Earthquakes and volcanoes, also known as geohazards, are two examples of what can happen at a subduction zone. The geohazards are caused when an oceanic plate slides under a continental plate or another oceanic plate. This process is called subduction.
A subduction zone is a region where the process of subduction occurs. Many subduction zones are located around the edges of the Pacific Ocean. The relationship between those two plates is known as the megathrust, and is the cause of some of the largest earthquakes on Earth. Two examples are the 8.8 magnitude earthquake in Chile of February, 2010, and the December, 2004 9.1 magnitude earthquake just offshore in Sumatra. The 2004 earthquake caused a massive tsunami.
One of the largest subduction zones is the Alaska/Aleutian Subduction Zone. This zone is approximately 2,500 miles long and stretches from Alaska to Russia. According to a study done at Columbia University, the North American plate and the Pacific plate are moving towards each other at a rate of about 2 to 3 inches each year.
Subduction can also cause mountain building, also known as orogenesis. This happens when the top plate pushes large amounts of debris that are laying on the bottom plate. Due to the nature of the movement, orogensis is also associated with massive earthquakes.