As tectonic plates grind against each other, several key geologic events occur depending on the type of plate boundary involved:
- At convergent boundaries , where plates move toward each other, one plate may be forced beneath another in a process called subduction. This leads to the formation of deep ocean trenches and intense earthquake activity along the subduction zone. As the subducted plate descends, it releases water into the overlying mantle, lowering its melting point and generating magma. This magma rises to form volcanic arcs, such as island chains or continental volcanic mountain ranges (e.g., the Andes or the Cascades). When two continental plates collide, they compress and uplift the crust, creating large mountain ranges like the Himalayas
- At divergent boundaries , where plates move apart, magma rises from the mantle to fill the gap, forming new crust. This process creates mid-ocean ridges and underwater mountain ranges. Earthquakes and volcanic activity occur but are generally less violent than at convergent boundaries. On continents, divergent boundaries can form rift valleys and eventually new ocean basins as the crust thins and splits
- At transform boundaries , plates slide horizontally past each other. The friction and locking between rough plate edges cause stress to build up, which is released as earthquakes when the plates suddenly slip. These boundaries do not create or destroy crust but are characterized by frequent seismic activity along faults, such as the San Andreas Fault in California
In summary, as plates grind against each other, the geologic events include earthquakes, volcanic eruptions, mountain building, formation of ocean trenches, rift valleys, and creation of new crust, all depending on whether the boundary is convergent, divergent, or transform
