Tuesday, July 1, 2008
Why Costa Rica Has So Many Volcanoes
Volcan Arenal - Costa Rica
Why does Costa Rica have so many volcanoes?
In the last post, I explained about tectonic plates and how they move relative to one another. Just as their movement causes earthquakes, they also cause volcanoes. Remember that there are two types of plates: continental and oceanic. The continental plate is made up of lighter materials than the oceanic plate. Costa Rica is the convergent boundary between the Caribbean and the Cocos plates. Where the collision between the two occurs, the continental plate floats up and over the oceanic plate which sinks. This causes a trench that forms a boundary. In the case of Costa Rica, this trench is off the Pacific coast and runs parallel to the coastline. This trench is called a subduction zone.
When the oceanic plate sinks beneath the leading edge of the continental plate, this is called subduction. As the two plates slide over and past one another, the oceanic materials continue to subduct or sink beneath the continental plate and as it moves inland away from the trench it gets deeper underground. Eventually it sinks deep enough to be melted into magma by the heat from the mantle. Volcanoes are the earth’s relief valves for this superheated, viscous material that is known as lava when it comes to the surface. There is a line of volcanoes through the central portion of Costa Rica where the melted oceanic materials return to the earth’s surface. This line of volcanoes extends through Costa Rica and well up into Nicaragua.
According to geologists, here in Costa Rica, there are at least 112 volcanoes. Five are considered active. They are Irazú, Poás, Turrialba, Arenal, and Rincón de la Vieja.
Volcanoes are considered to be either active, dormant, or extinct. A simple explanation will do for our purpose. Active, of course, means just that. The volcano is presently doing something. Dormant means it is inactive (asleep) and has not erupted for some time. Some scientists consider a volcano dormant if it has not erupted in the last 500 years or if it hasn’t erupted since history began to be recorded in that location. For example, the volcano may be showing no signs of activity other than the presence of hot springs in the area, but because of the hot springs it obviously is not extinct (dead). Extinct means dead. The volcano has done nothing since man has been around to observe and record, and there is no sign of any type of active.
Of the 112 volcanoes in Costa Rica, only the five mentioned above are active. The rest are either dormant or extinct. One of the dormant volcanoes is Barva which is the largest volcano in Costa Rica.
Irazú is my favorite volcano. Perhaps that is because I can see it from my living room window. It is the tallest volcano in Costa Rica and is affectionately called The Colossus. Poás, which has the second largest crater in the world, is perhaps an hour away as the crow flies, and Turrialba is about the same distance, but in the opposite direction. Rincón de la Vieja and Arenal, which has erupted everyday for the last 40 years and is considered one of the ten most active volcanoes in the world, are about an hour and a half away. Over the next few weeks, I will post about each of them and share some photos with you.