Boulder Tracks on Hillslopes in Southwest Egypt and Similar Features on the Moon

Tracks of mass unsted houtders are examined on the slope of a steep hill 3 km east of Peter and Paul in the southwestern desert of Egypt. The hill is what remains of a vol cania neck of trachytes and basal aonglomerates, The hill is surrounded by an apron of debris in which the tracks are grooved. One 2 m boulder left a straight trail and its motion appears to have been smooth. It continued to slide on the level surface surrounding the debris apron for about 5 m, perhaps lubricated by the fine sand that covers this surface. Another boulder left a chain of depressions suggesting that it bounced as it moved downslope. This boulder appears to have disintegrated oust before reaching the level ground, Erosional products from previous wetter climatic conditions appear to have been completely washed away in this region^ where eolian conditions predominate. The motion of boulders downslope seems to be basically controlled by gravity, or mass wasting. The resulting features are analogous to those on the Moon. Boulder tracks in southwestern Egypt are compared to those on mils of lunar craters such as Hyginus, and mountain slopes such as the massifs at the Apollo 17 landing site. On the Moon, boulder tracks occur as straight or curved depressions with sharp parallel borders, or as chains of depressions. The similarity of the tracks left by mass-wasted boulders in the two places attests to the extremely dry conditions in southwest Egypt. From this correlation it is speculated that similar tracks will be observed an martian hill slopes, when those are revealed by high resolution photographs. BOULDER TRACKS ON TRACHYTE HILL On the way from the Gilf Kebir to Gebel Uweinat, a hill about 3 km east of Peter and Paul was examined (Fig, 16.1). Like many other hills In the region, this one is composed of volcanic rock and rises steeply from the otherwise flat terrain of Paleozoic sandstones. The hills are composed of either trachyte or basalt. The trachyte hills form piles about 30 m high on the average, but may reach heights of up to 80 m.