Sahara desert
James Davis
Professor Pope/GLY 101
March 26, 2014
Research Paper
Sahara Desert Sahara Desert is the world’s largest desert. fahsdf asdfjk asdfjas dfasdkfj afoiwehfa djfaiweofj asdkfThe eastern Sahara is the driest region on Earth, where the received solar radiation is capable of evaporating over 200-times the amount of rainfall. It is characterized by a vegetation-free expanse of sandstone in the south and a limestone plateau in the north, with numerous sand sheets and sand dunes in numerous patterns. All of the dune fields occur within or near topographic depressions. This fact must be explained in any theory regarding the origin of the sand and the evolution of dune forms in space and time.
Two other important observations must also be taken into account. The first is that wind in this desert moves towards the south during most of the year, except where it is locally affected by topographic prominences. The second is that sands in these dune fields are composed mostly of well rounded quartz grains. The exposed rocks to the north of the sand seas are mostly limestones, which could not have been the source of the vast amounts of quartz sand. The two observations discount the possibility of the origin of the majority of the sand by wind erosion and transportation from the north. Therefore, it is more likely that the areas covered by dune sand were topographically low areas that received sediments from northward flowing rivers and streams in the geological past. When the conditions of climate changed, the wind sculptured the sand into various dune forms and sand ridges.
The patterns of dunes in the Great Sand Sea in particular support this theory. The largest linear forms were called “whale back” dunes by Bagnold who theorized that they grew so large that they no longer could move. However, dunes move because individual sand grains are dislodged by the wind. Furthermore, cross-sections made into these dunes show that the sand is horizonally layered
Professor Pope/GLY 101
March 26, 2014
Research Paper
Sahara Desert Sahara Desert is the world’s largest desert. fahsdf asdfjk asdfjas dfasdkfj afoiwehfa djfaiweofj asdkfThe eastern Sahara is the driest region on Earth, where the received solar radiation is capable of evaporating over 200-times the amount of rainfall. It is characterized by a vegetation-free expanse of sandstone in the south and a limestone plateau in the north, with numerous sand sheets and sand dunes in numerous patterns. All of the dune fields occur within or near topographic depressions. This fact must be explained in any theory regarding the origin of the sand and the evolution of dune forms in space and time.
Two other important observations must also be taken into account. The first is that wind in this desert moves towards the south during most of the year, except where it is locally affected by topographic prominences. The second is that sands in these dune fields are composed mostly of well rounded quartz grains. The exposed rocks to the north of the sand seas are mostly limestones, which could not have been the source of the vast amounts of quartz sand. The two observations discount the possibility of the origin of the majority of the sand by wind erosion and transportation from the north. Therefore, it is more likely that the areas covered by dune sand were topographically low areas that received sediments from northward flowing rivers and streams in the geological past. When the conditions of climate changed, the wind sculptured the sand into various dune forms and sand ridges.
The patterns of dunes in the Great Sand Sea in particular support this theory. The largest linear forms were called “whale back” dunes by Bagnold who theorized that they grew so large that they no longer could move. However, dunes move because individual sand grains are dislodged by the wind. Furthermore, cross-sections made into these dunes show that the sand is horizonally layered