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12 July 2014
One of the interesting things about inviting a geologist to any sort of historic site is the inevitable moment when they get distracted by the stones that have been used to build whatever fabulous architectural treasure it is that you’re admiring. Case in point: When I was invited to go to the New Horizons Symposium in the Chimalistac neighborhood of Mexico city, I spent at least a few minutes each day taking photos of the walls (much to the amusement of my fellow conference-goers).
17 August 2011
Last week I happened to be watching the National Geographic Channel and caught their new program, “How to Build a Volcano”. Being somewhat interested in volcano-building processes myself, I sat down with a pad of paper and got ready to take notes for a review.
The show started off with an exciting idea: bring together a special effects team and a group of volcanologists and try to replicate volcanic processes on a large (but controllable scale). Thus, building a volcano. The four volcanologists (Mike Manga and Ben Andrews of UC Berkely, Josef Dufek of Georgia Tech, and Ed Llewellyn of Durham University) worked with special effects expert Max MacDonald to create a 10-meter-high volcano in a Canadian quarry (and we all know from Mythbusters that anything involving an abandoned quarry is also going to involve explosions).
18 June 2011
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.
27 April 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:
25 January 2011
Following up from my post on rheomorphic flow in volcanic tuffs, it’s geology bake sale time! For my submission to this month’s Accretionary Wedge, hosted at Mountain Beltway, I’m trying to draw a few parallels between a confection more commonly known as “zebra cake” and deformation in pyroclastic deposits. To do a quick recap, rheomorphic flow occurs when parts of a pyroclastic deposit – either during or after deposition – become viscous enough to flow like a syrup. If there is flow banding in the deposit, it can become deformed and folded back on itself to form some visually striking patterns (such as in this piece of rhyolite from Mono-Inyo craters in California). So let’s bake a flow-banded pyroclastic deposit!
16 January 2011
In my first quick Google search about flow banding, I came up with Cole Kingsbury’s fairly new blog, Chaotically Flow-Banded. He gives a good basic description of what flow banding is: visually distinguishable “bands” or layers in volcanic rock that differ based on composition, texture, or geochemical characteristics. Cole focuses on flow banding in lava, which is a familiar feature to him because of his work on the Obsidian Dome near Long Valley in California. I’m also working on domes now (although slightly less felsic ones), but my first experience with flow banding came from mapping Miocene ash flow tuffs in Utah.
29 September 2010
Well, since everyone else is getting in on the columnar jointing meme/festival/whatever, I suppose I could throw a few photos out there… Columns in an ignimbrite on the east side of Santa Maria volcano in Guatemala. (A drive-by, unfortunately. I would have loved a close-up look at these!) Some of the oldest volcanics in the Vulsini volcanic district, Italy: a jointed trachyte from the Bolsena caldera complex. (The tree at …
20 September 2010
Telling apart different kinds of deposits associated with volcanic eruptions isn’t always easy. There are a lot of factors that can affect their appearance: the location and type of eruption, the magma/lava type, where they’re emplaced, etc. On Montserrat, volcanologists are lucky to have both ancient and modern deposits; they can look at what’s currently being erupted and compare it to the older volcanics on the island. We did quite …
8 September 2010
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 …
15 March 2010
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 …