The Pacific coastline of much of Central America is marked by a line
of active and quiescent volcanoes known to geologists as the Central
American Volcanic Arc. The volcanoes result from the upward movement of
magma generated along the subduction
zone between the Cocos and Caribbean tectonic plates. Frequent
earthquakes also occur along the plate boundary. This astronaut
photograph includes four stratovolcanoes—a
type of volcano common in active subduction zones—in El Salvador, near
the midpoint of the Central American Volcanic Arc.
While all of the volcanoes shown here have been active during the
Holocene Epoch (from about 10,000 years ago to the present), only the
2,130-meter- (6,990-foot-) high San Miguel (also known as
Chaparrastique) has been active during historical times. The most recent
activity of San Miguel was a minor gas and ash emission in 2002. The
stratovolcano’s steep cone shape and well-developed summit crater are
evident, along with dark lava flows. Immediately to the northwest, the
truncated summit of Chinameca Volcano (also known as El Pacayal) is
marked by a two-kilometer- (one-mile-) wide caldera. The caldera formed
when a powerful eruption emptied the volcano’s magma chamber, causing
the chamber’s roof to collapse. Like its neighbor San Miguel,
Chinameca’s slopes host coffee plantations.
Moving to the west, the eroded cone of El Tigre Volcano is visible.
El Tigre formed during the Pleistocene Epoch (1.8 million to about
10,000 years ago), and it is likely the oldest of the stratovolcanoes in
the image. Usulután Volcano is directly southwest of El Tigre. While
the flanks of Usulután have been dissected by streams, the mountain
still retains a summit crater that is breached on the eastern side.
Several urban areas—recognizable as light gray to white regions
contrasting with green vegetation and tan fallow agricultural fields—are
located in the vicinity of these volcanoes, including the town of
Usulután (lower left) and Santiago de Mara (upper left).
Astronaut photograph ISS023-E-22411
was acquired on March 31, 2010, with a Nikon D3X digital camera fitted
with an effective 340 mm lens, and is provided by the ISS Crew Earth
Observations experiment and Image Science & Analysis Laboratory,
Johnson Space Center. The image was taken by the Expedition
23 crew. The image in this article has been cropped and enhanced to
improve contrast. Lens artifacts have been removed. The International
Space Station Program supports the laboratory as part of the ISS
National Lab to help astronauts take pictures of Earth that will be
of the greatest value to scientists and the public, and to make those
images freely available on the Internet. Additional images taken by
astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of
Earth. Caption by William L. Stefanov, NASA-JSC.