Volcanic Activity EQ What occurs when a volcano

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 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