Chapter 14.70
VOLCANIC HAZARD AREAS

Sections:

14.70.010    Purpose.

14.70.020    Volcanic hazard areas.

14.70.030    Volcanic hazard area review procedures.

14.70.040    Volcanic hazard area standards.

14.70.010 Purpose.

At over 14,411 feet high, Mount Rainier dominates the skyline of the southern Puget Sound region. This glacier-clad mountain is a dormant volcano capable of generating large floods and lahars which have historically reached the floors of the lowlands south of the city of Seattle and out to Commencement Bay in the Port of Tacoma, spewing ash from pyroclastic eruptions. The purpose of this chapter is to promote the public health, safety, and general welfare of the citizens of Edgewood by providing standards that minimize the loss of life that may occur as a result of volcanic events emanating from Mount Rainier. (Ord. 17-513 § 3 (Exh. A)).

14.70.020 Volcanic hazard areas.

A. General. Volcanic hazard areas are areas subject to pyroclastic flows, lava flows, and inundation by debris flows, mudflows, or related flooding resulting from geologic and volcanic events on Mount Rainier.

B. Volcanic Hazard Area Categories. Volcanic hazard areas are areas that have been historically inundated by Case I, Case II, or Case III lahars or other types of debris flow; affected by pyroclastic flows, pyroclastic surges, lava flows, or ballistic projectiles in future eruptions; or are located in other drainages expected to be inundated by a future Case I, Case II, or Case III debris flow. 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 noncohesive 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 noneruptive 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 socalled “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 noncohesive lahars, glacial outburst floods, or other types of debris flow, all of noneruptive origin. The average time interval between Case III lahars at Mount Rainier is about one 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. The amount of time that is anticipated for a debris flow, lahar, flood, or avalanche to travel geographically has been classified into the following travel time zones:

1. Time Zone A. Time Zone A is an estimated one-hour travel distance from the source of the event.

2. Time Zone B. Time Zone B is an estimated one-and-one-half-hour travel distance from the source of the event.

3. Time Zone C. Time Zone C is an estimated two-hour travel distance from the source of the event.

4. Time Zone D. Time Zone D is an estimated two-hour or greater travel distance from the source of the event. (Ord. 17-513 § 3 (Exh. A)).

14.70.030 Volcanic hazard area review procedures.

A. The city’s Critical Areas Atlas – Volcanic Hazard Area Map provides an indication of where volcanic hazard areas are located within the city.

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 EMC 14.70.040. (Ord. 17-513 § 3 (Exh. A)).

14.70.040 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 14.70.040):

A. Bonus densities, as set forth in EMC 18.90.080, Housing incentives program, shall be prohibited.

B. All critical facilities 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 14.20 EMC, 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.

Table 14.70.040

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

Critical Facilities(2)

Not Allowed

Not Allowed

Not Allowed

Not Allowed

Special Occupancies(3)

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

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

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

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

Other Occupancies

No Limitation

No Limitation

No Limitation

No Limitation

(1) Bonus density as set forth in EMC 18.90.080, Housing incentives program.

(2) Critical facility as defined in Chapter 14.20 EMC.

(3) Special occupancy structures as defined in Chapter 14.20 EMC.

(Ord. 17-513 § 3 (Exh. A)).