Geology Cafe

Introduction to Geology

Chapter 5 - Igneous Rocks, Volcanoes and Volcanic Activity

The term "igneous" applies to natural process relating to the formation, movement, and cooling of molten materials—magma (fluid underground) and lava (molten material flowing on the surface). Igneous rocks are classified by their unique properties and characteristics which are related to composition of their host melt and the environmental setting where they form, underground or on the surface. Volcanic activity refers to igneous processes happening on or near the surface. These processes can sometime have catastrophic consequences on populations and property in areas where volcanic activity occurs.

1. Distinguish magma vs. lava, intrusive vs. extrusive, and plutonic vs. volcanic.
2. Explain Bowen's reaction series and magmatic differentiation.
3. Explain how igneous rocks are named, based on composition and texture.
4. Distinguish between granitic, andesitic, and basaltic rocks.
5. List and describe the types of igneous plutons.


Keywords and Essential Concepts

The Earth stores vast quantities of energy in the form of kinetic heat. Portions of the Earth's interior are molten, such as the outer liquid core. However, material in the mantle is thought to be under too much pressure to melt. However, in many places, heat flow near the Earth's surface is high enough and confining pressure is low enough for rocks to melt. This molten material may find zones of weakness, such as along fault zones, to inject, melt, or under great pressure, find means to migrate to the surface. Where it reaches the surface it produces volcanic eruptions and may flow on the surface in the form of lava flows. Some volcanic eruptions can be catastrophic enough to blow volcanic mountains apart and blanket large regions with volcanic ash and cinders, even causing changes to the global climate. Nearly a quarter of world's human population live in regions that could experience moderate to catastrophic effects of volcanic eruptions. Volcanic eruption on Hawaii
Volcano erupting on Hawaii

1. Distinguish magma vs. lava, intrusive vs. extrusive, and plutonic vs. volcanic.



magma—hot, fluid or semi-molten rock material underground (within the earth's crust). Magma that reaches the land's surface is called lava.

lava—molten rock flowing on the land's surface. Underground, molten rock is called magma.

intrusive igneous rocks—intrusive igneous rocks form in naturally insulated settings (rock is a poor conductor of heat) so that minerals crystallize slowly, forming large, visible crystals.


extrusive igneous rocks—rapidly cooling magma (or lava), on or near the surface, crystallizes quickly, preventing visible crystals from forming. Igneous rock that forms from the eruption of molten material at the surface. Extrusive rocks include lava flows and pyroclastic material such as volcanic ash.

plutonic rock
—A rock formed at considerable depth by crystallization of magma and/or by chemical alteration. It is usually medium- to coarse-grained with a granitic (phaneritic) texture. Plutonic rocks form by plutonism—magma moving, cooling, and crystallizing underground.

volcanism—Any of various processes and phenomena associated with the surface discharge of molten rock or hot water and steam, including volcanoes, geysers, and fumaroles. Volcanic rock is any rock formed by volcanism.

intrusive rock texture of granite intrusive vs. extrusive rocks—intrusive igneous rocks form in naturally insulated settings (rock is a poor conductor of heat) so that minerals crystallize slowly, forming large, visible crystals. Rapidly cooling magma, on or near the surface, crystallizes quickly, preventing visible crystals from forming. Both rocks shown here have the same mineral (and chemical) composition, but different texture due to the rate of cooling of the molten material.
extrusive rock texture: rhyolite
intrusive rock texture: granite extrusive rock texture: rhyolite

phaneritic texture—a term usually used to refer to igneous rock grain size and texture. It means that the size of matrix grains in the rock are large enough to be distinguished with the unaided eye as opposed to aphanitic (which is too small to see with the naked eye).

aphanitic texture—dense, homogeneous rock with constituents so fine grained that they cannot be seen by the naked eye.

