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Chapter 3: Volcanoes. Chapter 3.1. Key Concepts: Where are Earth’s volcanoes found? How do hot spot volcanoes form?. Definitions:. Volcano: a weak spot in the Earth’s crust where molten material (magma) comes to the surface
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Chapter 3.1 • Key Concepts: • Where are Earth’s volcanoes found? • How do hot spot volcanoes form?
Definitions: • Volcano: a weak spot in the Earth’s crust where molten material (magma) comes to the surface • Magma: a molten mixture of rock forming substances, gases and water from the earth’s mantle. • Lava: when magma reaches the Earth’s surface.
Volcanoes & Plate Boundaries • 600 active volcanoes on land, many more under the sea. • Volcanoes occur in belts that extend across continents and oceans. • Ring of Fire- major volcanic belt formed by the many volcanoes that rim the Pacific Ocean.
Volcanic belts form along the boundaries of the Earth’s plates • Diverging ( )and converging ()occur. • Results in fractures in the Earth’s crust • Magma reaches the surface.
Divergent Boundaries Mid Ocean Ridge Convergent boundary Points of subduction ex. Mount Etna – Eurasian and African plates Most volcanoes occur at
Volcanoes on Divergent Boundaries • Under ocean: point of Mid ocean ridges occurring ( long underwater mountain ranges) • Many have rift valleys down the center • Lava pours out of rift valley – creates new mountains. • Land - Great Rift Valley in East Africa
Volcanoes on Convergent Boundaries • Volcanoes form when: • Two oceanic plates collide • Oceanic and continental plates collide • In both situations, oceanic plates sink beneath a trench. • Rock above the plate melts to form magma. • Erupts to the surface as lava
Volcanoes on Convergent Boundaries • Magma – less dense than the surrounding rock • Magma rises to the surface and breaks through the ocean floor creating volcanoes. • String of islands formed: Island arc • Examples: Japan, New Zealand, Indonesia, the Philippines
Hot Spot Volcanoes • Hot Spot – an area where material from deep within the mantle rises and melts forming magma • Volcanoes form above a hot spot when magma erupts through the crust and reaches the surface.
Hot Spot Volcanoes • Some hot spots lie in the middle of plates far from plate boundaries. • Others occur on or near plate boundaries.
Hot Spot Volcanoes • A hot spot in the ocean floor can gradually form a series of volcanic mountains • Ex. The Hawaiian islands
Hot Spot Volcanoes • A hot spot can also form under continents • Ex. Yellowstone National Park, WY