Larger ash, like sand, falls back to the ground and can do great damage. A layer of ash a few inches thick is so heavy it can crush the roof of an average home. The terms ash, lapilli, and bomb refer to the sizes of volcanic material ejected. The consistency of this material is described by additional terms such as pumice which is a frothy material which contains so much trapped gas that it floats, scoria which is heavier than water, and spatter which refers to material which is still soft when it hits the ground. This suspension behaves like a liquid.
Pyroclastic flows are one of the most dangerous and destructive products of a volcano.
Lahars Lahars are another destructive effect of a volcano. A lahar consists of volcanic particles mixed with water - a type of mudflow in other words. Lahars can form in several ways and may not be associated with an eruption. The mudflow from Volcan de Agua which destroyed the capitol of Guatemala in 1541 was a lahar. At that time, the crater of the volcano was a small lake.