Volcanic Activity

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

What happens when a volcano erupts?

• 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, slow-moving 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