1. Bellringer How does the silica content affect the overall viscosity of a particular lava flow?

2. Volcanic Eruptions Notes

3. Magma Reaches Earth’s Surface A volcano has a pocket of magma below the surface, called a magma chamber. A long tube, called a pipe, connects the magma chamber to the surface. At the top of a pipe is an opening called a vent (most volcanoes have one primary vent, and one or more secondary vents). Magma leaves the volcano through the vent and becomes lava. The are covered by lava as it pours out of a vent is called a lava flow.

4. Magma Chamber Pipe Lava Flow Primary Vent Side Vent

5. Magma Reaches Earth’s Surface Remember, molecules of a liquid are closer together than those of a gas. If the molecules are allowed to spread out, a liquid will spontaneously turn into a gas. As magma gets closer to the surface, the pressure on the magma decreases. This allows the gases in the magma to begin to bubble out. These gas bubbles takes up more space than the dissolved gases. The bubbles force magma out of the vent, like the bubbles that force warm Coke out of a bottle.

6. Under Pressure Pressure Released, gas expands

7. Magma Reaches Earth’s Surface When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent. The gases in most magma include: Water Vapor (H 2 O) Carbon Dioxide (CO 2 ) Sulfur Dioxide (SO 2 ) Hydrogen (H 2 ) Carbon Monoxide (CO) Hydrogen Sulfide (H 2 S) Hydrochloric Acid (HCl)

9. Kinds of Volcanic Eruptions When magma pours out of a volcano, it is called a volcanic eruption. An eruption can happen slowly and quietly. Or an eruption can happen all at once with an explosion. How a volcano erupts depends on the magma.

10. Kinds of Volcanic Eruptions A volcano erupts quietly if the magma is low in silica (low friction) and flows easily (low viscosity). The lava may flow for many kilometers before it starts to harden into rock.

12. Kinds of Volcanic Eruptions A volcano erupts with an explosion if the magma is high in silica (high friction) and does not flow easily (highly viscous). Mama builds up in the pipe until it explodes out of the vent. The lava cools quickly.

13. The following slides are from the BAJIHO Volcano Eruption in CHILE, July 11, 2011, and are unedited.

19. That is not snow, it’s ash from the volcano!

20. Satellite imagery from above Chile, South America.

21. Kinds of Volcanic Eruptions The pieces that fly away from an explosive volcano are classified into 4 sizes: ✴ Ash - particles smaller than 2 mm (0.08 inches) in diameter ✴ Lapilli or volcanic cinders - between 2 and 64 mm (0.08 and 2.5 inches) in diameter ✴ Volcanic bombs - larger than 64 mm (2.5 inches) in diameter.

22. Kinds of Volcanic Eruptions A pyroclastic flow is a fast-moving current of superheated gas (which can reach temperatures of about 1,000 °C) and rock, which reaches speeds moving away from a volcano of up to 700 km/h. The flows normally hug the ground and travel downhill. They are a common and devastating result of certain explosive volcanic eruptions.

25. Stages of Volcanic Activity A volcano is active when it is erupting or showing signs that it will soon erupt. A volcano is dormant when it is no longer erupting but is likely to erupt again in the future. A dormant volcano many not erupt for thousands of years. But it can become active at any time. A volcano is extinct when it is no longer likely to erupt, even in the future. Sometimes it is hard to distinguish dormant volcanoes from extinct ones, since sometimes thousands to hundreds of thousands of years can pass between eruptions. Supervolcanoes can have a dormancy of millions of years.

26. Stages of Volcanic Activity The Jackson Dome is an extinct volcano that was once a small island in the middle of the ocean that covered most of the southeastern United States some 70 million years ago.

28. Supervolcanoes A supervolcano is a volcano capable of producing a volcanic eruption with an ejecta volume greater than 1,000 cubic km. This is thousands of times larger than most historic volcanic eruptions. Super-volcanoes can occur when magma in the Earth rises into the crust from a hotspot but is unable to break through the crust. Pressure builds in a large and growing magma pool until the crust is unable to contain the pressure.

29. Supervolcanoes Supervolcanic eruptions typically cover huge areas with lava and volcanic ash and cause a long-lasting change to weather (such as the triggering of a small ice age) sufficient to threaten species with extinction. There are currently 6 listed potential supervolcanoes on the planet: ✴ Yellowstone, Wyoming ✴ Long Valley, California ✴ Valles Caldera, New Mexico ✴ Lake Toba, Indonesia ✴ Taupo Volcano, New Zealand ✴ Aira Caldera, Japan

30. Monitoring Volcanoes Scientists try to predict when a volcano will erupt. They watch for signs that magma is moving upward. Scientists often can predict when a volcano will erupt. But they cannot predict what kind of eruption or how strong the eruption will be.