Tuesday, December 22, 2015

Explosive dangers at Kilauea volcano

- Janine

My first AGU Fall Meeting was so full of wonderful science - emergency management exchanges with Colombia to address hazards of lahars (Nevado del Ruiz), volcanic lightning, active monitoring of volcanoes, community preparedness, and all aspects of volcanic activity above, on, and below the surface. I had great conversations with people excited by their work and eager to communicate their work with the AGU masses.

One of the many posters that caught my attention was "Don't forget Kilauea: Explosive Hazards at an Ocean Island Basaltic Volcano" by USGS volcanologist Don Swanson. When I talk to people about volcanology the first thing to come up is usually how cool it must be to study lava flows at Hawaii. Well, I don't study effusive lava flows, I am on the explosive end of the spectrum with dome collapse block and ash flows, and I have not yet visited Hawaii. One thing is obvious, many people I talk to think of the relatively safe (with exceptions) pahoehoe lava flows when they think of volcanic activity, especially at Hawaii.

Kilauea Overlook, photo by NPS.
What many people are not aware of is the very dangerous explosive personality of Kilauea. Around 2.6 million people visit Kilauea volcano ever year according to the National Park Service, you may be one of them (I hope to be, one day). You may have even been lucky enough to see the beautiful lava flows like this one:

But do you know about Pele's more dangerous and explosive side?

According to Don Swanson (and references listed below) Kilauea's explosive nature includes: subplinian ash plumes up to heights of 10 km; phreatomagmatic (magma + water) and phreatic (steam) explosions; pyroclastic density currents (especially pyroclastic surge); volcanic ashfall; and ballistic ejecta (flying rocks) around the entire summit area with total eruption volumes up to 0.02 km3 (VEI 3) - based on studies of explosive events that occurred during the past 2,500 years.

These are relatively small events, but for any of those 2.6 million people visiting, or 2575 people living (2010 population) near the summit they can be deadly. Once these explosive episodes get going they can even last for centuries (Swanson and Houghton, 2015).

One of these phreatic (steam) eruptions occurred on November of 1790 produced a pyroclastic surge that killed a few hundred warriors and their families (Swanson et al., 2015). This same area is currently visited by around 5000 people per day.

Extent of the November 1790 pyroclastic surge with numbers indicating possible locations of groups impacted, Swanson and Houghton, 2015.
The below video is of a pyroclastic density current at Soufriere Hills Volcano on Montserrat. You can see the hot expansion of the ash and gas as it flows down the hill, similar processes to a pyroclastic surge that may be seen at Kilauea (this video is of a denser flow from a dome eruption). The 1790 event was likely composed mostly of fast moving superheated steam that took the victims by surprise (Swanson and Christiansen, 1973).

Eruptions that produce ballistic blocks are not uncommon at Kilauea. These are blocks that are thrown out of the crater during an explosion and deposit around the crater, as seen in the video below:
This small eruption at Tavurvur volcano shows ballistic blocks/bombs flying out of the eruption plume that then deposit around the crater.

The map below shows the locations of ballistic blocks from eruptions in 1790, 1924, and 2008 (Courtesy of Don Swanson):
Ballistic block locations from Swanson and Houghton (2015).
These blocks can get quite large - with measured blocks up to 195 cm in diameter, if you have visit the summit you would have walked right past them. See this HVO article for more information on ballistic blocks at Kilauea.

Block at the Kilauea Overlook, courtesy of Don Swanson, Swanson and Houghton, 2015.
The ash plume is estimated to have reached 30,000 feet high based on visibility reports. Depending on the wind direction at the time of eruption, ashfall could impact Ka‘ū, Puna, and Hilo, and very fine ash could reach Waikiki (Swanson and Houghton, 2015). An ash plume also produces hazards for the many trans-Pacific flights that travel near the island.

Why is this explosive potential not more widely known? There is little written history about the earlier eruptions for us to learn from. The work done by Swanson and others in uncovering the narrative and geologic evidence from the 1790 event give us a much different view of the seemingly effusive and "safe" Kilauea volcano. If you get the chance to visit Pele, keep her more explosive side in mind while you enjoy this beautiful effusive phase.

All images and information from Swanson and Houghton (2015) with the permission of Don Swanson, USGS Hawaii Volcano Observatory. Link to poster below.

References for more information:
Helz, R.T., et al., 2014. Microprobe analyses of glass from Kīlauea tephra: USGS Open-file Report OF2014-1090.

Mastin, L.G., 1997. Evidence for water influx in 1790: JGR, v. 102, p. 20,093–20,109.
Schiffman, P., Zierenberg, R., et al., 2006, Acid-fog deposition at Kilauea: Geology, v. 34, p. 921–924.

