Download 3-2 Notes: Volcanoes Eruptions • Volcano

3-2 Notes: Volcanoes
Eruptions
• Volcano- an opening in Earth’s crust through which molten rock, _____________ fragments, and hot gases erupt.
• A ___________________________ built up from erupted material is also called a volcano.
• The violence of the eruption depends on the type of ____________________ that erupts.
Magma
• Magma contains gases that expand as the magma is heated and _______________________.
• All magma contains ______________________.
• Magma that is high in silica doesn’t flow easily, so gases that are trying to expand get _______________________.
• High silica magma causes ______________________ explosions.
• Magma that is _________ in silica flows easily, so gases expand and escape easily.
• Low silica magma causes oozing, _____________________ eruptions.
• Underground, magma rises toward the surface when it is less _____________________ than the rock around it.
• It collects in a magma _______________________.
• It either cools into rock inside the chamber, or erupts when the chamber _____________________________.
• When magma erupts, we call it ________________.
Rocks
• Volcanoes release large amounts of rock
______________________________.
• These rock fragments form as:
• Molten rock is torn apart as gas ___________________ pop.
• Lava ______________ and hardens into rock as it flies
through the air.
• Rocks rip loose from the volcano’s walls during the eruption.
• Tiny rock fragments: volcanic ___________
• __________________ sized rock fragments: volcanic cinders
• Large rock fragments: volcanic _________________ or
volcanic bombs
Gases
• “Smoke” rising from a volcano is a mix of ________ and gases.
• The gases are mostly ______________ and carbon dioxide.
• _______________________ flow- a dense, superhot cloud of rock fragments that races downhill.
• Pyroclastic flows can be as hot as 800 degrees Celsius (1500 degrees F!) and move as fast as 160 km/hr (100
mph!)
• In AD 79, Mt. Vesuvius erupted and buried the town of Pompeii in a deadly pyroclastic flow, killing almost ________
people immediately.
Volcanoes Form Along Plate Boundaries
• Volcanoes are common along tectonic plate boundaries at subduction zones and _________________ boundaries.
• Volcanoes can also form over _____________________.
• There are ~1500 potentially active volcanoes in the world, _________ of which we know have erupted.
• ________ of the 500 volcanoes known to have erupted occur in the Ring of Fire.
Shapes and Sizes
• Most volcanoes erupt from openings in bowl-shaped pits called ____________________.
• The type of _____________________ a volcano erupts determines its shape.
Shield Volcano
• Shaped like a broad, flat ___________________.
• Lava is low in silica so it flows easily and spreads out in thin ____________________.
– Example: Mauna Loa in Hawaii, U.S.
p. 157
Cinder Cone
• Steep, cone-shaped ___________
• Formed by the eruption of cinders and _____________ fragments.
• Magma contains large amounts of ___________.
– Example: Sunset Crater Volcano, Arizona, U.S.
Composite Volcano
• Cone-shaped; built up by alternating ___________________ of lava and rock fragments.
• Magma is high in ___________________
• Tends to be steep near the top and flattens out toward the ____________________.
– Example: Mt. Fuji, Japan
• Composite volcanoes have _____________________ eruptions because:
– Gases trapped in the magma cause high pressure _________________________.
– ___________________, hardened lava plugs up previous openings, causing pressure to build again.
• Both shield and composite volcanoes can form _________________________.
• Caldera- a huge ___________ formed by the collapse of a volcano when magma rapidly erupts from underneath it.
Scientists Monitor Volcanoes
• In 1991, Mt. Pinatubo in the Philippines erupted for the first time in 500 years.
• Scientists knew it was becoming active months before and the area was evacuated, saving thousands of lives.
• Scientists monitor volcanoes for signs of eruption, such as:
– Small ________________________ in the area
– Explosions of steam.
– Changes in the ___________________ of the ground.
• Scientists also:
– monitor the temperature of ____________________ near volcanoes.
– Study the ages and types of rocks around a volcano to understand its _____________________.
– Keep a close watch on volcanoes near cities.
– Example: Mt. Rainier (____________________)
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 silica content.
D. Its temperature and volume.
____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
____3. Which of the following signs might indicate that a volcano might soon erupt?
A. increased wearing away of volcanic rocks.
C. rising temperatures in volcanic lakes
B. falling temperatures in volcanic lakes
D. decreased wearing away of volcanic rocks