In the theory of plate tectonics most of the geological characteristics are explained in consequence of tension among plates. However, some of most spectacular formations are caused by "hot spots" which are situated far from the edges of tectonic plates.
Hot spots are fixed places within the mantle or oceanic lithosphere, where rocks melt to generate
magma. When a hot spot is situated in the oceanic lithosphere a class of volcanoes known as shield volcanoes is built. These are constructed on the deep ocean floor and may be build high enough to rise above sea level as volcanic islands. The Hawaiian hot spot, for example, has been active at least 70 million years, producing a volcanic chain (of shield volcanoes)
that extends 3,750 miles (6000 km) across the northwest Pacific Ocean.
Another one, the Yellowstone hot spot has been active for at least 15 million years, producing a chain of calderas and other volcanic features along the Snake River Plain (US) that extends 400 miles (650 km)
westward from northwest Wyoming to the Idaho-Oregon border.
Where a hot spot lies beneath a continental plate the hot spot may generate enormous volumes of lava that accumulate layer upon layer. Thousands of square kilometers may be covered, these accumulations are called flood basalts.
An important example of a flood basalt is found in the Columbia Plateau region of southeastern Washington, northeastern Oregon and westernmost Idaho; about 130000 sq. km is covered by flood basalts, this is the same area as the state of New York!