The outer shell of the Earth is called the ‘Lithosphere’ and is encased by the crust, the area outside of the ‘Upper Mantle’. The Earth’s three primary layers are called:
- the crust (about 18 miles thick)
- the mantle (about 1,800 miles thick)
- the core or center.
The mantle’s outer surface is called the Upper Mantle which is cooler. Underneath that is the Lower Mantle and then the lithosphere, which comprises a set of close fitting tectonic plates. These tectonic plates consist of surfaces that overlap to create the continuous ‘crust’. The surface of the Earth is covered with “erosion” that leaves behind materials which we see deposited on all land masses (and ocean floors); soil, sand, rock, mud and oceans. This ongoing process takes place over millions of years. These materials sit over top of the plates. The tectonic plates are constantly shifting in undetected movements most of the time. A sudden shift of a plate will result in an Earthquake or Tsunami. Between the crust and the mantle is an area containing magma. Magma is super heated rock and gas in a fluid-like form. The electricity we produce using geothermal energy is the heat that originates in the earth’s core.
Magma is a molten rock and a combination of various, gasses, and chemicals, at temperatures ranging between 700 °C - 1300 °C (or 1300 °F - 2400 °F). As the geothermal heat rises, the magma swells and flows up through the volcano’s ‘conduit’, coming forth through a major fissure or shaft in the center of the volcano. As the magma comes to the earths surface the volcano forms.
This process is repeated over millions of years. When magma breaks through and spews up through a ‘vent’ the eruption can create a spectacular show that can continue for a long time. When magma flows down the slopes of the volcano, it’s called lava or molten rock. In 1963, when the Irazu Volcano erupted, it showered San Jose and its environs with clouds of ash and smoke for two years. On August 24th, 2000, the Arenal Volcano erupted and one person died, two were badly injured and nearly 1,000 people were forced to evacuate the surrounding area. There have been hundreds of eruptions and phreatic explosions in Costa Rica’s volcanic history.
More on the Volcanos of Costa Rica: