June 11: USGS Conference Call: What’s Causing Summit Explosions?

Once again the USGS media conference call at 11AM is full of so much juicy info I’ve moved it to a separate post rather than make my daily digest 10 pages long.

July 10, 2017 HVO webcam panorama of Halema’umau compared with June 10, 2018. (Click for Full-sized)

BigIslandVideo hasn’t put their edited/abridged version up, which they usually enhance with recent video footage. But they cut a lot of the Q&A anyway.

Below are my paraphrase/notes on the full, unabridged conference call (I skipped a non-geology questions where answer is “Agency X handles that; ask them.”]

Current Summary of Eruption:

[1:55] Janet Babb (USGS/HVO) – No significant changes to LERZ flow field. Fissure 8 “closely-spaced vents” fountaining to 160ft, “fast-moving channelized flow” to ocean at Kapoho. Minor overflows last night from “small ponded vent adjacent to Fissure 8 cone,” none exceeding previous flows. Weak activity at 16/18. Ocean entry “fairly impressive activity,” molten lava entering ocean across broad front: 1.4 miles straight across, but new shoreline more like 1.8 miles. Summit explosion 1:52am. “Since May 17, there have been 23 of these larger explosions.” Since end of May, “ash-poor.” Caveat: 6 of last 7 at night, unobserved, but afterwards few ash deposits. Last viewed explosion was June 7.

[4:50] Brian Shiro (Seismologist, USGS/HVO): “Large energy-release events at summit” occurred 1x day for past week, current interval ~20hours. Energy released during events equivalent to ~5.3 earthquake; felt/shaking reported only in immediate area of Volcano. Not felt as far away as same-sized quake because it’s explosive, longer-period shaking. In general, >3000 earthquakes at summit over past week. “Swarms pick up in few hours before each of these large eruption events.” “We call them eruptions to distinguish them from more typical earthquakes.”

USGS: “USGS-HVO geophysicists installed additional continuous GPS stations around Halema‘uma‘u this morning. These stations will allow scientists to better monitor and measure the ongoing subsidence of Halema‘uma‘u and the adjacent caldera floor.” (Full-sized)
Check-in from other agencies:

[6:40] Jessica Ferracane, Hawaii Volcanoes NP. Yesterday visited Jaggar Museum; damage to floors/ceiling but not exhibits. Many cracks at overlook, parking lot, paths around museum & HVO. First clear view of Halema’uma’u: “quite shocking” to see cracking/slumping of crater walls. Summit white-tailed tropic birds still nesting/flying!  [Googled “white-tailed tropic birds,” found dramatic video from 4 weeks ago of summit ash plume, birds flying in distance.]

[9:15] Robert Ballard, NWS. When trades blowing, ash has to get above 12-13K feet to go northeast to Hilo/Puna otherwise Ka’u gets it. Starting Thurs-Fri into next week, trades weaken; ash may stay near crater but vog could drift N. Radar should be fixed today.

Questions & Answers

Q&A: Reason ash cloud heights not given lately? Because radar out?

[15:00] Janet Babb: Yes, and because 6 of last 7 explosions happened in darkness. Other geophysical signals suggest <10k feet.

Q: How much has floor of summit crater subsided over last few weeks?

[17:00] Janet Babb: Greatest subsidence in one area of Halema’uma’u Crater, which has dropped to 1000 ft deep; seeing 6-7 meter drop after explosions. Other areas continuing to slump/subside, not as much. That’s localized subsidence within Halema’uma’u, NOT Kilauea caldera. Just added 2 GPS units to see how far that subsidence extends out from edge of crater.

USGS: Halema’uma’u Crater on June 5th (Full-sized)
USGS: Halema’uma’u Crater on June 12 (Full-sized)

Q: Significance of LERZ eruption concentrating at Fissure 8, not continuing underground?

[19:30] Brian Shiro: Appears magma has found a pathway… preferential conduit, at least for now… no reason for dike underground to propagate one way or other unless something changes, e.g. pressure. Change still possible, but this is typical with Hawaiian eruptions: varying activity at early stages, concentrates in one area at later stage. It’s how many pu’us, cones around island have formed.

