Chapter TWELEVE Volcanoes

If green dots are earthquakes and red triangles are volcanoes, What are two things that you notice about their locations?? 2

Section 1: Volcanoes and Earth’s Moving Plates What Are Volcanoes? A volcano is an opening in Earth that erupts gases, ash and lava. Volcanic mountains form when layers of lava, ash and other material build up around these openings.

Section 1: Volcanoes and Earth’s Moving Plates What Are Volcanoes? Kilauea (kee low AY ah), located in Hawaii, is the world's most active volcano. The most recent series of eruptions began in 1983 and still continues.

Section 1: Volcanoes and Earth’s Moving Plates How Do Volcanoes Form? Magma is forced upward because it is less dense than the rock around it. After many thousands or even millions of years, magma reaches Earth's surfaces and flows out through an opening called a vent.

Section 1: Volcanoes and Earth’s Moving Plates How Do Volcanoes Form? As lava flows out, it cools quickly and becomes solid, forming layers of igneous rock around the vent. The steep walled depression around a volcano's vent is called a crater.

Section 1: Volcanoes and Earth’s Moving Plates Where Do Volcanoes Occur? Divergent Plate Boundaries The mid-Atlantic ridge is an area where the plates are moving apart. When plates separate, they form long, deep cracks called rifts. Lava flows from these rifts and is cooled quickly by sea water.

Section 1: Volcanoes and Earth’s Moving Plates Where Do Volcanoes Occur? Sometimes, the volcanoes and rift eruptions rise above sea level, forming new islands such as Iceland. In 1963, the new island Surtsey was formed during a volcanic eruption.

Section 1: Volcanoes and Earth’s Moving Plates Where Do Volcanoes Occur? Convergent Plate Boundaries Forms volcanoes where an oceanic plate slides below a continental plate. Magma forms when the plate sliding below another plate gets deep enough and hot enough to melt partially and the magma is then forced upward to the surface. Volcanoes that form at convergent plate boundaries erupt more violently than other volcanoes do.

Section 1: Volcanoes and Earth’s Moving Plates Where Do Volcanoes Occur? Hot spots Form when areas between the Earth's mantle and core are unusually hot and rock at these areas is forced toward the crust where it melts partially. Magma breaks through the crust to form several volcanoes. Not at a plate boundary Formed Hawaiian islands

Section 2: Types of Volcanoes What Controls Eruptions? Trapped gases like water vapor and carbon dioxide build up in volcanoes. If the gas escapes easily, it is a quiet eruption. If gas and water vapor build up, eruptions can be explosive

Section 2: Types of Volcanoes Composition of Magma Quiet eruptions: magma that is low in silica and is basaltic. Has lava that pours from volcanic vents and runs down the sides of a volcano

Section 2: Types of Volcanoes Composition of Magma Explosive eruptions: magma that is high in silica and is andesitic. Has magma that is thick and when pressure builds up an explosion occurs. It often carries pieces of lava.

Section 2: Types of Volcanoes Forms of Volcanoes Shield Volcano Broad, gently sloping volcano formed by quiet eruptions of basaltic lava. The basaltic lava flows over Earth's surface covering large areas with deposits of basaltic igneous rocks when it cools.

Section 2: Types of Volcanoes Forms of Volcanoes Shield Volcano Accounts for the greatest volume of erupted volcanic material. Much of the new seafloor that originates at the mid- ocean ridge forms as underwater flood basalts.

Section 2: Types of Volcanoes Forms of Volcanoes Cinder Cone Volcano Steep-sided, loosely packed volcano formed when tephra falls to the ground. Tephra: bits of rock or solidified lava dropped from the air after an explosive eruption. Vary in sizes from volcanic ash, cinders, large rocks and blocks.

Section 2: Types of Volcanoes Forms of Volcanoes Composite Volcano Volcano built by alternating explosive and quiet eruptions that produce layers of tephra and lava. Found mostly where Earth's plates come together and one plate sinks below the other.

Section 3: Igneous Rock Features Intrusive Features Batholiths: large intrusive rock body that forms when magma being forced upward toward Earth's crust cools slowly and solidifies underground. Dikes: magma that is forced into a crack that cuts across rock layers and hardens. Sills: magma that is forced into a crack parallel to rock layers and hardens.

Section 3: Igneous Rock Features Forms of Volcanoes

Section 3: Igneous Rock Features Other Features Volcanic neck: solid igneous core of a volcano left behind after the softer cone has been eroded. When a volcano stops erupting, the magma hardens inside the vent. Erosion, usually by water and wind, begins to wear away at the volcano.

Section 3: Igneous Rock Features Other Features Caldera: large circular-shaped opening formed when the top of a volcano collapses. Crater Lake in OR is a caldera that filled with water and is now a lake.

Section 3: Igneous Rock Features Effects of Eruptions Examples of destruction: Lava flows destroy everything in their path. Falling volcanic ash can collapse buildings, block roads and can cause lung disease in people and animals. Volcanic ash and debris rush down the side of a volcano: pyroclastic flow.

Section 3: Igneous Rock Features Effects of Eruptions Examples of destruction: Temperature inside a pyroclastic flow can be high enough to ignite wood. Sulfurous gases from volcanoes can mix with water vapor in the atmosphere to form acid rain.

In your notes, create a diagram of a volcano In your notes, create a diagram of a volcano. It must include the following features (with correct lables): Ash cloud Pyroclastic flow Tephra Layers of ash Layers of lava Crater Main vent Dike Sill Magma chamber