Chapter 18E.60
VOLCANIC HAZARD AREAS

Sections:

18E.60.010    Purpose.

18E.60.020    Volcanic Hazard Areas.

18E.60.030    Volcanic Hazard Area Review Procedures.

18E.60.040    Volcanic Hazard Area Standards.

18E.60.010 Purpose.

At over 14,411 feet high, Mount Rainier dominates the skyline of the southern Puget Sound region. This glacier-clad potentially active volcano is capable of spewing ash from pyroclastic eruptions, and generating large volumes of lahars and floods which have, in the recent geologic past, inundated various watersheds and reached the shores of Puget Sound significantly altering pre-flood conditions. The purpose of this Chapter is to promote the public health, safety, and general welfare of the citizens of Pierce County by providing standards that minimize the loss of life that may occur as a result of volcanic events emanating from Mount Rainier. (Ord. 2004-57s § 2 (part), 2004)

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.

(Ord. 2004-57s § 2 (part), 2004)

18E.60.030 Volcanic Hazard Area Review Procedures.

A.    The Pierce County Critical Areas Atlas-Volcanic Hazard Area Map provides an indication of where volcanic hazard areas are located within the County.

B.    The Department will complete a review of the Volcanic Hazard Area maps for any development proposal to determine whether the proposed project area for a regulated activity falls within a volcanic hazard area.

C.    When the Department's maps or sources indicate that the proposed project area for a regulated activity is located within a volcanic hazard area, the Department shall apply the standards for regulated activities in volcanic hazard areas, as set forth in PCC 18E.60.040.

D.    Title and land division notification shall be required, as set forth in PCC 18E.10.080 C.

(Ord. 2004-57s § 2 (part), 2004)

18E.60.040 Volcanic Hazard Area Standards.

The following standards apply within the Inundation Zones for Case I, II, and III Lahars and within the Pyroclastic Flow Hazard Zone (refer to Table 18E.60.040):

A.    Bonus densities, as set forth in Chapter 18A.35 PCC, Development Regulations – Zoning, shall be prohibited.

B.    All essential facilities and hazardous facilities, as defined in Chapter 18.25 PCC, shall be prohibited, except sewer collection facilities and any other utilities that are located underground or not likely to cause harm to people or the environment if inundated by a lahar.

C.    Special occupancy structures, as defined in Chapter 18.25 PCC, are subject to the following:

1.    Travel Time Zone A. Special occupancy structures located within the Travel Time Zone A area shall be limited to a maximum 100 person occupancy.

2.    Travel Time Zone B. Special occupancy structures located within the Travel Time Zone B area shall be limited to a maximum 500 person occupancy.

3.    Travel Time Zone C. Special occupancy structures located within the Travel Time Zone C area shall be limited to a maximum 1,000 person occupancy.

4.    Travel Time Zone D. Special occupancy structures located within the Travel Time Zone D area shall be limited to a maximum 5,000 person occupancy.

D.    Covered assemblies, as defined in Chapter 18.25 PCC, are subject to the following:

1.    Travel Time Zone A. Covered assemblies located within Travel Time Zone A area and which are located within the Case II lahar inundation zone shall be limited to 100 person occupancy and covered assemblies located within Travel Time Zone A which are outside the Case II lahar inundation zone, but within the Case I lahar inundation zone shall be limited to a maximum 400 person occupancy.

2.    Travel Time Zone B. Covered assemblies located within Travel Time Zone B area and which are located within the Case II lahar inundation zone shall be limited to 500 person occupancy and covered assemblies located within Travel Time Zone B which are outside the Case II lahar inundation zone, but within the Case I lahar inundation zone shall be limited to a maximum 700 person occupancy.

3.    Travel Time Zone C. Covered assemblies located within Travel Time Zone C area shall be limited to a maximum 1,000 person occupancy.

4.    Travel Time Zone D. Covered assemblies located within Travel Time Zone D area shall be limited to a maximum 5,000 person occupancy.

