Abstract

Experiments and field observations indicate that both the gross shaping and the sculpturing of lineation and pit details on wind-eroded surfaces may be accomplished by the impact of particles which have been impelled aerodynamically by interfacial flow or by vorticity. The vorticity operates along lines of positive, negative, and secondary flow over all surfaces of an object.

The axis of vorticity is typically normal to or at some high angle to the surface undergoing erosion. Therefore, it is not the so-called roller vortex type which has been postulated by other investigators, for one typical erosion pattern left abundantly by the vortex configuration is a round pit either helically or radically scored. Often such pits occur in chains along the beds of the lineations. A second type of erosion pattern common in channels is parallel transverse lineation, which this writer has seen in development in snow flutes under influence of normal-axis vortices. Such vortices travel singly along lines of flow, pulling particles centripetally into the vortex configurations. In snow flutes, for example, vortices become visible due to suspended snow, and the secondary flow can be delineated. Where general windflow is essentially unidirectional, the erosional result of such vorticity is the creation of cross-lineated, essentially symmetrical grooves.

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