Inside Earth: Volcanoes

Section 2: Volcanic Activity

Major Volcanoes Around the World

What you need to know…

• What happens when a volcano erupts?

• How do the two types of volcanic eruptions differ?

• What are some hazards of volcanoes?

How Magma Reaches Earth’s Surface

Why does magma rise?

• Magma rises because it is less dense that the surrounding solid material

What happens when a volcano erupts?

• As the less dense magma rises, the pressure decreases

• The dissolved gas separates out and bubbles form

• A volcano erupts when an opening develops in weak rock on the surface

• During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them

• Once magma reaches the surface and becomes lava, the gases bubble out

Inside a Volcano

Magma Chamber

• The pocket beneath a volcano where magma collects

Pipe

• A long tube through which magma moves from the magma chamber to Earth’s surface

Vent

• The opening through which molten rock and gas leave a volcano

Where are vents located?

• Usually there is one central vent at the top of the volcano

• Often times there are additional vents that open on the volcanoes sides

Lava Flow

• The area covered by lava as it pours out of a volcano’s vent

Label a VolcanoUsing the labels given find the correct part.

Crater

• A bowl-shaped area that forms around a volcano’s central opening

• Lava collects there

There are three types of volcanic cones:

• ______ – explosive eruptions, small but steep slopes, pyroclastics

• _______ – nonexplosive eruptions, fluid basaltic lava, gentle broad slopes

• _________ – alternating between lava and pyroclastics, explosive and nonexplosive eruptions, steep and tall

CinderShield

Composite

Classify Volcanoes• Composite • Cinder • Shield

• Active • Intermittent • Dormant • Extinct

Question 1: How does magma rise through the lithosphere?

• Liquid magma in the asthenosphere is less dense than the rock in the lithosphere above it, so it flows upward through cracks in the rock– The magma is stored in the magma chamber

• It continues upward (through the pipe) until it reaches the surface (exiting through a vent) or it is trapped beneath layers of rock.

Characteristics of Magma

Silica

• A material that is found in magma,formed from the elements oxygen and silicon

• The more silica the magma has the thicker it is

What three factors contribute to how forceful a volcanic eruption is? Explain how each determines this.

• Amount of gas present• How thick or thin the magma is

(Temperature)– Thinner (hotter) is more fluid

• The silica content– If the silica content is high, magma is

thick– This causes the pressure to build

Types of Volcanic Eruptions

Quiet eruptions like the ones that take place on _______ have built up the big island over _______ of _______ of years.

• Mount Kilauea

• Hundreds

• Thousands

Pahoehoe

• A hot, fast-moving type of lava that hardens to form smooth, ropelike coils

Aa

• A cooler, slow-moving type of lava that hardens to form rough chunks; cooler than Pahoehoe

What is the difference between the two types of lava?

• Pahoehoe is a faster flowing lava that cools slowly resulting in a smooth texture

• Aa is a slower flowing cooler type of lava that hardens into rough chunks

Inferring What accounts for the differences between these two types of lava?

• The temperature of the lava• The speed at which the lava flows

Question 2: What types of lava are produced by quiet eruptions?

• Quiet eruptions produce two types of lava: pahoehoe and aa

– Pahoehoe is a fast-moving, hot lava

– Aa is a cooler, slower-moving lava

Pyroclastic flow

• The expulsion of ash, cinders, and bombs from a violent volcanic explosion

Question 3: What causes an explosive eruption?

• Magma that is thick and sticky causes a volcano to erupt explosively

• Magma can not flow freely causing pressure (gas) to build up until it explodes

How do the two types of volcanic eruptions differ?

• Quiet eruptions occur when the lava flows more easily because gas dissolved in the magma bubbles

• When the lava is thick and sticky the gas continues to store increasing pressure– When the pressure becomes so great an

explosion takes place when the gas pushes the magma out with incredible force

Stages of a Volcano

What are the three stages of a volcano? Explain each stage.

• Active– A volcano that is erupting or has shown

signs that it may erupt in the near future

• Dormant – A volcano that is not currently active, but

may become active in the future

• Extinct – A volcano that is unlikely to erupt again

Other Types of Volcanic Activity

Hot Spring

• A pool formed by groundwater that has risen to the surface after being heated by a nearby body of magma

Geyser

• A fountain of water and steam that builds up pressure underground and erupts at regular intervals

Geothermal Energy

• Energy from water and steam that has been heated by magma

• Geothermal energy is produced by drilling a well into the ground where thermal activity is occuring.

• Once a well has been identified and a well head attached, the steam is separated from the water, the water is diverted through a turbine engine which turns a generator.

• Usually the water is injected back into the ground to resupply the geothermal source.

Monitoring Volcanoes

How do geologists monitor the activity of a volcano?

• Measure tilt caused by magma movement underground using tiltmeters & laser-ranging devices

• Monitor temperature underground• Monitor small earthquakes that

occur in the area around a volcano

Volcano Hazards

What are some hazards of volcanoes?

• Fire• Bury entire towns• Damage crops• Landslides• Avalanches of mud• Damage car and jet engines

The _________ Islands are a volcanic group of islands 600 miles off the coast of Ecuador on the equator.

Galapagos

Lava flowing underground created this _____ _____, large enough to walk through.

lava tube

Kilauea on Hawaii is a good example of a _______ cone, with less explosive eruptions and less viscous lava.

shield

Mt Rainier and Mt St Helens are good examples of __________ cones, with explosive eruptions and erupted materials such as ash, bombs, and blocks.

Mt St Helens

Mt Rainier

composite

Crater Lake in Oregon is a __________formed from the collapse of the gigantic volcano Mount Mazama. ________________in the center of the lake is a small cinder cone.

caldera

Wizard Island

Igneous RocksIgneous Rocks

Igneous rocks comes from a Igneous rocks comes from a volcano. volcano.

These rocks can form from These rocks can form from cooled lava outside the cooled lava outside the

volcano. volcano.

These rocks can also form These rocks can also form from hardened magma inside from hardened magma inside

the volcano.the volcano.