ch. 6 science
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- What is the opening of Earth's crust where magma and volcanic gases reach the surface?
- volcano
- What is molten rock underground that feeds a volcano?
- magma chamber
- What is a crack which magma may rise?
- vent
- 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?
- viscosity
- 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
-underwater
-hardens into rounded lumps - How does pyroclastic material form?
- lava blasts into air
- Name the different types of pyroclastic material.
-
-volcanic bombs
-volcanic blocks
-ash
-lapilli - 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?
- crater
- 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?
-
-sheild
-cinder cone
-composite - 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
-darkness
-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?
- subduction
- 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?
- tiltmeter
- What theory helps explain the causes of both earthquakes and volcanoes?
- theory of plate tectonics