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6th Grade Science - Volcanoes

Holt Science & Technology - Earth Science, Chapter 9 Study Guide
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volcano
a vent or fissure in the Earth's surface through which magma and gases are expelled
magma
molten rock
lava
magma that flows onto the Earth's surface
what happens during an explosive volcanic eruption
clouds of hot debris, ash and gas rapidly shoot from a volcano - cause molten rock to be blown into tiny particles that harden in the air - can blast millions of tons of lava and rock - can demolish a mountainside in a matter of seconds
what happends during a non-explosive volcanic eruption
produce relatively calm flows of lava - can release hugh amounts lava
magma chamber
a body of molten rock deep underground that feeds a volcano
vents
cracks in the Earths crust which the magma chamber is attached and magma rises
high water conent in lava means
an explosive eruption is likely
silica-rich magma
has a stiff consistency and tends to harden a volcanoes vents
name 4 types of lava
aa, pahoehoe, pillow lava, and blocky lava
viscosity
how lava, or a liquid, flows
how can you predict the silica content based on viscosity
based on its flow - if it flows slower, it has a high silica content
describe four types of pyroclastic flow
volcanic bombs - large blobs of magma that harnden in the air, lapilli - means little stones in Italian, pebble-like bits of magma, volcanic ash - form when gases in still magma expand rapidly, volcanic blocks - the largest pieces
pyrolastic flow
produced when enormous amounts of hot ash, dust and gases are ejected from a volcano
shield volcanoes
are built of layers of lava released from repeated nonexplosuve eruptions - lava is runny and spreads out over a wide area - Mauna Kea in Hawaii
cinder cone volcanoes
are built from pyroclastic material during modeately explosive eruptions - has steep slopes - Paricutin in Mexico
composite vocanoes
are built from explosive eruptions follwed by quieter flows of lava - most common type of volcano - also called stratovolcanoes - Mount Fuji in Japan & Mount Hood in the US
volcanic eruption affects climate change how
volcanic ash and gas spread throughtout the atmosphere and can block out sunlight and cause global temperatures to drop - Mount Pinatubo in the Philippines
what type of lava flows from a shield volcano
runny lava - spreads out over a wide area
describe the eruption of a cinder cone volcano
usally erupt for only a short time
describe the eruption of a composite volcano
combination of both types of eruptions form alternating layers of pyroclastic material and lava - have broad bases and sides that get steeper toward the top
crater
a funnel shaped pit near the top of the central vent of a volcano
caldera
a large semi-circle depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink
lava plateau
a wide flat landform that resutls from repeated non explosive eruptions of lavathat spead over a large area
size of a caldera to a crater
caldera is usually bigger than a crater because everytime there is an eruption the caldera gets bigger
when does rock melt
when its temperature increases or when the pressure on the rock decreases
why doesnt rock of the mantel melt at Earth's surface
beceause it is not hot enough and there is not enough pressure
most common cause of magma formation
a decrease in pressure
are surrounding the Pacific Ocean known as the Ring of Fire
because it has so many colcanoes - area of tectonic plate boundaries
rift zone
an area of deep cracks that forms between two tectonic plates that are pulling away from each other
mid-ocean ridge
an underwater moutain chain where new ocean floor is formed - by lava that flows underwater
how does magma form at a divergent boundary
tectonic plates pull away and magma rises
how does magma from at a convergent boundary
subduction - the movement of one tectonic plate underneath another
how does subduction produce magma
causes increased and pressure near the oceanic crust to be released - water mixes with mantel rock, lowering the rocks melting point
hot spot
a volcanically active area of Earth's surface far from a tectonic plate boundary
methods that scientists predict volcanoes
study active and dormant volcanoes, study small earthquakes that occur before an eruption, study volume and composition of volcanic gases, use a tiltmeter to measure small changes in the angle of a volcanoes slope, use satellite images