The Sahara has not always been sand. ABC News reported that scientists have found a new dinosaur species deep in the desert, and the setting is stranger than it sounds: this is a place that flips between desert and grassland.
A desert that keeps changing
At 9.2 million square kilometres, the Sahara is the largest hot desert on Earth and the third-largest desert overall, behind only the polar deserts of Antarctica and the Arctic. It covers much of North Africa but leaves out the fertile Mediterranean coast, the Atlas Mountains and the Nile Valley. It runs from the Red Sea west to the Atlantic, with the Sahel, a belt of semi-arid savanna around the Niger River valley, along its southern edge.
For several hundred thousand years the region has swung between desert and savanna grassland on a cycle of about 20,000 years. The trigger is the slow wobble of Earth’s axis, which takes roughly 26,000 years to complete a turn. That wobble changes where the North African monsoon falls.
Why the rain is so scarce
Today the picture is harsh. The Sahara sits under the subtropical ridge, a belt of high pressure where dry air sinks, warms and stops clouds from forming. The Libyan Desert in the east is the sunniest and driest spot, rivalling Chile’s Atacama. Most of the Sahara gets under 20 millimetres of rain a year, and the central core can drop below 1 millimetre. Some areas go years without a drop.
The main source of rain is the Intertropical Convergence Zone, a band of low pressure near the equator that brings brief, irregular wet seasons to the Sahel and the southern edge. The Atlas Mountains add a rain shadow in the north.
Mountains, heat and extremes
The landscape is not flat dunes alone. Rocky plateaus, sand seas, gravel plains, dry valleys called wadis, and salt flats all appear. Volcanic mountains rise from the sand, including the Aïr, Ahaggar and Tibesti ranges and the Adrar des Iforas. The highest point is Emi Koussi, a shield volcano in the Tibesti of northern Chad.
Heat is relentless. Most of the desert sees more than 3,600 hours of bright sunshine a year. Bou Bernous in Algeria recorded a mean monthly maximum of 47 degrees Celsius, a mark matched only by Death Valley, and sand can reach 80 degrees Celsius or more. Nights are cooler by 13 to 20 degrees.
Sources
- Sahara
- US Proposes Radical Changes for UN Mission in Western Sahara – PassBlue
- Las Vegas driver hit 93 mph in wrong-way crash in west Las Vegas, police say
Photo: El Golli Mohamed (CC BY-SA 4.0)