2. Explain Bowen's reaction series and magmatic differentiation.

Volcanic rocks form as molten material cools into rock. As the molten material cools, chemical compounds in the melt crystallize into minerals at different temperatures, with "high temperature" minerals crystallizing first. These high temperature minerals are denser than the molten material and settle out. As the melt continues to cool, the composition of the melt changes as more crystals form and settle out. Finally the melt completely cools with the composition of the rock enriched in low temperature minerals. This process is called magmatic differentiation.

volcanic rocks magmatic differentiation—processes by which chemically different igneous rocks, such as basalt and granite, can form from the same initial magma. High-temperature minerals can crystallize and settle out, causing the molten material to be concentrated with component that may later form rock enriched in low temperature minerals (such as granite). The last rocks to crystallize in a magmatic intrusion will be enriched in low temperature minerals (quartz, mica, and potassium- and sodium- feldspars).
Magmatic differentiation

high temperature vs. low temperature minerals (rocks)—felsic minerals (and rocks) melt at lower temperatures that mafic minerals (and rocks). This was demonstrated by the work of "19th century petrologist" Norman Bowen, who showed that as a silicate-rich melt cools, minerals that form at higher temperatures will crystallize first. As these minerals crystallize, the chemistry of the remaining melt will change as it cools, allowing different minerals to form as the melt proceeds cooling. High-temperature minerals like olivine and Ca-rich feldspar cool first, minerals like quartz, K-rich feldspar, and biotite crystallize last. Fluids, such as gases and water, are concentrated in the remnants of a melt.

Bowen’s reaction series—observed order of formation of silicate minerals as they form in a cooling melt (magma) resulting in the orderly formation of high temperature to low temperature minerals (rocks)—felsic minerals (and rocks) melt at lower temperatures that mafic minerals (and rocks). This was demonstrated by the work of "19th century petrologist" Norman Bowen, who showed that as a silicate-rich melt cools, minerals that form at higher temperatures will crystallize first. As these minerals crystallize, the chemistry of the remaining melt will change as it cools, allowing different minerals to form as the melt proceeds cooling. High-temperature minerals like olivine and Ca-rich feldspar cool first, minerals like quartz, K-rich feldspar, and biotite crystallize last. Fluids, such as gases and water, are concentrated in the remnants of a melt.

types of igneous rocks Bowens Reaction Series
Classification of
Igneous Rocks
Bowen's Reaction Series

Bowen's Reaction Series Bowen's reaction series volcanic rocks
Igneous rock-forming minerals Igneous rocks Low- and high-temperature minerals

What is the significance of the composition of igneous rocks?

felsic—a term used to describe molten material (magma), minerals, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminum, sodium, and potassium. The term combines part of the words "FELdspar" and "SILica". Most felsic minerals are light in color and have a density less than 3 grams or cubic centimeter (g/cm3)

mafic—an adjective describing a molten material (magma), mineral, or rock which are enriched in magnesium and iron; the term combines part of the words "magnesium" and "ferric" (ferric iron are compounds with the Fe+3 ion). Most mafic minerals are dark in color and the relative density is greater than 3 grams or cubic centimeter (g/cm3). Common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include basalt and gabbro.

mafic rocks vs. felsic rocks
—mafic rocks (rich in iron and magnesium) are denser than felsic rocks (rich in silica and aluminum).

ultramafic—a rock composed chiefly of mafic minerals (rich in iron and magnesium, and less than about 45 percent silica, such minerals as olivine, augite, or hypersthene. Peridotite, pyroxenite and serpentinite are rocks with ultramafic rocks. The mantle is ultramafic in composition and has a density of about 3.5 grams or cubic centimeter (g/cm3).

oceanic crust vs. continental crust—oceanic crust is dominated by mafic and ultramafic intrusive igneous rocks whereas continental rocks are dominated by granitic (felsic) intrusive igneous rocks. The difference in density has an impact on isostacy of crust floating on the semi-fluid upper mantle (asthenosphere), with continental crust (about 2.7g/cm3) rising or floating above oceanic crust (about 3.5 g/cm3).

Isostacy and the density of crustal rocks Refining minerals in the crust
Isostacy and the density of crustal rocks Refining minerals in the crust through volcanism


3. Explain how igneous rocks are named, based on composition and texture.

Igneous rocks are named based on combinations of their composition, crystalline sizes, and textural characteristics.

volcanic rocks
Color of volcanic rocks

4. Distinguish between granitic, andesitic, and basaltic rocks.

Granite Mountains, Mojave National Preserve Granitic Rocks

granite—a common, coarse-grained (crystalline), light-colored, hard plutonic (intrusive igneous) rock consisting chiefly of quartz, orthoclase or microcline (feldspars), and mica.

rhyolite—a pale fine-grained volcanic (extrusive igneous) rock of granitic composition.


