The flanks of Koko Crater on the island of Oahu, Hawaii, show signs of extensive gully erosion. Koko Crater is approximately 400 meters (1,320 feet) high. Here we see valleys 3-5 meters (10-16 feet) deep that have been caused primarily by surface water flow and, close to the summit, by sapping. Although spaced further apart on Martian volcanoes such as Tyrrhena Patera, similar valleys might have formed on the older volcanoes on Mars as water from the original explosive eruptions was released at the surface. Note, however, that the valleys on Tyrrhena Patera might be 3-5 kilometers (1.9-3 miles) wide, which is wider than the entire Koko Crater cone.