ACTIVE VOLCANOES CONCENTRATED AT PLATE BOUNDARIES St Helens Iceland East African Rift.

ACTIVE VOLCANOES CONCENTRATED AT PLATE BOUNDARIES

St Helens

Iceland

East African Rift

Different types of volcanoes at different tectonic settings

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Japan,Aleutians

East African Rift

St Helens,Andes

IGNEOUS ROCKS

SILICATE MATERIAL (WITH GASSES) MELTS AT DEPTH

MELTED MAGMA LESS DENSE THAN SURROUNDING SOLID SO RISES

INTRUSIVE ROCK: SOLIDIFIES ("CRYSTALLIZES”/"FREEZES") AT DEPTH

EXTRUSIVE ROCK: LAVA ERUPTS AT SURFACE & FORMS.

COOLING LAVA RELEASES GASSES INTO ATMOSPHERE

IGNEOUS ROCKS CLASSIFIED BY THEIR CHEMICAL COMPOSITION (HOW MUCH SiO2 ), MINERALS, AND INTRUSIVE OR EXTRUSIVE

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.“every rock and tree and creature has a life, has a spirit, has a name…”

THREE IMPORTANT PAIRS OF IGNEOUS ROCKS

RHYOLITE / GRANITE (>63% SiO2): MOST OF CONTINENTAL CRUST, DENSITY ABOUT 2.8 g/cm3 , FORMS BY MELTING CONTINENTAL CRUST

ANDESITE */ DIORITE (63-52% SiO2) FROM MELTING OCEANIC CRUST, OFTEN AT SUBDUCTION ZONES

BASALT / GABBRO (<52% SiO2) MOST OF OCEANIC CRUST, DENSITY ABOUT 3.3 g/cm3, FROM MELTING MANTLE, OFTEN AT MIDOCEAN RIDGES

BECAUSE GRANITE IS LESS DENSE THAN BASALT:

CONTINENTS "FLOAT" HIGHER THAN THE OCEAN CRUST SO WE LIVE ABOVE SEA LEVEL

CONTINENTS NEVER SUBDUCT BACK INTO THE MANTLE SO FORMED EARLY IN EARTH HISTORY & ARE OLD (LESS THAN 500 MYR TO 4 BYR), COMPARED TO OCEANIC CRUST THAT SUBDUCTS SO IS YOUNG (0-200 MYR)

*LIKE ANDES

Igneous rock textures formed primarily by cooling rate

LARGE GRAINS SMALL GRAINS LARGE & SMALL GRAINS

MICROSCOPE IMAGE

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AS MAGMA COOLS MINERALS FORMDEPENDING ON TEMPERATURE ("FRACTIONAL CRYSTALIZATION")

REVERSE PROCESS OCCURS DURING MELTING ("PARTIAL MELTING")

PROCESS ILLUSTRATED WITH HALF-FROZEN APPLE JUICE

FRACTIONAL CRYSTALIZATION /PARTIAL MELTINGAS MAGMA COOLS SOLID MINERALS THAT "FREEZE" OUT DIFFER IN COMPOSITION FROM REMAINING LIQUID

CRYSTALLIZATION OF MAGMA AS TEMPERATURE DROPS

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CRYSTALS SINK TO BOTTOM

SiO2-POOR MINERALS FREEZE OUT

MAGMA BECOMES MORE SiO2-RICH

Evanston’s population “ages” over summer break

Higher temperature, lower viscosity (warm syrup flows more easily than cold)

Viscosity increases with increasing silica content due to silica chains

High viscosity lavas flow slowly and typically cover small areas. Low viscosity magmas flow more rapidly and cover thousands of square km.

Low viscosity magmas allow gases to escape easily.

Gas pressures can build up in high viscosity magmas - so violent eruptions (Blowing through a straw, it's easier to get water to bubble than a milk shake)

MAGMA VISCOSITY- VOLCANIC ERUPTION CHARACTERISTICS LARGELY CONTROLLED BY THE VISCOSITY - "GOOEYNESS" (RESISTANCE TO FLOW) - OF THE MAGMA: LOW VISCOSITY FLUIDS FLOW MORE EASILY THAN HIGH VISCOSITY FLUIDS

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High viscosity magma- SiO2 rich

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Low viscosity magma- low SiO2

MAGMA VISCOSITY & VOLCANO TYPE

High viscosity lavas flow slowly & typically cover small areas, forming composite volcanoes (stratovolcanoes) (e.g. Mt. St. Helens) that explode violently due to trapped gas

Low viscosity lavas flow rapidly & form shield volcanoes (e.g. Hawaii) with flows covering thousands of square kilometers

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Mount Saint Helens- stratovolcano (composite volcano) with viscous dacitic (SiO2-rich) magma containing lots of dissolved gas (mostly water vapor), before 1980 explosive eruption, after, & today

BEFORE

AFTER

pyroclastic flows

high-density mixtures of hot, dry rock fragments and hot gases that move away from the vent that erupted them at high speeds. Most pyroclastic flows consist of two parts: a basal flow of coarse fragments that moves along the ground, and a turbulent cloud of ash that rises above the basal flow. Ash may fall from this cloud over a wide area downwind from the pyroclastic flow.

A pyroclastic flow will destroy nearly everything in its path. With rock fragments ranging in size from ash to boulders traveling across the ground at speeds typically greater than 80 km per hour, pyroclastic flows knock down, shatter, bury or carry away nearly all objects and structures in their way. The extreme temperatures of rocks and gas inside pyroclastic flows, generally between 200°C and 700°C, can cause combustible material to burn, especially petroleum products, wood, vegetation, and houses.

www.fs.fed.us/gpnf/volcanocams/msh

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Mount St. Helens as part of the new dome collapses. USDA Forest Service photograph by taken moments after a 3.2 magnitude earthquake triggered the event

on July 18, 2005

Lahar

An Indonesian term that describes a hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys. When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 m in diameter.

