Abstract

The last 5 yr (1964–1969) of a 16-yr field experiment involving unidirectional windblown rock and mineral debris focused on study of ground-based objects. A large increase in wind-blown material crossing the plot resulted from accelerated fluvial flooding of the upwind alluvial source area starting in 1964. The plot itself was destroyed by such flooding in early 1969.

Maximum cutting of 2.8 cm in 15 yr on a vertical lucite rod occurred on its oblique upwind sides, at 10 to 15 cm above ground. Cutting rate in the last 3 yr was 15 times greater than in the preceding 12 yr, coincident with the increased flux of wind-borne material. A 30-cm gypsum-cement cube showed an 11-fold increase of cutting rate during the last 4 yr (3.6 cm/yr compared to 0.34 cm/yr). Total cutting on the front face was 18 times greater than on the two side faces combined, an average cutting ratio of 36/1. Common red bricks recorded an average front- to side-face cutting ratio of 20/1, and a front-to-top ratio of 45/1. Cutting of 1 to 2 mm occurred on hard crystalline rock within 15 yr, much of it in the last 5 yr.

Changes in orientation and position of gympsum-cement cubes and common bricks were produced by basal ground scour, tilting, rotation, creep, and tumbling. Newly placed hydrocal cubes developed upwind tilts as much as 17° in as little as 69 days (d), owing to basal scour. A slow upwind creep of 2 to 3 cm accompanied scour and tilt. A 90° rotation around a near-vertical axis of a brick demonstrated the importance of lever-arm length offered to the wind. Movements of many centimetres and complete reversals, bottom for top, were caused by tumbling. Separation of the base of cubes from the ground by tilting or by perching on residual pebbles, owing to scour or overturn, usually produced an instability favorable to movement.

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