Divergent Boundaries
A divergent boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which eventually become rift valleys. Most active divergent plate boundaries occur between oceanic plates and exist as mid-oceanic ridges. Divergent boundaries also form volcanic islands which occur when the plates move apart to produce gaps which molten lava rises to fill.
Transform Boundaries
A transform boundary is a type of fault whose relative motion is predominantly horizontal in either sinistral or dextral direction. Transform boundaries end abruptly and are connected on both ends to other faults, ridges, or subduction zones. While most are hidden in the deep oceans where they form a series of short zigzags accommodating seafloor spreading, the best-known (and most destructive) are those on land at the margins of tectonic plates.
Convergent Boundaries
A convergent boundary is an actively deforming region where two (or more) tectonic plates or fragments of the lithosphere move toward one another and collide. As a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent boundaries. When two plates move towards one another, they form either a subduction zone or a continental collision. In a subduction zone, the subducting plate moves beneath the other plate, which can be made of either oceanic or continental crust. During collisions between two continental plates, large mountain ranges, such as the Himalayas are formed.
Undefined Boundaries
Undefined boundaries refer to plate boundary zones that are made up of multiple fragmented plates or "micro-plates" that lay between major plates. Due to the amount of plate fragmentation in these areas the geological structure of those areas and their earthquake patterns are very complex and difficult to define. For more information on plate boundaries see Wikipedia
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