This photo shows how impressive some of the 1982 El Chichon pyroclastic flows were. Here two volcanologists are examining a tree that was surrounded and killed by the pyroclastic flow. After the tree died, bushes started to grow on the new land surface around the old dead trunk. Most recently, erosion of the pyroclastic flows by a river has exposed much of the lower tree trunk again, giving a good indication of the depth of the pyroclastic flows, which was even deeper than shown here since the base of the tree is still buried.
Images of Volcanoes
To VolcanoWorld