One of a series of small marine, lake, or riverine features, consisting of repeating wavelike forms with symmetric slopes, sharp peaks, and rounded troughs. Ripple marks are formed in sandy bottoms by oscillation waves, in which only the wave form advances rapidly, the actual water-particle motion consisting of almost closed vertical orbits. The presence of the bottom restricts the lowermost orbits into nearly flat ellipses, and the bottom water moves back and forth rhythmically. If the maximum horizontal velocity of this motion is capable of moving the grains composing the bed, ripple marks develop. See alsowave.