EQ: What occurs when a volcano erupts?
How do the different type of eruptions differ?

How Magma Reaches Earth
’ s
Surface
• Magma rises because it is less dense that the surrounding solid material

• As the less dense magma rises, the pressure decreases
• The dissolved gas separates out and bubbles form
• A volcanic 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

Crater
• A bowl-shaped area that forms around a volcano’s central opening
• Lava collects there

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.

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

Three factors contribute to how forceful a volcanic eruption is .
• 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
• Classified as a quiet eruption if its magma flows easily
• The gas in this magma bubbles out gently
• Quiet eruptions produce two types of lava:
– Pahoehoe – (pah HOH ee hoh ee)
– aa – (Ah ah)

Pahoehoe
• A hot, fast-moving type of lava that hardens to form smooth, ropelike coils. Cools slowly resulting in a smooth texture

Aa
• A cooler, slowmoving type of lava that hardens to form rough chunks; cooler than Pahoehoe.
Cools more quickly

What accounts for the differences between these two types of lava?
• The temperature of the lava
• The speed at which the lava flows

Explosive Eruptions
• 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

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

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

Three Stages of Volcanoes
• 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

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 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

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