Stationary crustal weaknesses.

1. HOT SPOTS

2. HOT SPOT - A thermal anomaly within Earth's mantle, generally consisting of a hot, rising plume of mantle material that generates volcanism- or increased volcanism- on Earth's surface. Hotspots are aptly named- they are spots of the Earth that are hot. They are spots because they are limited in area- no more than a few hundred kilometers in diameter at the largest. They are hot because their temperature is hotter (generally by 100-200 degrees C) than the ambient, surrounding mantle. Although they produce volcanism in Earth's crust, hotspots are really features of Earth's mantle. Hotspots are likely- at least in the case of the largest ones such as Hawaii and Iceland- plumes of hot, rising material that originate in the lower mantle, perhaps even as deep as the core-mantle boundary. Hotspots are almost stationary features in the mantle. There is evidence that hotspots can drift extremely slowly in the mantle, but hotspots are essentially stationary relative to the faster-moving tectonic plates. As a tectonic plate moves over a mantle hotspot, a chain of volcanoes is produced. The most famous of these chains is the Hawaiian Islands & Emperor Seamounts in the Pacific Ocean. These islands and seamounts are age progressive. The youngest island, Hawaii, is volcanically active and is where the crust is currently located over the hotspot. As the crust moves, another island will eventually form- in fact, one is forming underwater now, and it is named Loihi! Behind the main island of Hawaii, there are other, older islands that are not currently volcanically active. Beyond the islands, there is a long chain of underwater seamounts- these seamounts used to be subaerial islands but because of subsidence and erosion they are now underwater hotspot remnants.

3. YELLOWSTONE HOT SPOT Hot Spots occur on continents, too!

4. Yellowstone is actually a Caldera, or the crater that is left behind when a volcano erupts. ...and it’s on the move. Notice how the calderas follow the Snake River Valley in Idaho.

5. ICELAND is a Hot Spot, too! The Hot Spot is located on the eastern side of the island while the mid-Atlantic ridge runs through the island. The easter side of the island is part of the Eurasian plate while the western side is part of the North American plate.