Volcanoes and Igneous Activity Earth - Chapter 4

Volcanoes and Igneous Activity Earth - Chapter 4

Volcanism 2012 Pearson Education, Inc. Volcanism

Eruptive Style Volcanic Materials Volcanoes Other Volcanic Landforms Plate Tectonics and Igneous Activity 2012 Pearson Education, Inc.

Eruptive Style Explosive Effusive 2012 Pearson Education, Inc. Eruptive Style

Why do volcanoes have different eruptive styles? Pressure vs. resistance 2012 Pearson Education, Inc. Eruptive Style A volcano is like a giant pop can thats been shaken up

Pressure builds up When pressure is released, material is pushed out 2012 Pearson Education, Inc. Eruptive Style Pressure comes from gases dissolved in magma within the volcano

Mostly water vapor and carbon dioxide When magma rises toward vent, gases come out of solution and expand 2012 Pearson Education, Inc. Eruptive Style Resistance to this pressure comes from magmas viscosity

Viscosity = resistance to flow (thickness or stickiness) Higher viscosity = thicker, more resistant 2012 Pearson Education, Inc. Eruptive Style Explosive eruptions High-viscosity magma

resists gas pressure Effusive eruptions Low-viscosity magma offers little resistance 2012 Pearson Education, Inc. Eruptive Style Why are some magmas more viscous than

others? Temperature Silica content Silica = silicon and oxygen dissolved in magma 2012 Pearson Education, Inc. Eruptive Style Why are some magmas more viscous than

others? Temperature Hotter = less viscous (runnier) 2012 Pearson Education, Inc. Eruptive Style Why are some magmas more viscous than others?

Silica content More silica = more viscous (thicker) 2012 Pearson Education, Inc. Eruptive Style This volcano is fed by high-silica, low-temp magmas with high

viscosity This ones magma is low-silica and high-temp, and low viscosity 2012 Pearson Education, Inc. Eruptive Materials

2012 Pearson Education, Inc. Eruptive Materials Lava Aa lava flow Pahoehoe lava flow

2012 Pearson Education, Inc. Eruptive Materials Gases Water vapor Carbon dioxide Smaller amounts of other gases

2012 Pearson Education, Inc. Eruptive Materials Pyroclastics

Ash and dust fine, glassy fragments Lapilli walnut-sized material Cinders pea-sized material Blocks hardened or cooled lava Bombs ejected as hot lava 2012 Pearson Education, Inc.

Eruptive Materials Pyroclastic flow Hot, fast-moving cloud of pyroclastic material 2012 Pearson Education, Inc. Eruptive Materials Lahar

Volcanic mudflow Mixture of water, soil, and ash Triggered by melting of snow during eruption 2012 Pearson Education, Inc. Eruptive Materials Three Japanese lahars

2012 Pearson Education, Inc. Volcanoes 2012 Pearson Education, Inc. Volcanoes Shield volcanoes Largest type

Dome-shaped Effusive eruptions Much lava, few pyroclastics 2012 Pearson Education, Inc. Volcanoes Mauna Kea, a Hawaiian shield volcano

2012 Pearson Education, Inc. Volcanoes Composite cones Smaller than shield volcanoes Classic volcano shape Explosive eruptions Much pyroclastic material, little lava

2012 Pearson Education, Inc. Volcanoes Mt. Fuji, a composite cone in Japan 2012 Pearson Education, Inc. A Composite Volcano

Interbedded pyroclastic deposits and small lava flows 2012 Pearson Education, Inc. Figure 4.11 Volcanoes Cinder cones

Smallest type Loose pyroclastic materials 2012 Pearson Education, Inc. A Size Comparison of the Three Types of Volcanoes Figure 4.14

2012 Pearson Education, Inc. Other Volcanic Landforms 2012 Pearson Education, Inc. Other Volcanic Landforms Calderas

Pits caused by magma chamber collapse Three types Hawaiian-type Crater Lake-type Yellowstone-type 2012 Pearson Education, Inc. Other Volcanic Landforms

Hawaiian-type calderas On shield volcanoes Olympus Mons Kilauea 2012 Pearson Education, Inc. Other Volcanic Landforms Crater Laketype calderas

Catastrophic eruptions 2012 Pearson Education, Inc. Other Volcanic Landforms Yellowstone-type calderas Largest

2012 Pearson Education, Inc. Caldera outline (diameter approx. 30 mi) Other Volcanic Landforms Basalt plateaus Very large, flat areas covered with basalt

Outpourings of low-viscosity lavas from fissure eruptions 2012 Pearson Education, Inc. Other Volcanic Landforms Fissure eruption in Hawaii

Basalt plateau in Washington 2012 Pearson Education, Inc. Plate Tectonics & Igneous Activity 2012 Pearson Education, Inc.

Plate Tectonics & Igneous Activity Most volcanism occurs along tectonic plate boundaries Divergent boundaries: decompression melting Subduction zones: hydration melting 2012 Pearson Education, Inc.

Plate Tectonics & Igneous Activity The Ring of Fire is a chain of active volcanoes around the Pacific Ocean. It marks the boundaries of tectonic plates. 2012 Pearson Education, Inc. Plate Tectonics & Igneous Activity Hot spot (intraplate) volcanism

Not near plate boundaries Fed by magma reservoirs beneath the crust 2012 Pearson Education, Inc. Plate Tectonics & Igneous Activity Hawaiian Islands were formed by hot spot volcanism

North Kauai 5.1 my Oahu 3.7 my

Molokai 1.9 my Maui 1.3 my Hawaii (Big Island) < 1 million yrs old 2012 Pearson Education, Inc.

Plate Tectonics & Igneous Activity Hot spot animation 2012 Pearson Education, Inc. End of Chapter 6

2012 Pearson Education, Inc.

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