June 28: USGS on Latest Changes to Kīlauea Caldera [Pt. 3 of 3]

This post got long, so I’ve moved the Q&A session to Part 3. Again, I’m transcribing what HVO geologists had to say at the June 28 Volcano Village community meeting.

Part 1 was Kyle Anderson’s talk on seismicity and ground deformation— lots of nitty gritty science— while Part 2 was Don Swanson’s slideshow of some of the visible changes he’s observed within Kīlauea Caldera, with a lot of photos I haven’t seen anywhere else.

Here’s the video of the whole meeting.

Here’s my transcription of the Q&A session. A lot of these questions have already been answered online, but I like hearing direct, personal responses from some of the senior HVO scientists:

[54:20] Q: Can you comment on the Pahala ash layer (possible analogue for current event— or not?)

Don Swanson: The Pahala ash layer is a combination of several different deposits from different eruptions, some probably from Mauna Loa, perhaps some from Kīlauea— there’s some sketchy geochemical evidence that some came from Kīlauea. The youngest dates on Pahala are about 15,000 years, I think, but different locations give older ages, going back to 25 or 30,000 years. It’s kind of a wastebasket now. We don’t know much about it, because it is so old, and that’s why there’s not too much in the literature about it. Probably none of the ash came from Mauna Kea. It’s either Mauna Loa or Kīlauea.

[55:25] Q: I heard Don Swanson say “most certainly everything is going to be greater and more.” Tell us more?

Don Swanson: Well the bottom line is that we don’t know, and I think we’ve been talking about this in the staff a lot lately. We don’t know how long this is going to last. We don’t know if we’re at the beginning, middle, or toward the end of it. But as every day goes by, more cracks are forming, and there’s more subsidence taking place. So that was the reason behind my statement. We’re going to have more. But we don’t know how much more. Nor do we know if it’s going to get more benign or more nasty. And Tina and Kyle can talk to that, and others here as well. So we’re in a period of great uncertainty, but tomorrow we’re expecting one of these events, tonight. And so tomorrow there will be more downdropping, more cracks, and that I feel pretty comfortable saying. And that’s all I’m going to say.

[59:45]  Q: Based on what you’ve been posting, it looks like Halemaʻumaʻu has dropped down to the level of the water table, of the perched aquifer. What are the implications of that?

Don Swanson: Good question.  We have learned something from this eruption. And that is that it takes longer than our previous thinking was telling us for water to pour back into the conduit. We’ve had some theoretical models that have been run by hydrologists that suggest that it might take two months for groundwater to enter an empty conduit because of the heat. That’s theoretical. But—

So the explosions that we anticipated happening because of the interaction of groundwater and hot rock haven’t really taken place. The explosions that took place in late May, we think, were probably triggered not by steam from groundwater, but instead from gas that was coming off the magma.

And we think that could be what happened in 1924, too, which, if true, would upset the applecart, because 1924 has been considered to be a kind of classic example of a groundwater-driven explosion.

One of the lines of evidence for this— I want to mention this, because this is interesting— during this eruption, and during the 1924 eruption, early on at least, you could see the glow coming from the crater, and there were incandescent blocks that were ejected from the crater. That means that the temperature was something higher than about 600° Celsius. And steam can’t come anywhere close to getting that hot. Therefore that is prima facie evidence that more than steam was being involved.

Bottom line, to answer your question, is that the eruption has not proceeded the way that our dogma thought that it would. We learned a lot from this process. It could be that as the eruption continues, this two month period that it takes groundwater to pour into the conduit, it may indeed do so, and we may start getting eruptions that are powered by steam from groundwater [and?] magmatic gas.  Does that answer your question?


Don: I think the implications are the same because, as I’m saying, I think the 1924 explosions were created by the same processes that created the earlier ones here. So the hazards are not based on the model that we have for how the eruptions proceed. They’re based on the deposits that we’ve been able to map from these explosions.

[1:03:40Q: Okay with all the sides slumping in and coming down in the crater, and going down into the puka, when it gets down there, does it turn into magma, or is it just going to plug up the hole and then explode?

Kyle Anderson: So the slumping is occurring, we believe, as magma is evacuating the summit storage system to go down to the East Rift Zone. So what’s happening we believe is that that rock that’s composing most of the caldera floor is breaking up, it’s faulting, and it’s slumping down to replace magma. So it doesn’t become magma, and it doesn’t melt, probably. We’re just replacing magma storage with rocks. So one becomes the other. So effectively we’re reducing the volume of magma that’s stored in the summit as it’s evacuated towards the Rift Zone. Does that answer your question?

