Answer:
Lahars
can be of any size. They may be as small as several centimeters
wide and deep, flowing less than one meter per second. Steep,
unvegetated slopes during a heavy rain are often good sites to
observe such small flows. At the other extreme, they can be a
few hundred meters wide, tens of meters deep, flow at several
tens of meters per second, and travel over 100 kilometers from a
volcano. Such catastrophic lahars are triggered by volcanic
eruptions or by massive landslides such as the one that occurred
on May 18, 1980, at Mount St. Helens volcano.
