... times and geometric characteristics of its secondary effects. This next information may be unrelated preliminary information, to the specific impact of Mt. St. Helens but it is an absolute necessity that the uneducated individual becomes educated; this is the best defense against an eruption. Pyroclastic density currents (PDC) can be created in seconds, with an unpredictable path of destruction and can propagate at speeds of 100 - 300 meters a second. Lahars are much the same, there creation is unpredictable as well as there geometric path and are commonly compared to "quickly moving rivers of cement". The dangers secondary effects pose to a location can be as great the initial blast or eruption. Pyroclastic currents and lahars are not the only secondary effects that cause problems, actually there are so many that it would take much to long to explain them all. So we will limit this subject to ones ...

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