Rhyolite exposed in Grand Canyon of the Yellowstone
Granite Mountains, Mojave National Preserve, CA Rhyolite exposed in the Grand Canyon of the Yellowstone, WY

Granodiorite exposed in Yosemite NP Dacitic Rocks

granodiorite
—a coarse-grained (crystalline) plutonic igneous containing quartz and plagioclase, intermediate between granite and diorite in composition.

dacite
—an extrusive igneous (volcanic) rock with an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite.

Chaos Crags, Lassen Volcano
Granodiorite exposed in the Sierra Nevada (Yosemite NP) Chaos Crags on Lassen Volcano consists of dacite

Origin of Diorite Andesitic Rocks

diorite
—a crystalline intrusive igneous rock intermediate in composition between granite and gabbro, consisting essentially of plagioclase and hornblende or other mafic minerals; having a "salt and pepper"-like appearance.

andesite—A fine-grained, brown or grayish volcanic rock that is intermediate in composition between rhyolite and basalt, dominantly composed of plagioclase feldspar.


Eruption of Mount St. Helens, May 18, 1980
Origin of diorite Mount St. Helens has an andesitic composition


Black Canyon of the Gunnison Basaltic Rocks

gabbro
—dark-colored, crystalline intrusive igneous rock composed principally of calcic-plagioclase minerals (labradorite or bytonite) and augite, and with or without olivine and orthopyroxene. It is the approximate intrusive equivalent of basalt.


basalt
— A dark-colored igneous rock, commonly extrusive (from volcanic eruptions) and composed primarily of the minerals of calcic plagioclase and pyroxene, and sometimes olivine. Basalt is the fine-grained equivalent of gabbro.

Basalt lava flows in Hawaii Volcanos National Park
Gabbro cliffs in the Black Canyon of the Gunnison, Colorado Basalt lava flows in Hawaii Volcanoes National Park

peridotite Ultramafic Intrusive Igneous Rocks

peridotite—a dense, coarse-grained plutonic rock containing a large amount of olivine, considered to be the main constituent of the earth's mantle.

pyroxenite—a dark gray or greenish, granular intrusive igneous rock consisting chiefly of pyroxenes and olivine; a dominant rock type found in intrusive igneous rocks associated with oceanic crust.
Pyroxenite from Monterey County, CA
Peridotite from Hawaii Pyroxenite from Arroyo Seco Canyon, Monterey Co., CA

Names for volcanic rocks based on texture

Igneous rocks are classified by composition, color, and crystal grain size (such as andesite, granite, basalt, etc.), but it is also named by appearance or texture characteristics. Examples include:

pumice—volcanic rock with a light, frothy consistency due to the high volume of gas bubbles trapped in the rock as it cools as lava is ejected from a volcano. True pumice will float on water.

scoria—volcanic rock with a light, frothy consistency due to the high volume of gas bubbles trapped in the rock as it cools as lava is ejected from a volcano. True pumice will float on water.

vesicular lava rock
—any igneous rock that has gas bubbles trapped in a fine-grained volcanic rock.

obsidian
—a dark, glasslike volcanic rock formed by the rapid solidification of lava without crystallization (natural glass). Obsidian breaks with a conchoidal fracture like glass.

tuff—a volcanic rock that contains an abundance of visible fragments of volcanic rock that have been crushed or welded together by the heat released during an explosive volcanic eruption.

flow banded lava rock—volcanic rock that has a layered appearance due to flowing or stretching (like taffy candy) that formed as the lava was still flowing as it cooled.

volcanic rocks
Volcanic rock textures


Xenolith in granite xenolith—A rock fragment foreign to the igneous mass in which it occurs. Xenoliths are commonly composed of rock derived from the sides or roof of a magma chamber. The rocks sink into the magma chamber but escape melting as the magma cools to stone.
Dark xenolith in granite
Joshua Tree National Park
phenocryst porphyry—A hard igneous rock containing visible crystals, usually of feldspar, in a fine-grained (microcrystalline), typically dark gray, reddish, or purplish groundmass.

