A virtual walk through Kīlauea Volcano’s summit history: Part 1

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Join USGS Hawaiian Volcano Observatory scientist emeritus Don Swanson on a virtual walk, during which you learn about the past 500 years of Kīlauea Volcano’s history as revealed by rocks, craters, and cracks.

This virtual walk will be released in three parts, covering different sections of the Keanakākoʻi Crater trail. Along the walk, Don points out and explains some of the features that formed during the 2018 summit collapse events, as well as the best publicly accessible display of explosive deposits erupted from Kīlauea around 230–370 years ago, one of which probably relates to an important oral tradition. Don also shows two contrasting vents for the July 1974 eruption, highlights the thick deposit of pumice and scoria erupted in 1959, and ponders the origin of Keanakākoʻi Crater.

You can visit the Hawaiʻi Volcanoes National Park website to learn about walking the 2-mile round-trip Keanakākoʻi Crater trail, which begins at the Devastation Trail parking lot on Crater Rim Drive in Hawaiʻi Volcanoes National Park.


Date Taken:

Length: 00:23:42

Location Taken: HI, US


We’re going to start walking down toward Keanakāko‘i now to take a look at some of the features that are related to the last 2000–1500 years of Kīlauea’s history. I can't do everything in a couple hours, and so there will be a lot of holes that are left in the story. I can fill in some questions whenever you have them, but we'll try to do the best we can. Now, before we start walking, I wanted to show you where we are on the volcano. I’ve got a little geologic map here that—you can forget about the colors—but look at the dark lines on the map. And from that you can see that these dark lines are faults that are related to the collapse of the caldera of the summit of the volcano around 500 years ago. And we are now just right here. And you can see that there are faults that are outboard of us, as well as the main fault system, which is inboard. That means that we are here, within the caldera. So welcome to the caldera folks!


Even though this is what we usually call a caldera because it's the deepest depression, we’re really in an area that has gone down as a result of the collapse of the summit about 500 years ago. You get a sense of that when you drive here. You drove past Thurston Lava Tube [Nāhuku] and then you come down, down, down—you're coming down into a down-dropped portion of the caldera. So, I call this outer system of faults the structural boundary to the caldera. And this is loosely speaking the topographic portion of the caldera—the main topographic portion—and which we' often just shortcut and say is the caldera.


You can actually see these faults quite nicely on a LiDAR [Light Detection and Ranging] image that we have of the area. We are now right about in here, but you can see that this is a fault out here that's in back of Kīlauea Iki. And, in fact, up close you can see there are four little pit craters right along the fault I think that probably collapsed when the caldera collapsed. And faults are way out-board of the main topographic depression. They swing around here past Nāmakanipaio Campground. And then they come through here, the LiDAR doesn't show it very well, but there are geologic features that connect around here. So if you were to drive from here now down the Chain of Craters Road, you would be in the caldera going past Luamanu [Crater], and just before Puhimau Crater, you come up. And that is the outermost fault in the caldera. Once you get beyond that, caldera-wary folks can breathe a sigh of relief they're out of danger. It's kind of interesting that here we're in the forest, it doesn't really look like there's much going on, but in reality, we're in the caldera itself.


Okay, now we'll start walking. The first stop will be just inside the gate. No one get too far ahead of me, or behind me. I am going to be walking, as fast as I can, which is slow. So just bear with me.



We’re just starting down the Crater Rim Drive to Keanakāko’i. This portion of the road incidentally has been closed since February, I think it was, of 2008 because as things were building up to the eruption that later created overlook crater and the lava lake, there was a lot of sulfur dioxide fume being given off and trade winds blew across the road so the park closed this section of the road. I stopped here because this is a crack cutting the asphalt. This was a new crack that formed in 2018. And it's one of the farthest outboard faults from the active part of the caldera that formed, but it's a fault only in the road. The asphalt was very brittle compared to the substrate that it's built on and so the asphalt broke during the earthquakes and you will see scores of cracks cutting the road from here out to Keanakāko’i.


We’ve been walking through the fallout from high lava fountains from Kīlauea Iki that took place in 1959. This is the deposit we have here from that and you're welcome to take a look at it. Some of this is pumice—it will float in water. Much of it will not, though. There's really not a good name for this kind of stuff—scoria, maybe—but we use the general term tephra for any particles that are ejected by a volcanic eruption, so this we would call tephra.


This is a photograph that was taken in 1959 during the eruption. The long first episode of the eruption took place over a period of a week or 10 days—I’ve forgotten how long—and during a lull, the park came in here with a bulldozer and scraped off the road. This is just like scraping off snow from a road, and so that was this photograph. So the banks of the tephra on either side here are really thicker than the fall; they've been scraped up by the bulldozer


This was quite an eruption. This is a map showing the contours of thickness of the tephra from the eruption here in Kīlauea Iki—it's this smaller set of ovals here. This is a larger set from an earlier eruption—we don't need to pay attention to that—but this is the eruption. And we are now about here in this, so we're just about in the thickest part of the tephra fall.


Now, what happened here is something very interesting and it's about the only a biological thing that I know, botanical thing, so I’m going to be very careful what I say here. The tephra that fell here is very glassy and abrasive, and it defoliated the trees along here—just scraped the leaves away. And so a park employee, a guy named Garrett Smathers, a biologist, thought that he would do his PhD thesis on watching how a forest dies because of a volcanic eruption.


