The images and explanatory captions are available online at http://www.jpl.nasa.gov/images/io from NASA's Jet Propulsion Laboratory, Pasadena, Calif.

A high-resolution view of a cliff named Telegonus gives information about erosion on a world that has neither surface water nor wind. The cliff is slumping outward due to gravity.

The Tvashtar area on northern Io, where no volcanic activity was seen prior to December 1999, now has a cluster of hot spots. An infrared mapping image from Galileo's Aug. 6, 2001, flyby of Io shows that the surface within the Tvashtar area is hot at the sites observed in 1999 and 2000, as well as at newly observed sites. "The most explosive phase of the Tvashtar eruption may have ceased, but these observations reveal that the area is still active," said Dr. Rosaly Lopes, a volcanologist at JPL. Tvashtar appears to be an example of a volcanic site where activity starts vigorously then gradually declines, similar to many eruptions on Earth, she said.

Io's most powerful volcano, Loki, offers a contrasting style of eruption. The Loki hot spot brightens and fades over periods of several months, possibly in periodic cycles, a pattern not known on Earth. Scientists have proposed that Loki is either an active lava lake or a caldera whose floor is flooded by frequent lava flows.

Infrared mapping images of Loki from Galileo's Oct. 16, 2001, flyby of Io weigh in favor of the lava lake interpretation. They show a concentration of high temperatures along one edge, like a glowing shoreline. This suggests that hotter lava from underneath is showing through where a cooler lava crust is breaking up as it hits the crater wall. High- resolution nighttime pictures of another of Io's hot spots, Pele, also show the apparent overturning of cooler crust on a lava lake.

JPL, a division of the California Institute of Technology in Pasadena, manages Galileo for NASA's Office of Space Science, Washington, D.C. For more about Galileo, visit http://galileo.jpl.nasa.gov .