Followup Q: But when all those rocks pile up, is that going to drive a larger explosion?

Kyle: Currently there’s no evidence that that’s going to happen. We can’t rule it out. The pressure— if you remember one of the plots I showed, it was that blue line that showed the downward trend. That’s a proxy for the pressure in the reservoir. So overall it’s been on a downward trend. So we’re not in a situation where the overall pressure in the reservoir is increasing and leaning towards something larger.  That’s not to say that we can’t have some explosive activity associated with this depressurizing system, but it’s actually in contrast to what you normally think about at a volcano where it pressurizes and then explodes.

[1:05:30] Q: [Reports wild rumor that magma from Mauna Loa, Mauna Kea and even Hualalai are all feeding Halema’uma’u (!!!)]  My question is, do we know for sure if the magma from Halemaʻumaʻu feeds into Fissure 8, and then thirdly, what can make this all stop? Does it take a big earthquake?]

Tina Neal: Okay, there were a few questions there. Let me see if I can answer them, and then Kyle and Don are here to rescue me and Brian as well.

So first of all, you all know that— I think last week we downgraded the alert level for Mauna Loa from advisory to normal. And that’s because we have been for many months now seeing that volcano be very quiet. So I just want to remind everybody of that. We’re still watching Mauna Loa even though our attention is all focused on Kīlauea.

The volcanoes are all separately fed in their upper plumbing systems. So there is no magma mingling going on right now between volcanoes.

The question of whether Halemaʻumaʻu reservoir melt is now feeding Fissure 8 is still open to debate. We know we have flushed the system down there in the Lower East Rift Zone of magma that had been sitting around for some time. We’re seeing compositions come out of Fissure 8 that look a lot like what we were erupting at Pu’u O’o. So, for certain we’re seeing Middle East Rift kinds of composition. Whether we’re actually seeing Halemaʻumaʻu melt make it all the way down there we really can’t say with certainty.

So that’s the answer to… two questions.

The third question was, what is it going to take to stop this? Good question.

We’re having lots of discussions about this. And I think what Kyle said is one of the things we can say with certainty, is that as long as magma’s leaving the reservoir, and potentially going into the rift zone and potentially feeding the ongoing eruption in the Lower East Rift Zone, things will continue largely as we’re seeing them. The Lower East Rift Zone appears very steady. There’s no sign that it’s really slowing down. The gas emission values that were just taken yesterday were among the highest we’ve seen yet. So, no sign that that’s really slowing down.

But we don’t know absolutely for certain that there’s an immediately open connection between the summit and the Lower East Rift Zone either. So even if the Lower Puna eruption were to stop tomorrow, we could still see deflation and exiting of magma from the shallow…from the summit reservoir system for some time. So it may not be an immediate response.

A big earthquake, a big structural adjustment of the volcano, I suppose could alter things enough that the system is so perturbed that deflation stops. But it’s a little hard for me to envision how that might happen.

We don’t know how these things end. At some point, supply will resume to the summit area that exceeds the outflow. And at that time, deflation will stop, and subsidence will stop. But exactly when that is, we really don’t know.

Q: How much has the summit reservoir drained, and how much has the summit elevation dropped?

Kyle Anderson: So it’s become a little more difficult to quantify how much material has left the summit reservoir, and that’s because these slumping events are happening in a way that makes our simple deformation models a little bit more difficult to use. The best we can do right now is say that the volume of material that’s subsiding down into the vent towards the reservoir is probably, to first order, very roughly, about the amount of material that’s left. So as of June 21st, Halemaʻumaʻu had increased in volume by about 300 million cubic meters. That’s a rate of about, I think, 12 or 13 million cubic meters a day. That is probably a first order, again, just first order proxy for how much is going out towards the rift. It’s a very high rate. I think it’s 130 or 140 cubic meters a second.

In terms of how much magma was stored up here before versus how much is left, again it’s a good question. We used to believe that the shallow Halemaʻumaʻu reservoir right there beneath the crater was probably on the order of 1 to 3 cubic kilometers or somewhere in that range. So by that metric we’ve evacuated more than 300 million cubic meters. That’s maybe 30% of that reservoir.

