Volcano and Earthquake Hazards in the Crater Lake Region, Oregon
Hazards of Lahars (Volcanic Debris Flows) and Their Runout Flows
Definition of Lahars Hazard Zone
The boundaries of the Lahar Hazard Zone (LA on plate 1) were determined as in flood-hazard mapping in arid and semi-arid regions. The Lahar Hazard Zone includes any area potentially inundated by flows of the magnitudes estimated below. A lahar generated on the upper slope of Mount Mazama would be expected to quickly bulk to a debris flow but would attenuate continuously with decreasing slope as flow is lost through deposition of sediment and is not replaced by tributary inflows. Meteorologic flood hazards would surpass those of lahars from Mount Mazama at low elevations where flow spreads on broad alluvial reaches of low and decreasing slope and tributary inflow adds to the flow wave. Thus, areas farther from Crater Lake, where exceptional meteorologic floods will be a more significant hazard than floods and lahars related to volcanic activity, are excluded from the Lahar Hazard Zone.