Io's most distinctive feature is unquestionably the volcanic center, Pele. Pele is the site of an ongoing, high-velocity volcanic eruption. Deposits of sulfurous materials from Pele's plume are ejected out to more than 600 km (375 miles) from the vent. Its plume is nearly invisible, except in back-lit photographs, and it is thought to be an example of a stealth plume. Stealth plumes occur when the sulfur dioxide gas in the volcanic vent is at a very high temperature. Upon being expelled from the vent, the gas rapidly expands resulting in an undetectable, high-velocity jet of cold gas from which no snow is produced.
A dramatic display of how quickly volcanic activity can change the face of Io is shown in these three images of the Pillan Patera region near Pele. The images show the changes that occurred between April 1997 and July 1999. The image on the left was taken in April 1997. By September 1997 (center), a huge eruption occurred which produced a new dark spot the size of Arizona around the volcanic center named Pillan Patera. This eruption obscured a portion of Pele's red ring. By July of 1999 (left), red sulfurous material had once again begun to cover a portion of the dark material around Pillan, but had not yet been obscured it. This may be an indication that both the Pele and the Pillan plumes were still active. Another change in the 1999 image shows that a small volcano had erupted to the right of Pillan depositing dark material surrounded by a yellow ring.
This is a temperature map of the Pele region imaged by the infrared spectrometer onboard the Galileo spacecraft. Red indicates the hottest lava flows, and purple represents cooler areas. The hottest lava flow temperatures recorded are approximately 1400 K (2000 Fahrenheit), which is similar to the temperatures of basaltic flows found on Hawaii's Kilauea volcano.
This image shows an outline of fresh, hot lava that follows the margin of Pele's caldera. Scientists believe that the Pele caldera is filled with liquid lava and has a floating crust. The lava lake appears to be confined to the dark southern part of the caldera which covers an area of about 15 km by 10 km (10 miles by 6 miles). Most of the lava lake is covered by a cooler crust that floats on top of the molten lava. The behavior of this lake is similar to that of Hawaiian lava lakes, although Pele's lake covers an area several thousand times larger than the lava lakes in Hawaii.Photo Credits: NASA/JPL