here to help us understand what's happening, our science correspondent, miles o'brien, and thomas wagner of n.a.s.a., an expert on volcanos. we welcome you both. miles, to you first. was this as unexpected as we're reading? >> it was, judy. this was what's called a "freeatic" eruption. it means it was shallow and involved some hot water essentially, steaming water that entered into a crevice and came in contact with magma, which is many thousands of degrees. it causes an understand and insh like what you would have in your oven and causes that cloud to come out. this is not something that those censors, and japan has many censors on their volcano, this is not the type of thing they predict well. >> woodruff: so they're not always unpredictable, are they? >> no. it depends on what's going on in the volcano. in hawaii there are big bodies of ma "gma" moving around. you can think of a volcano like a crazy plumbing system in a big old building. >> woodruff: there are many different kinds of volcanos active around the world, but they're operating at different speeds. >> some volcanos like the