NASA's Galileo spacecraft acquired the images in this mosaic of Hi-iaka Patera (the irregularly shaped, dark depression at the center of the image) and two nearby mountains on November 25, 1999 during its 25th orbit. The sharp peak at the top of the image is about 11 kilometers (about 36,300 feet) high, and the two elongated plateaus to the west and south of the caldera are both about 3.5 kilometers (11,500 feet) high. The ridges on the northwestern mountain are often seen on Ionian mountains and are thought to be formed as surface material slides downslope due to gravity.