Having said that, that’s just the reservoir right in that area. We have evidence, based on the slumping throughout the caldera, that we may be pulling magma from larger regions. So there’s probably more magma storage involved in evacuating the summit than just that shallow Halemaʻumaʻu reservoir… is there another part to your question?

[How much has the summit dropped?] 

Kyle: So, it depends on where you want to measure. Throughout the caldera there’s been tremendous subsidence, in some places more than 300 feet. The bottom of Halemaʻumaʻu Crater is now a few hundred meters below where it was before. As you get further from the crater, those levels go down tens of feet maybe throughout the caldera. Then, when you get out of the caldera, it’s maybe a foot or two. So it’s really localized, very strong subsidence right in the region of Halemaʻumaʻu, considerable still throughout the caldera, and then much less outside of it.

[1:13:45] Is there any evidence that there might be a deeper aquifer below? I know drilling results around the island have found multiple layers of aquifers. Is there a chance the magma column will interact with a lower aquifer?

Kyle: So I guess I don’t have a lot to add to what Don said in regards to the aquifer. I don’t know of any evidence of another one. The best we can say about the water table in the region of the summit is from Keller Well, which is I think a couple of kilometers from the vent. In that well, the water table is about 600 meters above sea level. That is not right next to the reservoir or in the crater. So we really don’t know how it varies spatially and in terms of other aquifers. I really don’t know, and I dont’t know that anyone would, really.

[1:15:10Q: Why does it take so much longer for magnitude 5 EQs to show up on the USGS list online than the 3s?

Brian Shiro: It’s a good question. I’m Brian, by the way. So, we added that to our Frequently Asked Questions list. You can check that out on our website; it’s been up since this morning. And the answer is that the earthquakes less than about magnitude 4 are not giving us very many problems, and we’re able to post them just as we always have, automatically, very quickly. Our computer system is working very hard, as you might imagine, with all these earthquakes. When you get to the really large earthquakes, you’re starting to see some mislocation. We don’t want to alert people too much with magnitude 4 point something earthquake in a place where it really isn’t there.

And so we want to personally look at that and verify it. And so if it’s a normal fault-driven earthquake, that’s a pretty quick process. But if it’s one of these big collapse events that we were talking about today that happens at the summit, these are unusual beasts. They are due to this downdropping of material, they are due to gases getting compressed and expanded, they are due to basically a lot of processes happening all together. And it takes a human to look at that.

And to accurately characterize the energy released by these, we really need to wait for the seismic waves to reach farther-out stations than just the nearby ones. And so in fact we’re waiting until it reaches all the way to California and Alaska. And so that takes on the order of half an hour. And again, the person has to look at it and work on it together. So we’re coordinating with our partners at the National Earthquake Information Center in Golden, Colorado with this each time it happens, whatever time of day or night. And we try to do it in less than an hour. That’s our goal.

Q: Do you have an estimate of the freshwater lens up at this altitude?

Don Swanson: the question was if we have an estimate of the elevation of the water table.
[Comment from querant] 
Don: Well, the water table is not perched. The Keller Well [aka “NSF Well”] penetrated the water table, and the rocks were saturated all the way down to sea level. So that’s all that we have.

Q: When/how will they name Fissure 8?

Tina Neal: Thank you for that question. I was here as a young geologist in 1983 when this little fissure broke out on the letter O on the topographic map. And it became the “O Vent.” And then it became “Puʻu O.” And then it became “Puʻu ʻŌʻō.” So, the USGS and HVO, we name things in the field for convenience, and we as you know started numbering the fissures in the Lower East Rift Zone just so we could keep track of them.  And as it turned out it was Fissure 8 that became the locus of sustained effusion. And we’re still calling it Fissure 8. It’s now grown into a substantial landform. And it’s probably time for us to talk about naming that feature, but it’s not our job.  And frankly I haven’t had the mental space and emotional energy to think about that process, but we’ll have to consult with the right folks in the region to do the proper thing. But I have no doubt— it’s a big conversation online? Okay. Well, I’m glad they’re talking about that, I guess, and not Mauna Loa conspiracy theories or something. [Sorry, Tina, the internet has time for both.] Yeah. So, we are starting to talk about it, and we will confront that as soon as we feel right.

Q: [Mentions display at Jaggar Museum, concerns.]  Are we headed towards something like that 1400 event? [When caldera dropped about 2000 feet.] 

