3.2 Notes: Volcanoes Form as Molten Rock Erupts

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1 3.2 Notes: Volcanoes Form as Molten Rock Erupts Think about What happens when a volcano erupts? Volcanoes erupt many types of material Earth s thin outer layer is, but most of Earth is extremely hot rock and molten metal. A volcano is an opening in Earth s crust through which molten rock, rock fragments, and hot erupt. A built up from erupted material is also called a volcano. Volcanoes can erupt violently or gently. The violence of an eruption depends on the type of feeding the volcano. Magma A major part of all magma is (a mixture of Silicon and Oxygen). Magma also contains gases which expand as the magma rises. Magma that is high in silica resists, so expanding gases get trapped. silica magma causes violent, dangerous explosions Magma with little silica flows easily, as gases bubble up and escape through it easily. Magma rises to the surface as long as it is less than the surrounding rock. Once magma rising, it collects in an area called a magma chamber. It either cools into rock in the chamber, or erupts when the chamber with magma. When magma erupts, we call it. Rock fragments Volcanoes also release large amounts of rock fragments, which form as Magma is torn apart as gas bubbles cools and hardens into rock as it flies through the air Rocks rip loose from the volcanoes walls during eruption Tiny rock fragments = volcanic rock fragments = volcanic cinders Large rock fragments = volcanic or volcanic bombs Volcanic gases rising from a volcano is a mix of ash and gases. Main gases released are vapor and carbon dioxide. During an eruption, volcanic gases can mix with rock fragments and stay near the ground. This mixture forms a pyroclastic flow-a dense cloud of superhot gases and rock fragments that races downhill. Pyroclastic flows can be as hot as degrees Celsius (1500 degrees F) and move as quickly as km/hr (100 mi/h)! Pyroclastic flows are the most dangerous type of volcanic eruption. Most volcanoes form along plate boundaries Volcanoes are common along tectonic plate boundaries at zones. Volcanoes are also common along divergent plate boundaries. Most volcanoes at divergent boundaries are, but they can form on land as well. Example: Volcanoes in Africa s Great Rift Valley Volcanoes can also form over. These hot spots can build up islands like Hawaii. There are about 1500 potentially active volcanoes in the world, and that have erupted during recorded history. of these are found along subduction zones in the Pacific Ocean. Volcanoes can have many shapes and sizes Most volcanoes erupt from openings in bowl-shaped pits called. The type of feeding a volcano determines its shape.

2 1. Volcano Shaped like a broad, flat dome Lava is in silica so it flows easily and spreads out in thin layers. Example: Mauna Loa in Hawaii. 2. Steep, cone-shaped hill Formed by the eruption of and rock fragments Gas-rich magma Example: Sunset Crater Volcano, Arizona 3. Volcano Cone-shaped; built up by layers of lava and layers of rock fragments Magma is in silica Steep near the top, flattens out at the bottom. Example: Mount Fuji, Japan Composite volcanoes have eruptions for two reasons: Expanding gases trapped in the magma cause explosions. Hardened lava from earlier eruptions often plug previous openings. Both shield and composite volcanoes can form features called. A caldera is a huge crater formed by the collapse of a volcano when magma rapidly erupts from underneath it. Example: The crater on top of Mauna Loa. Example: Crater Lake in Oregon. Scientists monitor volcanoes In 1991, Mt. Pinatubo in the Philippines erupted after years of inactivity. Luckily, scientists knew it was becoming active months earlier and the government was able to evacuate the area. This action saved tens of thousands of lives. Scientists monitor volcanoes like Pinatubo for signs of future eruptions, such as: Small in the area Explosions of steam near the volcano s top. Changes in the of the ground. Scientists also monitor the temperature of openings, springs, and lakes near volcanoes. Scientists study the ages and types of volcanic rocks around a volcano to understand the volcano s history. Scientists pay special attention to volcanoes that are near major cities. Example: Mt. Rainier near Seattle. Example: Mt. Vesuvius near Naples, Italy Review 1. Volcanoes in the Ring of Fire are supplied with magma rising from A. Spreading centers C. Rift Valleys B. Hot spots D. Subduction zones 2. Before magma erupts it collects under a volcano in a A. Chamber C. Crater B. Caldera D. Vent 3. The explosiveness of a volcanic eruption depends mostly on the of the magma. A. Gas content C. Amount B. Silica content D. Temperature 4. The type of magma erupting from a volcano determines the volcano s A. Size C. Shape B. Age D. Location 5. Volcanic ash can be carried thousands of kilometers from an eruption by A. Lava flows C. Landslides B. Pyroclastic flows D. Winds 6. In a volcanic region, water moving through the ground gets by magma or hot rock. A. Melted C. Erupted B. Dissolved D. Heated