In reality, to his astonishment and to the astonishment of his professor at the University of Hawai‘i at Mānoa, Dieter Mueller-Dombois, the trees came back to life. Air roots sprouted right away in the summer of 1959 [sic, 1960], the trees started growing again, and the forest was rejuvenated. Smathers and Mueller-Dombois have a really nice pamphlet about this area, about plants that have come back during the course of time since 1959.


Now it looks like many of the trees are dying back and I think that's just a natural die back.  As far as I know there's no disease that has come in, catching the trees at all. But anyway, Garrett Smathers made quite a name for himself because he wrote his pHD thesis on how a forest survived being defoliated rather than how it was destroyed by the defoliation.


We're continuing to go through the 1959 tephra deposit. But as we go around the curve in the road here, you will see that it is beginning to thin out. And also the forest is thinning out as well. And you'll see it'll open up quite dramatically. The reason for that, I think, is related to the volcano.


First of all, the substrate that the vegetation is growing on is the same here all the way along the road into the area where there's very little vegetation. So it isn't a question of there being older soil here, and younger soil there. But what is happening, as we get closer to the edge of the forest, we're getting into the area of more acidic soil. The soil is more acidic because it's subjected to an increasing amount of SO2 rain—sulfuric acid rain—as we get closer toward Halema‘uma‘u. So gradually the quality of the soil decreases because of its acidity, to the point where it's really difficult for much of the vegetation to sustain itself. So it's really quite a nice transition here.


It used to be thought, Howard Powers, the Scientist-in-Charge of the Hawaiian Volcano Observatory in the latest 1960s, thought that it was due to the fact that the 1790 eruption—which we'll talk about later—was concentrated farther west. That was a really good idea, I think, but it turns out to be incorrect because I've mapped the 1790 deposit, which just extends across this entire area. So it really isn't the fact that as we go west we get into younger, or more intense, eruptive deposits. It's a question of what the sulfur dioxide fume is imparting to the soil in the way of its acidity.


We've now reached the largest crack that we can walk to today that cut across the road [in 2018]. But you'll see you don't see the crack cutting/extending off the road. It's confined to the road itself. And so I think this is another example of where the crack in the road was not related to a fault, but was related to shaking of the road. But this one was very large, as you get the feeling here and it was even larger where I'm standing now before it was repaired. What I think happened is that there was a gully going across here, as you can see, heading down here. There was a gully before the road was paved and I think it was the fill in the gully that shook and collapsed and caused the crack to form. This is another example of sort of an engineered crack, rather than a crack that's related to actual faulting. It is not a criticism of the engineer—who could have foreseen that something like this would happen, but I think that's what did happen. From as far as we can walk, we'll see just beyond some larger cracks and those are tectonic cracks. Those are cracks that are related to ground cracks that extend off of the road itself but everything we've seen here walking in is related to just the more brittle nature of the asphalt as opposed to its substrate.


Today is a very nice day and for those of you haven't been here before, don't expect it when you come out here. But if you do come on day like this, it's magnificent. You can see Mauna Loa, the broad high mountain just ahead of us. And if you look off to the right, to the north, you can see Mauna Kea with the telescopes glittering in the sunlight. Many people don't realize that this island has two volcanoes that are so high, much more than 13,000 feet high—4000-meter peaks right before us here. It's really an unusual day. And then of course, between us and Mauna Loa and Mauna Kea is the topographic caldera that we'll be looking down into briefly.


You look off to either side of the road here and you're continuing to see the 1959 tephra, but you can tell that it's very much thinner than it was before we started or at a place where we started. Then the question comes in—what is the tephra hiding? What is below the 1959 tephra? And there are two things that are below it. First off, you would come down to a thick series of ash and tephra deposits from explosive eruptions between around 500 and 200 years ago, and I will be showing you a lot of those deposits later in this walk. And they total a thickness over here of 3–4 meters [10–13 feet], something like that. Below them, you then get into lava flows; lava flows that were erupted during the construction of the summit of Kīlauea between about 1000 and 1400 CE/AD. And it's those lava flows that constructed what we call the observatory shield and all the lava flows that you can see over here in the wall of the topographic caldera—almost all of them anyway—were erupted during this time, between around 1000 and 1400 years.


So here you have the 1959, tephra, and the older tephra deposits obscure a really great thickness of lava flows that built a shield. The thickness of those flows totals something like 400–500 meters [1300–1600 feet], something on that order. This makes it difficult for geologists working here. If you're making a geologic map here, do you map what's at the surface—the 1959 tephra and the older tephra—or do you sort of see through that and try to map the lava flows underneath. That's sort of a problem that we field geologists always face.


I have a little story to tell about when Garrett Smathers, the guy who did his work on that forest back here. In 1969, I was at the summit of Mauna Loa and found some grass growing right in front of the summit rest cabin. I brought some of that grass down and gave it to Garrett, and Garrett figured out that it was Kentucky Bluegrass from horse feed and so he published a paper about it. At that time at least, it was the highest known occurrence of living Kentucky Bluegrass.


We're going to turn off the road now and walk out to a view spot here.