Tina [SWOOPS IN]: I’m going to start and then turn it over to the expert [pointing at Don]. So obviously that’s a really important question that everyone here has thought about, including us. And I would just like to say that we’re all living on top of a volcano here, and we all live in earthquake country, and we should always be prepared for sudden events that can harm the infrastructure and harm our homes, and be ready to take care of ourselves. And as you saw in Lower Puna, be ready to move quickly if we have to, for any reason: hurricane, earthquake, tsunami, you name it. So that’s one message.

The second message is that we have had a number of conversations with experts on the mainland, with people who worked on Kīlauea for a long time, experts looking at caldera collapses at volcanoes around the world, trying to extract as much insight from people— in Japan, in Iceland— about this process. And at this point our conclusion is that the likelihood of moving to something of that scale is very small. How small, I can’t tell you. We’re really not able at this point to put a probability number on it that we feel comfortable with. But I will say it’s very small, and I would be comfortable saying it’s highly unlikely. That doesn’t mean it’s impossible.

We’re not seeing any sign of that right now. We’re not seeing sign that that’s imminent. We’re not seeing sign that we’re really progressing towards that, at least as best we can tell. But I wouldn’t want to say it’s completely off the table.

And with that— Don Swanson has studied this process here at Kīlauea, knows it better than anyone, and can probably give us the best context.

Don: If I know it better than anyone else, that’s an indication that we know very little about it. The collapse that took place around 1500 (not around 1400, but anyway, that’s a detail)  — we don’t know whether that collapse took place incrementally over a period of perhaps years to decades, and then culminated in some final collapse which defines the outermost caldera— we don’t know that.

I have inferred from interpretation of Hawaiian chants* that the last stage of the caldera downdropping was abrupt, because that’s when Hi‘iaka was digging to recover the body of Lohi‘au. And I would imagine that that was recording a relatively rapid event. But we don’t know what kind of events might have led up to that.

*[See Don Swanson’s 2008 paper, “Hawaiian oral tradition describes 400 years of volcanic activity at Kīlauea.”]

Tina put it properly that we think with our current data that it is unlikely that we’re going to have such a widespread, wholesale caldera collapse. But the important thing is that with the current data that’s what we think. As time goes on— I think Tina would agree— that we may acquire more data that would indicate— give us perhaps more reason to think that there could be a larger-scale collapse. Where we stand now, we think it’s unlikely. Where we might stand in a couple months, depending on how things progress, might be somewhat different.

I do want to point out, though, that the formation of a larger caldera than the depression that we have out here now isn’t necessarily immediately going to be a bad thing. After— as best I can piece together— after the caldera collapsed around 1500, there was a very large eruption of reticulite — and those of you who are living here in Volcano know that when you’re digging in your yards, you’re coming upon this reticulite— that was from very high fountains that if they formed today would burn forests and buildings in the Volcano area if it were dry. [DON!!! *facepalm*] But then after that there wasn’t a whole lot happening on a large scale for another hundred years or so. A lot smaller eruptions, but confined mainly to the area around where Halemaʻumaʻu is today.

So… long addition to what Tina had to say— we think that it’s unlikely now that we’ll have a big one. Ask me in a month or two, and I might have a different answer. And even if we have a big one it isn’t necessarily going to be terrible.

[Kudos to Tina Neal for running interference before Don shared his views, shaped as they are by a long career spent studying massive effusive and/or explosive events. I respect him so much, but he forgets that the general public tends to ignore scientists saying “the overwhelming evidence points to X” and instead latches onto the low-probability worst-case-scenario. On top of which, these people are stressed from two months of earthquakes. They don’t need a new very-remote-possibility to worry about.]

[1:25:10] Q: This is an earthquake question. It seems in the last week or two, the earthquakes that proceed the 5.3 magnitude equivalent pressure wave are getting bigger. We’re seeing 3.8, 3.9s— no 4.0s that I’ve seen — and it seems like they’re getting deeper, .7, .8 miles, instead of .1 below the surface and sometimes zero. So I’m wondering, what does that mean? Is the caldera breaking apart ever deeper and deeper and deeper as time goes on? 