phenocryst—a large or conspicuous crystal in a porphyritic volcanic or igneous rock, distinct from a more fine-grained groundmass (mineral matrix). Phenocrysts (crystals) form in magma at depth before it reaches the surface where the magma (or lava) cools quickly for form the fine-grained
Feldspar phenocrysts in andesite porphyry
Pegmatite pegmatite—a coarsely crystalline granite or other igneous rock with crystals several centimeters in length, and sometimes containing rare minerals rich in rare elements such as uranium, tungsten, beryllium and tantalum. Fluids (water, CO2, etc.) dissolved in the magma in the late stages of cooling allow larger crystals to form in pockets within a larger plutonic body.
Pegmatite vein in granite

5. List and describe the types of igneous plutons.
When molten rock move through the earth, it melts or forces its way through other existing rocks. As the magma cools underground it forms bodies of igneous rocks which are recognizable when exposed by erosion (or mining). This diagram illustrates modern and ancient intrusive and extrusive (volcanic) features. Modern and ancient volcanoes
pluton—a body of intrusive igneous rock (plutonic rock) that crystallized from magma slowly cooling below the surface of the Earth. Types of plutons include batholiths, dikes, sills, laccoliths, stocks, and other igneous bodies.

plutonic rock—A rock formed at considerable depth by crystallization of magma and/or by chemical alteration. It is usually medium- to coarse-grained with a granitic (phaneritic) texture.

Large scale plutonic features: these features are typically extensive, measurable or mapable in the range of tens to hundreds of miles in size.

batholith—a great mass of igneous rock, extending to great depths, formed from extensive magmatic intrusions (plutons) over a long period of time and throughout a region, typically associated with volcanic arcs.


volcanic arc—a generally curved linear belt of volcanoes above a subduction zone, including the volcanic and plutonic rocks formed there.

volcanic field
—an area of the Earth's crust that is prone to localized volcanic activity. They usually contain tens to hundreds of volcanoes, vents and lava flows.

hotspot
—a place in the upper mantle of the Earth at which extremely hot magma from the lower mantle upwells to melt through the crust usually in the interior of a tectonic plate to form a volcanic feature. Examples include the Hawaii or Yellowstone hotspots.

Salinian basement Yosemite plutons Granite Mountains Ryans Peak pluton, Joshua Tree National Park, California
batholith regions in California include the Sierra Nevada, Mojave region, and Peninsular Ranges Sierra Batholith includes granitic rocks exposed in
Yosemite National Park
Batholith rocks exposed in the Granite Mountains
Mojave National Preserve
Granite pluton
Ryans Peak
Joshua Tree National Park

Hawaiian Hotspot Yellowstone_hotspot Columbia River Basalt region California Volcanic Rocks
The Hawaiian Hotspot is a deep-seated igneous plume rising beneath the overriding Pacific Plate. The hotspot has been active of 80 million years. The Yellowstone Hotspot is a deep-seated igneous plume that has migrated beneath the North American Plate as it has moved westward.
Columbia River Basalts California's volcanic areas.

Intermediate- to small-size plutonic features: these are features associated with ancient plutonic activity (and now exposed by erosion of the landscape) stock—a stock is a discordant igneous intrusion having a surface exposure of less than 40 square miles, differing from batholiths only in being smaller. Circular or elliptical stocks may have been vents feeding former volcanoes.

laccolith—a mass of igneous rock, typically lens-shaped, that has been intruded between rock strata causing uplift in the shape of a dome. dike—a vertical or near vertical wall of igneous rock formed where magma squeezed into a fault zone before crystallizing. Dike form in volcanic regions, and often appear as dark castle wall-like features on landscapes where the host rock surrounding the intrusion have eroded away. sill—a tabular, typically more horizontal than vertical, sheet of intrusive igneous rock that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock.

hydrothermal veins
—fractures in rock that have been filled with minerals (commonly quartz and/or calcite) precipitated from groundwater or hot fluids of magmatic origin.

