Resolution_2025 Kittitas County Hazard Mitigation Plan

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2025 Hazard Mitigation Plan Kittitas County, Washington Chapter 4: Hazard Identification and Risk Assessment 174 4.6.8. Volcanic Activity 4.6.8.1. Description Volcanoes are openings, or vents where lava, tephra (small rocks), and steam erupt onto the Earth’s surface. The vent of a volcano can be visible as a small bowl shaped depression at the summit of a cone or shield-shaped mountain. Magma, molten rock beneath the surface of the Earth, is stored within and beneath the volcano. The volcano’s vent is connected to one (1) or more of the magma storage areas which allows the volcano to erupt over and over again in the same location. Continuous eruptions create a slow accumulation of the erupted lava (i.e., magma that has been erupted onto the Earth’s surface) which makes the volcano grow.216F 216 Over 80% of the Earth’s surface above sea level is of volcanic origin.217F 217 All volcanoes have their own unique characteristics, but most volcanoes are classified as one (1) of the three (3) classic types listed on Table 4-126.218F 218 The physical characteristics of a volcano are determined by the magma’s chemistry which controls eruption dynamics and how easily lava can flow. Additionally, the volcano’s explosivity is impacted by gas content and the rate of eruption.219F 219 Table 4-126. Volcano Types Type Definition Cinder Cone Considered the simplest type of volcano is made of small pieces of solid lava, called cinder, which erupt from a vent. As the magma rises from within the Earth, the ground shakes before a powerful blast throws molten rocks, ash, and gas into the air. The rocks cool quickly in the air and fall to the Earth and break into small pieces of bubbly cinder that pile up around the vent. They accumulate as a small cinder cone that can be as high as 1,000 feet above the surrounding ground. Eruptions that form cinder cones also feed lava flows that spread outward from the eruptive vent. When climbing a cinder cone one can usually find the bowl-shaped crater marking the location of the vent. If eruptions of cinder and lava flows happen repeatedly from the same vent, the overlapping layers can form a composite volcano (stratovolcano). Composite Volcano (Stratovolcano) Some of the Earth's grandest mountains are composite volcanoes, sometimes called stratovolcanoes. They are usually tall with steep even sides and are made out of repeating layers of lava flows, volcanic ash, cinders, blocks, and volcanic bombs. Some composite volcanoes rise over 8,000 feet above their surroundings, but they reach much higher elevations when compared to sea level. Shield Volcano Are built almost entirely of fluid lava flows and some of the most massive volcanoes are shield volcanoes. Lava pours out of vents in all directions, either from the summit (top) or along two (2) to three (3) rift zones (fractures) that radiate out from the summit like spokes on a bicycle wheel. As lava flows overlap one another, they construct a broad, gently sloping dome shape that from a distance appears similar to a warrior's shield. Shield volcanoes build up slowly by the growth of thousands of lava flows that spread widely over great distances, and then cool as thin sheets. 216 United States Geological Survey. (n.d.). About Volcanoes. Retrieved from https://www.usgs.gov/programs/VHP/about-volcanoes. 217 United States Geological Survey. (n.d.). How Much of the Earth is Volcanic? Retrieved from https://www.usgs.gov/faqs/how-much-earth-volcanic. 218 United States Geological Survey. (n.d.). About Volcanoes. Retrieved from https://www.usgs.gov/programs/VHP/about-volcanoes. 219 National Park Service. (2022). Volcanoes, Craters, & Lava Flows: Type of Volcanoes. Retrieved from https://www.nps.gov/subjects/volcanoes/types-of-volcanoes.htm.