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 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 Earth’s plates

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.

Most volcanoes occur at Divergent Boundaries Mid Ocean Ridge Convergent boundary Points of subduction ex. Mount Etna – Eurasian and African plates

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

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