Because the shape of a plume is irregular, it's easy to miss an anomaly completely. To increase the odds of encountering a plume, crew members drag the CTD in a vertical sawtooth pattern, up and down through the deep waters above the ridge. The pattern is called a "tow-yo," and can be several kilometers long. Several 'clouds' of heat may be detected during the course of a tow. They may represent plumes from several different vents.