What is a mineral? What is a rock? • Naturally occurring • Any solid mass of mineral •Inorganic or mineral-like matter that • Solid occurs naturally. • Orderly internal structure • Coal and obsidian are accepted, but (crystalline) concrete or asphalt are not. • Chemical composition and physical • All rocks started by crystallizing out of properties that are fixed or vary liquid hot rock that is undergoing within a defined range cooling. WE = weathering & erosion HP = heat & pressure HM = heat to melting Igneous W E H M H P W E HP Sedimentary Metamorphic H P WE VOLCANOES – HAZARDS AND PREDICTION 1 Case Study 1 Mammoth Lakes California Map of Mammoth Lakes Area Tuya development 2 Case Study 2 Mt Pinatubo Philippines 3 Case Study 3 Lake Nyos Cameroon 4 Case Study 4 Hawaii Case Study 5 Mt Paracutin Mexico 5 Case Study 6 Mt. Pelee Martinique 6 Case Study 7 Tambora Indonesia Case Study 8 Yellowstone Wyoming 7 Track of N. America over Yellowstone Hot Spot The red symbols mark volcanic centres that erupted after the caldera-forming event 640 kyr ago.The areas of known past or present thermal activity are Case Study 9 coloured yellow. The ring-fracture zone of the caldera is shown green, and the slumped zone between the ring-fracture zone and the best estimate of the caldera rim is shown salmon. The park boundary is the dashed black line. Faults active in the Quaternary are marked with Toba Lake black lines. The labelled features are Norris Geyser basin (NGB), Mammoth Hot Springs (M), Sour Creek dome (SC), Mallard Lake dome (ML), Hebgen Lake (HL) and Yellowstone Lake (YL). The Sumatra white arrows show interpreted magma migration paths. The red square in the inset map (bottom right) shows the location of the study area. 8 Case Study 10 Mt Vesuvius Italy 9 10 11 Modern View from the summit of Vesuvius 12 Magma types, characteristics & Styles of Volcanic Eruptions volcanoes produced • The main factor controlling the style of an Least Shield eruption is the viscosity of the lava, which Mafic Least Least Least Volcanoes, (basaltic) Silica Viscous Gas Pyroclasts basalt is influenced by temperature, chemistry, plateaus, (~50%) (1-2%) and cinder and dissolved gasses cones Inter- Mid Composite Mid Mid Some cones • Higher temperature, more basaltic mediate Viscous Pyroclasts (andesitic) Silica Gas chemistry, or more dissolved gasses all (~60%) (3-4%) Most Volcanic make the lava less viscous (more runny) Felsic Most Most Most domes, (rhyolitic) Silica Viscous Gas Pyroclasts Composite • Less viscous lava is less explosive upon cones, (~70%) (4-6%) Pyroclastic flows eruption VOLCANIC LANDFORMS • Shield Volcanoes – are formed by basaltic lava – have gentle slopes, 50 -100 – e.g., Mauna Kea volcano in Hawaii • Tephra (Cinder) Cones – Are formed by andesitic to basaltic lava – Smallest volcanoes with slopes 250 – 350 • Stratovolcanoes – also called composite volcanoes – emit both tephra and viscous lava – have steep slopes, 100 -300 – major continental volcanoes are this type – e.g., Mt. Fuji, Mt. Rainier, and Mt. Baker Tension Mount Fuji, Japan, a snow-clad giant towering over the surrounding countryside, displays the classic profile of a stratovolcano 13 Tephra Cone in Arizona Tension Mauna kea, a 4200-m-high shield volcano in Hawaii, as seen from Mauna Loa. Note the gentle slopes formed by highly fluid basaltic lava. Satellite View of Hawaii Figure 5.9B Olympus Mons on Mars 5-9 Source: Photograph courtesy of USGS Photo Library, Denver, CO. 14 Parasitic Cinder Cones on a Shield Volcano - Hawaii Parasitic Cinder Cones on a Shield Volcano - Hawaii Non-Explosive Eruptions • Low viscosity basaltic lava tends to erupt at a higher temperature and with less dissolved gas. • Tends to produce lava flows at the surface. • Lava Flows –Pahoehoe = smooth and ropy –Aa = sharp and blocky Lava fountaining Pahoehoe 15 Aa Skylight to Lava tube 16 Fissure Eruption 17 Explosive eruptions • Andesitic and Rhyolitic magma is more viscous and has a higher gas content. • Bubbles can come out of solution so rapidly that the magma gets “shattered” into fragments: • Pyroclastics –ash, lapilli & bombs 18 Ash cloud Pyroclastic flow - nuee ardente Bomb Other hazards with volcanoes • Earthquakes (and landslides) • Poisonous or suffocating gas • Acid lakes • Lahars (hot mud flows) • Caldera collapses • Snakes? • Lateral blasts 19 Nevado del Ruiz 20 Debris Flow 21 Mt. St. Helens Dome Thermal Activity at Yellowstone Volcanic Activity • Molten rock close to earth surface –Geysers and Hot springs –Travertine terraces –Fumaroles/Gases 22 Fumaroles Predicting Volcanic Eruptions • Increased seismic activity • Increased gas output • Ground swelling • Increased temperature • Strange animal behavior (less reliable) 23.