The second major type of lava flows on the flanks of Alba Mons are called tube- and channel-fed flows, or crested flows. They form long, sinuous ridges that radiate outward from the central region of the volcano. They are typically - wide. An individual ridge may have a discontinuous channel or line of pits that run along its crest. Tube- and channel-fed flows are particularly prominent on the western flank of the volcano where individual ridges can be traced for several hundred kilometers. The origin of the ridges is uncertain. They may form by successive buildup of solidified lava at the mouth of a channel or tube, with each pulse of flowing lava adding to the length of the ridge.