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2025 Hazard Mitigation Plan Kittitas County, Washington Volcano is exhibiting signs of elevated unrest above known background level. OR After a change from a higher level, volcanic activity has decreased significantly but continues to be closelv monitored for oossible renewed increase. Advisory Watch Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain. OR Eruption is undenvay but poses limited hazards. Warning Hazardous eruption is imminent, underway, or suspected DefinitionType Color codes, which are in accordance with recommended lnternational Civil Aviation Organization (ICAO) procedures, are intended to inform the aviation sector about a volcano's status and are issued in conjunction with a Volcano Alert Level (Table 4-131). Notifications are issued for both increasing and decreasing volcanic activity and are accompanied by text with details (as known) about the nature of the unrest or eruption, especially in regard to ash-plume information and likely outcomes. Table 4-132 outlines Volcano USGS Aviation Color Code..228 Table 4-132. United States Geological Survey Aviation Color Code 4.6.8.4. Prohabilityand Frequency The probability of occurrence for volcano activity occurring in Kittitas County is low because a significant occurrence of this hazard is likely to occur within 100 years. Many Cascade volcanoes have erupted in the recent past and are expected to remain active in the foreseeable future. Given an average frequency of one (1) or two (2) eruptions per century during the past 12,000 years, these disasters are not part of the planning area's everyday experience. However, in the past 100 years, Lassen Peak in California and Mount St. Helens in Washington have erupted causing significant damage. USGS classifies a volcano active when it has erupted within the Holocene (The youngest geologic time period, considered to include the past approximately 12,000 years. lt is almost equivalent to postglacial 228 lbid Volcano is in typical background, noneruptive state. OR After a change from a higher level, volcanic activity has ceased, and volcano has returned to noneruptive backqround state. Yellow Volcano is exhibiting signs of elevated unrest above known background level. OR After a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase. Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain. OR Eruption is underway with no or minor volcanic ash emissions (ash-plume height specified, if possible). Eruption is imminent with significant emission of volcanic ash into the atmosphere likely. OR Eruption is underuvay or suspected with significant emission of volcanic ash into the atmosphere (ash-plume heiqht specified, if possible). ,.lii:Iitltr.i: Color Definition ,irii.t,.)i: Chapter 4: Hazard ldentification and Risk Assessment 180