Shiprock, New Mexico Devils Tower, Wyoming dikes and sills Bear Butte, South Dakota
stock with radiating dikes
Google satellite view
Shiprock, New Mexico
stock-core of an ancient volcano exposed as
Devils Tower, Wyoming
dikes (vertical) and sills (horizontal), Black Canyon,
Lake Mead NRA, Arizona
laccolith-a large blister-like intrusion exposed in
Bear Butte, South Dakota
dikes and sills Sill in Grand Canyon Palisades Sill along the Husdson River Hydrothermal veins
dikes (vertical) and sills (horizontal), Black Canyon,
Lake Mead NRA, Arizona
Massive volcanic sill exposed along the Colorado River in the Grand Canyon Palisades Sill crops out across the Hudson River from New York City in New Jersey. hydrothermal veins (dikes)
North Cascades NP, Washington

Volcanism and Volcanoes

volcanism—Any of various processes and phenomena associated with the surface discharge of molten rock or hot water and steam, including volcanoes, geysers, and fumaroles.

volcano—a hill or mountain, typically conical in shape, having a crater or vent through which lava, rock fragments, hot vapor, and gas are or have been erupted from the earth's crust.

Parts of a volcano
Parts of a volcano
Types of volcanoesTypes of volcanoes:

* fissure eruptions (flood basalt)
* shield volcanoes
* cinder cones
* composite cones
* dome volcanoes
* calderas
Map of volcanic rocks
Volcanic provinces of North America: volcanic rocks and volcanic features are found throughout North America.
Mount Shasta
Mount Shasta, located in northern California, is the largest volcano in the Cascade Range
 

Features associated with volcanoes and volcanism

volcanic cone
—a hill or mountain formed by the accumulation of volcanic material around a vent where magma reaches the surface. The size and shape of a volcanic cone depends on the volume of material ejected over time, the composition and temperature of the material (lava, rock and gases) vented from the volcano, and the nature of the eruption (explosive or otherwise).

shield volcano
—broad, domed volcano with gently sloping sides, characteristic of the eruption of fluid, basaltic lava.

cinder cone
—a cone-shaped hill formed around a volcanic vent by fragments of lava (blocks, cinder, ash) blown out during eruptions.

composite cone
—(also called stratovolcano), a typically tall and large, steep volcanic cone built up of many layers of both lava and pyroclastics (tephra, pumice, and volcanic ash), often created by a series of cyclic eruptions in which pyroclastics are created by explosive eruptions until the vent is open, then lava flows occur. Most large continental volcanic cones are this type.

dome volcano
—a volcano composed of lava domes; a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Lava domes can vary from basalt to rhyolite in composition although most preserved domes tend to have high silica content .

lava flows
—a deposit of volcanic rock formed from lava flowing and cooling on the land's surface; also applies to the action of flowing lava on the land's surface.

fissure eruption
—volcanic eruptions along rift fault zones that can flood large area with basalt flows.

flood basalt
—the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Another older name is trap basalt.

crater—a large bowl-shaped vent or collapsed top of a volcano created by explosive eruptions. Also a large bowl-shaped hole created by an meteor or asteroid impact and explosion.

caldera—a large volcanic crater, typically one formed by a major eruption (explosion) or the inward collapse of a volcanic cone following an eruption.

Shield Cone, Halualai Volcano, Hawaii Cinder cone, Mojave National Reserve Mount Shasta Lava Dome, Mt. St. Helens
Shield Cone
Halualai Volcano, Hawaii
Gentle slope formed from hot fluid basaltic lava flows.


Cinder Cone
Mojave National Reserve, CA
Formed from gaseous lava eruptions producing a cone composed of ash and cinders (tephra).
Composite Cone
Mt. Shasta, California
Formed from both lava and tephra eruptions from multiple vents over time, typically andesite in composition
Lava Dome
Mount St. Helens, Oregon
Thick, relatively cool, partially molten lava being pushed up from underneath. Andesitic in composition.

SP Cinder Cone and lava flow Flood basalts, John Day, Oregon San Francisco volcanic field Yellowstone Caldera
SP Cinder Cone and volcanic flow, northern Arizona (NASA satellite view) Flood basalt layers
John Day, Oregon
Formed from hot, fluid basaltic lava spreading over a large area.

