They are all features associated with volcanic activity on Earth. Ridges form where tectonic plates move apart, e.g. the Mid-Atlantic ridge and Iceland. Trenches form in some cases where plates meet (The Marianas Trench off Japan's coast). Hot spots produce volcanic activity in areas far away from plate edges (such as the Hawaiian archipelago).What are ridges, trenches and hot spots?
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Ridges occur at divergent plate boundaries typically in the ocean they are referred to as MORs Mid Ocean Ridges. The two most famous being the Eastern Pacific Rise and the Mid Atlantic Ridge; both of these ridges are the result of two plates moving apart slowly and liquid hot magma rises up in the void thus creating new ocean crust (basalt). As the magma reaches the the ocean water it cools quickly and lithifies into basalt and builds up over time creating a ridge.
Trenches occur at areas of ocean-continent crust convergent plate boundaries. When two plates collide the more dense of the two (the ocean crust) will subduct below the continental crust. The area where the subduction is occurring is typically where the trench is located.
A hot spot occurs commonly with convergent plate boundaries like trenches. The crust being subducted is forced down and the geothermal gradient causes the crust to melt and a thermal plume is generated (a big bubble of magma) this rises up and heats the crust overlying it. The Hawaiian islands are an example of a plate migrating over a hot spot.
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