now about how the system at depth has changed since 2018. Is this stuff that’s coming out of the ground now brand new? Is it really fresh from the mantle, which might be suggested by the inflation? Is it maybe a mix of old and new? Or is it all old stuff? When we can look at the gas, the samples that we’re able to collect from spatter and Pele’s hair, and the deformation signals, I think we’re going to see a really neat story that allows us to look into the magma chamber and try to understand what happened over the two years that Kīlauea was dormant.
 

MS: Was it really dormant since 2018?

MP: It wasn’t quiet, but it wasn’t erupting. In about October 2018, we started seeing repeated deflation-inflation (DI) events. That’s where the summit deflates over the course of a day or two, and then suddenly inflates again. It’s a very small amount of deformation — you only see DI events on sensitive tiltmeters. But we had always tracked that back to the magma chamber that’s about a mile or so deep beneath the summit. Seeing these DI events start up again was a sign that the magma chamber wasn’t empty. There was still something in there that was able to change pressure.
 

 

MS: Were there precursory signs of the current eruption?

MP: We knew very soon after the end of the 2018 activity that magma was still there. It just took a little while to pump up the system. We suspect that as soon as the 2018 eruption stopped, the volcano started to refill from beneath. By early 2019, it reached the point where it could pressurize the reservoir and push the ground up. In the last couple of months, we’ve really seen an increase in the rate of inflation of the volcano and also in the seismicity beneath the summit.

So it’s clear that things were really becoming pressurized. That’s going to culminate in either an intrusion … or an eruption. We had the intrusion on December 2. And then we had the eruption on December 20.
 

MS: Was this expected?

MP: Something like this was expected. It’s difficult to know the timing, of course. But we had seen Kīlauea inflating and refilling with magma since early 2019. So we knew that the system was recharging.
 

MS: What do we know about the magma chambers below Kīlauea?

MP: We know that there are at least two chambers and maybe three. There’s one that’s kind of ambiguous; it’s hard to tell how important and permanent it is. But there’s one reservoir that’s about 3 to 5 kilometers [approximately 2 to 3 miles] or so beneath the south part of the caldera. And then there’s a shallower reservoir that’s maybe 1 to 2 kilometers [approximately 0.6 to 1.25 miles] beneath the more central part of the caldera. And that’s the one that collapsed and drained in 2018. We believe they’re connected, but the connection is somewhat complex and difficult to work out.
 

 

MS:Does the magma just sit in these chambers and periodically erupt, then eventually fill up and erupt again? Where does Kīlauea’s lava come from?

MP: The ultimate source of Kīlauea’s magma is the mantle. There’s a melting anomaly that is feeding these volcanoes. But then some of it also is resident in the volcanoes. Some magma comes into the volcano and it sort of sits around and percolates and gets old. But some of the other magma is going to be very fresh. Looking at the composition of this stuff, we can get a sense of what we presume is fresh stuff coming in from the mantle. That should have a primitive, young signature in terms of its chemistry.
I’m very curious to see the proportion of new material versus old that erupted. I’m sure we’re seeing an influx of new stuff into the chamber — the inflation suggests that — but how much stuff does it have to mix with on the way up?
 

 

MS: How do you determine the age of the erupted material without sampling the lava? I imagine sampling would be rather difficult right now!

MP: The lava samples are coming to us, because there’s Pele’s hair and [other volcanic] glasses that are coming off the eruption. We can just go and collect these samples on the ground outside of the eruption area. There will also be gas emissions. Really fresh magma is going to have a lot of gas in it because [the magma] won’t have sat around for a while and lost its gas. So the gas emission measurements will be important. And we can also look at where the deformation is coming from. It’s almost certainly the shallow magma body, but we may see other areas that were activated.
 

 

MS: How do we know if one of the rift zones is going to reactivate along with the summit?

MP: Well, we don’t know that any will. Traditionally, over the last few hundred years anyway, the bulk of the activity at Kīlauea has focused at the summit.

We sort of got used to the East Rift Zone [erupting], because starting in the 1950s, the rift zone was really active with lots of little eruptions and then the long one starting in 1983. But for the entirety of the 1800s, almost all of the eruptive activity was at summit. And even during the period of frequent rift zone eruptions in the 1950s through the early 1980s, there were many eruptions at the summit. So, a summit eruption is normal for Kīlauea. In fact, this one seems, at least at first, to be very similar to others that have lasted hours to days and pour lava into Halema’uma’u crater.
 