3 3.2 Notes: Volcanoes Form as Molten Rock Erupts Think about What happens when a volcano erupts? Volcanoes erupt many types of material Earth s thin outer layer is cool, but most of Earth is extremely hot rock and molten metal. A volcano is an opening in Earth s crust through which molten rock, rock fragments, and hot gases erupt. A mountain built up from erupted material is also called a volcano. Volcanoes can erupt violently or gently. The violence of an eruption depends on the type of magma feeding the volcano. Magma A major part of all magma is silica (a mixture of Silicon and Oxygen). Magma also contains gases which expand as the magma rises. Magma that is high in silica resists flowing, so expanding gases get trapped. High silica magma causes violent, dangerous explosions Magma with little silica flows easily, as gases bubble up and escape through it easily. Magma rises to the surface as long as it is less dense than the surrounding rock. Once magma stops rising, it collects in an area called a magma chamber. It either cools into rock in the chamber, or erupts when the chamber overflows with magma. When magma erupts, we call it lava. Rock fragments Volcanoes also release large amounts of rock fragments, which form as Magma is torn apart as gas bubbles pop Lava cools and hardens into rock as it flies through the air Rocks rip loose from the volcanoes walls during eruption Tiny rock fragments = volcanic ash Medium rock fragments = volcanic cinders Large rock fragments = volcanic blocks or volcanic bombs Volcanic gases Smoke rising from a volcano is a mix of ash and gases. Main gases released are water vapor and carbon dioxide. During an eruption, volcanic gases can mix with rock fragments and stay near the ground. This mixture forms a pyroclastic flow-a dense cloud of superhot gases and rock fragments that races downhill. Pyroclastic flows can be as hot as 800 degrees Celsius (1500 degrees F) and move as quickly as 160 km/hr (100 mi/h)! Pyroclastic flows are the most dangerous type of volcanic eruption. Most volcanoes form along plate boundaries Volcanoes are common along tectonic plate boundaries at subduction zones. Volcanoes are also common along divergent plate boundaries. Most volcanoes at divergent boundaries are underwater, but they can form on land as well. Example: Volcanoes in Africa s Great Rift Valley Volcanoes can also form over hot spots. These hot spots can build up islands like Hawaii. There are about 1500 potentially active volcanoes in the world, and 500 that have erupted during recorded history. 400 of these are found along subduction zones in the Pacific Ocean. Volcanoes can have many shapes and sizes Most volcanoes erupt from openings in bowl-shaped pits called craters. The type of magma feeding a volcano determines its shape.

4 1. Shield Volcano Shaped like a broad, flat dome Lava is low in silica so it flows easily and spreads out in thin layers. Example: Mauna Loa in Hawaii. 2. Cinder Cone Steep, cone-shaped hill Formed by the eruption of cinders and rock fragments Gas-rich magma Example: Sunset Crater Volcano, Arizona 3. Composite Volcano Cone-shaped; built up by layers of lava and layers of rock fragments Magma is high in silica Steep near the top, flattens out at the bottom. Example: Mount Fuji, Japan Composite volcanoes have violent eruptions for two reasons: Expanding gases trapped in the magma cause explosions. Hardened lava from earlier eruptions often plug previous openings. Both shield and composite volcanoes can form features called calderas. A caldera is a hug crater formed by the collapse of a volcano when magma rapidly erupts from underneath it. Example: The crater on top of Mauna Loa. Example: Crater Lake in Oregon. Scientists monitor volcanoes In 1991, Mt. Pinatubo in the Phillippines erupted after 500 years of inactivity. Luckily, scientists knew it was becoming active months earlier and the government was able to evacuate the area. This action saved tens of thousands of lives. Scientists monitor volcanoes like Pinatubo for signs of future eruptions, such as: Small earthquakes in the area Explosions of steam near the volcano s top. Changes in the tilt of the ground. Scientists also monitor the temperature of openings, springs, and lakes near volcanoes. Scientists study the ages and types of volcanic rocks around a volcano to understand the volcano s history. Scientists pay special attention to volcanoes that are near major cities. Example: Mt. Rainier near Seattle. Example: Mt. Vesuvius near Naples, Italy Review 1. Volcanoes in the Ring of Fire are supplied with magma rising from A. Spreading centers C. Rift Valleys B. Hot spots D. Subduction zones 2. Before magma erupts it collects under a volcano in a A. Chamber C. Crater B. Caldera D. Vent 3. The explosiveness of a volcanic eruption depends mostly on the of the magma. A. Gas content C. Amount B. Silica content D. Temperature 4. The type of magma erupting from a volcano determines the volcano s A. Size C. Shape B. Age D. Location 5. Volcanic ash can be carried thousands of kilometers from an eruption by A. Lava flows C. Landslides B. Pyroclastic flows D. Winds 6. In a volcanic region, water moving through the ground gets by magma or hot rock. A. Melted C. Erupted B. Dissolved D. Heated

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