Cascade Volcanoes There are 13 potentially active volcanoes in the Cascade Range of the northwest-ern United States

Mt. St. Helens – prior to the 1980 eruption

Mt. St. Helens after the 1980 eruption

Precursory stages of the Mt St Helens eruption

A seismically-induced landslide reduced lateral and vertical confinement, triggering the May 18, 1980 eruption of Mt. St Helens

Cross sections thru Mt St Helens showing deep rotational slide blocks which slid off the peak

Atmospheric impacts of the May 18, 1980 Mt St Helens eruption

The Mt St Helens eruption shot volcanic ash to an altitude of 60,000 feet, into the stratosphere

Relative distribution of blown down trees and lahar debris flows in the Toutle River Valley on the north side of Mt St Helens

The St Helens blast flattened Douglas fir trees over an area of 400 square kilometers

Lahars, debris flows, and debris chocking of rivers caused by the Mt Lahars, debris flows, and debris chocking of rivers caused by the Mt. St. Helens eruption

Profiles of volcanic landforms

Volcanoes Nuée ardente – A deadly pyroclastic flow Fiery pyroclastic flow made of hot gases infused with ash and other debris Also known as glowing avalanches Move down the slopes of a volcano at speeds up to 200 km per hour Lahar – volcanic mudflow Mixture of volcanic debris and water Move down stream valleys and volcanic slopes, often with destructive results

A nueé ardente on Mt. St. Helens after the May 1980 eruption

Viscous lava flow passing through the village of Goma in the Congo during the eruption of Mt. Nyiragongo in January 2002

Other volcanic landforms Fissure eruptions and lava plateaus Fluid basaltic lava extruded from crustal fractures called fissures Example = Columbia River Plateau Lava domes Bulbous mass of congealed lava Associated with explosive eruptions of gas-rich magma

Columbia River Plateau

Lava dome at Mt. St. Helens

A lava dome