Swanson, D.A., Christiansen, R.L., 1793. Tragic base surge in 1790 at Kilauea Volcano. Geology, 1: 83-86.

Swanson, D.A., Rose, T.R., et al., 2014. Cycles of explosive and effusive eruptions at Kīlauea: Geology, v. 42, p. 631–634

Swanson, D.A., Weaver, S.J., Houghton, B.F., 2015. Reconstructing 1790 lethal eruption: GSA Bull., v.127, p. 503-515.

Swanson, D.A., Houghton, 2015. Don't Forget Kīlauea: Explosive Hazards at an Ocean Island Basaltic Volcano. AGU Fall Meeting, San Francisco, PA43C-2202.

Wolfe, E.W., Morris, J., 1996. Geologic map of the Island of Hawaii: USGS MI Map I-2524.

Friday, December 11, 2015

In the Company of Volcanoes at AGU

-Alison and Janine

The largest geoscience conference happens every year in San Francisco. The American Geophysical Union (AGU) meeting draws more than 20,000 participants from around the world every December. We gather to share our new results, catch up with friends and colleagues, and drink beer. Janine and Alison will both be attending this year. Although we have been to conferences in three other countries together, this will be Janine's first AGU and the first conference in the US where we both be in attendance. Both of us have posters to present on our research, and then will spend the rest of the visit stuffing our brains full of new information and names of new colleagues. If you are going to AGU we'd love you to stop by and chat!

Janine and Alison in Japan for the IAVCEI conference in 2013.
So what sort of topics get covered in a 20,000 person conference? Way more than we could fit in a blog post, but you can get the idea just from our examples.

Alison will be presenting in a session called "Eruptive Processes and Watery Hazards of "wet" Volcanoes on Land, in the Sea, or under Ice".

Her poster is Wednesday afternoon in Moscone South, or the poster hall that is a sea of scientists, figures, and concrete. You can read her abstract on the AGU website V33B-3104: Distribution of ejecta in analog tephra rings from discrete single and multiple subsurface explosions. A shorter title for this would be "where and how stuff gets flung out of explosion craters" (Also, Alison knows there haven't been any new explosion videos in a while. This will be rectified in the new year).

Sediment transport in progress, also known as an explosion from the 2014 experiment session.

If you want to learn more about "What dominates a crater's size, the largest single explosion of the formation process or the cumulative energy of many? Results of multiblast crater evolution experiments" Alison's colleague Ingo Sonder will be presenting a poster in the same session (V33B-3105).

For those who want to see pictures of actual volcanoes, but still think about how these experiments improve our understanding of how they form, Alison's advisor Greg Valentine will be giving a talk called (V32A-03) "Tephra ring interpretation in light of evolving maar-diatreme concepts: Stracciacappa maar (central Italy)" on Wednesday Morning from 10:50 to 11:05 in Moscone South 310.
Real deposits: Alison's favorite outcrop of maar ejecta in Frijoles Canyon, New Mexico, USA.

If you're into huge, dangerous, hot, and fast volcanic avalanches, Janine will be presenting "The 2005 and 2010 dome collapse driven block and ash flows on Shiveluch volcano, Kamchatka: Morphological analysis using satellite- and field-based data" (V23A-3066) on Tuesday afternoon in Moscone South poster hall. This is about how complex these (very) large block and ash flows are, from some of the largest dome collapse events around the world.

The February 2005 Shiveluch block and ash flow destroyed 10 square kilometers of forest and threw trees and rocks around like match sticks.

For those who want variety there are lots of posters discussing non-volcano things including a whole bunch of new stuff Pluto and its Kupier Belt friends, heliophysics (or all about our Sun), ground water, magnetospheres (planetary magnetic fields), geodesy (the shape of the Earth), geoinfromatics (where computers meet maps and geology), and paleobiology (things that aren't alive anymore). There are also a whole bunch of sessions devoted to geoscience education. For example Alison's husband, Topher Hughes, will be presenting in the GeoEd poster session on Wednesday morning, "'What's a geoscientist do?' A student recruitment and education tool" (ED31B-0891).

Geoscientists tend to love what we do. We also don't all do the same thing. When students hear early on that geoscientists aren't all old white dudes in lab coats they can better imagine themselves fitting into the field. Hopefully they can find something they love as much as Alison does these rocks from Askja Volcano in Iceland.

Janine and Alison will both try to tweet from the conference at #AGU15. Though from past experience, it is a full on conference and it is a lot of work just to keep up, so tweeting and blogging take a back seat.