what is a mineral? what is a rock? - inside minesinside.mines.edu/~cshorey/newfiles/lecture...

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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)