Geology Test 1 - Volcanoes (5)

Front 1

viscosity

Back 1

a measure of a fluid's resistance to flowing

Front 2

high viscosity means

Back 2

hard to flow

Front 3

viscosity due to

Back 3

polymerization of silicon and oxygen in magma

Front 4

high silica content =

Back 4

high viscosity

Front 5

mafic magmas have significantly lower _____ content than felsic magmas

Back 5

silica

Front 6

felsic magmas are (more/less) viscous than mafic minerals

Back 6

more (because more silica)

Front 7

high temperature =

Back 7

lower viscosity (flows easier)

Front 8

water dissolved in magmas =

Back 8

lower viscosity

Front 9

magmas rise from depth of Earth until: (3 things)

Back 9

1) density matches surrounding rock
2) no avenue to rise through
3) lost so much heat that viscosity is too high

Front 10

lava

Back 10

magma that has erupted onto Earth's surface

Front 11

basaltic lava

Back 11

commonly flows over large distances, low viscosity

Front 12

rhyolitic lava

Back 12

very high viscosity, never travels far nor fast

(rhy = high)

Front 13

felsic lava

Back 13

very viscous, commonly plugs up shallow plumbing of volcanoes

prevents gas from escaping

lava domes

Front 14

lava flow

Back 14

masses of molten rock that pour onto Earth's surface during an effusive eruption

moving lava

Front 15

ash

Back 15

rock, mineral, volcanic glass fragments smaller than .2 mm in diameter

hard, does not dissolve in water

shattering of rocks during violent eruption

Front 16

pyroclastic flow

Back 16

ground-hugging avalanche of hot ash, pumice, rock fragments, volcanic gas

gushes down side of volcano very fast

Front 17

Lahar

Back 17

volcanic mudflows or debris flows

rapidly flowing mixture of rock debris and water

formed by rapid melting of snow and ice by PYROCLASTIC flows

Front 18

tuff

Back 18

relatively soft, porous rock

compaction and cementation of volcanic ash

Front 19

nuees ardente

Back 19

pyroclastic flows generated by dome collapse

Front 20

pillow lava

Back 20

when basalt erupts underwater

mounds of lava pillows form by repeated oozing and quenching of hot basalt

Front 21

shield volcanoes

Back 21

broad, gentle slopes

built by eruption of fluid basalt lava

enormous, low angle cones

Front 22

cinder cone

Back 22

steep, conical hill of volcanic fragments that accumulate around and downwind from a vent

rock fragments are glassy with gas bubbles (magma exploded into air and cooled quickly)

Front 23

composite (strato-) volcano

Back 23

steep, conical volcano

built by eruption of viscous lava flows and pyroclastic flows

highly explosive

many vents

Mt. St. Helens

Front 24

caldera

Back 24

large, usually circular depression at summit of volcano

formed when magma is withdrawn or erupted from a shallow underground magma reservoir

removal of magma leads to loss of structural support, leading to collapse

Front 25

dome

Back 25

rounded, steep sided mounds built by very viscous magma

too viscous to flow away

Front 26

aa

Back 26

lava flows that have rough, rubbly surface composed of broken lava blocks called clinkers

Front 27

pahoehoe

Back 27

basaltic lava that has smooth surface

advances as small lobes and toes that continually break out from cooled crust

Front 28

pumice

Back 28

light, porous volcanic rock

forms during explosive eruptions

like a sponge, network of gas bubbles

all types of magma make it

Front 29

obsidian

Back 29

dense volcanic glass

rhyolitic in composition

black in color

cooled really fast

Front 30

supervolcano

Back 30

capable of producing eruption with over 1000 square km of particles

Front 31

Hawaiin eruptions

Back 31

lava flows from a vent in a relatively gentle, low level eruption

basaltic magma of low viscosity and low content of gas

very little volcanic ash

Front 32

Plinian eruptions

Back 32

large explosive events that form enormous dark columns of gas high into stratosphere

Front 33

strombolian eruptions

Back 33

intermittent explosion or fountaining of basaltic lava from a single vent or crater