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lesson 6: Igneous Rocks and Volcanism

Terms in this set (45)

lava
magma flowing out of the earth's surface
the slower a rock cools....
the bigger the crystals
intrusive igneous rock
rock that has forced its way into surrounding rock.
cool slowly in earth's interior allowing large coarse crystals to form
porphyry
igneous rock that has a mixed texture in which large crystals "float" in a predominately fine grained matrix
extrusive igneous rocks
formed when lava or other material erupts from volcanoes, rapid cooling at earth's surface produces the fine grained texture or glassy appearance of this rock
-aka volcanic rocks
pyroclasts
-form in violent eruptions
-form when fragments of lava are thrown high in the air
-range from volcanic ash to hugh bounders
felsic rock
poor in iron and mg and rich in minerals high in silicon
-ex: quartz feldspar
-light in color
-granite : intrusive
-rhyolite : extrusive
mafic rock
-largely pyroxene and olivine
-rich in mg and fe
-dark colors
- intrusive: gabro
-extrusive: basalt
ultramafic
-composed mostly of mafic minerals
-peridotite
-rarely found as extrusives because they form at such high temperatures
viscosity
measure of a liquid's resistance to flow
decompression melting
as the material rises and the pressure decreases below a critical point, solid rock melts spontaneously without the introduction of any additional heat
magma chamber
magma filled cavaties in the lithosphere that form as rising pools of melted rock push aside surrounding solid rock
mantle plumes
-sites of decompression that form within lithospheric plates rather than along the margins of plates
-may produce a trail of volcanos
-produced where basaltic magmas form
mantle plumes that reach earth's surface and form hot spots are responsible for the outpours of...
basalt
volcanism
the natural process that gives rise to volcanoes and volcanic rock
volcano consists of
1. magma chamber - magma is transported from deep within earth
2. plumbing system: transports the magma to earth's surface
3. vents: at earths surface
4. hill or mountain: constructed from accumilation of lava
what is the shape of a volcano determined by?
composition of magma
basalt magmas form what type of volcano?
broad, gently sloping forms
andesite and thyolote magmas form what type of volcano?
narrow, conial forms, more likely to explode
Basalt Lava
-extrusive mafic
- lowest silica content
-most common
- produced on mid ocean ridges and hot spots
-fluid
pillow lavas
basaltic magma that cools underwater
pahoehoe
basaltic lave that forms when a highly fluid lava speads om sheets and a thin rope
andesitic lava
-extrusive igneous rock
-intermediate Si compsition
-more viscous than basalt
-temps lower than basalt
-come from volcano belts above subduction zones
phreatic explosion-
-the most destructive eruptions come from this
-steam explosions which occur when hot gas charged magma encounters ground water or sea water generating lots of steam
rhyolite lava
-extrusive igneous rock
-felsic
-large Si content
-produced in zones where heat from mantle has melted the continental crust
-viscous
vesicles
gas cavities or holes in rocks formed from water vapor and gas escaping from lava as it erupts
pyroclastic deposits
include fragments thrown from volcanoes during explosive eruptions (pyrclasts) and flows of hot gases mixed with dust and ash (pyroclastic flows)
gas rich, viscous rhyolitic and andesitic lavas are likely to produce explosive or non explosive eruptions?
EXPLOSIVE
volcanic ash
finest pyroclasts less than 2 mm in diameter
volcanic bombs
pyroclasts as large as houses
lithified
as pyroclasts fall to the earth and cool they become welded together to
tuffs
rocks created from smaller fragments of pyroclasts
breccias
rocks created from larger fragments of pyroclasts
pyroclastic flows
occur when hot ash dust and gases are ejected in a glowing cloud that rolls downhill at high speeds
What does the shape of a volcano depend on?
the composition, amount, the type of material erupted, and where it erupts
central eruptions
discharge lava or pyroclasts from a central vent
create a cone shape
shield volcano
a broad shaped volcano built by successive flows of basaltic lava from a central vent
volcanic dome
rounded, steep sided mass of rock produced by andesitic and rhyolitic lavas - viscous
cinder cones
formed from volcanoes discharging pyroclats building up
-steep slopes
stratovolcano
A concave shaped volcano formed from alternating layers of lava flows and beds of pyroclasts
crater
bowl shaped pit found at the summit of most volcanoes centered on the vent
caldera
large, steep walled, basin shaped depression formed by a violent volcanic eruption in which large volumes of magma are discharged rapidly from a large magma chamber, causing the overlying volcanic structure to collapse catastrophically through the roof of the emptied chamber
fissure eruptions
produce the largest kind of eruptions through large vertical cracks in earth's surface
-happen along mid atlantic ridges
flood basalts
-highly fluid basaltic lavas erupting from fissures on continental plates can spread out in thin sheets over flat terrain, which pile up into immense basaltic lava plateus called flood basalts
ash flow deposits
eruptions of pyroclasts on continents have produced extensive sheets of hard volcanic tuffs called ash flow deposits
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