Monday, December 19, 2016

Spectacular volcano videos: Identifying eruption processes

- Janine

It's the end of the year, it's cold (there is ice covering everything outside as I write this), and it's time to give your brain a bit of a break. That makes it a great time to watch videos of volcanoes. We are lucky that so many people post amazing videos of volcanic eruptions online for all of us to enjoy (see below warning), and we can learn a lot from them too. When I am looking at my satellite images of dome collapse block and ash flow and column collapse pyroclastic flow deposits on Shiveluch and Mount St. Helens volcanoes I have videos of these processes running through my mind. This is a short guide to what you are seeing in these incredible videos.

WARNING: There are very dangerous and life threatening hazards associated with retrieving this footage, and here at In the Company of Volcanoes we strongly discourage anyone from trying to take your own.

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This video shows the dome at Unzen volcano undergoing a partial collapse in 1991. This shows how a near-solid body of rock rapidly fragments down to smaller pieces of rock and ash, creating a billowing ash plume rising from the block and ash flow (a type of pyroclastic density current that originates from a dome collapse event). This eruption episode was a deadly one, killing 43 people, including 3 volcanologists - Maurice and Katia Krafft, and Harry Glicken, when a collapse larger than the previous activity caused a pyroclastic surge to sweep over where the group was standing. Having watched this video many times, I am still impressed by how rapidly this solid rock reduces to tiny pieces. I believe this footage of the dome collapse is not the one that caused the fatal pyroclastic surge, as the dome was covered in cloud during that eruption.

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This video, posted by Earth Uncut TV, shows another dome collapse, this one at Sinabung Volcano in Indonesia on 21 January, 2014. This eruption has been ongoing since August 2010 and numerous phases of dome growth/lava effusion and consequent collapse have formed a pyroclastic fan at the base of the volcano. You can see trees that have been killed by pyroclastic flows for scale. This high-quality footage shows the front of the flow racing down the volcano, and the expanding ash cloud above, entraining and heating air to expand and rise upward. You can see older deposits that formed lobes on the pyroclatsic fan ahead of the flow. Watch closely and you can even see a large 'dust devil' formed due to the hot ground.

The video below (by Photovolcanica) shows the Sinabung lava lobe collapsing, in slow motion, to produce a block and ash flow.



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Speaking of domes - a dome is a solid plug of rock that is extruded at the surface - there was an excellent chance to study how these work at Mount St. Helens volcano in 2004-2008. USGS took this time-lapse footage of a particular dome type - a spine, that you can see moving nearly vertically and crumbling as it goes. The highest recorded temperatures seen in cracks of a spine were over 700 degrees C, and growing at rates up to 25 meters per day. Read more about the Mount St. Helens spine growth and see thermal images here.
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Mount St. Helens put on a much bigger show on May 18, 1980. This video is made using the photographs taken by Gary Rosenquist, showing the first moments of the eruption. A cryptodome had been growing under the northern flank of the volcano, making the whole side of the volcano unstable. Immediately after a M5.1 earthquake the northern face failed and began to slide northwards as a debris avalanche, which depressurized the cryptodome, sending a lateral blast out from the volcano which you can see overtaking the debris avalanche.
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Block and ash flows are usually formed when hot dome rock collapses, so why not look at them using a thermal infrared camera. This above video was taken by the Montserrat Volcano Observatory of the Soufriere Hills volcano on Montserrat. You can see the hotter colors (yellow-white) of the base of the block and ash flow racing down the Ganges Fan, where the denser part of the flow is made of hot rock, and the cooler - but still hot, (pink-orange) expanding ash cloud forming overhead.

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On to a different style of eruption, and one from my home country - New Zealand. In 1995 and 1996 Ruapehu volcano erupted. Ruapehu volcano has a crater lake at the top, and when the magma hits this water we get a phreatomagmatic (magma + water) surtseyan eruption, where jets of water and ash shoot out of the crater and fall back down to the ground. In this video by Geoff Mackley you can see the white steam plume in the background, and the dark ash-rich jets rapidly rising, and pretty quickly falling back down because they are so dense.

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Another great video of a phreatomagmatic eruption is from Kuchinoerabujima volcano in Japan, taken by the Japan Meteorological Agency webcam that monitors the volcano. A 9 km ash plume rose from the Shindake crater with material quickly falling back to the ground and producing pyroclastic flows that you can see moving down the slopes.

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A very significant and deadly hazard at volcanoes are lahars -flows of water, rock, and debris that race down a volcano because of heavy rains, melting ice, or crater lakes. This particular video was taken by volcanologist Sandy Budi Wibowo on 28 February, 2014, and was shown at the recent Cities on Volcanoes 9 conference in Chile. He shows the different stages of a lahar on Merapi volcano in Indonesia. you can see the flow front going through, and the large boulders that are carried by the lahar.

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A closer view of just how much rock can be carried by a debris flow can be seen in this footage taken in 2003 at Semeru volcano in Indonesia. These flows are highly erosive and can carve out channels and destroy anything that get in their path. They can be triggered by even tiny volcanic events (like the Armero tragedy), or by non-volcanic related rainfall or the collapse of a crater lake wall. Video by Franck Lavigne at the University La Sorbonne. These can travel great distances away from the volcanoes and are a big hazard around volcanoes that house glaciers, like Rainier in the USA.

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Over to the name that (pretty much) no one outside Iceland can pronounce - Eyjafjallajökull in 2010, posted by Fredrik Holm. This is an incredible video of an ash plume right at the crater. My favorite part of this is the ballistics - the large chunks of rock that you can see being thrown out of the volcano in an arc projectile then hitting the ground nearby. This is something you definitely want to view from a distance.