Lahars vary in size and speed. Small lahars less than a few meters wide and several centimeters deep may flow a few meters per second. Large lahars hundreds of meters wide and tens of meters deep can flow several tens of meters per second--much too fast for people to outrun.

ICELAND - Part of the Mid-Atlantic Ridge

- Made of Recently Erupted Basalt

- Formed in past 15 million years

Thingvellir

Eurasian plate

North American plate

20 mm/yr

1973 Eruption on the island ofHeimaey, Iceland

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East Africa Rift - New Spreading Center Forms by

Rifting Continental Crust

Africa is splitting up into Nubia (West Africa) and Somalia (East Africa)

2001 Eruption near Goma, Congo

Along the East African Rift

CHAINS OF ISLANDS & SEAMOUNTS

ACTIVE VOLCANISM NOT ASSOCIATED WITH SPREADING RIDGES

WHAT FORMS THESE “HOTSPOTS”?

HOTSPOT / PLUME HYPOTHESISAssume hotspots result from plumes of hot material rising from great depth, perhaps core-mantle boundary

Plumes would be secondary convection mode, ~ 5% of heat transfer

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LINEAR VOLCANIC CHAINS THOUGHT TO BE DUE TO PLATE MOTION

OVER A FIXED OR SLOWLY MOVING

HOTSPOT

ISLANDS GET OLDER ALONG CHAIN

EVENTUALLY SUBSIDE BELOW SEA

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BEND ?BEND ?

HAWAIIAN-EMPEROR BEND - WHAT WE BELIEVED

2002 ERUPTION: BIG ISLAND OF HAWAII

Brian White (CAS 2000)Seth Stein

http://hvo.wr.usgs.gov/cam/index.htm

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YELLOWSTONE- NORTH AMERICAN HOTSPOTACTIVE VOLCANIC, SEISMIC, AND GEOTHERMAL REGION

YELLOWSTONE ERUPTIONS FORM TRACE ACROSS SNAKE RIVER PLAININ EXPECTED PLATE MOTION DIRECTION

YELLOWSTONE-LARGE ERUPTION --->HUGE CALDERA 0.6 MILLION YEARS AGO

EARLIER ERUPTIONS FORM TRACE ACROSS SNAKE RIVER PLAIN

BUT, YELLOWSTONE SEISMIC TOMOGRAPHY PROBLEM

LOW VELOCITY ANOMALY (PRESUMABLY ASSOCIATED WITH HOT UPWELLING)

ONLY IN UPPERMOST MANTLE

MANTLE PLUMES?

NEAT IDEA BUT MANY PROBLEMSUNCLEAR WHETHER HOTSPOTS REFLECT

- HOT PLUMES FROM GREAT DEPTH (CORE-MANTLE BOUNDARY)- LOCALIZED UPPER MANTLE INTRAPLATE VOLCANISM

- OR SOME ARE ONE AND SOME THE OTHER?

The two main ways in which melting occurs in the mantle

MELTING AT LOWER PRESSUREWATER LOWERS MELTING

TEMPERATURE

MIDOCEAN RIDGE SUBDUCTION ZONE

GEOTHERM - TEMPERATURE vs DEPTH

SOLIDUS - MELTING CURVE

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Stands 27 kilometres (88,600 feet) high over its base (about three times the height of Everest above sea level)

Caldera is 85 km (53 miles) long, 60 km (37 miles) wide, and up to 3 km (1.8 miles) deep with six overlapping pit craters.

Outer edge is defined by an escarpment up to 6 km (4 miles) tall unique among the shield volcanoes of Mars.

Olympus Mons is roughly the size of the state of Missouri

MARS: Olympus Mons

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What type of volcano is Mt. Doom (Orodruin) in the “Lord of the Rings”?

3 MAIN ROCK TYPES: IGNEOUS, SEDIMENTARY, &

METAMORPHIC

IGNEOUS- COOLS FROM MOLTEN ROCK

SEDIMENTARY- RECOMBINED FRAGMENTS OF MINERALS, ROCKS, &/OR ORGANIC ORIGIN

METAMORPHIC- PRE-EXISTING ROCKS CHANGED IN COMPOSITION, MINERALOGY, OR TEXTURE FROM HIGH TEMPERATURES, PRESSURES, &/OR FLUIDS

IGNEOUS ROCKS classified by chemical composition & cooling rate

Felsic- more FELdspar and SIlica

Mafic- more Magnesium and iron (Fe) ----------------------Texture reflects cooling:

Extrusive/Fine Grain

Intrusive/Coarse Grain

LESS DENSE MORE DENSE

LESS SiO2

SiO2

(Mg,Fe)2SiO4

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SINGLE CRYSTAL GROWING FOR INTEGRATED CIRCUIT (IC or MICROCHIP) PRODUCTION                            

ICs are built on single-crystal silicon substrates of high purity and perfection. Single-crystal silicon is used instead of polycrystalline silicon since the former does not have defects associated with grain boundaries.

- Silicon inside the chamber is melted (Si melts at 1421 deg C).

-  A slim seed of crystal silicon (5 mm dia. and 100-300 mm long) is introduced into the molten silicon.

-  The seed crystal is withdrawn at a very controlled rate, and grows.

- Wafers are sliced off the crystal  and circuits built on them

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http://science.howstuffworks.com/oil-refining2.htm

Successive stages of development of Crater Lake, Oregon

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