1) What is a hotspot?
A volcanic "hotspot" is an area in the upper mantle from which heat rises in a plume from deep in the Earth. High heat and lower pressure at the base of the mantle facilitates melting of the rock. This melt, called magma, rises through cracks to the surface and forms volcanoes. As the tectonic plate moves over the stationary hot spot, the volcanoes are rafted away and new ones form in their place. This results in chains of volcanoes, such as the Hawaiian Islands.
To see history of just one island, visit: http://www.youtube.com/watch?v=t5go-78gCJU
Animation by Jenda Johnson, Earth Sciences Animated
Narrated by Roger Groom, Mt. Taber Middle School
Edited by Anita Grunder and Don Swanson
More animations: http://www.iris.edu/hq/inclass/search/animation