GeoLog

Geochemistry, Mineralogy, Petrology & Volcanology

Imaggeo on Mondays: “Vancouver! Vancouver! This is it!”

Mount St Helen's, Washington, seen from Johnston Ridge.

On May 18th 1980 Mount St Helens (an active stratovolcano of the Cascades located in the North West US), erupted explosively following a magnitude 5.1 earthquake. The quake triggered a devastating landslide which swept away the volcano’s northern flank – in what is the largest debris avalanche recorded on Earth to date. Removal of a section of the edifice depressurised the volcano’s magmatic system triggering powerful lateral eruptions, which removed the top 300 m of the volcano.

In total, 57 people lost their lives, 250 homes were destroyed and the local infrastructure, including bridges, highways and railways, were badly damaged. Prior to the eruption, the flanks Mount St Helens and its surrounding areas were covered in a dense forest. Following the lateral blasts, all trees within a 10 km radius of the volcano were obliterated, while those further afield were badly scorched.

Andy Smedley, an atmospheric scientist, visited Mount St Helens recently, as part of a road trip around Washington and Oregon states.

“What I can tell you is that the scale is still fairly awe-inspiring, as is the devastation still evident on the ground,” he says of his visit to this extraordinary mountain. “The image in question was taken from the Johnston Ridge, which is named after David Alexander Johnston,” goes on to say Andy.

At the time of the eruption, Johnston was a volcanologist with the United States Geological Survey, in charge of volcanic-gas studies and spent long hours working on the flanks of the volcano. On the morning of the eruption he was one of the first geologists on the mountain. Observing the volcano from what he though was a safe distance (10 km from the vent), upon a ridge know at the time as Coldwater II, Johnston was one of the first to report the eruption: “Vancouver, Vancouver! This is it!” He was swept away by the lateral blast shortly after.

Alongside his USGS colleagues, Johnston was pivotal in ensuring the area around Mount St Helens remained closed to the public after unrest at the volcano was detected in early 1980. The data Johnston collected in the run-up to the devastating blast was crucial to unravelling the processes which governed the eruption.

Coldwater II has since been renamed to Johnston Ridge in memory of the dedicated geologist. There is also a visitor centre, with the same name, from which Andy took this impressive photo of Mount St. Helens.

“The peak is about 6 miles away from the camera and there’s very little vegetation that’s returned in the intervening 36 years [since the eruption],” describes Andy “you get some sense of the size of the eruption from the debris flows down the front flanks of the mountain, but it’s also worth pointing out the new lava dome building and Crater Glacier, one of the youngest glaciers on Earth, both within the 1980 crater.”

“Though it can’t be seen in the image, another thing that struck me was the extent of the blast – it can still be clearly seen by the ranks of toppled tree trunks pointing away from Mount St Helens that surround the nearby hills and extend for some miles on the drive up.”

As volcanic eruptions go, Mount St Helen’s wasn’t particularly large (VEI 5), but Andy thinks it’s relative proximity to centres of population in Washington State and Oregon made it stand out in the public’s consciousness.

“It’s not often that the contiguous USA experiences such a full on eruption (I think the nearby Lassen Peak was the last in 1915), and to have it right there on people’s doorsteps, with the ash column eventually blowing across several states, seemed to make its mark.”

By Laura Roberts, EGU Communications Officer

 Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

Imaggeo on Mondays: Gole dell‘ Alcantara

Imaggeo on Mondays: Gole dell‘ Alcantara

On account of Mount Etna (Europe’s largest volcano), the island of Sicily is peppered with geological wonders. Starting with the summit craters of the volcano itself, right through to over 200 caves formed within lava tubes, the island is packed with volcanic sights.Chief among them is Gole dell ‘Alcantara, a system of gorges formed 8,000 years ago in the course of the river Alcantara in eastern Sicily.

The network of gorges have a maximum depth of 40 m and a width of up to 5 m. They are the result of intense, deep erosion,  of 300,000 year old basaltic rocks, by flowing water. The lavas were once thought to originate from the nearby Monte Moio; an unusual crater not linked to the main Etna volcanic plumbing system. More recent research, including detailed petrographic studies, points towards the craters of Monte Dolce, in the medium-low side of Etna, as being the source of the lavas exposed in the Gole dell ‘Alcantara.

As today’s featured image shows, the lavas exposed throughout the gorge walls are remarkable. Erupting in river waters meant that the lavas cooled faster than they would have done otherwise, giving rise to fractures which formed prismatic structures. Some are chaotic, but others are arranged horizontally (locally known as the woodpile), slightly arching (the harp) and in a radial configuration known as the rosette. The most common configuration is the ‘organ pile’ where vertical fractures form, up to 30m high.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

GeoTalk: Drilling into the crater which contributed to the demise of dinosaurs

GeoTalk: Drilling into the crater which contributed to the demise of dinosaurs

Six months ago, somewhere in the tropical waters off the coast of Mexico, scientists began drilling into one of the most iconic geological features on Earth: the Chicxulub crater; the 66 million year old remnants of a deadly asteroid impact, thought to have contributed to the demise of dinosaurs and most other forms of life which inhabited the Earth at the time.

