Sooooo, you're taking an early autumn hike with your friends on a Japanese mountain when it suddenly starts to erupt! What a crazy situation. Had flashbacks to 9/11, seeing that ash cloud envelope the hikers.

I'm not sure what the best course of action would be for the folks high up on the slope. You can't outrun the ash cloud. If there's a building, I suppose sheltering inside would be best. If out in the open, perhaps fashioning a dust mask would be the first priority. That ash apparently turns into almost like a concrete in your lungs if you breathe it in. Reports say 7 hikers lost consciousness in eruption.

It doesn't seem like the ash cloud was hot enough to kill anyone outright, at least according to the reports I've seen so far. So, I guess it's a simple ashfall rather than a flesh-cooking pyroclastic flow, but who knows, perhaps it's simply too early for the fatalities to be found.

Here's a first person POV of the eruption by someone on the mountain.

Here's a helicopter view of the eruption.

Woke up this morning to read this in the news:


Here's a Japanese newscast that shows a brief video of the rescue operations. The video shows a Japanese Self-Defense Force helicopter winching up one hiker near the ash covered summit, while other hikers are escorted down the mountain on foot. I noticed that the hikers had triage tags hanging from theirs wrists.

Wired has an article by geologist Erik Klemettion on this incident.

In short, it can happen with no warning, on volcanoes that do not appear active.

He lists a couple of preps, such as bringing a dust mask and goggles, and even a helmet for those worried about such an eruption.

A quote from this very informative article: "how many people hike at places like Mount St. Helens, Lassen Volcano National Park or Mount Rainier every day without specific knowledge that they are hiking on a potentially active and explosive volcano?"

Even a tiny bit of reading by visitors to these areas would reveal their nature (to say nothing of the broad clue in the full title for Lassen) and the recent volcanic history for each (active fumaroles near the summit of Rainier have sheltered bivouacking climbers on more than one occasion). In addition to the threat of volcanic eruption, the hazards of a sudden lahar - a quick slide of wet volcanic ash triggered by several possible mechanisms, is as great as the problems of a volcanic eruption.

And yet Fujisan is the most frequently climbed mountain in the world, and indeed it is beautiful and worthwhile....

I wonder if even a certified climbing helmet would be of much use when rocks start falling from the sky.

I have seen mention of fracture injuries in a number of articles about this eruption. I'm curious if they were caused by rocks ejected into the air? Then again, panic could lead people to slip and fall as they fled the eruption in haste, and if you notice in the videos, many of the hikers are rather advanced in age and generally more prone to fractures.

Just curious because I have witnessed a helmet destroyed by a fist sized rock falling all of 70 feet, although it did save the life of its wearer. Rocks ejected by an eruption will have serious velocity.

Note that the death toll is at least 36 - probably will go higher.

I read somewhere that one hiker covered his head with his pack as rocks fell from the sky and a metal thermos or water bottle in the pack ended up smashed.

According to this story, 36 bodies recovered so far, with at least 24 bodies still on the mountain.
Photos of the rescue and recovery operation.

Apparently there had been some seismic activity, but the eruption was not predicted.
A discussion of why it is tough to predict this type of eruption.

Death toll up to 47 bodies recovered. All reported missing have now been accounted for.

Article confirms that most of the injured hikers were due to falling rocky debris, so the many mentions of fractures that I saw were due to impact injuries and not falls.

The chance of getting caught in an eruption is tiny, but the story interests me in terms of how people reacted and survived such a situation.

It's not easy to deduce if certain actions increased chances for survival. There were a large number of survivors who took shelter inside buildings near the summit, and some found dead nearby in the open, but we don't know if those who died were simply closer to the eruption than the ones who took shelter. The largest number of survivors are those who hiked down, but we don't know how high up they were. They might have just been at a lower elevation when the eruption started.

I do get the sense that taking shelter improved survival. I'm not sure what I would do when the adrenaline is pumping--head downhill or head for shelter, particularly if the shelter is possibly above you, towards the imminent threat.

This is the first article I've seen that describes what things were like for some of the hikers on the volcano. Scary stuff, with very large boulders falling from the sky and crashing around some of them.

Some interesting insight by a veteran climber of many volcanoes around the world in this article.

I was wrong about the recovery effort being over. This article says the official, confirmed death toll is up to 48 now and a dozen more bodies were recovered in a previously unsearched area. The recovery effort continues.

Apparently there was some warning, seconds to minutes. No telling if it would help - volcano summits probably have little to hide under & behind, and that assumes a mask can handle the ash.

SUCH a sad event. There are some situations that no human can survive. This was one of them ... for people high up on that volcano. Prayers for their families.

Pete

Last I heard, there were 54 deaths on Mt Ontake.

From the preparedness angle--if anyone could really prepare for something like this--I ran across this article the other day.