I didn’t realize I’d missed one of Steve Brantley’s excellent 10-minute slideshow presentations at the weekly Puna Community Meetings. This one took place on Tuesday, June 12 at Pahoa High School.
I learn something from every one of these talks, which sum up Kilauea eruption activity of the past week in a way that’s easy for the general public to understand without talking down to them.
Video of meeting is archived here. Steve’s presentation starts at timestamp 42:10. Where possible, I’ll be including images in my transcript which match his slides.
(Steve Brantley is a USGS geologist, deputy-scientist-in-charge of Hawaiian Volcano Observatory.)
Hello everybody. Thank you for coming out again and thank you for your perseverance. I’ll show a couple slides of what’s been happening down in this part of the neighborhood and end with some slides of the summit area, which continues to change very dramatically.
So this is the overview slide I’ve showed for the past few times. It gives you the overall picture. It’s an image, cartoon, from the summit area all the way out to the eastern tip of the island. The summit area here [under “Kilauea Caldera” label], eastern tip [down by “Kapoho Crater”], with a cross section showing you the general picture of the magma reservoir system from the summit of the volcano down through the East Rift Zone and into the Lower East Rift Zone.
So here’s the summit reservoir [indicates larger, lower tank-shaped area under “Kilauea Caldera”], here’s the magma conduit system [indicates yellow-orange “pipe” extending east, to the right] in the East Rift Zone. And magma moved, beginning April 30, all the way out to here [end of black arrow] to erupt on May 3, and that magma’s continuing to erupt, obviously, in the Lower East Rift Zone. And then in early May, the summit of the volcano began to deflate and subside as a consequence of magma moving out of the magma reservoir. So that’s just the big picture.
[Slide as above, with caption added:
Cone: ~115 ft tall
Fountains ~up to 160 ft
Channel width: ~300 ft]
So the Fissure 8 continues to erupt. There’s been no real change that we can tell in the amount of magma or lava coming out onto the surface. The fountains have changed in height a little bit. They’re a little less than they were maybe a week or so ago, but lava is still being expelled from that vent. It’s built up a cone that’s a little over a hundred feet tall. The fountains are up to, what, 160 feet or so. And in this image just to give you a sense of scale, the channel right in here [pointer crosses channel just where split comes back together] is about 300 feet wide. So the width of a football field… the length of a football field.
Uh, that’s not a very good image. [Lousy slide projector makes this picture almost all black.] A little bit further, a view of the channel, the vent from a little bit further away.
Last week I mentioned one of the concerns is perhaps a little bit of an overflow or perhaps a failure of the levee along the side of that lava channel. But in the past week that lava channel has been very stable as you all know. There have been a few spillovers, but they basically just dribble over the side, maybe help to raise the perched channel a little bit higher. That channel’s now about 20-30 feet above the old ground surface. So there’s still the possibility that there could be some spillovers, a little failure from the levees, but so far, those failures heal themselves very quickly, and the lava has remained in the channel.
Lava continues to flow from Fissure 8 all the way to the ocean. It’s a distance of about 8 miles. The entry area does change quite a bit depending on where the lava dribbles into the ocean. That width of the entry area is now about a mile and a quarter wide, and about 250 acres of new land has been added to this part of the island. The distal edge of that lava delta area changes day to day. Some new land that forms will slip away and slide into the ocean, and so it’s a very dynamic situation at the coast.
So let’s go up to the summit. This is a map showing you the number of earthquakes that have occurred in the past week. There are over 3,000 of those little symbols there. Most of them are magnitude 1. The largest ones are in the magnitude upper 4s or 5 range. And these are the big circles that you see right here. [laser pointer on screencap above.] The black is the approximate location of Halema’uma’u. And you can see that those larger events are happening or located in that general area. And you’ll understand why.
You know, that image is so dark. Can we turn out the lights, possibly? Otherwise you’re not going to be able to see this. I’m going to try toggling this…
…nope, you’re not going to be able to see it. [Slide projector screen totally washes out these images.]
So what I’m going to do is invite you to come back to the corner of the room and I’ll have a sort of an image from June 1 until this morning. And it shows that the northern part of the Halema’uma’u Crater is starting to slump and slide into the Halema’uma’u Crater. So I’m just going to go through these quickly, because you can’t see them.
So this is an aerial view looking into the new, expanded Halema’uma’u Crater. And how many of you drove at one time up to that parking lot? Quite a few. OK. So you know what I’m talking about. This is the parking lot. And what you’re seeing is ground cracks, several of them that are running right through the parking lot area. And those ground cracks have offset a couple of meters. And so this part of Halema’uma’u Crater rim on the south side is starting to slip into the crater proper as the magma withdraws from below.
And my final slide is a — trying to put this a little bit in perspective. We’ve talked about this whole Halema’uma’u Crater dropping, enlarging, and now adjacent parts of the caldera floor are starting to be enveloped into the crater. So we’re creating more volume. The crater’s getting larger.
So how does this compare to some of the earlier known events at Kilauea in the past, say, couple of hundred years? So this is a plot from a colleague. He made this a couple days ago based on work by the scientists in charge at the time: Mr. Finch, 1940. And what he did is to plot the volume lost at specific times during the past 200 years.
So here we are, 2018, going back to 1800. This is the collapse volume [y-axis]. As you go up, this is getting bigger. So, 1924, Halema’uma’u enlarged. We’re on about the same scale of that in terms of volume now. And I wanted to point out there have been some larger subsidence events in the history of the volcano that we know about, just the early 1800s, when Halema’uma’u was active, and when the whole caldera was much deeper. When westerners first arrived about 1823 or 24, and viewed into the Kilauea crater— caldera, it was on the order of about 1700 feet deep. Right now, it’s only about 500 feet deep.
So change is the name of the game at the summit of the volcano and we just happen to be witnessing and experiencing that at this time. We’re tracking this the best we can, and we’re trying to keep our website updated with information about the relative scale of the subsidence and slumping at the crater. Thank you for your patience.