Post on 19-Mar-2020
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What is a mineral?• Naturally occurring• Inorganic• Solid• Orderly internal structure
(crystalline)• Chemical composition and physical
properties that are fixed or vary within a defined range
What is a rock?• Any solid mass of mineral or mineral-like matter that occurs naturally.
• Coal and obsidian are accepted, but concrete or asphalt are not.
• All rocks started by crystallizing out of liquid hot rock that is undergoing cooling.
Igneous
Sedimentary Metamorphic
W E
WE = weathering & erosion
HP
HP = heat & pressure
H M
HM = heat to melting
W E
WEH P
H P
VOLCANOES – HAZARDS AND PREDICTION
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Case Study 1
Mammoth LakesCalifornia
Map of Mammoth Lakes Area
Tuya development
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Case Study 2
Mt PinatuboPhilippines
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Case Study 3
Lake NyosCameroon
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Case Study 4
Hawaii
Case Study 5
Mt ParacutinMexico
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Case Study 6
Mt. PeleeMartinique
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Case Study 7
TamboraIndonesia
Case Study 8
YellowstoneWyoming
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Track of N. America over Yellowstone Hot Spot
The red symbols mark volcanic centres that erupted after the caldera-forming event 640 kyrago.The areas of known past or present thermal activity are 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 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 white arrows show interpreted magma migration paths. The red square in the inset map (bottom right) shows the location of the study area.
Case Study 9
Toba LakeSumatra
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Case Study 10
Mt VesuviusItaly
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Modern View from the summit of Vesuvius
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Styles of Volcanic Eruptions• The main factor controlling the style of an
eruption is the viscosity of the lava, which is influenced by temperature, chemistry, and dissolved gasses
• Higher temperature, more basaltic chemistry, or more dissolved gasses all make the lava less viscous (more runny)
• Less viscous lava is less explosive upon eruption
Magma types, characteristics & volcanoes produced
Mafic (basaltic)
Least Silica (~50%)
Least Viscous
Least Gas (1-2%)
Least Pyroclasts
Shield Volcanoes, basalt plateaus, and cinder cones
Inter-mediate (andesitic)
Mid Silica (~60%)
Mid Viscous
Mid Gas (3-4%)
Some Pyroclasts
Composite cones
Felsic (rhyolitic)
Most Silica (~70%)
Most Viscous
Most Gas (4-6%)
Most Pyroclasts
Volcanic domes, Composite cones, Pyroclastic flows
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
Mount Fuji, Japan, a snow-clad giant towering over the surrounding
countryside, displays the classic profile of a stratovolcano
Tension
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Tephra Cone in Arizona
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.
Tension
Satellite View of HawaiiFigure 5.9B
5-9 Source: Photograph courtesy of USGS Photo Library, Denver, CO.
Olympus Mons on Mars
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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
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Aa
Skylight toLava tube
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Fissure Eruption
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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
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Ash cloudPyroclastic 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
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Nevado del Ruiz
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Debris Flow
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Mt. St. Helens Dome
Volcanic Activity
• Molten rock close to earth surface–Geysers and Hot springs–Travertine terraces–Fumaroles/Gases
Thermal Activity at Yellowstone
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Fumaroles
Predicting Volcanic Eruptions
• Increased seismic activity• Increased gas output• Ground swelling• Increased temperature• Strange animal behavior
(less reliable)