The flanks of Koko Crater on the island of Oahu, Hawaii, show signs of extensive gully erosion. Koko Crater is approximately 400 meters high. Here we see valleys 3–5 meters deep that have been caused primarily by surface water flow and, close to the summit, by sapping. Although spaced further apart on martian volcanos such as Tyrrhena Patera (slide #18), similar valleys may have formed on the older volcanos on Mars as water from the original explosive eruptions was released at the surface. Note, however, that the valleys on Tyrrhena Patera may be 3–5 kilometers wide, which is wider than the entire Koko Crater cone.
Photograph courtesy of P. Mouginis-Mark.