San Francisco Volcanic Field covers 1,800 square miles in northern Arizona. Eruptions from about 600 vents (forming volcanoes) occurred in the last 7 million years. Caldera-Map of Yellowstone National Park, Wyoming
Massive eruption of rhyolitic material followed by basalt flows filling in crater.

Mount Rainier, Washington Mount St. Helens, Washington Crater Lake, Oregon Valles Caldera
Google view of Mount Rainier, Washington Google view of Mount St. Helens Google view of Crater Lake,
Oregon
Google view of Valles Caldera, New Mexico

Features formed from flowing lava

a'a—a lava rock with a ropey, frothy surface texture formed as a cooling crust on a fluid lava flow.

pa'hoe'hoe—textural description basaltic lava forming smooth undulating or ropy masses on the surface of a rapidly cooling lava flow.

pillow basalt—a volcanic rock formation consisting of stacked pillow-shaped pods of basaltic lava formed by lava flowing and rapidly cooling on the surface of a subaerial lava flow.

lava tube—a natural tunnel within a solidified lava flow, formerly occupied by flowing molten lava.

Aa lava, Hawaii Pahoehoe lava flowing lava on Hawaii
A'a lava, Hawaii Pa'hoe'hoe lava, Hawaii Flowing lava, Hawaii

Lava tube, El Malpais National Monument, New Mexico Lava tube, Valentine Cave, Lavabeds National Monument, California Pillow basalt, Marin Headlands, California
Lava tube entrance
El Malpais NM, New Mexico
Lava tube
Lavabeds NM, California
Pillow basalts
Marin Headlands, California

Volcanic features associated with explosive volcanic eruptions

tephra—rock fragments and particles ejected by a volcanic eruptions; types include ash, lapili (pea-sized fragments), cinders (pebble-sized), blocks (cobble- to boulder-sized), and bombs (drip-shaped blobs of lava ejected that remain liquid on the inside with an outer crust when they land).

pyroclastic flow
—a dense cloud of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at great speed and with destructive force.

volcanic tuff—a term describing rocks composed of volcanic ejecta, such as broken pieces of volcanic glass, phenocrysts, rock fragments, etc.

lahar
—A landslide or mudflow of volcanic materials on the flanks of a volcano. Also the name of the deposit created by a landslide or mudflow on a volcanic landscape.

Pyroclastic flow tephra fall Cascade eruptions in last 4,000 years Caribbean  volcanic arc
pyroclastic flow
Mayon Volcano, Philippines
major tephra falls map
of the Western United States
Cascades eruptions of the past 4,000 years Volcanic arc in the Caribbean region

What causes to rocks melt?

The heat released by volcanoes and volcanic activity comes from heat convection from the Earth's core and mantle.

geothermal gradient—In most regions, the average temperature increases an average of 20 to 30 degrees C per kilometer with increasing depth in the upper crust. This temperature gradient varies with depth and location, depending on plate-tectonic settings. Regions experiencing plutonism and volcanism are locations where hot material may be located closer to the surface.

melting—rocks will melt (generating magma) if heat flow increases in an area to the point that minerals reach their melting points. Other factors that cause melting include the introduction of volatiles (water and gases) into rocks under pressure, or if there is a decrease in pressure confining hot rocks (such as the release of pressure caused by a great earthquake).

degassing—the process of separation of volatile gases (H2O, CO2, SO2, etc.) and steam from molten material (magma or lava).

Magma of granitic composition can have as much at 5 percent water dissolved in it. The release and expansion of gases is the driving force in volcanic explosions and eruptions.

Where do volcanic gases come from? Some of it is new (such as at divergent zone) and some of it is recycled: Studies of carbon isotopes (C13/C12) show that carbon emitted from Cascades volcanoes has essentially the same isotopic signature as carbon in sediments deposited in the ocean basin trenches offshore of Oregon and Washington.

Convection heat flow in through the mantle Volcanic gases Volcanic gases Volcanic gases
Heat convection through the mantle is the source of heat driving volcanic activity. Why do volcanoes erupt? Gases from volcanic eruptions Volcanic gases from different plate-tectonic settings

How hot is magma/lava?

