What made Japan’s deadly volcanic eruption so unpredictable?

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    In Japan, rescue efforts at the Mount Ontake volcano have been hampered by toxic gases and fears of another eruption.

    On Saturday, more than 250 people were out hiking and enjoying a nice fall day, when a surprise eruption littered the mountain with falling Boulders, thick smoke and piles of ash. At least 36 people were killed. And questions have been raised as to why there wasn't more warning.

    Here to help us understand what's happening, our science correspondent Miles O'Brien, and Thomas Wagner of NASA, who is an expert on volcanoes.

    And we welcome you both.

    Miles, to you first.

    Why was it — was this as unexpected as we're reading?


    It was, Judy. This was what's called a phreatic eruption, which means it was shallow and involved some hot water essentially.

    Steaming water that entered into a crevice and came in contact with magma, which of course is many thousands of degrees, causes like an instantaneous flash like you would have in your oven, and caused that pyroclastic flow to come out.

    This is not the kind of thing that all those sensors which are on that volcano — and Japan has well-sensored volcanoes — this is not the kind of thing that they predict well.


    And, Thomas Wagner, when it comes to predictability, they're not always this unpredictable, are they?


    No. It depends on what's going on in the volcano.

    Like, in a place like Hawaii, you have got big bodies of magma moving around. They cause the volcano to deform and tilt. But eruptions are difficult things. You can think of a volcano like a big crazy plumbing system in a big old building.


    And you were talking me that there are many different kinds of volcanoes active right now around the world, but they're operating at different speeds.



    And some volcanoes, like the Japanese volcanoes, have a lot of water dissolved in the magma, and they have more explosive eruptions, just like if you shook up a soda and took the top off, whereas that Hawaii, you don't have a lot of water and you get more lava flows.


    So, Miles, clearly, these deaths, 36 deaths, tragic. But for the volcano itself, how significant an eruption is this?


    Well, this is — scientists will be looking very closely at what may lie ahead here.

    If you will hearken back to 1980, Mount Saint Helens, before the huge eruption there, there was a series of these phreatic eruptions, these eruptions involving boiling water. And they were viewed as a precursor to the eruption which we ultimately saw which caused such devastation in that part of the world.

    So volcanoes are in some sense predictable, but in some sense not. You can see a lot of the warning signs. It's very difficult to know when they're going to blow. Think of the island of Montserrat. And that island dealt with evacuations. Half the island is now completely evacuated, but it lingered in a state of near eruption for many, many years.

    There were many questions to scientists, saying to them, why can't you figure this out better?


    And, Thomas Wagner, just continuing with that, is it easy to predict when it settles down by watching it?


    No, because you get different kinds of eruptions.

    And so like that's why, in some cases, we look use satellites to look at how a volcano deforms. In other cases, we will actually have people go out and map the old deposits around a volcano to figure out what its history is and where you might be likely to get another eruption.

    And the hazards are different, too. In this case, we had a phreatic eruption. In some cases, a tiny eruption melts snow on top and makes a mud flow. One of those killed 20,000 people in South America in the '80s. And sometimes you get lava flows. And that's why it's important to sort of understand the particular hazards around the volcano you're on.


    And, Miles, you talked about what scientists learn from this. What are scientists looking at here?


    Well, what they're going to do, and as we — as I mentioned, the Japanese have a well-sensored volcanic system, if you will, as well as great ability to predict earthquakes as well.

    This is a nation that kind of lives on the knife edge when it comes to seismic activity and volcanoes. So they will be looking at those sensors, seeing what was damaged, putting in the types of devices that will allow them to further analyze it.

    At the time of the hike, it was considered safe to be there. It was level one out of a scale of one to five, on the safe end for hikers to be in proximity of that volcano. Perhaps over time, they will not be as generous with that rating, as they consider the possibility that this could be a precursor to something bigger.


    And, very quickly, Thomas Wagner, here in the U.S., nothing quite like this?



    We have like Mount Rainier. We have all the Cascade Volcanoes. The USGS, though, has a great program monitoring those and studying those. And there are really good maps of the hazards that people should make themselves aware of.


    Well, this is certainly — if you didn't have a reason to do that before, you do now.

    Thomas Wagner with NASA and our own Miles O'Brien, we thank you.


    Thank you.


    You're welcome, Judy.

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