Volcanoes and Earthquakes
Volcanoes and Earthquakes GPH 111 Volcanoes and Earthquakes Game Plan: Types of eruptions and the importance of viscosity Rock class and landform type Dangers associated with volcanic eruptions How earthquakes work Earthquake danger Volcanoes Stem from the release of magma on to earth’s surface At least 1,500 active volcanoes on the planet (1 eruption in recorded history) 50 volcanic eruptions every year Mt. Pinatubo, 1990 Types of Rock Erupted (igneous extrusive) Basalt - silica content between 48% and 55% Andesite - silica content between 55% and 60% Dacite - silica content between 60% and 70% Rhyolite - silica content between 70% and 77% Increase in silica content, increase in viscosity. Activity Time Rock Types Generate Viscous to Non-viscous flows of lava Basalt - low silica, low viscosity (like……), trapped gasses released easily Andesite - medium silica, higher viscosity (like……), trapped gasses release much less easily Dacite and Rhyolite - high silica, high viscosity (like…….), trapped gasses have a hard time escaping, but if they do… Rock class determines landform type and eruption style: Cinder Cones - (basalt) mildly explosive Shield Volcanoes - (basalt) mildly explosive Composite Volcanoes - (andesite to dacite) mild to highly explosive Lava Domes - (dacite to ryholite) nonexplosive Calderas - (andesite to ryholite) extremely violent and explosive Cinder Cones - Constructed from fountains of lava that rain around the vent. SP Crater, N. AZ They can also issue low volatile flows, quietly oozing from the vent. Hawaii - Cinder Cone in Action “Basalt Landform” Shield Volcanoes - Mauna Loa Basically really big, long duration cinder cones Olympus Mons “Basalt Landform” Composite Volcanoes Build up over time with alternating ash fallouts and lava flows, tendency to generate extremely violent events mixed with more moderate events. Mt. Fuji - classic composite cone “Andesite - Dacite Landform” Composite Volcanoes - Mt. Saint Helens “Andesite - Dacite Landform” Composite Volcanoes - Mt. Saint Helens “Andesite - Dacite Landform” Composite Volcanoes - Mt. Pinatubo “Andesite - Dacite Landform” Composite Volcanoes - Marianas Trench “Andesite - Dacite Landform” Lava Domes - Highly viscous eruptions that build internally and externally Lava Dome developing in Mount St. Helens Mt. Elden, N. AZ “Dacite - Rhyolite Landform” Calderas - Highly explosive eruptions that lead to structural collapse from an emptied magma chamber Long Valley Caldera, 15 miles wide, rhyolitic, 760,000 years old released 160 cubic miles of material Show Movie - Crater Lake, 6 miles wide, 7,700 years ago andesitic “Andesite to Rhyolite Landform” Dangers associated with eruptions: Lahars a hot or cold mixture of water and rock fragments flowing (70 mph) down the slopes of a volcano and into river valleys Mt. St. Helens, 1980 Pyroclastic flows fluidized masses of rock fragments and gases that move rapidly in response to gravity (can travel over 400 miles per hour, and reach temperatures approaching 2,000° F) Mt. St. Helens, 1980 Mt. Pelée, 1902 Dangers associated with eruptions: CO2 Emissions - Release of CO2 from buried magma into the atmosphere through faults, fissures, and lakes. Mammoth, CA – 1,300 tons of sulphur dioxide released every day. “What might some positives be?” Positives associated with Volcanism: Fertile Soils Enriched soils from mineral rich volcanic ashfalls Geothermal Energy Magma in the earth heats groundwater and the steam is used to power generators New Land Lava flows from continents into oceans can generate new land for development If you knew this would happen…. What would you do… How sure do you need to be? Earthquakes Detected with Seismographs (movie) Rated based on the Richter Scale Elastic Rebound theory (Demonstration) Evidence and Damage from an Earthquake 3.0 on the Richter Scale represents 31.5 times more energy than a 2.0, and 992 times more than a 1.0 Elastic-Rebound Theory How do earthquakes work? 1989 Loma Prieta Earthquake Epicenter - location at the surface Focus - actual location of maximum movement Field Evidence of an Earthquake… Fault Scarps – Steplike linear landform coincident with a fault trace and caused by geologically recent slip on the fault Fissures – Cracks or ruptures on earth’s surface from earthquakes, but without offset Earthquake Damage “Earthquakes don’t kill people, buildings do.” Japanese saying Things to Know: Basic volcanic rock breakdown based on silica and their viscosity Basics associated with volcanic forms linked to the different rock types - Cinder cones, Shields, Composite Cones, Lava Domes, Calderas That low viscosity eruptions tend to be much less violent than high viscosity eruptions and why Dangers associated with volcanism Positives associated with volcanism Problems with volcanic or earthquake prediction How Earthquakes are generated with regard to the Elastic-Rebound Theory Field evidence associated with earthquakes Help: Chapter TL
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