Gish Bar Patera, Io: Geology and Volcanic

Introduction: Since the two Voyagers passed by Jupiter in 1979, it has been known that volcanic activity is ubiquitous on the surface of Io. With over 400 volcanic centers, Io is even more volcanically active than the earth with massive flood basalt-style eruptions and komatitite lavas a common occurrence. Additionally , some volcanoes appear to be giant lava lakes, with violent activity churning the crust of the lake for periods of 20 years or more. Finally, sulfur is believed to play a large role in Io's volcanism, be it as a primary lava or as a secondary product of large, high-temperature eruptions. By studying one volcano in particular, Gish Bar Patera, one can observe many of these characteristics in one volcanic center. Geology of Gish Bar Patera: Gish Bar Patera is one of the many large volcanoes on Io. It lies at the base of an eleven-kilometer tall mountain at 15.6° N, 89.1° W. The patera itself is quite large at 106.3 km by 115.0 km with an area of 9600 km 2. The irregular shape of the caldera shows signs of multiple collapses [1]. Recent collapses appear to have eroded the southern portion of the mountain; however, no recent flows can be seen at this portion of the mountain's base. Galileo SSI imaging from orbit C21 (July 1, 1999) provided our first good look at Gish Bar (Figure 1A). The images reveal two main active areas at Gish Bar. The active region to the northwest has a mottled floor from several eruptions. The smaller subpatera to the southeast is covered in green material with darker material along the edges. The rest of the patera is covered in orange to yellow material, indistinguishable in lower resolution images from the surrounding terrain. A 500-meter tall wall surrounds the entire patera. According to Williams et al., albedo variations within paterae floors represent various ages of lava [2]. As lavas cool, they accumulate brighter frost. Thus, the surface becomes brighter as the lava ages. This principle can be used to determine the relative ages of lavas seen in the C21 imagery of Gish Bar. In the middle area there are dark lava flows mixed with bright orange flows and green channels/ridges. These perhaps correspond to activity that took place in late 1996 to early 1997 or later. Near the center of the patera are curious orange flows. The albedo of these flows would …