Ergs are vast expanses of sand dunes like this area in Oman. Sometimes they are also called sand seas because the dunes look and act like very slowly moving ocean waves.
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The towering ridge of a sand dune in the Arabian Desert points to the afternoon sun. The Sahara, Arabian, Iranian, and Thar deserts all connect together to form a 6,000-mile (9,600-kilometer) expanse of drylands in North Africa.
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Minerals, algae, and cyanobacteria give this geyser in Nevada's Black Rock Desert its brilliant colors.
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Lacking virtually any wildlife that could be harmed with its patrons, the off-highway-vehic...