Brian Shiro: That’s a good question. You’re asking about these earthquake swarms that are occurring over a period of many hours leading up to these large collapse/explosion events. And we know you’re feeling them very strongly when you’re up here. Every time I’m up here, I feel it too. We’ve seen basically a marching of the earthquakes in certain degree, outward from Halemaʻumaʻu. So as the area of deformation has expanded, the area of earthquakes has expanded, too. And so we think that the faults which are driving those somewhat smaller earthquakes in the magnitude 3 range up to about magnitude 4,  that those faults which go around the circumference of the crater are getting longer and perhaps a little larger, and that’s maybe why the magnitudes are getting bigger, too. So larger areas are slipping for those.

Q: We seem to have a magic line that includes the perimeter of the park, that it doesn’t seem to go beyond that line. But now that you said…very lightly… that we had some holes by the Visitor Center, and of course we have the cracks in the road… is it going to move farther out from the magic line of  the perimeter of the park? 

[1:27:00] Tina: I’ll start, and then Ingrid [Johanson] or Asta [Miklius] maybe you want to come up and speak a little bit about the deformation field. So, some of the cracks that you’re referring to on the road that happened during the bigger events early in the sequence are just due to the ground shaking. The ground’s shaking so hard that the road fill moved and cracked the asphalt. They’re not due to faulting related to the subsidence that we’re talking about. That also may be true for some of the other road cracks further on towards the golf course as well. So right now we’re not seeing anything outside — when you say the magic boundary of the park, I think, do you mean the big caldera walls, the steep caldera walls? We’re not seeing a lot of motion outside that boundary.

Asta or Ingrid, do you want to come speak about that a little bit more? Sort of the limits of deformation that we’re really seeing.

So this is Ingrid Johanson, another research geophysicist.

Ingrid: So I might actually defer to Don at some point, because Don has made a survey of a lot of the cracks around Halemaʻumaʻu. But I will say that there are a couple different processes that have produced cracks. Close to Halemaʻumaʻu, it’s mainly been these large slump-blocks falling down into the crater. Up along the crater rim, the cracks there are more likely due to the repeated rockfalls that are happening with each of these Type As [collapse/explosions] just eroding support from that cliff edge. I think it’s unlikely that the crack behind the Visitor Center is due to a downdropping. Of course, I haven’t looked at it, so I shouldn’t say for sure that it’s not.

Likewise as Tina said, these cracks on the road weren’t associated with fault motion, the type of motion that we would expect to see from a piece of that moving down into the caldera.

Tina: As Ingrid indicated, you have to actually look at the cracks in context to understand the mechanism that formed them. So that is one thing we’re hoping to do more of in the coming weeks, spend more time in the field, on the roads and the safe trails, to really look at some of these cracks, to look for evidence that it may be marching further outward.

[1:32:00] Q: Is there any significant subsidence outside the caldera circumferential faults?

Ingrid: So at the moment the really rapid deformation is confined to within the caldera, so, on the southern boundary by that caldera fault that was visible in Don’s photograph. There’s actually a small sliver of the caldera floor on the northeast side that has been relatively stable. So it’s been showing relatively less motions. So the rapidly deforming area has  in fact only been a portion of the caldera floor. So I guess the short answer to the question was no, we’re not seeing significant subsidence outside the caldera bounding faults.

[1:33:20] Q: This is a chicken and egg question. I’ve heard it both ways. Does the earthquake come first, or do the landslides come first?

Tina: We’ve been trying to— we’ve had a contest at HVO, who can draw the best cartoon about what’s going on. I think Brian’s winning.

Brian Shiro: So, what comes first, a landslide or an earthquake?  Well, at least with these big collapse events that we’ve been seeing, it’s the downdropping that happens— this happens underground, under the caldera— essentially the piece of the floor underground that moves as a result of the magma being withdrawn. But as a result there are numerous rockfalls that occur at that instant all around the edges of the caldera. And they make a loud sound as well, and they kick up a lot of dust, as Don mentioned too. So the event itself, the seismic event is first, the rockfalls come shortly after. It’s all recorded by the instruments, and we try to sort it out.


[NOTE: I skipped over the park service because I’m concentrating on the geology, but Jessica Ferracane’s presentation on the morning press conference at the park included a few images of changes within the caldera.  [Photo of Halemaʻumaʻu where road to parking lot cuts off.] And park Facilities Manager Jon Christensen’s “Facility impacts of on-going eruptive activity”  presentation showed more. He also did a quick slide retrospective of Jaggar Museum starting in the 1920s.]