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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br /> <br /> <br />Chapter 4: Hazard Identification and Risk Assessment 179 <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, and VEI 2.225F <br />225 <br />Table 4-130. Volcanic Explosivity Index <br />Volcanic Explosivity Index Erupted Tephra Volume <br />(km3) | 1 km3 = 0.24 miles3 Examples <br />Non Explosive 0 0 N/A <br />Small 1 0.0001 Mount St. Helens (October 1, 2004) <br />Moderate 2 0.001 Mount St. Helens (December 7, 1989) <br />3 0.01 Mount St. Helens (June 12, 1980) <br />Large 4 0.1 Merapi, Indonesia (2010) <br />Very Large <br />5 1 Mount St. Helens (May 18, 1980) <br />6 10 Pinatubo (1991) <br />Krakatau (1883) <br />7 100 <br />Tambora (1815) <br />Mazama (7,700 years ago) <br />Long Valley Caldera, CA (760,000 years <br />ago) <br />8 1,000 Yellowstone Caldera (600,000 years ago) <br /> <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.226F <br />226 <br /> <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.227F <br />227 <br />Table 4-131. United States Geological Survey Volcano Alert Levels <br />Type Definition <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 /> <br />225 United States Geological Survey. (2016). Glossary – VEI. Retrieved from <br />https://volcanoes.usgs.gov/vsc/glossary/vei.html. <br />226 United States Geological Survey. (n.d.). Volcanic Alert-Levels Characterize Conditions at U.S. Volcanoes. <br />Retrieved from https://www.usgs.gov/programs/VHP/volcanic-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.usgs.gov/fs/2006/3139/fs2006-3139.pdf.