Three main types of boundaries exist between tectonic plates. The first, called a divergent boundary, occurs most often at mid-oceanic ridges. Here, two plates move away from each other, forming a break, or rift, in Earth's crust. Magma from the mantle rises to fill the gap, creating new crust.
Tectonic Plates, Earthquakes, and Volcanoes | Science | Interactive | ...
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