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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br />Figure 4-22. Volcanoes Within 100 Miles of Kittitas Gounty <br />4.6.8,3. Hazard ExtenUlntensity <br />Volcanic eruptions can range from emissions of gases to quiet eruptions of lava flows that can be safely <br />observed to powerful eruptions that can blow apart mountains and devastate many square miles. For <br />example, the explosive disintegration of Mount St. Helens' north flank in 1980 vividly demonstrated the <br />power of Cascade volcanoes. However, the 1980 eruption of Mount St. Helens, which covered over <br />22,000 square miles with ash is considered a relatively small volcanic eruption. Larger eruptions, such <br />as the 1883 eruption of Krakatoa in the south Pacific, produced enough ash to slightly lower the <br />temperature of the entire earth for several years..22a <br />USGS utilizes the Volcanic Explosivity lndex (VEl), outlined in Table 4-130, as a numeric scale that <br />measures the relative explosivity of historic eruptions. The explosivity value is determined by the volume <br />of products, eruption cloud height, and qualitative observations (by using terms like gentle to mega- <br />colossal). The VEI is open-ended with the largest volcanic eruptions in history (i.e., supereruptions) given <br />a magnitude of eight (8), and a value of zero (0) for non-explosive eruptions. The scale is logarithmic, <br />22a Washington State Department of Natural Resources. (n.d.). Volcanoes and Lahars. Retrieved from <br />lce eolo <br />-* <br />tilh, <br />. -f-+-. <br />.eiirr"d: <br />'1 c9[ <br />.l <br />'r5E <br />) <br />'€39 <br />./ ,?ai, <br />. .t t Ii.ze, \ <br />Knms <br />.,5q&' -. <br />I <br />i18t <br />4], -'\q) <br />I <br />'6' <br />I -. -3edP- <br />:141; <br />l.i <br />_ tia. <br />'$q1 i <br />0 Sou16: <br />Esrl <br />unknown Cindercone LoEl Road <br />Shield .i Composite Minor Roed <br />Fissure .l Caldera Other Road <br />--- <br />River Ramp <br />: LimitedAcc6s ---- Fetry <br />** Highway Pedesilrian WaY <br />l\4sjor Road l'//, '2 Municipatlies <br />I I lsL* <br />,'ipa' <br />Kitlitas <br />tlzl <br />County <br />{00within 9Smil <br />NOAA <br />NOAA <br />-r24: <br />,cri <br />Chapter 4. Hazard ldentification and Risk Assessment <br />ic-hazards/volca <br />178