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22 April 2013

Remembering to be small: Accretionary Wedge #56

As geologists, we spend a lot of time looking for the big picture. We want to know how a mountain range formed, or where tectonic plates were millions of years ago, or what global repercussions an eruption could have, or what effect the melting of an ice sheet could have on sea level around the world. We think about time in boggling spans that far exceed anything we could experience in a single lifetime – millions, even billions of years. And we are always trying to tell far-reaching stories to explain the history of our planet, using words and figures and photos.

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28 November 2012

Increased activity at Santiaguito

A quick note for today: It appears that activity at the Santiaguito lava dome complex in Guatemala has increased significantly, with collapses occurring at the lava flow on the southeastern flank of the Caliente dome. Plumes are visible on GOES satellite images and are reaching 5 km in height (plumes from ash-and-gas eruptions of Caliente are usually less than 1 km high).

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27 October 2011

More “translating”: The 1929 dome collapse at Santiaguito

Last week I talked about “translating” eyewitness accounts of the 1902 eruption of Santa Maria in Guatemala. As all of you probably know by now, the Santiaguito lava dome complex started growing in the 1902 eruption crater in 1922. At first there was just one dome (which was called Santiaguito then and which we now call Caliente). There isn’t much in the literature about the early days of the dome growth; most of the accounts we have about the area come from German explorers Karl Sapper (an ethnographer and linguist) and Franz Termer (a professor of geography and anthropology).

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4 July 2011

Report on IVM-Fund trip to Guatemala: Part 3

From April 29 – May 3, 2011, Dr. Jeff Witter of the International Volcano Monitoring Fund (IVM-Fund) made a trip to the Santiaguito Volcano Observatory (OVSAN) to deliver a set of volcano monitoring equipment. This equipment was purchased with the proceeds from a fundraising effort that I and the OVSAN personnel conceived of and that Jeff helped put into action. Jeff did a great writeup of his experiences in Guatemala, and asked that I share it with everyone who has contributed to the fundraiser.

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18 June 2011

Favorite geology word: Autobrecciation (Accretionary Wedge #35)

Well, ash-flow tuff got taken pretty quickly, but I’m fairly certain no one will come up with my favorite geology term (or the particular meaning I’m going to talk about). That word is autobrecciation. I’m not talking about the autobrecciation that happens when the surface of a lava flow breaks up and gets incorporated into a lava flow, but the meaning used in several volcanology papers about rockfalls and lava dome collapses: volatile-rich, pressurized lava dome rocks fragmenting explosively in response to rapid decompression, which occurs at a critical pressure difference between the overpressurized rock and the surrounding environment (i.e., the point when the pressure overcomes the tensile strength of the rock). As you can see in the video, the rocks basically disintegrate into a lot of fine material (and probably some leftover rock chunks), which is the perfect recipe for a pyroclastic flow.

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10 June 2011

Valles Caldera

I meant to post this last year after my brief trip to Los Alamos, but now that I’m back on the Hill for the summer, it seems a shame not to show off the scenery!

The Jemez Volcanic Field in northern New Mexico – which includes the Valles Caldera – straddles the Rio Grande Rift in the east and the Colorado Plateau in the west. The Jemez contains volcanic rocks erupted from >13 to 0.13 million years ago, with compositions ranging from basalt (low silica content) to rhyolite (high silica). The best known of these is the Bandelier Tuff, a thick sequence of pyroclastic deposits which were erupted in several phases around 1.62 to 1.25 million years ago. The total volume of material in the Bandelier is around 300 cubic km (~75 cubic miles), and it covers much of the area in the Jemez Volcanic Field. (The Bandelier tends to be unwelded and relatively soft, and canyons have cut down through it in many places, creating wonderful vertical exposures as well as the mesas and plateaus that Los Alamos is built on.)

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27 April 2011

Soufriere Hills Volcano: Recent deposits in 2010 and 2011

Last year I wrote about the February 2010 dome collapse deposits of the Soufriere Hills lava dome, and this year at the SHV: 15 Years On Conference I had the chance to revisit some of the very same spots. These deposits are mainly pyroclastic material (ash, dome rock and pumice), left behind after pyroclastic flows, surges, and a 50,000 ft (~15 km) high ash plume were created during a major collapse of the lava dome. These deposits extended the eastern coastline of Montserrat almost a km in the area of the old Bramble Airport, and surges were even observed flowing out over the ocean on the eastern side of the island. Here are a few before-and-after shots of the deposits:

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12 April 2011

Soufriere Hills Volcano: 15 Years On Conference

If you’re wondering where I’ve been for the past week or so, the answer is attending the recent Soufriere Hills Volcano: 15 Years On conference, held from April 4-8 on the Island of Montserrat. (I gave a talk, which hopefully goes a little way toward justifying a trip to a Caribbean island in the last weeks of the semester!) The conference was fantastic, and I learned so much about lava dome eruptions (in addition to my own research) that I’ll probably be slotting whole chunks of new material into my dissertation.

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8 September 2010

February 2010 dome collapse deposits at Soufriere Hills

If you ever want to visit a post-apocalyptic wasteland, someplace that’s been run over by pyroclastic flows would be a great choice. On February 11 of this year, a partial dome collapse on the northeastern flank of the Soufriere Hills lava dome produced spectacular pyroclastic flows, surges, and a 50,000 ft (~15 km) high ash plume. The pyroclastic flows extended the eastern coastline significantly in the area of the old …

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15 March 2010

Looking backward: Past eruptions at Volcán Santa Maria

On our way to visit the Santiaguito Volcano Observatory, Gustavo Chigna of INSIVUMEH (the Guatemalan equivalent of the USGS) was kind enough to take an afternoon off and show us some of the older deposits near Santiaguito. Our first stops were at an exposure of the air-fall deposit from the October 24, 1902 eruption of Volcán Santa Maria. This eruption was a devastating one, stripping the land for more than …

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5 March 2010

Watch your step: Field work on lava domes

I suppose I’ve left you all hanging long enough, so now it’s time to show off the first batch of photos from Guatemala. The trip started out in Guatemala City, where we loaded up our rental car and drove to Quetzaltenango (known as Xela or Xelaju to most people). From Xela we drove to a finca, or farm/plantation, and then spent three hours hiking through jungle, over landslide scars and …

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1 March 2010

Back in los Estados Unidos

Just a quick note to let you all know that I’m finally back from Guatemala with samples in hand and only a bit of surface damage. (Much better than last time.) It was a really successful trip, minus the bits where we had to deal with driving around Guatemala, and I’m really happy that the field work went as well as it did.I’m still in the process of unpacking and making …

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16 February 2010

Dome collapses

In light of the recent dome collapse at Soufriere Hills, I thought I’d expound a little on the subject, which is a major part of my research. Lava domes, if they last long enough, tend to go through cycles of growth and collapse. These can be relatively short, like the domes at Soufriere Hills or Mt. St. Helens (remember, a few years is short even on a volcanic timescale), or long, …

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