Mars has the largest flood channels in the solar system. They are called outflow channels because they emerge full-size from depressions or large canyons. Most outflow channels formed after the smaller highland river systems ran dry. Based on their size, they may have discharged up to millions of cubic meters of water per second for short periods of time.
One of these outflow channels (Ravi Vallis) begins in "chaos" terrain, where the surface has collapsed or broken apart. The other channel (Mangala Vallis) emerges from fractures in the bedrock.
Mars Odyssey, THEMIS
NASA/JPL/Arizona State University image
Blue arrows show the direction of water flow in these outflow channels. Streamlined islands (orange arrows) formed around obstacles, such as the small crater at center left. Scablands, cataracts, and grooves carved into the channel floors are similar to features found on Earth where large floods have occurred, such as the Channeled Scabland of eastern Washington state.
Mars Odyssey, THEMIS
NASA/JPL/Arizona State University image
Most outflow channels drained into the Chryse Basin and the northern lowlands. Some scientists think these floods could have formed a northern ocean. The colors in this image centered on the north pole reflect elevation differences, from blue (lowest) to white (highest).
Mars Orbiter, Laser Altimeter
NASA/JPL/GSFC image
