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ESCI 111 Exam 1
Terms in this set (19)
what is magma? what is in magma?
magma is completely or partly molten rock, which, when cooled, solidifies into igneous rocks.
three components of magma: melt (liquid), crystals of silicate minerals (solid), and volatiles (gaseous)
what is lava?
molten rock that reaches Earth's surface
what are igneous rocks? how do they form? what do they form from?
cooled, solidified magma composed mainly of silicate minerals; parent material for igneous rocks is formed by partial melting of solid rock that occurs at various levels within Earth's crust and upper mantle to depths of about 250 kilometers
what are the two types of magma? how are they different? where are we most likely to find them?
basalt: flowing and volcanic field
andesite: flowing and moderately explosive; stratovolcano
rhyolite: very explosive; caldera
what are intrusive and extrusive rocks? what are their important characteristics? how does the location of formation affect the texture of the rock?
intrusive: aka plutonic rocks; form when magma crystallizes at depth; observes at Earth's surface in locations where uplifting and erosion have stripped away the overlying rocks; occur in the White Mountains, New Hampshire; Stone Mountain, Georgia; Mount Rushmore in the Black Hills of South Dakota; and Yosemite National Park, California
extrusive: aka volcanic rocks; form when molten rock solidifies at the surface; when lava solidifies of when erupted volcanic debris fall to Earth's surface; abundant in western portions of the Americas, where they make up the volcanic peaks of the Cascade Range and the Andes Mountains; also many oceanic islands, including the Hawaiian chain and Alaska's Aleutian Islands
what are the six textures of igneous rocks? be able to briefly explain each texture and what it tells us about the rock
Aphanitic; fine-grained; small crystals; light, intermediate, or dark in color
Phaneritic: coarse-grained; can distinguish the individual minerals without a microscope
Porphyritic: large crystals embedded in a matrix of smaller crystals
Vesicular: nearly spherical voids are left by gas bubbles;
Pyroclastic: fragmental; formed from the consolidation of individual rock fragments ejected during explosive volcanic eruptions; particles may be very fine ash, molten blobs, or large angular blocks torn from the walls of a vent during eruption
Pegmatitic: coarse-grained; crystals larger than one centimeter in diameter; most occur as small masses or thin veins within or around the margins of large intrusive igneous bodies
what are plutons? how and where do they form?
the structures that result from the emplacement of magma into preexisting rocks formed below Earth's surface
what are sills, laccoliths, and dikes?
sills: horizontal, concordant bodies that form when magma exploits weaknesses between sedimentary beds or other rock structures
laccoliths: igneous intrusions that can lift the sedimentary strata they penetrate, so as to arch the beds above while leaving those below relatively flat
dikes: discordant bodies that form when magma is forcibly injected into fractures and cut across bedding surfaces and other structures in the host rock
what are batholiths? how do they form? where can we find them in the US?
batholiths: the largest intrusive igneous plutons; occur as mammoth linear structures several hundred kilometers long and up to 100 kilometers wide; can find them in Sierra Nevada, California: Coast Mountains of western Canada into southern Alaska, Peru; produced by hundreds of discrete injections of magma that form smaller plutons that intimately crowd against or penetrate one another
what factors affect the viscosity of magmas?
primarily temperature and silica content; the more silica, the greater viscosity (flows slower)
why do some volcanoes erupt violently while others erupt non-violently?
effusive: pressurized gases expand (non-violent)
explosive: gases remain dissolved until pressure drops; bubbles begin to form and increase in side; fracturing occurs when the expanding magma exceeds the strength of the overlying rock (violent)
name and briefly describe the materials extruded during an eruption. (lava, gases, and pyroclastic materials)
lava: more than 90% of lava flows are estimated to be mafic (basaltic) in composition
Gases: volatiles; remain in molten rock because of confining pressure; when pressure is reduced, the gases begin to escape
Pyroclastic materials: pulverized rock and fragments of lava and glass; aka tephra; range in size from dust and sand sized particles to pieces that weight several tons
contrast a shield volcano and a stratovolcano (composite volcano). explain how they are different. give an example of each.
shield volcano: produced by the accumulation of fluid basaltic lavas and exhibits the shape of a broad, slightly domed structure that resembles a warrior's shield; ex// Mauna Loa
stratovolcano (composite volcano): most picturesque yet potentially dangerous; most are located in a relatively narrow zone that rims the Pacific Ocean; ex// Ring of Fire
what are cinder cones? how do they form?
cinder cones (scoria cones): built from ejected basaltic lava fragments that begin to harden in flight, producing the vesicular rock scoria
what are some of the main hazards from volcanoes?
pyroclastic flows: consisting of hot gases infused with incandescent ash and larger lava fragments; tsunamis, vocanic ash and aviation, respiratory health, and weather and climate
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