Aeolian dust ripples: Their occurrence, morphometrical characteristics, dynamics and origin

• Published in: Catena (Giessen) Vol. 18; no. 3; pp. 379 - 407
• Main Author: Goossens, Dirk
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Cremlingen-Destedt Elsevier B.V 01.06.1991; Catena
• Subjects: Bgi / Prodig; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geomorphology; Geomorphology, landform evolution; Geomorphometry; Physical geography; Surficial geology; Belgium; Europe; experimental studies; sedimentary rocks; geomorphology; dunes; wind transport; winds; time factor; loess; clastic sediments; velocity; ripple marks; size distribution; Sedimentology; Grain size distribution;Granulometry; Experimentation; Earth surface processes; Geomorphometry; Eolian features; Ripple-marks
• ISSN: 0341-8162; 1872-6887
• DOI: 10.1016/0341-8162(91)90033-T

In this paper, the main morphometric and dynamic properties of aeolian ripples formed in a wind tunnel during the deposition of natural, silt-sized dust particles over a flat horizontal surface are investigated. Ripples and ripple patterns are studied after 15, 30, 45, 60, 75 and 90 minutes of dust deposition, and this for 4 free stream wind velocities ranging from 113 cm·s −1 to 160 cm·s −1 (friction velocity: 3.0 to 3.9 cm·s −1). All velocities are well below deflation threshold. The following ripple parameters are investigated: general ripple shape, ripple spacing, ripple height, ripple flattening, ripple length, ripple symmetry, ripple singularities, ripple orientation, ripple sinuosity and ripple migration. Mean values for the ripple fields as well as dispersion within the ripple fields are examined, and correlations with mean wind speed are made. All parameters are also investigated at different stages of ripple development. The main morphometrical characteristics in which aeolian dust ripples differ from the well-known aeolian sand ripples that are found on almost all sand dunes and sand sheets are ripple spacing (which is of the order of centimeters for sand ripples but only of millimeters for dust ripples) and ripple symmetry (dust ripples are much more symmetric than sand ripples, and the asymmetry may be expressed in two directions: some ripples have steep leeward sides and gentle windward sides, others are inversely asymmetric). An important dynamic observation is that dust ripples may migrate upwind, although all ripples migrate downwind once a critical wind speed is exceeded. The dust ripples investigated are only formed if sediment is supplied to the air stram. Two different (but counteracting) processes play a role in dust ripple dynamics: an aerodynamic process and an impact process, of which the first causes an upwind and the second a downwind migration of the ripples. It will depend on which process is the dominant whether dust ripples will migrate upstream or downstream.