tokyo. travel plans of thousands of people are now in doubt as the ash cloud moves from iceland and further south. the uk's official weather center is telling cnn that this plume will cover all british air space within the next 24 hours. so far 252 flights, mainly out of scotland v been canceled. we want to talk to an expert who can tell us more about what's going on and a reality check of that ash. dr. watson is a lecture at bristol university and joins me now on skype. hi there. how much of a threat is this ash? >> oh, well, let's -- let's not -- if an aircraft flies through a dense ash cloud it's in real trouble. this stuff is like very, very fine sand or glass. you mentioned what would happen if you took a piece of sand paper to your car, that's roughly what would happen to an