If you’ve ever wondered what my nightmares are like, they pretty much go like this.

On Sept. 27, a group of hikers was enjoying the fall weather on the Japanese volcano Mount Ontake. Suddenly, the volcano erupted, letting loose an incredible pyroclastic flow, a torrent of superheated ash that barrels down the slopes of the volcano like a thundering wall of death. The hikers tried to get away, but the flow was far faster … still, one of them managed to get video.

(Yes, it’s vertical, so turn your head. And give the videographer a break, they were all literally running for their life.)

My heart was pounding in my throat watching that; ever since I started reading about volcanoes years ago, pyroclastic flows fill me with visceral terror. They are implacable and unyielding; my friend and geologist Mika McKinnon calls them “rolling clouds of murder.” It is almost beyond imagination that the hikers survived. In fact, given how many people were on the mountain that day, it’s truly remarkable anyone survived. However, there have been no confirmed deaths as I write this (one had been reported but was subsequently retracted).

Update, Sept. 28, 2014 at 15:00 UTC: Well, damn. I’m very sorry to add that overnight reports say at least 31 people have been killed by the eruption. Here is more information on what may have happened, written by volcanologist Erik Klemetti.

I’d write about the science behind all this, but Mika has already done an outstanding job on io9.

I love volcanoes; they are fascinating and something about them draws me in. I will happily travel to see more … but as I do, something like this will always be at the very least at the back of my mind. As long as it isn’t literally at my back.

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