Eolian features in the western desert of Egypt and some applications to Mars

Abstract

Relations of landform types to wind regimes, bedrock composition, sediment supply, and topography are shown by field studies and satellite photographs of the Western Desert of Egypt. This desert, which lies at the core of the largest hyperarid region on earth, provides analogs of Martian wind-formed features. These include sand dunes, alternating light and dark streaks, knob 'shadows,' and yardangs. Surface particles have been segregated by wind into deposits (dunes, sand sheets, and light streaks) that can be differentiated by their grain size distributions, surface shapes, and colors. Throughgoing sand of mostly fine to medium grain size is migrating southward in longitudinal dune belts and barchan chains whose long axes lie parallel to the prevailing northerly winds, but topographic variations such as scarps and depressions strongly influence the zones of deposition and dune morphology. Sand from the longitudinal dunes on the plains is commonly redistributed into barchans in the depressions. These barchans are generally simple crescents that are morphologically similar to many of the dunes seen on Viking orbiter pictures of the north polar sand sea on mars. Light streaks are depositional features consisting of dune belts and elongate sheets of coarse to medium sand and granules. Intervening dark streaks are erosional features consisting of strips of desert-varnished bedrock and lag gravel surfaces exposed between the sand deposits. The shape of both light and dark streaks is controlled by wind flow around topographic highs. Dark zones (shadows) in the lee of mountains, hills, and knobs are erosional products from the topographic highs; they change shape only in response to movement of the adjacent lighter-colored sand deposits. Streamlined yardangs carved in crystalline limestone constitute one of the largest yardang fields on earth. Yardangs occur also in sandstone of the Nubian Series and in lacustrine sediments. The variables that affect the patterns of wind erosion and deposition in the Western Desert are topographic effects on wind velocities and directions, resistance of the bedrock, sand supply, and climatic change with time; vegetation is essentially absent and is not a controlling factor.

Wind streaks: geological and botanical effects on surface albedo contrast

“…These conclusions are consistent with many previous studies of terrestrial wind streaks as possible analogs to streaks observed on other planets (e.g. Iversen, 1978, Greeley andIversen, 1985;El-Baz et al, 1979). In contrast, the botanical effects observed at the Sleeping Beauty streak will be restricted to Earth.…”

“…Desert pavement surfaces are prevalent, particularly in the wind streak itself, and the Amboy flow and pavements have been used in the development and confirmation of the accretionary mantle model of desert pavement development McFadden et al, 1987;Williams and Zimbelman, 1994). Cinders from the cone do not significantly contribute to the pavement in the streak Iversen, 1978, Greeley andIversen, 1987) as they do around one Egyptian wind streak described by El-Baz et al (1979). The Amboy streak owes much of its albedo contrast to the higher degree of desert pavement development in the streak caused by the cone blocking sand from traversing through the streak area, possibly enhanced sand transport via saltation over the abundant surface rocks, and by the creation of lateral winds in the lee of the cone that inhibits sand from entering the streak (Greeley and Iversen, 1985).…”

Sliding Friction on Wet and Dry Sand

“…However, in view of our results, it seems very possible to drag the sleds over wet sand with the manpower available to the Egyptians [5]. In fact, the value of the friction coefficient of wood on wood is in the range of 0.25 < μ d < 0.7 [18]; especially for the polydisperse sand here, which is closest to the Egyptian desert sand [17], we arrive at friction coefficients as low as 0.3;thus,thedraggingcan bejustas easy over sand as over the wooden sleepers. In addition, the "optimal" friction coefficient of 0.3 that we find here coincides remarkably well with estimates that have been made on the basis of the tomb drawings.…”

“…5). The Egyptians were pulling their sled through desert sand, which is very polydisperse [17] (Fig. 6).…”

Detection of Land Use and Land Cover Changes for New Cairo Area, Using Remote Sensing and GIS

“…In Egypt, remote sensing and its applications have emerged as early as this technology was invented. Early studies were based on visual interpretation of MSS data to map sand accumulations in the Western Desert [9]. During 1980s, soil salinization was a good target to be monitored using satellite images [10].…”