Although the Sahara Desert has been around for hundreds of thousands, possibly millions of years, climate variations have produced some eras that were wetter than others. Today, Lake Chad seems like little more than a muddy puddle surrounded by increasingly dune-streaked wetland (tan stripes across the green vegetation). But between 5,000-10,000 years ago, a much larger lake extended across the area, a low-lying basin, and the lake’s surface level was perhaps 120 meters higher above sea level than the level is today. Today, part of the former lake bed, the Bodele Depression, is probably the largest single source of wind-blown dust in the world. In the image, a dust storm is whipping across the Bodele, north and northeast of Lake Chad, softening the orange sands of the Sahara into a pale tan. The airborne dust is rippling in the currents of the wind, the waves of dust forming dark lines that give texture to the storm.
This particular storm was blowing on November 18, 2004, when the Moderate Resolution Imaging Spectroradiometer (MODIS) flew over on NASA’s Terra and Aqua satellites. The images record the growth of the storm through the day. The frequency of such storms is apparent in the landscape of the desert beneath the storm. The desert rocks and sands are scoured into sweeping lines that follow the contours of this and many previous storms.