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VOLCANOES Volcano Basics • Active – a volcano that has erupted recently (geologically speaking) • Dormant – (sleeping) has erupted within the past few thousand years – will likely erupt again • Extinct – hasn’t erupted in 10’s of thousands of years; unlikely to erupt again Mt. Rainier active Mount Baker dormant Shiprock Peak – extinct volcano magma: molten rock inside the Earth lava: magma that has emerged on the Earth’s surface er lava magma What makes a Volcano Violent? viscosity: a fluid’s resistance to flow high viscosity = high resistance to flow (THICK) Low viscosity = low resistance to flow (THIN) Nope…not movin’ • Low viscosity magmas allow gases to escape easily and move easily through cracks. • In higher viscosity lavas, gas pressures build up and erupt explosively. • VIRTUAL LAB!! Viscosity is determined by silica content and temperature. The higher the silica content, the higher the viscosity. The hotter the magma, the less viscous it is. TYPES OF VOLCANOES 1. Shield 2. Composite 3. Cinder cones Shield Volcanoes - largest volcanoes (tallest when measured from the ocean floor) - shaped like a gentle arch or shield -basaltic lavas (low silica content) - usually non-explosive eruptions - results in lava flows - found in Hawaii (Mt. Kilauea) and Iceland lava tubes: caves left behind after lava flows • Composite Volcanoes - coned shaped; sometimes called stratovolcanoes - lava contains mostly andesite or rhyolite (higher silica content) - more viscous Combination of explosive activity (pyroclastic) and lava flows Responsible for most deaths of any type of volcano ex. Mount Saint Helens Mt. Pinatubo Mt. Fuji Mt. Vesuvius Mount Saint Helens, Washington State Mt. Saint Helens, after eruption Mount Pinatubo, 1994 Mount Fuji, Japan Mount Vesuvius / Ruins of Pompei Cinder Cones - smaller volcanoes - form quickly -are active for a few years and then usually go dormant Wizard Island ex. Paracutin, Mexico - 1943, hole in ground 2 weeks prior, small tremors 1st day grew 10 m By 5th day it was 100 m tall After 2 yrs, it was 400 m tall went quiet after 9 years WHERE ARE VOLCANOES? Ring of Fire • Area of the world where volcanoes are common • Outlines the Pacific Ocean hot spot: area of volcanic activity independent of lithospheric plates ex. Hawaii Features of Volcanoes crater - depression found at the top of a volcano; formed by the explosion of the upper portion of the cone hot springs: water is heated by the hot rock and reaches Earth’s surface geyser: heating and circulation of water forms a pattern (RARE!) ex. Old Faithful Half of the 1,000 geysers in the world are in Yellowstone National Park, WY (United States) caldera: a giant crater that can be more than 12.5 miles in diameter -formed by rare, very violent eruptions -none have occurred in recorded history (they are 1000 times more violent than Mt. St. Helens!) - Yellowstone caldera was formed 600,000 years ago! Crater Lake, OR Long Valley, CA Aniakchak, AK Volcanic Hazards I. Primary Effects II. Secondary Effects Lava flows: eruption of magma at Earth’s surface Lava flows vary based on the composition of the magma. Pyroclastic Activity: explosive volcanism where tephra is physically blown into the atmosphere tephra: any material that is blown out of a volcano (mostly ash) ash fall: huge quantities of rock, glass and gas are blown high into the air - kills vegetation contaminate water structural damage jet engine “flame out” respiratory irritation lateral blast: explosions of gas and ash from the side of the volcano; destroys part of the mountain ex. Mt. St. Helens Poisonous Gases - CO2, carbon monoxide, sulfur dioxide, and hydrogen sulfide - can cause acid rain; contaminates water supply and vegetation Secondary Effects lahar: debris flows and mudflows -volcanic debris becomes saturated with water -ex. Mt. Pinatubo, Philippines Buildings buried after lahars at Pinatubo Aerial View, Pinatubo Aftermath Predicting Volcanoes 1. Monitoring of Seismic Activity- often the earliest sign 2. Thermal monitoring measuring ground temperatures 3. Topographic Monitoring mountain may tilt and swell before an eruption 4. Volcanic Gas Emissions changes in composition of gases may indicates rising of magma 5. Geologic History geologists map and date rocks around the area