Volcanoes Table of Contents Essential Question: How Does A Volcano Erupt? What happens when a volcano erupts? What are the stages of Volcanic activity? 6.2 Volcanic Eruptions Pgs 200-207
Vocabulary 6.2 • Magma Chamber- The pocket beneath a volcano where magma collects. • Pipe- A long tube through which magma moves from the magma chamber to Earth’s surface. • Vent- the opening through which molten rock and gas leave a volcano. • Lava flow- the area covered by lava as it pours out of a volcano’s vent. • Crater- a bowl-shaped area that forms around a volcano’s central opening. • Silica- a material found in magma that is formed from the elements oxygen and silicon; it is the primary substance of Earth’s crust and mantle. • Pyroclastic flow- • Dormant-Not currently active but able to become active in the future (as a volcano) • Extinct-A volcano that is no longer active and unlikely to erupt again.
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What Happens When a Volcano Erupts? Pg. 200 • Inside a Volcano • All volcanoes have a pocket of magma beneath the surface, called a magma chamber, where the magma collects. • Magma moves upward through a pipe, a long tube that extends from Earth’s crust up though the top of the volcano, connecting the magma chamber to Earth’s surface. • Molten rock and gas leave the volcano through an opening called a vent. • A lava flow is the spread of lava as it pours out of a vent. • A crater is a bowl-shaped area that may form at the top of a volcano around the central vent.
Fig. 1 Volcanic Eruptions pg. 201 Inside a Volcano A volcano is made up of many different parts. Place each word in its proper place in the diagram
2 Types of Volcanic Eruptions pg. 202 • During an eruption, dissolved gases trapped in the magma expand, form bubbles, and exert great force. • 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. • Geologists classify volcanic eruptions: • as quiet • or explosive. • Whether an eruption is quiet or explosive depends in part on the magma’s silica content and whether the magma is thin and runny or thick and sticky.
Volcanic Eruptions pg. 202 The “Wakulla Volcano” was a column of smoke that was last seen near Tallahassee in 1886. (no volcanic activity in FL for millions of years)
DO THE MATH!! Volcanic Eruptions pg. 202 Magma Composition Magma varies in composition. It is classified according to the amount of silica it contains. The less silica that the magma contains, the more easily it flows. 1. What materials make up both types? __________________________________ 2. Which type of magma has more silica? How much silica does this magma contain? __________________________________ 3. Which of these magmas do you think might erupt in a dramatic explosions? Why? ________________________________________________________________________________________________________________________________________________
Quiet Eruptions pg. 203 • Silicais a material found in magma that forms from the elements oxygen and silicon. • Characteristics of a quiet eruption: • A volcano erupts quietly if its magma is hot or low in silica. The gases in the magma bubble out gently. The lava oozes quietly from the vent and can flow for many kilometers. • Characteristics of an explosive eruption: • A volcano erupts explosively if its magma is high in silica. Trapped gases build up pressure until they explode. The erupting gases and steam push the magma out with incredible force. Both kinds of eruptions can cause damage far from a crater’s rim.
Volcano Hazard pg. 205 • Volcanoes can cause great damage far from a crater’s rim. • Quiet eruption= lava flows, setting fire to everything in its path. They can cover large areas with thick layer of lava. • Explosive eruption= Dangerous chemicals are belch out from the volcano- such as hot rock and ash. • A pyroclastic flow is a mixture of hot gases, ash, cinders, and bombs that flow down the sides of a volcano when it erupts explosively. • Landslides of mud, melted snow, and rock can also form from an explosive eruptions.
Did You Know? • Stromboli volcano lies on an island off the coast of Italy. The volcano has been erupting almost constantly for at least 2,400 years! Expanding gases dissolved in magma cause the eruption to be nearly constant.
What are the Stages of Volcanic Activity? Pg. 296 • Geologists often use the terms active, dormant, or extinct to describe a volcano’s stages of activity. • An active, or live, volcano is one that is erupting or has shown signs that it may erupt in the near future. • A dormant, or sleeping, volcano is a volcano that scientists expect to awaken in the future and become active. • An extinct, or dead, volcano is a volcano that is unlikely to ever erupt again. • Hot-spot volcanoes may become extinct once they drift away from the hot spot
Geologist use special instruments to detect changes in the volcanoes. • For example: • Tiltmeter- detects slight surface changes in elevation and tilt caused by magma moving ground. • Geologist also monitor: gases escaping from the volcano, small earthquakes before eruption, and rising temperatures in underground water.
Fig. 5. Volcanic Eruptions pg. 206 • Cascade Volcanoes • The Cascade volcanoes have formed as the Juan de Fuca plate sinks beneath the North American plate. • Circle the 3 volcanoes that appear to be the most active. • _________________________________________________________________ • 2. Why migh geologists still consider Mount Jefferson to be an active volcano? • _________________________________________________________________________________________________________________
Volcanic Eruptions pg. 207 Magma at Mount Rainier Mt. Rainier Mount Rainier is part of the Cascade volcanoes. All past eruptions of Mount Rainier have included ash and lava.