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2025 Hazard Mitigation Plan <br />Kittitas County, Washington ffii#l <br />with each interval on the scale representing a tenfold increase in observed ejecta criteria, with the <br />exception of between VEI 0, VEI 1, andVEl2.-225 <br />Table 4-130. Volcanic Explosivity lndex <br />USGS employs a nationwide volcano alert level system for characterizing conditions (i.e., quiet, unrest, <br />eruption) at volcanoes throughout the United States. The USGS volcano alert level system has two (2) <br />parts - ranked terms to inform people on the ground about a volcano's status and ranked colors to inform <br />the aviation sector about airborne ash hazards (i.e., Aviation Color Code). Volcano activity notifications <br />for Kittitas County are issued through the USGS Cascades Volcano Observatory.-226 <br />Volcano Alert Levels are intended to inform people on the ground about a volcano's status and are issued <br />in conjunction with the Aviation Color Code. Notifications are issued for both increasing and decreasing <br />volcanic activity and are accompanied by text with details (as known) about the nature of the unrest or <br />eruption and about potential or current hazards and likely outcomes. Table 4-131 outlines the USGS <br />Volcano Alert Levels. 227 <br />Table 4-131. United States Geological Survey Volcano Alert Levels <br />225 United States Geological Survey. (2016). Glossary - VEl. Retrieved from <br />https://volcanoes. usqs.sov/vsc/g lossarv/vei. htm l. <br />226 United States Geological Survey. (n.d.). Volcanic Alert-Levels Characterize Conditions at U.S. Volcanoes. <br />Retrieved from https://www.usgs.qov/proqrams/VHPivolcanic-alert-levels-characterize-conditions-us-volcanoes. <br />227 United States Geological Survey. (2014). U.S. Geological Survey's Alert-Notification System for Volcanic <br />Activity. Retrieved from https://pubs.usss.qovifs/2006/31 39/fs2006-3139.pdf. <br />0 0 N/ANon Explosive <br />Mount St. Helens (October 1,2004)Small 1 0.0001 <br />2 0.001 Mount St. Helens (December 7, 1989) <br />Moderate <br />3 0.01 Mount St. Helens (June 12, 1980) <br />0.1 Merapi, lndonesia (201 0)Large 4 <br />Mount St. Helens (May 18, 1980)5 1 <br />6 10 Pinatubo (1991) <br />Krakatau (1883) <br />100 <br />Tambora (1815) <br />Mazama (7,700 years ago) <br />Long Valley Caldera, CA (760,000 years <br />aqo) <br />7 <br />Yellowstone Caldera (600,000 years ago) <br />Very Large <br />8 1,000 <br />Volcanic Explosivity Index Erupte d Tephra Volume <br />1 km3 = 0.24 miless Examples <br />Normal <br />Volcano is in a 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 />DefinitionType <br />Chapter 4: Hazard ldentification and Risk Assessment 179