What are Volcanic Hazards?

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Volcanologists monitoring Mt. St. Helens

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In this video we will describe the most common types of volcanic hazards associated with a volcanic eruption. We begin by considering the threat of an eruption from a Cascade Range volcano for citizens of Portland and Seattle. These are examples of composite volcanoes. Eruptions of these types of volcanoes produce tephra, lahars, pyroclastic flows and lava. Tephra represents the debris blasted into the air and can range in size from tiny glass shards to large blocks blasted out of the volcanic cone. When tephra combines with water it forms lahars that can transport all sizes of debris. Fast moving, toxic pyroclastic flows are among the most dangerous volcanic hazards. Lava plays a relatively modest role in eruptions of composite volcanoes but is a common product of shield volcanoes such as those in Hawaii.

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