Q: Clarify: you’re calling these explosions “eruptions”?

[20:30] Brian Shiro: depends on your definition of earthquake. Ground is shaking, regardless of what’s causing it. In this case we know shaking caused by explosive events. Not a conventional EQ caused by slippage along a fault. So mechanism of movement different, but what we recordon seismometers is ground motion. To distinguish “force type” from what people think of as EQs, USGS has been calling them “eruptions” as closest available category [in their software]. Other categories include nuclear test, mining blast, etc.
Because it’s not slippage on fault, model used to calculate magnitude doesn’t entirely apply. They’ve been quoting Moment Magnitude, related to energy released. Typical EQ magnitude related to length of fault that moved. With explosion, it’s volume change, outward motion.


Q: 20-hour interval sounds like geyser. Is it helping you get a model of what’s going on? 

[23:00] Janet Babb: Interval varies; at first was 24-48 hour. Has been getting shorter but last was 27. “You are correct in that there’s a whole lot of science going on right now trying to understand these events, and try to figure out exactly what is happening.” Still not certain, a lot of unknowns.

Brian Shiro: “Our thinking evolves with every new event, piece of information.” Working model as of yesterday: evacuation of magma from shallow reservoir under Halema’uma’u, now “somewhat gravitationally unstable” because not being held up, leads to earthquakes “as well as, ultimately, these explosions.” Model: plug or piston sitting inside cylinder angled a bit like cork in wine bottle, slips down every several hours, and that results in big events. Don’t know what’s controlling interval; may be related to strength of rock at sides of plug (“radial fault”), or it could be gas pressure from underneath, or combination of both. Good news: incremental slippage acting like relief valve so pressure doesn’t build too much.

May 26: Screengrab from HVO Webcam at 9:30 AM.

Q: Do you still think steam playing significant role in eruptions/explosions?

[28:00] Brian Shiro: We don’t know, but “a few pieces of evidence” suggest steam not “driving factor”: gasses released include “magmatic gas component,” sulfur compounds one wouldn’t see in pure steam explosion. Geodetic signals (tilt, seismic) point to a more complex mechanism. Behaved differently prior to May 26 explosion[s]. And again since May 29 behaved differently. So may be different mechanisms in play. (“A possible explanation”.)They think that overlook crater/lava lake conduit was still partly open prior to that change, now blocked, so energy going into ground rather than up.

[29:50] Janet Babb: When this started, basing assumptions on what happened in 1924; a time when they had far less sophisticated monitoring tools. With new data from modern tools, may change the way they think 1924 happened. There’s “a lot of science taking place, a lot of fascinating discoveries happening right now.”

Cutaway view of Kilauea in volcano, showing the East Rift Zone and magma chambers. From May 22 USGS talk by Steve Brantley.

[31:00] Q: Somewhat confused question based on a diagram of Kilauea: how much is/could magma chamber drain; could it cause much larger collapse? [Translation: Caldera-forming event possible?]

Janet Babb: This questions sounds like it’s based on idealized diagram of Kilauea with magma rising up from mantle plume, entering summit magma chamber. “Please keep in mind that illustration is greatly oversimplified.” That chamber was feeding summit lava lake and Middle East Rift Zone eruption at Pu’u O’o for past 35+years. Summit lava lake has drained, but still magma reservoir beneath summit of Kilauea. Magma is coming up from mantle, into that chamber, and then down through rift zone; but now it’s moving all the way down to LERZ instead of only to Middle East Rift Zone. Know lava erupting now came from Pu’u O’o because of change in chemistry, hotter. Hard to tell if summit lava lake’s magma is or will erupt in LERZ, because it’ll be changed as travels down rift zone.

Brian Shiro: M6.9 earthquake on May 4 “opened up a lot of space in Middle East Rift Zone.” Southward motion of south flank of Kilauea, “which would increase volume of that central storage area,” so magma drained from summit could be “squirreled away” without  reaching LERZ.