Glossary of ch. 6 science

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What is the opening of Earth's crust where magma and volcanic gases reach the surface?
What is molten rock underground that feeds a volcano?
magma chamber
What is a crack which magma may rise?
How does the size of a vent affect the type of eruption?
if vent is narrow and long, the eruption may be more explosive
What 3 factors cause magma to erupt more explosively?
-high water content
-more silica
-longer, narrower vent
What is the thickness of lava calles?
What's true of the viscosity the higher it is?
the thicker it is
What is Pahoehoe lava?
-high viscosity
-flow like melted wax
-hardens into wrinkled surface
What is Block lava?
-high viscosity
-flows slowly; does not travel far
-cools in big chunks
What is Aa lava?
-lower viscosity
-flows faster
-becomes brittle and jagged on surface
What is Pillow lava?
-lower viscosity
-hardens into rounded lumps
How does pyroclastic material form?
lava blasts into air
Name the different types of pyroclastic material.
-volcanic bombs
-volcanic blocks
What are volcanic bombs?
large blobs of magma that hardens in the air
What are volcanic blocks?
solid rock that is blasted from volcano
What is ash?
tiny slivers of hardened magma
What is lapilli?
small pebbles of magma that harden in the air
What are enormous amounts of gas, dust, and ash that are ejected and speed downhill?
pyroclastic flow
What are nonexplosive volcanic eruptions?
-more common
-lava flows from this
What are explosive eruptions?
-rarer and more destructive
-debris, ash, and gas shoot our
What is a funnel-shaped pit near the top of the central vent of a volcano?
What are 2 reasons that a caldera may be formed?
-magma chamber partially empties and chamber's roof collapses
-volcano top blown off
How are calderas and craters different from eachother?
caldera larger and is a huge depression in the earth
What are the 3 types of volcanic cones?
-cinder cone
What is a sheild volcano?
-gently sloping sides
-nonexplosive eruptions
-mainly lava flow
What is a cinder cone volcano?
-explosive eruptions
-steep slopes
-pyroclastic eruptions
What is a composite volcano?
-most common
-explosive and nonexplosive eruption
-broad base
-steeper slopes
What is a wide, flat landform that results from repeated nonexplosive eruptions of lava that spread over a large area?
lava plateau
Why does a volcanoes crater tend to get larger over time?
-next eruption may blast away hardened lava
-after eruption the lava in a vent may sink causing the vent to collapse and form a larger crater
What are columns of rising magma?
mantle plumes
describe the difference among an extict, dormant, and active volcano.
extict-hasn't erupted and never will
dormant-hasn't erupted for awhile , but probably will
active-is erupting
How might a volcanic eruption affect the climate?
-sun blocked
-temperature change
-acid rain could change land and water
What is an area of deep cracks between tectonic plates?
rift zone
What are volcanoes far from the volcano boundary?
hot spot
What is 1 plate sinks under the other?
What happens if the temp. of rock remains constany but the pressure on the rock decreases?
more rock will melt
Explain how convergent and divergent plate boundaries cause magma formation.
divergent-lava flows out and creates new crust (most underground)
convergent-subduction causes increase in temp. and pressure; rock melts
Why does an oceanic plate tend to subduct when it collides with a continental plate?
oceanic plate is denser and thinner
What causes an increase in the # and intensity of small earthquakes before an eruption?
the movement of magma
Describe 4 methods that scientists use to predict volcanic eruptions?
-measure seismic activity to help track magma motion
-study volume nd composition of volcanic gas
-measure slope cuz ground may swell or bulge
-use sattellites like GPS yo detect changes in slope
What is the instrument that helps scientists detect small changes in the angle of a volcano's slope?
What theory helps explain the causes of both earthquakes and volcanoes?
theory of plate tectonics

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