Lava flow Lahar Volcanic Hazards Ash fall Pyroclastic

Lava flow Lahar Volcanic Hazards Ash fall Pyroclastic flow Landslides

Volcanic Hazards

Mt. St. Helens: before the 1980 eruption Bulge: plug that is pushed out by magma within the conduit.

Pyroclastic eruption • Mt. St. Helens • Landslide • Release of pressure • Lateral blast • Pyroclastic flowdown with the pull of gravity • Ash cloud-vertical • Ash fall

Landslide • Gravitational force “pulls” unstable material down slope • Fills canyons and valleys with debris

Landslide, Mt. Shasta • 300, 000 years ago • 20 times more material than the Mt. St. Helens landslide

Lateral Blast: extreme pyroclastic flow • In the case of Mt. St. Helens, the landslide “uncorked” the vent. • Gas and debris were released under tremendous force • Burns and destroys anything in its path

Lateral Blast • Large area completely devastated (23 X 19 miles) • Trees knocked down • Vegetation burned off

Mt. Unzen, Japan Geologists examined volcanoes all around the world. Mt. Unzen, Japan and Mt. Hood, Washington have the potential for lateral eruptions.

Pyroclastic flow: hot gas propels pyroclastic debris Montserrat, 1997 Gravitational force pulls hot gas and pyroclastic debris down slope from the initial vertical eruption.

Pyroclastic Flow • Mt. Pinatubo, Philippines • 1991 • May reach 100 miles per hour • Burns or suffocates anything in its path

Vertical Eruptions: Plinian • If the initial eruption is vertical the force sends debris into the stratosphere

Global cooling: debris blocks sunlight

Mt. Pinatubo Major eruptions blocking Sun’s radiation Cooled global temperatures by. 5 -. 6 degrees Centigrade

Volcanism • 1815 - Large eruption in the tropics; once thought to be Tambora in Indonesia – Global temperatures fell – Crops failed throughout Europe and famine spread – Mary Shelly told her house guests the story of Frankenstein and his creator died in the arctic because they were unable to go outside during their vacation

Ash fall • Acts as an abrasive • Clogs machinery, covers vegetation, irritates lungs and eyes Photomicrograph of ash from the Mt. Tehama eruption (Lassen Peak) Ash deposited associated with the eruption of the Long Valley Caldera

Iceland • Located on the North Atlantic midoceanic ridge • Hot spot • What type of lava? • Viscosity? • Eruptive style?

Iceland's Eyjafjallajokull volcano • Volcanic eruption under ice produces steam and other gases to propel pyroclastic debris into the atmosphere • European air travel was interrupted for weeks

Mt. Yasur, May 30, 2010 • Some flights rerouted or cancelled in Australia

Volume of Pyroclastic Debris Ash

Lahars • Remobilized ash, rock and debris by water • Water source needed: rain, snow melt

Mt. St. Helens

Mt. Rainier: lahars from the last 5600 years

Lahars: Mt. Pinatubo

Lava Flow • Destroys everything in path • People and animals can usually escape

Iceland: The Eldfell volcano on the island of Heimaey • New land was created during the 1973 eruption.

Jokulhlaup • One third of country is covered by active volcanoes • About 13% covered by glaciers • The lava melts the ice cap • At one point the large volume of water pours rapidly to the adjacent area

Gas Emissions • Sometimes gas release is concentrated and toxic to vegetation and people Horseshoe Lake near Mammoth, California

Carbon dioxide leaked out of Lake Nyos, Africa suffocating 1700 people and all animal life.

Understanding Volcanic Hazards • Past history – How often – Types of hazards – Extent of hazards – Location of past events Ash deposits associated with the eruption of Santorini, Greece