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In this footage shot by a very lucky drone (spot the near-misses) you can see molten bombs and gas being ejected from Yasur volcano on Tanna Island, Vanuatu. This strombolian activity occurs when slugs of gas rise through a conduit, bursting at the surface and sending the walls of the molten lava bubble flying through the air. With the drone's very close calls you can see the molten bombs twisting and deforming as they fly through the air.

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For a much bigger eruption, and one that gave little warning, we go to Chile to see Calbuco volcano erupting on 22-23 April 2015. This beautiful high-resolution footage by Timestorm Films shows the 15 km high ash plume of the first of two large eruptions. This is a sub-Plinian eruption with a vertical ash column and a laterally spreading umbrella cloud at the top as the ash reaches neutral buoyancy with the surrounding atmosphere. More on the Calbuco eruption can be found in an earlier blog post here.

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This footage of an eruption at Sakurajima volcano in Japan shows the great show of volcanic lightning caused by ash or ice particles interacting within an ash plume, setting of these impressive electrical discharges. New research is being done looking at how tracking lightning strikes can help volcanologists understand large volcanic eruptions from space, so watch this area of research.

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Another great phenomena that isn't caught on camera as much are shock waves. This above video (by Linda McNamara) is of an eruption on Tavurvur volcano in Papua New Guinea. Just as the eruption starts you can spot a bright arc expanding away from the vent - this is the shock wave. You can see it going downwards across the cone kicking up ash, through the sky, and then hit the people on the boat. Shock waves occur when so much energy is released during an explosion that the wave initially travels faster than the speed of sound.

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What goes up has to come down, and volcanic ash fall is something that people who live around active volcanoes have to live with. Volcanic ash is not like the soft ash you find after burning wood, it is pulverized rock, glass, and minerals that are very erosive and bad for human health. The above footage is of the Ontake volcano eruption of September 27, 2014. The end of the video shows how quickly ash can block out the sun. You can learn more about volcanic ash, the hazards, health effects, what to do if you are caught in it, and see what it looks like under a microscope here.

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This footage shows clean up efforts after the Calbuco eruption. You can see how shoveling ash is like shoveling sand, or for those of you not around a beach (like me right now), heavy snow. This can easily collapse roofs, especially if water is added by rainfall, and is a large hazard around volcanoes that produce large ash columns. You can read more about the fate of volcanic ash here.

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One of the strangest lavas on Earth occurs at Ol Doinyo Lengai volcano in Tanzania. As you can see in the video above (shot by Jeffrey Brown), the lava runs kind of like water, and sort of sounds like it too! This is carbonatite lava - a cooler (500-600 degrees C) carbonate-rich lava that erupts as a black liquid, then cools to a white rock.

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A more run-of-the-mill (but still awesome!) lava is found on Hawaii - usually what people think of when I say I am a volcanologist (no I haven't been to Hawaii, yet). These lavas are much hotter and erupt at temperatures over 1000 degrees C. The CenterStudyVolcanoes posted this great high-speed footage of a lava flow in Hawaii, showing how the flow moves as breakout lobes, inflating as time passes. You can see the surface folding and breaking apart, giving the beautiful morphologies and textures you can see on many basaltic pahoehoe lavas.

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Not all lavas behave the same. A more viscous version is a'a lava, like this footage taken at Kilauea volcano on 1 June, 2010 by volcanochaser. Since there is a high glass content due to the rapid cooling (quenching) of the lava you can hear the loud 'clinkery' noise coming from chunks of lava breaking and cascading down the flow front. Lavas produce these a'a textures when the flow becomes more viscous due to lava composition, slope changes, cooling, or the increase in the number of crystals forming in the lava. You can also get 'blocky' lavas, where large chunks of lava ride along the flow surface.

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If you can't get enough of lava then a hot, churning lava lake is for you. This footage, shot by Geoff Mackley and his team shows the intense Marum volcano lava lake on Ambrym Island, Vanuatu. The hot, very fluid lava is gas-rich, causing the convection or bubbling at the surface of the lava body. Lava lakes are actually pretty rare so this is a chance to see how a large body of hot lava behaves. Note: I would never, ever encourage anyone to attempt to get this kind of footage.

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Another type of eruption where you can see hot masses of low-viscosity lava is during a fissure eruption, and for this we can go back to Iceland. In August of 2014 the Holuhraun eruption began north of the Bárðarbunga caldera and erupted enough lava over six months to cover an area of 84.5 km2. You can actually see how much of your home town/city would be covered by this amount of lava here. In this drone footage you can see how the eruption has built up it's own walls that hold the lava lake. You can also see the large amount of gas with high amounts of sulfur dioxide that became a hazard for people living downwind of the volcano. Video credit goes to DJI/Eric Cheng.

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Sometimes underwater eruptions go completely unnoticed, and sometimes the only clues are huge pumice rafts that cover thousands of kilometers and travel with ocean currents for months.This video posted by Stuff.co.nz was taken by a pilot, and shows the pumice raft that originated north of New Zealand round the Tonga-Kermadec trench. If this wasn't seen by a pilot, we might not even know it happened.
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Aside from being incredible videos to watch, there is so much we can learn from watching footage of volcanic activity. We can calculate eruption rates, timing and sequence of events, volumes, temperatures (with thermal infrared), velocities, and where hazardous rocks tend to fly during an eruption. All of this helps us to understand volcanic processes and hazards, so we can eventually get people out of the way and protect lives.

This, and it provides inspiration at the end of a long day of Ph.D. dissertation writing.




Note: Where credit isn't given to the source, the original source was not listed. Please give full credit to any videos and images you post online.

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