MS: Do we have any sense of whether this might be a days-long eruption or a years-long one? Is there anything in the signals that would give you any idea?

MP: Initially, we can look at the deformation. Ever since this eruption started, the volcano has been deflating, so it’s losing pressure. That depressurization is a sign that there’s more [magma] coming out than there is going into the magma chamber. If that continues, the volcano won’t be able to sustain the eruption anymore, because it will have dropped below some pressure threshold and it won’t be able to push the magma up the pipe anymore. We don’t know where that breakeven point is, but it’s a sign that this is probably not going to be a super long-term eruption.

Rather, what seems more likely is that we will get into a situation of cyclicity, typical of Kīlauea, where we would see inflation and then an eruption lasting hours to days. And it might be in the East Rift Zone or the summit. Then after it sort of bled off that pressure and deflated, it would go quiet for a while and begin to pressurize, inflate and pop again.
 

 

MS: Are we seeing any evidence of magma moving throughout the system and possible eruptions in the East Rift Zone or elsewhere?

MP: There had been some evidence that the East Rift Zone was refilling, especially soon after the 2018 eruption ended. But after that initial activity, all the signals of recharge activity moved to the summit. We still struggle to understand what that East Rift Zone inflation signal was. But so far, it doesn’t look like anywhere else has been reactivated.
 

MS: Wasn’t the biggest recent earthquake, the magnitude-4.4, in the East Rift Zone? Can you explain that in terms of the summit eruption?

MP: Yeah, that’s interesting. The magnitude-4.4 appears to be on the large fault that underlies Kīlauea’s south flank. That fault is one of the reasons that there’s this southward motion of the entire volcano. It’s sort of sliding on the interface between the volcano and the underlying oceanic plate. And if you push that fault with a dike intrusion in the East Rift Zone, you tend to see strong earthquakes soon thereafter. In 2018, when that huge dike intruded into the East Rift Zone, it was followed by a magnitude- 6.9 earthquake. Similar situations occurred in 2011 and 2007.
 

 

MS: Are the earthquakes causing the intrusions or the intrusions causing the earthquakes?

MP: We’ve seen it go both ways: that a dike intrusion in the East Rift Zone can push the South Flank Fault to break, and the South Flank Fault, moving away from the island, can pull open the rift zone. So they have this this interesting chicken-and-egg feedback going where they can activate one another.

What makes this case interesting is this was a summit eruption. I’m not familiar with summit eruptions commonly triggering felt seismicity right on the south flank. That may be that just because I haven’t studied that particular sort of thing. But I’m curious about the release. It makes you scratch your head a bit.

It’s also possible that it’s entirely coincidental. Although it seems to me a bit too coincidental. It feels like the summit pressurized, maybe pushed the South Flank Fault a bit, and it broke, causing this moderate earthquake.
 

 

MS: Do you expect the seismicity to continue?

MP: As the volcano depressurizes, the seismicity will likely decay. But seismicity and deformation go hand in hand. That’s something that’s difficult to admit because deformation researchers and seismic researchers like to compete with each other, all in good fun. But deformation and seismicity are both a consequence of the same thing: When you’re pressurizing the system, you’re inflating [it] and you’re stressing the rock and causing little cracks. As we see the volcano begin to relax and de-stress, we should see a decrease in earthquake activity as well.
 

 

MS: What are you watching for and excited or interested to see going forward?

MP: My specialty is in volcano deformation, so I naturally gravitate to that. I’m very excited about what we’re going to see deformation-wise because it tells you where the magma is and where it has gone. You can look at these signals and say, “I can see storage areas located in this place or that place. And the eruption came from this storage area, not that one.” Looking back at another time when the summit was very active in the 1960s, we saw evidence of deformation all over the place. But it was difficult to resolve because the tools at the time could only take measurements in a few places, and they weren’t continuous. Well, now we have continuous GPS; we have synoptic views from radar satellites. We will see the summit in a way that hasn’t been possible, with this new technology that’s going to be like turning the light on in a dark room. Suddenly, it’ll all start to come into focus. I’m excited about all the things that are going to be possible and all the things we’re going be able to see. I’m also super interested in the chemistry of the material that’s coming out, because it’s going to tell you something about where it came from and how long it’s been sitting around.
 

MS: So much for Earth giving us a break, huh?

MP: Yeah, 2020 wasn’t going to let us off the hook that easily.