Volcanoes and Other Mountains As a scientifically literate citizen, what 3 questions would you ask about this volcano if you moved to the city in the foreground (Tacoma, Washington)? The Good Earth/Chapter 6: Volcanoes and Other Mountains

The Volcano Commandos 1,500 active volcanoes worldwide a third have records of previous eruptions 2 or 3 eruptions per decade are major disasters 500 million people live near active volcanoes Fewer than 200 volcanoes have instruments to assess potential for eruption The Good Earth/Chapter 6: Volcanoes and Other Mountains

What exactly is a Volcano? Location where molten rock and other mantle materials, are released, to the surface.

Parts of the Volcano Magma: Lava: Molten rock Less dense than crust Crater Magma: Molten rock Less dense than crust Lava: Magma that has reached the surface and erupted out of the volcano Lava Pipes Central vent

Parts of the Volcano Magma Chamber Pipes Vents Crater Underground pools of magma Pipes Pathways for magma Vents Area where magma reaches the surface Crater Depression at the top of a volcanic form after an eruption

2 Types of volcanoes Shield Made from fast flowing basaltic lava (Basaltic: A hard, dense, dark volcanic rock) Large and flat due to movement of the lava

Hawaiian Islands formed this way

http://www.history.com/shows/how-the-earth-was-made/videos/how-was-hawaii-formed - how-was-hawaii-formed

Volcano types 2. Strato-volcanoes majority of the worlds volcanoes are these most explosive and destructive Associated with subduction zones

Where do they occur? All boundaries except transform Famous Volcanoes / areas of volcanoes

The Mount St. Helens Eruption Cascade Mountains – volcanic arc in Pacific Northwest Major cities within 100 km of active volcanoes Mount St. Helens eruption of May 18, 1980 The Good Earth/Chapter 6: Volcanoes and Other Mountains

The Mount St. Helens Eruption Cascade Mountains Volcanoes formed above subduction zone where Juan de Fuca plate slides beneath North America Mount St. Helens is most active volcano in conterminous US The Good Earth/Chapter 6: Volcanoes and Other Mountains

The Mount St. Helens Eruption Prior Activity Early (March) unrest featured Minor eruptions Earthquakes Release of volcanic gases Followed by change in shape of cone (bulge on North flank) Increasing frequency of earthquakes The Good Earth/Chapter 6: Volcanoes and Other Mountains

The Mount St. Helens Eruption May 18 Eruption A moderate earthquake triggered a massive landslide (debris avalanche) on the North side of the volcano Debris clogged streams Pressure released on near-surface magma Lateral blast produces an initial sideways eruption to North Later vertical eruption The Good Earth/Chapter 6: Volcanoes and Other Mountains

Eruption of Mount St. Helens reduced height of volcano by 400 meters Features near volcano were blown over or carried away by products of eruption Geologist David Johnston (right) died at this site (Johnston’s Ridge) located 10 km from the volcano. (this is 6.25 miles or from here to the pro-football hall of fame. The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Major products of volcanic eruptions: Airborne – lateral blast, tephra, volcanic gases Flows on land – lava, pyroclastic flows, lahars The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Airborne Eruption Products Rare lateral blasts can destroy objects up to 12 km away and knock down trees more than 25 km distant Effect of lateral blast only seen on North flank of Mount St. Helens The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Airborne Eruption Products Tephra represents particles blasted into air by eruption Volcanic bombs and ash are found near and far from eruption source, respectively Blobs of magma solidify to form lava bombs Wind can transport fine volcanic ash for hundreds of kilometers downwind The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Airborne Eruption Products Volcanic gases (water vapor, sulfur dioxide, carbon dioxide) may affect climate patterns Sulfur dioxide may block insolation, temporarily (up to 1 year) reducing global temperatures Widespread release of carbon dioxide and higher temperatures due to faster rates of volcanic activity approximately 120-80 million years ago Trees killed by excessive carbon dioxide released by magma under Mammoth Mountain, California. The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Eruption Products on Land Low viscosity lava can flow up to 50 km from its source Lava transported to front of lava flows in long lava tubes Lava flows build up in a series of layers The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Eruption Products on Land Low viscosity lava can flow up to 50 km from its source Lava transported to front of lava flows in long lava tubes Lava flows build up in a series of layers Walter’s Kalapana store, Hawaii, was buried in lava within a few weeks in 1990 The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Eruption Products on Land Higher viscosity lava remains within volcano crater Lava dome formed in crater of Mount St. Helens The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Eruption Products on Land Pyroclastic flow – dense cloud formed from combination of tephra and volcanic gases Fast moving, up to 700 C The Good Earth/Chapter 6: Volcanoes and Other Mountains

Products of Volcanic Eruptions Eruption Products on Land Lahars – mudflows formed when volcanic debris mixes with streams or melting ice Often confined to stream channels Lahar along Muddy River reached depths of 20 meters following Mount St. Helens eruption The Good Earth/Chapter 6: Volcanoes and Other Mountains

Ring of fire area surrounding the pacific plate with VERY high activity of Volcanoes