Table 18E.60.040 Volcanic Hazard Area Standards

Facility/ Occupancy List

Case I Lahar Inundation Zone

Case II Lahar Inundation Zone

Case III Lahar Inundation Zone

Pyroclastic Flow Hazard Zone

Bonus Densities (1)

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Essential Facilities (2)

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Hazardous Facilities (3)

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Special Occupancies (4)

In Travel Time Zone A – Limited to 100 person occupant load.

In Travel Time Zone B – Limited to 500 person occupant load.

In Travel Time Zone C – Limited to 1,000 person occupant load.

In Travel Time Zone D – Limited to 5,000 person occupant load.

In Travel Time Zone A – Limited to 100 person occupant load.

In Travel Time Zone B – Limited to 500 person occupant load.

In Travel Time Zone C – Limited to 1,000 person occupant load.

In Travel Time Zone D – Limited to 5,000 person occupant load.

Not Allowed

Not Allowed

Covered Assemblies (5)

In Travel Time Zone A – Limited to 400 person occupant load.

In Travel Time Zone B – Limited to 700 person occupant load.

In Travel Time Zone C – Limited to 1,000 person occupant load.

In Travel Time Zone D – Limited to 5,000 person occupant load.

In Travel Time Zone A – Limited to 100 person occupant load.(6)

In Travel Time Zone B – Limited to 500 person occupant load.

In Travel Time Zone C – Limited to 1,000 person occupant load.

In Travel Time Zone D – Limited to 5,000 person occupant load.

Not Allowed

Not Allowed

Other Occupancies

No Limitation

No Limitation

No Limitation

No Limitation

(1)    Bonus Density as set forth in Chapter 18A.35 PCC, Development Regulations – Zoning.

(2)    Essential Facility as defined in PCC 18.25.030.

(3)    Hazardous Facility as defined in PCC 18.25.030.

(4)    Special Occupancy structures as defined in PCC 18.25.030.

(5)    Covered Assemblies as defined in PCC 18.25.030.

(6)    Occupancy may be increased pursuant to the requirements of PCC 18E.60.050.

(Ord. 2004-57s § 2 (part), 2004)

18E.60.050 Increased Occupancy for Covered Assembly

The occupancy limits for covered assembly structures within the Case II Lahar Inundation Zone, Travel Time Zone A, may be increased by the Director to a maximum of 400 persons when the following criteria have been met:

A.    The applicant has demonstrated through submittal of a travel time analysis the amount of time that is anticipated for a lahar to reach the proposed project and evacuation route.

B.    The applicant has demonstrated through submittal of a volcanic hazard emergency evacuation plan that:

1.    The proposed project is located directly adjacent to a safety zone (area completely located outside the limits of a Case I lahar) that is within walking distance in an amount of time less than the anticipated time that it takes a lahar to reach a given point (refer to PCC 18E.60.020 C.). (Note: The time that it takes a lahar to reach a given point is calculated from either the source of the event to the given point, or from the source of the lahar warning signal to the given point, i.e., only the Puyallup and Carbon River drainages at this time have the Acoustic Flow Monitoring System. Other drainages, such as the Nisqually and White Rivers, have no warning systems. Persons in those areas would be reliant on other emergency notification systems, such as the National Weather Radio. At this time, no other warning system is planned for the Nisqually or White River drainages.) The time of walking distance shall be calculated based upon the amount of time necessary for physically or mentally challenged individuals to get from the proposed project to the safety zone.

2.    The estimated travel time analysis for the lahar to reach the evacuation route is less than the estimated travel time for physically or mentally challenged individuals to have cleared the evacuation route and reached the safety zone.

3.    The evacuation route must be at a slope and surface to be considered handicapped accessible (e.g., slopes may not exceed 1' in 12' rise and surface must be an all weather, hard material) as determined by the County Building Official.

4.    The evacuation route has been determined not to contain any other potential natural hazards, such as landslide or flood hazards, to cause a blockage or destruction of the evacuation route during an event (i.e., seismic event triggers a landslide that results in the evacuation route becoming impassible).

5.    The evacuation route is not located adjacent to any highways or arterial road networks that may cause a life safety threat to evacuating pedestrians.

6.    The safety zone is an area with adequate ingress/egress (i.e., a direct exit once individuals reach this location).

(Ord. 2004-57s § 2 (part), 2004)