Thur. April 24 Do Now: How does using the process of fracking to extract natural gas and oil cause earthquakes? In your opinion, what is the most important benefit of fracking? In your opinion, what is the greatest danger is using fracking to obtain natural gas and oil?

Learning Intentions Learn about the role of plate tectonics in causing volcanoes and learn what causes eruptions to be gentle or highly explosive. Identify the main types of volcanoes: shield volcanoes, stratovolcanoes, and cinder cones. Learn about other forms of volcanic activity such as geysers, hot springs, hydrothermal vents, and geothermal energy.

Vocabulary Terms caldera Ring of Fire cinder cone volcano geothermal energy hydrothermal vent Ring of Fire shield volcano stratovolcano viscosity

VOLCANOES Volcanoes are places where molten (melted) rock and other materials from the earth’s mantle are released. Molten rock below the earth’s surface is called magma. Below ground, magma forms pools called magma chambers. Magma reaches the earth’s surface through pathways called pipes. Areas where magma reaches the earth’s surface are called vents. Molten rock that reaches the earth’s surface and erupts or flows out of a volcano is called lava.

Volcanoes also release gases and rock fragments into the air Volcanoes also release gases and rock fragments into the air. Rock fragments are called pyroclasts, dust particle size fragments are called ash. A crater is a depression formed at the top of a volcanic mountain after an eruption. Later a lake may form in the crater.

Volcanoes The eruption of Mount St. Helens in 1980 reduced the height of this mountain from 2,932 meters (9,677 feet) to 2,535 meters (8,364 feet). Early in the morning of May 18, 1980, an earthquake triggered a landslide that caused the bulge to eject magma, water, and gases.

Solid rock melts and becomes magma under certain conditions that lower the melting point of the material. At subduction zones, water is the key for solid rock to melt and become magma.

Like earthquakes, most volcanic activity is found at the edges of tectonic plates, namely at divergent and convergent plate boundaries, but does not occur at transform plate boundaries.

There are three main types of volcanoes: 1-Shield Volcanoes 2-Stratovolcanoes (also called composite volcanoes) 3- Cinder Cone Volcanoes They have different shapes and are formed from different types of material: lava, pyroclasts, ash, and gases. The viscosity, or thickness, of the lava flowing from the volcano is the most important factor in determining the shape of the volcano.

Low viscosity, fast-flowing lava is associated with shield volcanoes. Because this lava easily flows down hill, shield volcanoes are gently sloped and flattened.

High viscosity lava is associated with stratovolcanoes (also called composite volcanoes). These volcanoes range in height from 500 to 10,000 meters.

Cinder cone volcanoes are steep stacks of loose pyroclasts (clumps and particles of lava). Cinder cones are rarely higher than 300 meters.

Lava viscosity also determines how explosive an eruption will be. Explosive eruptions occur when the lava has a lot of water and dissolved gases. Gentle eruptions are associated with fast-flowing lava from oceanic crust.

Volcanoes also form when an oceanic plate slides under another oceanic plate.

Hydrothermal Vents Hydrothermal vents are deep sea, chimney- like structures that occur along midocean ridges.

Some gemstones are also associated with volcanic activity. For example, diamonds form at high temperatures deep underground when carbon crystallizes inside rocks called kimberlites.

Geothermal energy is a useful product of volcanic activity. When steam from magma collects below ground, it can be tapped just like water in a well. The pressurized steam can be used to generate electricity.

Now do your practice problems in your note sheet!