The image shows the textures of lava flows on the floor of the caldera Chaac, which is shown in false color at lower resolution (185 meters or 607 feet per pixel element) in the bottom image.

Calderas are depressions caused by collapse during volcanic eruptions. The one shown here is approximately 100 kilometers (63 miles) long and 30 kilometers (19 miles) across.

Using shadow lengths from the new high-resolution observations, the northeastern (upper right) scarp, or line of cliffs, has been estimated to be 2.8 kilometers (9200 feet) high.

The lava flows are similar in texture to lava flows within the caldera at Hawaii's Kilauea volcano. This suggests that the floor of Chaac has been covered by a combination of lava flows and lava lakes.

The light-colored material surrounding the caldera may be composed of sulfur-dioxide frost or some other sulfur-rich material on the surface of Io.

Galileo scientists believe that the greenish color on the caldera floor is a form of contaminated sulfur created when sulfur-rich material escaping from volcanic vents reacts chemically with warm lava flows. The high-resolution view shows numerous lava flows.

Click for some Io Lava wallpaper

The darkest flows are thought to be the most recent because they have not been covered by the sulfurous materials which coat most of Io's surface. The top image was acquired by Galileo on February 22, 2000. It was taken at a distance of 600 kilometers (370 miles) and is centered at 11.9 degrees north latitude and 157.6 degrees west longitude. North is to the left, and the Sun illuminates the surface from the bottom of the image - which has been rotated 90 degrees clockwise here for easier viewing.

The color image was created by combining a black and white image taken on February 22, 2000 at a distance of 18,800 kilometers (11,700 miles) from Io with lower-resolution (1.3 kilometers or 0.81 miles per picture element) color images taken on July 3, 1999 at a distance of 130,000 kilometers (81,000 miles).

The image is centered at 11.6 degrees north latitude and 157.7 degrees west longitude. North is to the top and the Sun illuminates the surface from the left.

JOVIAN DREAMS
Galileo Gets Extension On Jovian Adventure
Washington - March 8, 2000 - NASA plans to renew the solar system passport of the Galileo spacecraft by extending the mission exploring Jupiter and its moons through the end of 2000, when Galileo may embark on a joint scientific expedition with another solar system explorer, the Saturn-bound Cassini spacecraft.