February 5, 2014
As the Tectonic Plates bend, creak, snap, and rattle in earthquakes, blobs of heated rock rise through them from within and punch through the surface, puffing out vast clouds of rock dust and volatile gas, and pouring out mounds upon mounds of hardening molten rock. Volcanoes may fall under the purview of some other realms of the blogosphere, but a spate of recent videos are just too stunning (and informative!) for me to pass up. Besides, I think rumbling, roaring volcanoes land neatly on topic here.
With diligent monitoring and constantly improving technology, volcanic eruptions are being recorded by ever more agencies and videographers around the world. (Here’s an extensive list of volcano webcams by Erik Klemeti.) Below I have assembled what I’ve been struck by as the most spectacular, [freely available] high definition videos of these eruptions. Credit goes to a small number of lucky/plucky/adrenaline junky individuals (namely YouTube users Photovolcanica, Boris Behncke, hitosi49, and TyphoonHunter).
Indonesia’s Mount Sinabung has been terrorizing villages in northern Sumatra for weeks now with ongoing eruptions. The government is struggling with difficult decisions in a massive long-term evacuation, a challenge that’s been documented over on Wired’s Eruptions blog. Currently the volcano is extruding a lava dome, a plug of already hardened rock that’s being shoved out the mouth of the volcano like toothpaste. For phenomenal footage of this process in action I’ll refer you to videos of Mt. St. Helens, which spent the mid 2000s doing this. (You can also see St. Helens’ lava dome pushing the crater glacier out of the way. A USGS animation of sequential elevation surveys shows just how much material has been added!) With this style of eruption, rather than spewing a jet of rock into the stratosphere, the volcano is mainly threatening life on its flanks with pyroclastic flows, those scalding clouds of ash that cascade bewilderingly fast down the slopes of volcanoes, scorching and stripping bare everything they touch, and chasing down handsome geologists.
At Sinabung this year, videographer Richard Roscoe captured close-up the initiation of one of these surges by collapse of a portion of the unstable lava dome. The high-def closeup allows you to see how and why pyroclastic flows form.
Any rock fall produces a huge cloud of dust as the rock [literally] pulverizes itself under its own weight and the force of the impact; when this happens to the extremely hot rocks recently extruded from a volcano, however, the vastly increased surface area allows an enormous amount of heat to escape very suddenly, and the cascade of crumbling rock and dust begins to be swept up by currents of heat rising out of it. Thus is born and perpetuated the roiling, billowing cloud of doom that we all recognize as a pyroclastic flow.
If the daylit video above didn’t convince you, watch this nighttime long-exposure time lapse of the same process. With little ambient light, the red heat of the rocks shines through so that you can see just how much is being released up into the cloud of dust, carrying it turbulently upward:
(Tangentially, if I ever wanted one of those cheesy rec-room light-up wall mounts, it would be of that scene^)
So that’s what generates some pyroclastic flows (other happen when the eruptive column collapses and all the ash suddenly rains back down… or when earthquakes shake a fresh volcanic edifice). What happens when they’ve cleared? The heat rising from their fresh deposits generates whirlwinds, of course: ash devils!
Now how about an even more extreme temperature contrast? In the stunningly gorgeous video below, Sicily’s Mt. Etna spews molten rock onto its snowy flanks. The result is not only an expanding cloud of hot ash but also of bright white steam from the ice vaporizing under the hot ejecta.
Of course while gas, steam, and ash are lofted up, heavier particles (that is to say, rocks and boulders) rain back down after being thrown from the mouth of an exploding volcano. The videos from this Japanese videographer capture with breathtaking detail the expulsion and rain of ash, rocks, and enormous boulders from Mount Shinmoedake in Japan. I love watching the dark, falling particles interact with the lighter rising plumes of gas and dust.
…and stunning nighttime: