Hi funk,
This is actually a pretty fair question. Catastrophes DO occur. Do a search for the Siberian Traps or the Alvarez event. The point is that when really big disasters happen, there is evidence in the rocks. Geology doesn't lie. If there was a huge, global catastrophe like the postulated biblical flood, there would be unequivocal evidence found all over the world that a geologist would recognize almost instantly. For every major disaster on record down through history, there is a smoking gun. Even little ones (like a meteor impact or a single volcanic cataclism like the explosion of Mombacho Volcano 10,000 ya in Nicaragua) will show local evidence. In more than two hundred years, no one has found the Flood's smoking gun.