Sahara

The Sahara is the largest hot desert in the world, covering much of North Africa, an area roughly the size of the United States. Despite its reputation, only about a quarter of it is covered in sand dunes. Most of it is rocky plateau and gravel plain.^[1] It has also snowed in the Sahara: snow fell near the town of Aïn Séfra in Algeria in 1979, and again several times since 2016. It is the only desert to have been photographed with a light dusting of snow on its dunes and to look, briefly, confused.

The green Sahara

Between roughly 11,000 and 5,000 years ago, the Sahara was much wetter. Changes in the Earth's orbit brought stronger monsoon rains, and large parts of it were grassland with lakes and rivers, home to hippos, crocodiles, giraffes and elephants. Rock paintings from this period show people swimming, in what is now one of the driest places on Earth.^[2]

The desert has turned green and back again many times over hundreds of thousands of years. It is, therefore, not so much a desert as a lake on a very long break.

Sand

The sand in the Sahara can be blown thousands of kilometres. Dust from the Sahara regularly crosses the Atlantic Ocean, where it falls on the Amazon rainforest and adds nutrients to its soils. The world's largest desert therefore helps to fertilise the world's largest rainforest, by post.

• Size: about that of the United States.
• Covered in dunes: about a quarter.
• Snowfalls recorded: several.
• Green: 11,000–5,000 years ago.

See also

• Sand – a quarter of it
• Snow – occasionally
• Camel – a well-adapted resident

References

1. Dune, D. (1999). Mostly Gravel. Erg Press.
2. Monsoon, M. (2008). “When It Was Green”. Palaeoclimate Notes 5,000: 1.
3. Flurry, F. (2016). Snow on the Dunes. Unexpected Books.