Today we speak to Sonia Tikoo, Assistant Professor of Planetary Sciences, Department of Earth and Planetary Sciences, Rutgers University, and one of the researchers part of an international team which is currently trying to decipher the secrets held by the rocks of the Chicxulub crater at a core repository in Bremen.

First, could you introduce yourself and tell our readers a little more about your career path so far?

In general, my work involves using the magnetism recorded within rocks to understand problems in the planetary sciences.  I started doing research in palaeomagnetism during college but I really wanted to work in something involving space so I transitioned into planetary science during graduate school.  During my PhD at MIT, I worked on studying the palaeomagnetism of lunar rocks from the Apollo missions to understand the history of the now-extinct lunar dynamo magnetic field.  It was really cool to explore the different ways that small planetary bodies could also generate long-lived magnetic fields lasting a billion years or more.  I subsequently started studying how shock and impact cratering events affect magnetic records within rocks during my postdoc at UC Berkeley, and that experience eventually led me to the work on Chicxulub that I’m doing right now!

Meet Sonia, pictured with colleague William Zylberman, holding up some samples collected from the IODP cores.

Meet Sonia, pictured with fellow palaeomgnetist William Zylberman, holding up some samples collected from the IODP cores.

For those readers who may not be so familiar with the project, could you give us a whistle-stop tour of aims of the research and why it’s important?

In addition to being the crater linked to the demise of the dinosaurs (cool in and of itself!), Chicxulub is also the best-preserved impact structure on Earth and it is the only crater with an intact and well-defined peak ring (a ring of elevated topography within the crater that forms during the collapse stage of crater modification).  As part of IODP/ICDP Expedition 364, we are planning to address a lot of questions regarding this crater, including: (1) how peak rings (stay tuned for our paper on that which is coming out very soon!), (2) how rocks are damaged or weakened by impact shock, (3) how much hydrothermal circulation occurs after the impact, and how long it lasts, and (4) how life recovered within and above the crater following the impact and Cretaceous-Paleogene extinction?

In terms of my specific job…studying the palaeomagnetism of rocks from the crater can be used as a powerful tool to answer some of the aforementioned questions because the magnetizations within rocks can be modified by high temperatures and pressures, and new magnetic minerals can form via hydrothermal activity.  All of these things happen during large impacts on Earth and on other bodies as well, and we see these effects in the crustal magnetism of planetary surfaces.  The entire Science Party is going to be quite busy working on these problems over the next couple years.  What we learn here is not only going to tell us about Chicxulub but also about peak-ring basins across the solar system, and as a planetary scientist I find that angle to be particularly exciting.

What is your role specific role in the project?

Sonia is pictured drilling into cores from the IODP 364 Expedition, to collect smaller samples for palaeomagnetic experiments.

Sonia is pictured drilling into cores from the IODP 364 Expedition, to collect smaller samples for palaeomagnetic experiments.

I’m serving as a palaeomagnetist on the expedition.  There are two groups of scientists associated with Expedition 364 – the Offshore Science Party (the team that recovered the core at sea) and the Onshore Science Party (the team that conducts sampling and preliminary analyses here in Bremen). There wasn’t a magnetometer on the drilling vessel, so I became a member of the Onshore Science Party.  My job here is to collect samples and develop a first-pass dataset of measurements that characterizes the magnetization of the various rock units in the core, spanning both the post-impact sediments and the underlying impactite rocks. The sediment data will eventually be used for magnetostratigraphy and to develop an age model for the post-impact period, and the impactite data gives us a sneak peek at what we will be working with in much greater detail during our post-expedition research as we try to understand the different types of magnetization present in the crater’s peak ring.

So, the experiments are taking place right as we speak?! Can you tell us more about what it is like working at the core repository?

Yes, they are running right now!  Working on an IODP/ICDP expedition is a totally intense, totally rewarding experience!  The Onshore Science Party here in Bremen involves around 45 members of the Onshore Science Party and a team of IODP scientists and technicians working together continuously for a month.

First, one team splits the large drill core into halves.  The core halves then get passed onto teams that do detailed visual descriptions of the cores and some physical properties measurements.

Then the core goes to the sampling room, where we collect specimens for both the immediate measurements we are conducting here in Bremen as well as for the post-expedition research that the Science Party members will be conducting at their home institutions.

Starting bright and early at 7:30 every morning, I drill and prepare sample plugs for moisture and density, P-wave, and paleomagnetic analyses. In the afternoons, I usually shift over to processing magnetic data and writing reports while another paleomagnetist, William Zylberman, conducts measurements in the lab.

The final IODP report writing team. (Credit: Sonia Tikoo)

The final IODP report writing team. (Credit: Sonia Tikoo)

Of course, every other team like physical properties, petrology, biostratigraphy, or geochemistry is doing the same kind of fast-paced work in their own way and we’re always comparing notes and taking advantage of our built-in collaborations. Some scientists have been working on Chicxulub or the K-Pg boundary for decades and others of us (like me!) are first-timers.

There is a fantastic energy associated with having so many talented scientists with all these different avenues of expertise working closely together (and trying to get everything done before our month here is over)!

 

If you want to learn more about the IODP Expedition and associated research, you’ll find some resources here:

 

Geotalk is a regular feature highlighting early career researchers and their work.

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