Columns: Not just for basalt anymore
I write the Eruptions blog on Big Think. I've been mesmerized with volcanoes (and geology) all my life. It helps that part of my family comes from the shadow of Nevado del Ruiz in Colombia, where I could see first hand the deadly effects of volcanic eruptions. Since then, I've taken a bit of a winding path to become a volcanologist. I started as a history major at Williams College, almost went into radio, but ended up migrating to geology, including an undergraduate thesis on Vinalhaven Island, Maine. I followed this up by changing coast to get my Ph.D. from Oregon State University. Then I ran a MC-ICP-MS lab at University of Washington for a spell (and wrote for an indie rock website). I spent three years as a postdoctoral scholar at University of California - Davis studying the inner workings of magmatic systems. I am now an assistant professor at Denison University and have projects in New Zealand, Chile and Oregon.
I am fascinated by volcanoes, their eruptions and how those eruptions interact with the people who live around the volcanoes. I started this blog after getting frustrated with the news reports of volcanic eruptions. Most of them get the information wrong and/or are just sensationalistic. I will try to summarize eruptions as they occur, translate some of the volcanic processes that are happening and comment on the reports themselves.
And no matter what people tell you, I definitely do not have a cat named Tephra. (OK, I do).
You can find out more about my research by visiting my website. If you have any comments, questions or information, feel free to contact me at eruptionsblog at gmail dot com.
There has been a wave of articles over the last few weeks out on the geoblogosphere on columnar jointing in lavas – with many, many great images of columns seen around the world. I thought I’d jump in the fray, but as usual, basalt seems to have gotten the center stage when it comes to looking at columnar jointing in volcanic deposits – but columns aren’t just for basalt!
First a bit of a review:
Columnar jointing is a product of differential cooling in a volcanic deposit. Remember, they are hot and when they are deposited as lava flows or tephra deposits, they encounter the Earth’s surface that, comparatively speaking, is cold. The tops and bottoms of the deposits are especially exposed to the cold surface of the Earth. When most lavas or tephra cool, they tend to contract. When they contract, they respond to the change in volume by fracturing (brittle deformation) and can produce 4, 5, 6 or 8-sided shapes that terminate with convex/concave surfaces. These shapes then propagate through the deposit to form long “columns” that keep (roughly) the shape of the fracture formed at the cooling surfaces (e.g., the top or bottom of the deposit).
These columns can be tall – extending throughout thick flow units like we see along the Columbia River Gorge in the Columbia River Flood Basalt. The section of the cooling unit that has columns is called the colonnade, while irregularly fractured areas between the columns is called the entablature. The sequences of colonnades and entablatures can also be geographically extensive, sometimes laterally continuous for tens of kilometers. Some of the best examples of columnar jointing are in large basaltic lava flows thanks to their high thermal gradient – places like Giant’s Causeway, Fingal’s Cave and the Devil’s Post Pile.
However, columnar jointing can occur in any composition of volcanic unit. In 2008, I trekked through the Long Valley Caldera in California and in the Bishop Tuff – the huge (~200 cubic km) rhyolite tuff from the caldera-forming eruption 774,000 years ago – you can find very impressive columnar jointing.
The photos above and below were taken along the Gorge Power Plant Road in Long Valley that descends into the Owens River Gorge. At the bottom of the Gorge is a power plant that sits on the basal vitrophyre (bottom, glassiest unit) of the Bishop Tuff, which is a classic welded tuff. The unit with the columns is one of the moderately-welded, pink units in the tuff that have extensive fiamme – flattened pumice.
The columns can be quite large - with diameters close to a meter at some points - and they are not the straight up-and-down columns that we sometimes think of when it comes to columnar jointing.
In fact, one of the most impressive parts of the columns is that they twist-and-turn, implying that the cooling surfaces in the tuff were not simply the top and bottom of the unit.
You can also see columnar jointing in some of the darker, highly welded Tuff in some of the other gorges around the caldera.
So, columnar jointing can be found in a lot of other types of deposits than merely basaltic lava flows!
Top left: A view into Long Valley from the area near Bishop, CA. Click on the image to see a larger version.
Giving our solar system a "slap in the face."
- A stream of galactic debris is hurtling at us, pulling dark matter along with it
- It's traveling so quickly it's been described as a hurricane of dark matter
- Scientists are excited to set their particle detectors at the onslffaught
Two massive clouds of dust in orbit around the Earth have been discussed for years and finally proven to exist.
- Hungarian astronomers have proven the existence of two "pseudo-satellites" in orbit around the earth.
- These dust clouds were first discovered in the sixties, but are so difficult to spot that scientists have debated their existence since then.
- The findings may be used to decide where to put satellites in the future and will have to be considered when interplanetary space missions are undertaken.
Once again, our circadian rhythm points the way.
- Seven individuals were locked inside a windowless, internetless room for 37 days.
- While at rest, they burned 130 more calories at 5 p.m. than at 5 a.m.
- Morning time again shown not to be the best time to eat.
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