1. Volcanoes

2. A Volcano is…
An opening in Earth’s crust through which molten rock, gases, and ash erupt.
Also, the landform that develops around this opening.
**Click on picture
to watch a video.

3. Where Volcanoes Form Hot Spots
Volcanic Eruptions occur when magma rises to the surface. This will happen when the asthenosphere melts enough to flow.
Most volcanoes occur at:
CONVERGENT boundaries that have SUBDUCTION.
DIVERGENT boundaries
Hot Spots

4. Volcanoes at Convergent Boundaries (Subduction)
2 plates collide – the denser oceanic plate subducts (pushed under) the continental plate
As the denser oceanic crust is pushed lower, it melts into magma.
When continental and oceanic plates converge, a volcano forms on land.
Example: Ring of Fire – Pacific Plate
When 2 oceanic plates converge together, a volcano forms an island.
Click on picture to watch a video of volcanoes forming at convergent boundaries.

5. Volcano- Convergent
Sibayak, Indonesia
Mt St. Helens

6. Volcanoes at Divergent Boundaries
Plates moving apart – large cracks formed – magma fills cracks = FISSURES
These fissure volcanoes are located at the Mid-Atlantic Ridge and the Great African Rift Valley
Click on diagram to watch a video on formation of Mid-Atlantic Ridge.

7. Divergent- Great Rift Valley

8. Hot Spots
Sometimes, volcanoes occur at places that aren’t plate boundaries.
We call these HOT SPOTS.
Hot spots are areas where hot magma rises from deep in Earth’s mantle = MANTLE PLUMES
Magma escapes where the crust is the thinnest or weakest.
It breaks through the crust and forms a volcano
These islands continue to form above the ocean floor.
The Pacific Plate moving over a hot spot in Earth.
Some of these volcanoes are dormant. Some islands are still being created.

9. Example of Hot Spot
Hawaii is made up entirely of volcanoes from the hot spot under the Pacific Plate.
Click on diagram to see a video about the formation of Hawaiian Islands over a Hot Spot.