The Ring of Fire, caused by shifting of tectonic plates, can be considered to run virtually the entire perimeter of the Pacific Ocean, including along South America's western coast, Antarctica's Pacific coast, Oceania, the Far East and Central America. This continuous ring encompasses seventy-five percent of the world's volcanoes and results in many of the world's major earthquakes.
When two tectonic plates interact with one another, one of three things happen:
- Extensional movement: the plates move away from each other, usually resulting in deepening of an ocean
- Transform movement: the two plates pass next to each other, usually not causing new mountains, valleys, or similar land formations
- Compressional movement: the two plates hit each other, often forcing one over the top of the other
The three types of movement can cause different kinds of earthquakes.
Extensional earthquakes are shallow and typically lower than 8 on the Richter scale. They are felt only along the axis of the plates.
Transform earthquakes are also shallow (less than 25km) and tend to be smaller than 8.5 on the Richter scale.
Compressional earthquakes can be shallow or very deep (hundreds of kilometers) and can exceed 9 on the Richter scale, being stronger than either of the other two types.
The Ring of Fire was largely formed by the Pacific tectonic plate being forced underneath or over other tectonic plates. This sometimes allows magma to rise to the surface and form volcanoes, and sometimes causes earthquakes. Though plates tend to move less than 10cm a year, such movement can be unpredictable and is why even dormant volcanoes can erupt suddenly.