Open AccessCross‐ripple patterns and wave directional spectra
Author(s) -
Cheel Richard A.,
Hay Alex E.
Publication year - 2008
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008jc004734
Subject(s) - wavelength , ripple , geology , seafloor spreading , sonar , optics , spectral line , orientation (vector space) , geometry , physics , acoustics , geophysics , mathematics , quantum mechanics , voltage , astronomy
Rotary sonar images of the seafloor during SandyDuck97 are used to investigate the geometry of the cross‐rippled bed state relative to the directional properties of the incident waves. The sonar imagery indicates that the cross‐ripple pattern is a quasi‐regular diamond‐shaped lattice constructed of variable length ladder‐like tiles, each with shorter‐wavelength ripples residing within the troughs of the longer‐wavelength component. The longer‐wavelength crests were oriented at approximately ±30° with respect to the incident wave direction. Most wave directional spectra were not bimodal in direction and, for the small number (17%) which were, the distribution of the angular separations of the two peaks was very broad and indicated no preferred value. Thus, contrary to some previous suggestions in the literature, these results indicate not only that cross ripples do not require waves propagating from two different directions for their formation but also that for most of the occurrences during this experiment, cross ripples formed when the incident wave field was unimodal in direction. Finally, the orientation angles of the long‐crested ripple components exhibit no dependence on mean current velocity.