Lava/Rock composition (place) Geologic setting Temperature (C)
sample (estimate range)
Temperature (F)
sample (estimate range)
Type of volcanic eruption
Basalt
(Kilauea, Hawaii):
hotspot - shield volcano 1170 (1000-1250)
2138 (1832 to 2282) hot, fluid eruptions with extensive lava flows, rare exposive eruptions
Basalt
(Erta Ale, Ethiopia)
divergent zone - rift zone - shield volcano 1130 2066 hot, fluid eruptions with extensive lava flows, rare exposive eruptions
Andesite
(Mount Pelee, Martinique)
convergent zone - arc - composite cone 1075 1967 exposive eruptions andpyroclastic flows
Andesite
(Lascar volcano, Chile)
convergent zone - arc - composite cone 1069 (950-1200) 1956 (1742 to 2192) both exposive eruptions and lava flows
Dacite
(Mototombo, Nicaragua)
convergent zone- arc - composite cone (800 to 1100) (1472 to 2012) both exposive eruptions and lava flows, lava domes, pyroclastic flows
Dacite
(Mount St. Helens, Washington)
convergent zone- arc - composite cone (750 to 850) (1382 to 1562) both exposive eruptions and lava flows, lava domes, pyroclastic flows
Rhyolite (Yellowstone National Park) continental hotspot (700-900) (1292 to 1652) very large, catastrophic explosive eruptions, regional ashfall coverage

How does volcanism affect groundwater?

fumerole
—an opening or vent in or near a volcano, through which hot sulfurous gases, steam, and other gases emerge.

hot spring—a spring that is produced by the emergence of geothermally heated groundwater from the Earth's crust, and usually defined as spring water warmer than the human body.

geyser—a hot spring in which water intermittently boils and erupts, sending a tall column of water and steam into the air.

black smoker—a geothermal vent on the seabed that ejects superheated water containing much suspended matter, typically black sulfide minerals that accumulate around the vent on the seafloor.

Fumerole, Hawaii Hotspring, Yellowstone Geyser, Yellowstone Black smokers on the seafloor
Fumerole with sulfur deposits, Hawaii Boiling hot spring, Yellowstone, Wyoming Grand Geyser
Yellowstone, Wyoming
Examples of black smokers on the seafloor

Volcanism on other planets and moons

Moon Volcano on Venus Olympus Mons on Mars Volcano erupting on Jupiter's moon IO
Dark areas on the moon are great lava-filled basins that formed early in its history. With surface temperatures around 800 degrees, the surface of Venus is a volcanic planet. Olympus Mons on Mars is the largest volcano in the solar system. Jupiter's moon Io is covered with volcanoes, many are currently active.
Volcanic Hazards-Bad days when you might want to say "I hate when that happens"

Volcanic disasters Volcano Hazards Krakatoa eruption Volcanic bad day on Mt. Vesuvius
Worst Volcanic Disasters Volcano hazards Krakatoa Volcano Mt. Vesuvius

Santorini Volcano Thera Volcano tamboraMt. 1902 Erupt of Mt. Peleee
Santorini (Thera) Volcano Santorini (Thera) Volcano Mt. Tambora Volcano Mt. Pelee

Selected Resources:

Volcanoes (Robert Tilling, 1997 U.S. Geological Survey)

Geology of National Parks—selected parks with volcanoes and igneous rocks

Hawaii Volcanoes National Park
Mount St. Helens
Crater Lake National Park
Mount Shasta
Mount Rainier
Yellowstone National Park
Sunset Crater National Monument
Lava Beds National Monument
Capulin Volcano National Monument
El Malpais National Monument
Devils Tower National Monument
Pinnacles National Monument
Big Bend National Park
Columbia River Gorge National Scenic Area
Grand Coulee and the Columbia River Plateau

Early Earth and Plate Tectonics video
Understanding Volcanoes: Plate Tectonics video
Hawaii Volcanoes video
Volcanic Eruptions video
Lahar at Fuego Volcano video
Tacoma Lahar video
Uuzen (1991) pyroclastic flow video
Pyroclastic Flow video
Pyroclastic flows on Mt Merapi Java Indonesia video
Explosive Eruptions at Kilauea Volcano, Hawaii

Quiz questions

http://geologycafe.com/class/chapter5.html
1/12/13