3 2 NOTES VOLCANOES ERUPTIONS Volcano an opening

3 -2 NOTES VOLCANOES

ERUPTIONS • Volcano- an opening in Earth’s crust through which molten rock, rock fragments, and hot gases erupt.

ERUPTIONS • A mountain built up from erupted material is also called a volcano.

ERUPTIONS • The violence of the eruption depends on the type of magma that erupts.

MAGMA • Magma contains gases that expand as the magma is heated and rises.

MAGMA • All magma contains silica.

MAGMA • Magma that is high in silica doesn’t flow easily, so gases that are trying to expand get trapped.

MAGMA • High silica magma causes violent explosions.

MAGMA • https: //www. youtube. com/watch? v=Jm. Puypq. IQE

MAGMA • Magma that is low in silica flows easily, so gases expand escape easily.

MAGMA • Low silica magma causes oozing, flowing eruptions.

MAGMA • Underground, magma rises toward the surface when it is less dense than the rock around it.

MAGMA • It collects in a magma chamber.

MAGMA • It either cools into rock inside the chamber, or erupts when the chamber overflows.

ROCKS • Volcanoes release large amounts of rock fragments. • These rock fragments form as:

ROCKS • Molten rock is torn apart as gas bubbles pop.

ROCKS • Lava cools and hardens into rock as it flies through the air.

ROCKS • Rocks rip loose from the volcano’s walls during the eruption.

ROCKS • Tiny rock fragments: volcanic ash

ROCKS • Medium sized rock fragments: volcanic cinders

ROCKS • Large rock fragments: volcanic blocks or volcanic bombs

GASES • “Smoke” rising from a volcano is a mix of ash and gases.

GASES • The gases are mostly water and carbon dioxide.

GASES • Pyroclastic flowa dense, superhot cloud of rock fragments that races downhill.

GASES • Pyroclastic flows can be as hot as 800 degrees Celsius (1500 degrees F!) and move as fast as 160 km/her (100 mph!)

GASES • In AD 79, Mt. Vesuvius erupted and buried the town of Pompeii in a deadly pyroclastic flow, killing almost 16, 000 people immediately.

VOLCANOES FORM ALONG PLATE BOUNDARIES • Volcanoes are common along tectonic plate boundaries at subduction zones and divergent boundaries.

VOLCANOES FORM ALONG PLATE BOUNDARIES • Volcanoes can also form over hot spots.

VOLCANOES FORM ALONG PLATE BOUNDARIES • There are ~1500 potentially active volcanoes in the world, 500 of which we know have erupted.

VOLCANOES FORM ALONG PLATE BOUNDARIES • 400 of the 500 volcanoes known to have erupted occur in the Ring of Fire.

SHAPES AND SIZES • Most volcanoes erupt from openings in bowlshaped pits called craters.

SHAPES AND SIZES • The type of magma a volcano erupts determines its shape.

SHIELD VOLCANO • Shaped like a broad, flat dome.

SHIELD VOLCANO • Lava is low in silica so it flows easily and spreads out in thin layers.

SHIELD VOLCANO • Example: Mauna Loa in Hawaii, U. S.

CINDER CONE • Steep, coneshaped hill • Formed by the eruption of cinders and rock fragments.

CINDER CONE • Magma contains large amounts of gas. • Example: Sunset Crater Volcano, Arizona, U. S.

COMPOSITE VOLCANO • Cone-shaped; built up by alternating layers of lava and rock fragments.

COMPOSITE VOLCANO • Magma is high in silica • Tends to be steep near the top and flattens out toward the bottom.

COMPOSITE VOLCANO • Example: Mt. Fuji, Japan

COMPOSITE VOLCANO • Composite volcanoes have violent eruptions because: –Gases trapped in the magma cause high pressure explosions. –Cooled, hardened lava plugs up previous openings, causing pressure to build again.

SHAPES AND SIZES • Both shield and composite volcanoes can form calderas.

SHAPES AND SIZES • Caldera- a huge crater formed by the collapse of a volcano when magma rapidly erupts from

SCIENTISTS MONITOR VOLCANOES • In 1991, Mt. Pinatubo in the Philippines erupted for the first time in 500 years.

SCIENTISTS MONITOR VOLCANOES • Scientists knew it was becoming active months before and the area was evacuated, saving thousands of lives.

SCIENTISTS MONITOR VOLCANOES • Scientists monitor volcanoes for signs of eruption, such as: –Small earthquakes in the area

SCIENTISTS MONITOR VOLCANOES –Explosions of steam.

SCIENTISTS MONITOR VOLCANOES –Changes in the tilt of the ground.

SCIENTISTS MONITOR VOLCANOES • Scientists also: –monitor the temperature of water near volcanoes.

SCIENTISTS MONITOR VOLCANOES –Study the ages and types of rocks around a volcano to understand its history.

SCIENTISTS MONITOR VOLCANOES –Keep a close watch on volcanoes near cities. –Example: Mt. Rainier (Seattle)

REVIEW 1. What makes a pyroclastic flow so dangerous? A. Its speed and temperature B. Its speed and its cinder content C. Its temperature and its silica content

REVIEW 2. Volcanoes form at A. converging boundaries and diverging boundaries only. B. hot spots and faults only C. diverging boundaries and hot spots only D. converging boundaries, diverging boundaries, and hot spots

REVIEW 3. Which of the following signs might indicate that a volcano might soon erupt? A. increased wearing away of volcanic rocks. B. falling temperatures in volcanic lakes C. rising temperatures in volcanic lakes D. decreased wearing away of volcanic rocks