Main Types of Plate Boundaries

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Convergent Boundaries

Ocean to Ocean: This is where two oceanic plates collide with each other, causing usually the older plate (since it has higher density) to sink under the younger, less dense plate. Due to the disappearance of the older plate, a trench will appear at the place where the plate was pushed, into the mantle. As the older plate is travelling lower in the mantle, the plate begins to heat over time. Eventually the plate is melted. This leads to a line of volcanoes growing on the upper ocean plate, forming an island arc.

Ocean to Continental: When a continental plate and an oceanic plate collide with each other, the oceanic plate will sink under the continental plate, and into the mantle. A trench will soon appear to takes its spot in its absence. By the time the oceanic plate is in the mantle, it has melted. This creates volcanoes up on the continental crust.

Continental to Continental: This is an interesting case, for continental plates are too buoyant. This means if two continental plates collide with each other, they both go up. This would lead to a mountain forming. Due to its thick crust, magma can't penetrate it. Therefore, there are usually no volcanoes forming from this, although many earthquakes happen from this.

Divergent Boundaries

  • Ridge (Ocean) - When a divergent boundary happens under an oceanic lithosphere. The convection currents underneath the lithosphere, soon it lifts up the lithosphere, creating a mid-ocean ridge. This soon stretches the lithosphere and creates a deep fissure. If the fissure opens, pressure is reduced in the heated mantle. It responds by melting and new magma flows into the fissure. Soon the magma solidifies, and these steps are repeated many times.

  • Rift (Land) - This is where a divergent boundary occurs right under a continental lithosphere. It pushes the lithosphere upward. This causes faults to form on both sides of the rift. During this process, water flow into the rift-valley to form a lake. The rift could grow deeper and wider from this. If this keeps continuing, the rift could drop down to sea-level, and ocean water could flow in. A new ocean basin could be created!

Transform Boundaries

This type of plate boundary doesn't destroy plates nor create any plates. However, these boundaries are locations where two plates slide past each other.
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