When plate A collides with plate B, the outcome depends on the types of plates involved (continental or oceanic) and their densities:
- If plate A is an oceanic plate and plate B is a continental plate, the denser oceanic plate A is forced beneath the lighter continental plate B in a process called subduction. This creates a subduction zone, forming deep ocean trenches at the edge of the continent. As plate A sinks deeper, high heat and pressure release gases and water from the subducting plate, causing the mantle above to melt and form magma. This magma rises to the surface, leading to volcanic eruptions on plate B. Earthquakes and tsunamis can also occur due to the intense tectonic activity in this zone
- If both plates A and B are continental, neither is dense enough to be subducted. Instead, the collision causes the crust to buckle, fold, and thicken, pushing the land upward and forming mountain ranges such as the Himalayas. This process also generates earthquakes due to the intense stress and deformation at the collision boundary
- The collision causes crustal deformation, including folding, buckling, and sometimes breaking of the crustal material. Over time, this leads to significant topographical changes like mountain building and uplift
- The dynamics of the collision are influenced by factors such as plate velocity, subduction angle, and the strength of the crust. Slow convergence can cause strong coupling and dragging of lithospheric mantle, while faster convergence may trigger slab break-off and polarity reversals in subduction zones, intensifying deformation near the collision zone
In summary, when plate A collides with plate B, either subduction occurs if one plate is oceanic and denser, leading to trenches, volcanic activity, and earthquakes, or crustal collision and mountain building happen if both are continental plates, causing uplift and seismic activity due to crustal compression and deformation
