Chapter 10 Volcanoes and other Igneous Activity

Transcription

1 Chapter 10 Volcanoes and other Igneous Activity Section 10.1 Volcanoes and Plate Tectonics Origin of Magma forms in the crust and upper mantle when solid rock partially melts. The formation of magma depends on several factors, including heat, pressure, and water content. occurs when rock rises and melts due to reduced pressure. wet rock melts faster than dry rock Volcanoes and Plate Boundaries Most volcanoes form along and plate boundaries. Some volcanoes form far from plate boundaries above in the crust. as plates pull apart magma rises to fill the gap in rift valleys. Most are found at mid-ocean ridges, but some are found on the continents. The Great Rift Valley in Africa is an example Volcanoes and Plate Boundaries - Convergent occurs where plates collide and one plate subducts (goes under) another plate. There are 2 types. 1. the oceanic crust is more dense and underneath the continent. This creates an ocean trench and a subduction zone. As the oceanic crust melts back into the mantle, magma rises creating inland volcanoes on the continent. The Cascades of California, Oregon, and Washington are and example. -the area on Earth that has the most earthquakes and volcanoes. It is an area of subducting plate boundaries, where the Pacific Plate is moving under the neighboring continental and oceanic plates. The Cascade Mountain Range of the Western United States is a part of the Ring of Fire.

2 2. with another oceanic crust. One plate will be denser than the other and subduct beneath. This creates a very deep, and when the plate melts back into the mantle magma raises upward and creates an island arc of volcanoes. The Aleutian Islands of Alaska are an example. Intraplate Volcanism: Hot Spots weak area of the Earth s crust within a plate that allows magma to come to the surface in the form of a mantle plume. Examples in the United States include the Hawaiian Island chain and Yellowstone National Park. Section 10.2 The Nature of Volcanic Eruptions The primary factors that determine whether a volcano erupts explosively or quietly include characteristics of the and the amount of in the magma. the substance s resistance to flow; whether the magma is thick and sticky or thin and runny. The more silica in magma the greater the viscosity =. Factors Affecting Eruptions: Viscosity are very viscous (thick) because of their high silica content. They trap gases inside. This makes them erupt violently. Mostly found on the continents. are less viscous (thin) because of low silica content. They allow gas to be released easily. This allows them to erupt quietly. Mostly found in the oceans. Volcanic Material Depending on the type of eruption, volcanoes may produce lava flows or eject pyroclastic materials, or both. All volcanic eruptions also emit large amounts of gases. Basaltic lavas flow faster than Granitic lavas

3 faster moving basaltic lava that wrinkles and looks like twisted ropes Slower moving basaltic lava that forms a surface of rough, jagged blocks. Volcanoes release tremendous amounts of into the atmosphere. These gases include water vapor, carbon dioxide, nitrogen, sulfur, chlorine, hydrogen, and argon. Particles produced in volcanic eruptions are called. fine dust and ash carried by the wind (less than 2mm) cinders; small particles that range in size from small beads to walnuts. (2-64mm) Larger than 64mm and made of hardened lava. They can be as large as houses. Glowing lava that is ejected during the eruption. The outside crusts over in the air and they splatter when they make impact. Volcanoes opening through which lava flows out. repeated eruptions eventually build up a mountain. steep-walled depression at the top of the volcano, which contains the vent. Types of Volcanoes made of alternating basaltic lava flows. They are broad, gently sloping, tall, slightly domed structures. Ex. Hawaiian Islands made of loose pyroclastic material, such as ash and lapilli. They are relatively small compared to other volcanoes.

4 also called stratovolcanoes. Most dangerous volcanoes on Earth. Made of both layers of lava and pyroclastic material. Most are found in the Pacific Ring of Fire. Generate explosive eruptions due to trapped gases. Mt. Fuji in Japan >>>>>>> Volcanic Landforms: depression in a volcanic mountain caused by a collapse of the crater. Crater Lake in Oregon is a caldera caused by the eruption of Mt. Mazama. Wizard Island is the cone forming in the lake. a landform made of magma that hardened inside a volcano and was later exposed by weathering and erosion. Ship Rock, New Mexico and Devils Tower, Wyoming are examples Volcanic Hazards superheated volcanic particles and gases moving hundreds of miles per hour down the slopes of a volcano. mudflows that happen when water-soaked volcanic ash and rock slide rapidly downhill. Ice and snow melted by an eruption can trigger a. Section 10.3 Intrusive Igneous Activity the structures that result from the cooling and hardening of magma beneath Earth s surface. Types of Plutons: a pluton that forms when magma flows between parallel layers of sedimentary rock.

5 also forms between parallel layers of sedimentary rock. Laccoliths are lens-shaped which pushes up the overlying rocks. They can make dome mountains. a pluton that forms when magma moves into fractures that cut across rock layers. larger than a pluton, a large body of intrusive igneous rock that has a surface exposure of more than 100 square kilometers.