Volcanoes

Chapter 6

6.1 Volcanoes and Plate Tectonics

• Volcanoes from along _________________– Both __________________________

• Divergent:– Plates _______ and allow magma to reach surface

• Convergent:– One plate ______________________– __________ is brought down with the plate and

eventually forms magma that rises to the surface

plate boundariesdivergent and convergent

fracture

sinks under the otherWater

6.1 Volcanoes and Plate Tectonics

• Island arcs– Result of ____________________– _______________ plate subducts into deep ocean

trench– Water in the sinking plate leaves and causes

____________________________________– Magma ______________________ ocean floor to

form volcano– These volcanoes form ___________________

convergent boundaryOlder, denser

the mantle to melt and form magmarises and breaks through

a string of islands

6.1 Volcanoes and Plate Tectonics• Hot Spots– Hot spots _______________________ for millions

of years while the earth’s plates move over them– Some lie close to plate boundaries and some are

____________________– ________________formed from a plate moving over a hotspot

remain in the same place

in the middle of platesHawaiian islands

6.2 Volcanic Eruptions

magma chamber

lava flow

side ventvent

pipe

crater

6.2 Volcanic Eruptions• Eruptions:– ____________ rises to surface– Dissolved gases in magma ___________________– Pressure in magma __________ and size of

bubbles ____________– Force of expanding gases __________________

the volcano to the surface• Two types of eruptions

1. _______________2. _______________

Magmaexpand and bubble

QuietExplosive

fallsincrease

pushes magma up

6.2 Volcanic Eruptions

• Quiet Volcanic Eruptions– Magma is _______________– Gases bubble gently– Lava oozes quietly and ______________________– 2 types of lava produced and form 2 types of rock:

1. _________________ forms from lava that is fast-moving, thin, and runny. Looks like ropelike coils

2. _________ forms form cooler, thicker lava. Has a rough texture with jagged chunks of lava

low in silica

can flow many kilometers

Pahoehoe

Aa

6.2 Volcanic Eruptions• Explosive Volcanic Eruptions– Magma is _________________, thick, and sticky– Magma blocks the volcano pipe like a cork– Gases are _______________the magma and build

up ____________ until the force is great enough to push the magma out volcano

– Throws lava in the air that cools • Smallest pieces are called _________________• Pebble-sized pieces are ________________• Larger pieces that range from gold ball to car size are

called ______________

high in silica

pressuretrapped behind

volcanic ashcinders

bombs

6.2 Volcanic Eruptions

• Volcano Hazards– __________________ cause fires and can bury

everything in their path– Explosive eruptions send out hot rock and ash,

and __________________– Explosive eruptions can also cause ____________

of mud, rock, and melted snow

Quiet eruptions

pyroclastic flowlandslides

6.2 Volcanic Eruptions

• Stages of activity:1. Active (___________):– erupting or will erupt in the near future2. Dormant (_____________): – Expected to become active in the future3. Extinct (_________):– Unlikely to ever erupt again

live

sleeping

dead

6.3 Volcanic Landforms

• Landforms from Lava and Ash:– ________________– ___________________– ___________________– _________________

• Other Landforms:– ______________• Huge holes left from a volcano that has collapsedCalderas

Shield volcanoesCinder cone volcanoesComposite volcanoesLava plateaus

6.3 Volcanic Landforms

• Cinder Cone Volcanoes– Formed from ____________________with

magma that had high silica content– Ash, cinders, and bombs ____________________in a steep, cone-shaped hill or mountain

an explosive volcano

build up around the vent

6.3 Volcanic Landforms• Composite Volcanoes– ________________________– Eruptions alternate between _____________ and

explosive with ash, cinders, and bombs– Tall, cone-shaped mountain with layers that

alternate with _______________– Can be more than

___________________________

The silica content varieslava flows

lava and ash

4,800 meters tall

6.3 Volcanic Landforms

• Shield Volcanoes– Thin layers of lava come out of a ________– The lava hardens on top of previous layers– Wide, gently sloping mountain– ____________________ on the ocean floor are

usually formed this way

vent

Hot spot volcanoes

6.3 Volcanic Landforms• Lava Plateaus– Lava flows from several cracks in the earth’s crust– Lava is ___________________ so it travels far

before it cools and solidifies– ________________ with this type of lava flow

form high, level plateaus

thin and runny

Millions of years

6.3 Volcanic Landforms

• Landforms from Magma:– ________________– ________________– ________________– ________________

Volcanic necksDikes and sillsDome mountainsBatholiths

6.3 Volcanic Landforms

• Volcanic Necks– Forms from ___________________ in the pipe of

a volcano and then the surrounding rock wears away

magma that hardens

6.3 Volcanic Landforms• Dikes– Magma forces itself ___________________and then hardens

• Sills– Magma squeezes ____________________rock layers andhardens

across rock layers

between horizontal

6.3 Volcanic Landforms

• Dome Mountains– Forms when a large body of hardened magma is

__________________________________– The magma forces rock layer to ____________

into a dome shape– Rock above the dome mountain wears away, leaving the hardened magma exposed

pushed towards the Earth’s surfacebend upward

6.3 Volcanic Landforms

• Batholiths– A mass of rock formed by a large

_________________ cooled inside the crust

– Millions of years or weathering and erosion wear away the ____________________ and the batholith moves upward

– _______________ carve the batholith into a mountain

body of magma

overlying rock

Ice and water

Volcanic Eruptions