Previously dormant volcanoes in two widely separated areas of the Pacific "ring of fire" are showing signs of life, as documented by new images taken by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (Aster) on NASA's Terra satellite.

Chiliques volcano in Chile. Credit: NASA/JPL

Geologists had previously considered Chiliques, a simple 5,778-meter (18,957-foot) stratovolcano with a 500-meter (1,640-foot)-diameter circular summit crater in northern Chile, to be dormant. However, a January 6, 2002 nighttime thermal infrared image from Aster found a hot spot in the summit crater, as well as several others along the upper flanks of the volcano's edifice, indicating new volcanic activity. Examination of an earlier nighttime thermal infrared image from May 24, 2000 showed no such hot spots.

Stratovolcanoes such as Chiliques account for approximately 60 percent of Earth's volcanoes. They are marked by eruptions of cooler, stickier lavas such as andesite, dacite and rhyolite. Because these lavas tend to plug up volcanic plumbing, gas pressures can more easily build up to high levels, often resulting in explosive eruptions. They are typically made up of about half lava and half loose or fragmented rock ejected from the volcano, and are therefore also commonly known as composite volcanoes. Mount Saint Helens in Washington and Mount Pinatubo in the Philippines are examples of stratovolcanoes.

The daytime image of Chiliques was acquired on November 19, 2000 and was created by displaying Aster bands 1, 2 and 3 in blue, green and red. The nighttime image is a color-coded display of a single thermal infrared band. The hottest areas are white, and colder areas are darker shades of red. Both images cover an area of 7.5 by 7.5 kilometers (4.7 by 4.7 miles), and are centered at 23.6 degrees south latitude, 67.6 degrees west longitude.

Meanwhile, a couple of thousand miles to the northwest, a 10-by-20-kilometer (6.2- by-12.4-mile) section of ground near one of the long-dormant Three Sisters volcanoes in the Cascade Mountains of west-central Oregon has risen approximately 10 centimeters (3.94 inches) since 1996. According to the U.S. Geological Survey, this indicates the slow flow of magma or underground lava into the area. A simulated natural color image from Aster has been draped over digital topography from the U.S. Geological Survey National Elevation Dataset to create this new perspective view of Three Sisters.

Three Sisters volcanoes in Oregon. Credit: NASA/JPL

The Three Sisters area -- which contains five volcanoes -- is only about 273.6 kilometers (170 miles) from Mount St. Helens, which erupted in 1980. Both are part of the Cascades Range, a line of 27 volcanoes stretching from British Columbia in Canada to northern California.

With its 14 spectral bands from the visible to the thermal infrared wavelength region, and its high spatial resolution of 15 to 90 meters (about 50 to 300 feet), Aster will image Earth for the next six years to map and monitor the changing surface of our planet.

Aster is one of five Earth-observing instruments on Terra, and is its only high- resolution imaging sensor. Japan's Ministry of Economy, Trade and Industry built the instrument. JPL is responsible for the American side of the joint U.S.-Japan science team that is validating and calibrating the instrument and data products.

Aster's broad spectral coverage and high spectral resolution will provide scientists in numerous disciplines with critical information for surface mapping, and monitoring dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats; monitoring potentially active volcanoes; identifying crop stress; determining cloud morphology and physical properties; evaluating wetlands; monitoring thermal pollution; monitoring coral reef degradation; mapping soil and geology surface temperatures; and measuring surface heat balance.

NASA's Earth Science Enterprise is a long-term research and technology program designed to examine Earth's land, oceans, atmosphere, ice and life as a total integrated system.

JPL is a division of the California Institute of Technology in Pasadena.