How high can explosive eruptions go and how far can the debris and ash be spread?
Well, that depends on how big the eruption is and how big the debris is that you are concerned about. As you might imagine a big eruption will send material farther. Additionally, the big material from any eruption doesn’t get thrown as far as the finer stuff. Volcanologists go out into the field to figure out the distribution of erupted pyroclastic material. They will go to numerous sites around the volcano and measure (in general) 3 things: 1) the total thickness of the pyroclastic deposit at each location; 2) the average size of the 10 largest pumice at each location; and 3) the average of the 10 largest lithic clasts at each location (a lithic is a pre-existing rock that is blown apart in the explosive eruption). They then draw contours around the data that they have collected. In some cases, if the geologists are studying a very old eruption, they may not even know where the vent was. The contours of the thickness and size measurements should close around the vent so that its loca