Plate boundaries

Tectonic plates can meet in three main ways, as indicated in the following Figure.

 

Figure 14.5: Plate boundaries

These three main types of boundaries are described below.

 
• Divergent boundaries: In such a boundary two plates are moving away from each other. An example of this is the Mid-Atlantic Ridge, where magma rises from deep within the Earth. This leads to an increase in volcanoes and earthquakes in the region.      
• Convergent boundaries: There are two main ways that two plates can converge. In a collision boundary, the two plates push almost equally against each other, buckling the material up in the middle. This leads to the formation of mountain ranges, such as the Himalayas and the Alps. In a subduction boundary, one plate slips beneath the other, leading to the formation of a deep trench. The Mariana Trench in the Pacific Ocean, which at 11 km is the deepest point in the world's oceans, is an example where this is occurring.  
• Transform boundaries: These occur when two plates slip past each other. This slipping however generally doesn't happen smoothly - because of friction the plates remain in place for a while, building up a kind of stored potential energy from the forces trying to move them, and then this energy is released suddenly when the forces become too large. This sudden release of energy results in an earthquake. A notable example of a transform boundary is the San Andreas fault in California.