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