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Holt Science & Technology - Earth Science, Chapter 9 Study Guide


a vent or fissure in the Earth's surface through which magma and gases are expelled


molten rock


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


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


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


a funnel shaped pit near the top of the central vent of a volcano


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

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