Tectonic Landscapes: Hotspots Some volcanoes do not occur on plate boundaries. These volcanoes are formed over hotspots.

A hot spot occurs because of the intense heat of the outer core A hot spot occurs because of the intense heat of the outer core. This heat radiates through the mantle bringing hot solid rock upward to the hot spot. These areas of rising solid rock are called mantle plumes. Because of lower pressure in the upper region of the mantle the rock begins to melt. This forms magma which rises through the mantle until it reaches the surface, causes the crust to dome and crack, forming a volcano.

Case study: The Hawaiian Islands, which are entirely of volcanic origin, have formed in the middle of the Pacific Ocean more than 3,200 km from the nearest plate boundary. The Hawaiian Islands are located over a hotspot. The magma rises through the Pacific Plate to supply the active volcanoes.

As the plate moves over the stationary hotspot, new volcanoes are formed.

Why are volcanoes located over a hot spot progressively older and eroded? The Hawaiian volcanoes are progressively older and increasingly eroded the further they are from the hotspot as they were once located above the stationary hot spot but were carried away as the Pacific Plate drifted to the northwest.

4. 6 million years ago there was only one island in this group 4.6 million years ago there was only one island in this group. As the Pacific plate moved slowly northwesterly it produced the Hawaiian Islands, one at a time. Today the big island of Hawaii sits over the same hot spot that produced the other islands. http://volcano.oregonstate.edu/hot-spot-volcanoes-hawaii-and-yellowstone-lesson-9

2 Questions for next Tuesday 1- Explain how volcanoes form over hotspots. Use an annotated diagram or diagrams in your answer. (4)

Booklet page 39