18E.60.020 Volcanic Hazard Areas.
A. General. Volcanic hazard areas are areas subject to pyroclastic flows, lava flows, and inundation by lahars, debris flows, or related flooding resulting from geologic and volcanic events on Mount Rainier.
B. Volcanic Hazard Area Categories. Volcanic hazard areas are those areas that, in the recent geologic past, have been inundated by a Case I, Case II, or Case III lahars or other types of debris flow, or have been affected by pyroclastic flows, pyroclastic surges, lava flows, or ballistic projectiles. Volcanic hazard areas also include areas that have not been affected recently, but could be affected by future such events. Volcanic hazard areas are classified into the following categories:
1. Inundation Zone for Case I Lahars. Areas that could be affected by cohesive lahars that originate as enormous avalanches of weak chemically altered rock from the volcano. Case I lahars can occur with or without eruptive activity. The average reoccurrence rate for Case I lahars on Mount Rainier is about 500 to 1,000 years.
2. Inundation Zone for Case II Lahars. Areas that could be affected by relatively large non-cohesive lahars, which most commonly are caused by the melting of snow and glacier ice by hot rock fragments during an eruption, but which can also have a non-eruptive origin. The average time interval between Case II lahars from Mount Rainier is near the lower end of the 100 to 500 year range, making these flows analogous to the so-called "100-year flood" commonly considered in engineering practice.
3. Inundation Zone for Case III Lahars. Areas that could be affected by moderately large debris avalanches or small non-cohesive lahars, glacial outburst floods, or other types of debris flow, all of non-eruptive origin. The average time interval between Case III lahars at Mount Rainier is about 1 to 100 years.
4. Pyroclastic-Flow Hazard Zone. Areas that could be affected by pyroclastic flows, pyroclastic surges, lava flows, and ballistic projectiles in future eruptions. During any single eruption, some drainages may be unaffected by any of these phenomena, while other drainages are affected by some or all phenomena. The average time interval between eruptions of Mount Rainier is about 100 to 1,000 years.
C. Travel Time Zones. The ability to evacuate people from within a volcanic hazard area correlates to the distance from the source of an event (i.e., those areas closest to the event will have less time to evacuate than those areas farther away from the source of an event) and the amount of time for evacuation from the public notification (via a warning alarm system) that a lahar event has occurred. The amount of time that is anticipated for a debris flow, lahar, flood, or avalanche (estimated at 100,000,000 cubic feet of volume) to travel from either the source of the event or the point where the AFM alarm is sounded is classified into the following travel time zones:
1. Travel Time Zone A.
a. Travel Time Zone A on the Nisqually and White River systems is that area within an estimated one-hour travel distance from the source of the event.
b. Travel Time Zone A on the Puyallup and Carbon River systems is that area within an estimated one-half hour travel distance from the point where the AFM alarm is sounded.
2. Travel Time Zone B.
a. Travel Time Zone B on the Nisqually and White River systems is that area greater than an estimated one-hour travel distance and less than or equal to an estimated 1-1/2 hour travel distance from the source of the event.
b. Travel Time Zone B on the Puyallup and Carbon River systems is that area greater than an estimated one-half hour travel distance and less than or equal to an estimated one-hour travel distance from the point where the AFM alarm is sounded.
3. Travel Time Zone C.
a. Travel Time Zone C on the Nisqually and White River systems is that area greater than an estimated 1-1/2 hour travel distance and less than or equal to an estimated two-hour travel distance from the source of the event.
b. Travel Time Zone C on the Puyallup and Carbon River systems is that area greater than an estimated one-hour travel distance and less than or equal to a 1-1/2 hour travel distance from the point where the AFM alarm is sounded.
4. Travel Time Zone D.
a. Travel Time Zone D on the Nisqually and White River systems is that area greater than an estimated two-hour travel distance from the source of the event.
b. Travel Time Zone D on the Puyallup and Carbon River systems is that area greater than an estimated 1-1/2 hour travel distance from the point where the AFM alarm is sounded.