A seething caldron of magma and gas lies beneath the Gazelle Peninsula in Papua New Guinea. It’s called the Rabaul caldera, named for the township of Rabaul that sits upon it. A caldera is like a failed geologic souffle — if a volcano is what the finished product should look like, a collapsed version is a caldera.
In 1994, one of the Rabaul caldera’s vents, Mount Tavurvur, erupted along with Mount Vulcan and destroyed much of the Rabaul township. In 1937, Tavurvur and Vulcan erupted simultaneously, killing over 500 people.
About a week ago, Tavurvur erupted again. One couple in the right place at the right time caught the eruption on video, and got to see something incredible.
Australian couple Linda and Philip McNamara were sailing off the coast when Tavurvur blew its top. While they were there for the immense could of ash and magma, what was most amazing was the shockwave.
You’ve probably seen ground shockwaves before (thanks MythBusters) — an expanding circle of disturbed dust from the epicenter of an explosion. With a fast enough camera you can see it move across the ground. If you are lucky, you might even see the aerial shockwave move through the air as a bubble of compressed gas expands outwards and light bends a bit differently through it, allowing you to follow along (here is a fantastic example). But the Tavurvur eruption looked like it created its own clouds. What is going on?
Think of temperature as its most basic. What we know as hot or cold is just a measure of how hard atoms and molecules are bumping into stuff. The harder a molecule can bump into something, the hotter that molecule is. A room full of hot air has atoms and molecules jiggling around much more than the air inside a freezer.
Now assume that you have air at some temperature — some atoms and molecules jiggling around at some velocity — and you almost instantaneously thrust some out of the way, too fast for any other air to take its place. The collective energy of the remaining air would go down, and therefore the temperature would drop. When air temperature rapidly drops in a humid environment, fog forms. Fog like this is called a “Wilson Cloud,” formally named after the curious physics uncovered in our nuclear weapons tests at Bikini Atoll in 1946.
It was fleeting, but with a powerful and lightning-fast push Mount Tavurvur created Wilson clouds by smashing its own gases against the sky’s.
Kyle Hill is the Chief Science Officer of the Nerdist enterprise. Follow the continued geekery on Twitter @Sci_Phile.
HT: Washington Post