Chp 18.3 Notes TYPES OF VOLCANOES & WHERE THEY OCCUR Main Idea 1: Not all volcanoes are built the same. A volcano’s shape is determined largely by: 1. magma’s viscosity 2. force of any eruptions 3. amount of weathering

Composite Volcano Describe: Large, symmetric volcano with sharp peaks, & violent eruptions. Magma: Very viscous Eruption: Can be slow seeping or violent explosions.

Shield Volcano Describe: have gradual slopes & peaceful eruptions Magma: Not very viscous Eruption: Travels a long distance.

Kilauea Shield Volcano

Cinder Cone Volcano Describe: small volcano with steep slopes and a hole at top made of cinders

Caldera Describe: A depression that forms when a volcano collapses on itself.

Lava Dome Describe: volcano that forms from very viscous magma at the peak of another volcano. Lava domes can act like a cork and can eventually result in explosive pyroclastic flows. Magma type: Very viscous (thick & resistant to Flow) Mount St. Helens

Main Idea 2: Volcanoes occur in specific regions of Earth. Subduction Zone Volcano: Describe: where oceanic crust is Pushing under continental crust. Magma/Eruption: Very viscous & can lead to violent eruptions. Examples: Ring of Fire around Pacific Rim where magma comes rising from mantle. Mt. Pinatubo, AK Aleutian Chain are examples

Rift-Zone Volcano: Where 2 plates are diverging, spreading apart, at an ocean ridge or in the middle of a continent. example: African Rift Valley.

Hot Spot Volcano: Where magma rises through a thin portion of the crust. Example: Most famous example is Hawaiian Islands. the hot spot stays in same place & ocean crust keeps moving, so there is a chain of islands.