Alex Young & Filmon Sissay Hotspots Image above showing a hotspot forming an island in the Hawaiian-Emperor chain Alex Young & Filmon Sissay

What is it? Most volcanoes occur near the Earth's plate boundaries, but some do not. For example, the Hawaiian islands have been formed over millions of years by volcanic eruptions thousands of miles from the edges of the Pacific plate. Island formation is still happening on Hawaii every time the shield volcanoes Kilauea and Mauna Loa erupt. The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be unanimously hot, and provide a great deal of molten magma. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them. One suggests that they are due to hot mantle plumes that rise as thermal diapirs from the core-mantle boundary. The other hypothesis claims that it is not high temperature that causes the volcanism, but lithospheric extension that permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, proclaiming that the mantle source beneath them is, in fact, not anomalously hot at all. Well known examples include Hawaii and Yellowstone.

Yellowstone When considering the Yellowstone super volcano, one of, if not the largest super volcano in the World, the effects could be catastrophic and change the face of the planet as we know it.  Currently, there are 3,000 earthquakes in the area each year and along with various other changes, it has led scientists to worry that an eruption could occur soon, although this is very unlikely.  An eruption in the next couple of centuries is not expected. 

Continued Yellowstone has approximately 10,000 thermal features, with 200 to 250 geysers erupting each year, making it the place with the highest concentration of active geysers in the world, due to its location in ancient caldera. Norris Geyser Basin is the hottest geyser basin in the park and is located near the northwest edge of Yellowstone Caldera on the intersection of three major faults. Some of the effects are predicted to be: •10,000km3 of land erupted •25 mile high ash cloud •Everything within a 100 mile radius of the eruption will be destroyed •The ash in the atmosphere could lower global temperatures by 20°C •1,000 miles away, the layer of ash that will be deposited on the ground will be up to 10ft thick •Two thirds of the USA will be uninhabitable •87,000 could be killed •1 in 3 people affected would die •Huge impact on transport, energy, electricity, agriculture, and general production •The UK would receive the ash cloud 5 days after the eruption •The global economy will be placed under huge pressure and likely collapse due to the damage to the USA This is a worst case scenario but if and when the volcano erupts, the effects will be considerable.

Hawaii Hawaii is geologically a unique place on Earth because it is caused by a 'hot spot.' Most islands are found at tectonic plate boundaries either from spreading centers (like Iceland) or from subduction zones (like the Aleutian Islands). There are few 'hot spots' on Earth and the one under Hawaii is right in the middle of one of the largest crustal plates on Earth - the Pacific Plate. A geologic 'hot spot' is an area in the middle of a crustal plate where volcanism occurs. It is easy to geologically explain the volcanism at plate spreading centers and subduction zones but not as easy to explain a 'hot spot.' The molten magma breaks through the crustal plate (theories describe this as either from a weak/thin part of the plate or a particularly hot part of the molten magma). A hot spot under the American plate is why Yellowstone National Park has geysers and other thermal features. If the hot spot is under the seafloor (as it is in Hawaii) it produces undersea volcanoes. Some of these volcanoes build up to the surface of the ocean and become islands. Over millions of years the plate may move across the 'hot spot' and the original volcano become extinct but a new volcano will begin to form in the area of the 'hot spot.'

Continued The northwest moving Pacific Plate has moved across the 'hot spot' that created the Hawaiian Islands for millions of years. This movement has left the northwest trending island chain (of over 20 islands and atolls) we call Hawaii. As islands move northwest, away from the 'hot spot,' they begin to erode and become volcanically inactive. Over time the island may erode so much it is no longer an island but an underwater seamount. Kauai is the oldest of the main Hawaiian Islands now, having formed some 5 million years ago, with its volcano considered to be extinct and fully in the process of erosion. Oahu is next, its volcanism is considered to be inactive. Then Maui with its Haleakala crater that could still come to life one more time. And the youngest island is the 'Big Island' of Hawaii itself, with surface lavas all less than one million years old. It still has active volcanism. On the seafloor 20 miles to the southeast of Hawaii is an active volcanic area with periodic eruptions. This area is called Loihi and will be the site of the next Hawaiian Island if geologic processes continue as they have for millions of years but it may be over 10,000 years before this happens.

How super volcanoes are formed at a hotspot Super volcanoes are much more bigger than an ordinary volcano. They develop in a small amount of place around the world. At destructive margins or over parts of the mantle that are really hot are called hotspots. E.g. Yellowstone National Park in USA is on a top of a supervolcano. They are formed at destructive plate margins. Magma rises through the cracks in the crust to form a large magma basin below the surface. The pressure of the magma causes a circular bulge on the surface several kilometres wide. The bulge eventually cracks, creating vents for lava to escape through. When the lava is erupted the magma basin empties and the bulge is no longer supported so it collapses spiting or spewing up more lava. When the eruption is done there is a big crater called caldera. This is left when the bulge collapses. Sometimes this gets filled with water forming a lake. E.g. Lake Toba Indonesia.

Classifications of volcano Volcanoes are classified as extinct, dormant, or active. An extinct volcano is a volcano that is not now erupting and is not likely to erupt in the future. Kohala, shown above, has not erupted for 60,000 years and will probably not erupt again. A dormant volcano is a volcano that is not now erupting but has erupted in historic time, since written records were kept (the last 200 years in Hawaii), and is likely to do so in the future. Mauna Kea has not erupted in historic time but is expected to erupt again in the future. There is no precise distinction between an active and dormant volcano. Because some volcanoes remain inactive for thousands of years between eruptions, it can be difficult to distinguish between an active and a dormant volcano. Volcanologists at the Smithsonian Institution estimate that 1,500 volcanoes worldwide have the potential of erupting. An active volcano is a volcano that is erupting or is expected to do so in the near future. Kilauea volcano has erupted from its summit and side 63 times since 1790. Kilauea has been erupting continuously since January 3, 1983.

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