Volcanoes

The Aleutian Islands are a volcanic island arc. Which statement explains how the Aleutian Islands formed?

• A. Earthquakes at the boundary of the Pacific and North American Plates formed the Aleutian Islands.

• B. Subduction of the Pacific Plate beneath the North American Plate formed the Aleutian Islands.

• C. Divergence of the Pacific and North American Plates formed the Aleutian Islands.

• D. Horizontal movement of the Pacific and North American Plates in opposite directions formed the Aleutian Islands.

Very large volcanoes that form due to increased pressure and magma build up over time and that have had an eruption with a VEI (Volcanic Explosivity Index) of 8 are classified as:

• Hot spots

• Normal volcanoes

• Supervolcanoes

• All types of volcanoes

Based on the information in the table, which of the following volcanoes is most likely classified as a supervolcano?

• Mount Etna

• Yellowstone

• Kilauea

• Mount Fuji

The Hawaiian Islands formed over a ___________, which is a relatively fixed location in the mantle where the magma is much ____________ than the surrounding magma.

• convergent boundary; colder

• hot spot; hotter
• divergent boundary; hotter
• reverse fault; colder

Look at the image. Describe two differences between a volcano that forms above a hot spot and a volcano that forms at a subduction boundary.

Answer explanation

Hot spots form when there is an area of the mantle with extra hot magma that erupts through the crust to form a volcano. Most other volcanoes form along the subduction zone of convergent plate boundaries. Hot spots often form in the middle of a plate, far away from plate boundaries, where most other volcanoes form.

The “Ring of Fire” describes volcanoes that are positioned in and around the Pacific Ocean Plate. The "Ring of Fire" is highlighted in the map. Use the map to construct an explanation describing how the volcanoes in the "Ring of Fire" formed and why volcanoes are likely to form in this region.

Answer explanation

Volcanoes form in the "Ring of Fire" because this is an area where oceanic and continental tectonic plates meet. When an oceanic plate and a continental plate collide, the oceanic plate (such as the Pacific Plate) subducts beneath the continental plate (such as the Indo-Australian Plate). When one plate subducts beneath another, magma rises and erupts, forming volcanoes.