Atlas Mountains

Long ago, this land was low, with deep dips in the ground.

Then Africa and Europe slowly pushed together. The squeezed land rose up into mountains.

During the Triassic and Jurassic periods, the land here was being pulled apart. Long, low basins formed and filled with layers of rock, such as red beds, marl and limestone.

Later, as Africa and Europe moved toward each other, those basins were squeezed. Their rock layers folded and were pushed up along faults, and the old basins became the Atlas Mountains. Geologists call this turning of a basin into mountains inversion.

Arboleya, Teixell and colleagues (Journal of African Earth Sciences, 2004) describe the Atlas ranges of Morocco as intracontinental fold-thrust belts derived from the Cenozoic inversion of Jurassic extensional or transtensional troughs, as a consequence of convergence between Africa and Europe. Mesozoic sedimentation began in Triassic rift basins filled with red beds and basalts; Jurassic basins later collected thick marls and limestones.

Their transect found only about 12% shortening, too little to explain the high topography by crustal thickening alone; Cenozoic alkaline volcanics in the Middle Atlas and low seismic velocities suggest a thermally anomalous mantle contributing to uplift. Miller and Becker (Geology, 2014) found offsets at the flanks of the High Atlas where Jurassic normal faults were reactivated, and concluded that an upwelling component from a hot mantle anomaly is also required to support the range.

Winds from the ocean bring rain and snow to the mountains.

On the far side, the land is dry. That is where the Sahara begins.

Westerly winds carry moisture from the Atlantic Ocean, and the Atlas Mountains act as a weather barrier. On the ocean side lie coastal grasslands and wetlands; beyond the mountains, the land stays dry. This is called a rain shadow.

In winter, snow caps the highest peaks. NASA notes that two ski resorts in the Atlas, one near Marrakech and one near Ifrane, get fairly regular snowfall each January and February, and that this snow stores water that farms in Morocco depend on.

NASA's Earth Observatory explains that westerly winds bring Atlantic moisture, while the Atlas Range blocks it, creating a rain shadow between the coastal grasslands and wetlands and the Sahara. Snow in the Atlas is not unusual: in a 2012 image story, NASA noted regular January-February snowfall at ski areas near Marrakech and Ifrane and called the snow cover a crucial reservoir of water for Morocco's agriculture-based economy.

Snow beyond the mountains is rarer. On 19 December 2016, snow fell on Ain Sefra, an Algerian town between the Atlas Mountains and the northern edge of the Sahara; NASA reported that its last recorded snowfall had been in February 1979.

Cedar trees grow in the Atlas Mountains.

Monkeys called Barbary macaques live here too.

In the central Atlas Mountains, Morocco's Atlas Cedar Biosphere Reserve holds about 75 percent of all the world's Atlas cedar trees, UNESCO says. Green oaks and maritime pines grow in its forests too.

Animals listed there include the Barbary macaque, a kind of monkey, Cuvier's gazelle and a bird called the lesser kestrel. The reserve also has lakes and wetlands of international importance.

UNESCO's Man and the Biosphere Programme lists the Atlas Cedar Biosphere Reserve in Morocco (1,375,000 ha; year of nomination 2016). It holds 75 per cent of the global population of Atlas cedar (Cedrus atlantica), with green oak (Quercus rotundifolia) and maritime pine (Pinus pinaster); its main ecosystem is the Haute Moulouya plain, an arid steppe at 1,500 m, and peaks in the High Atlas section to the south reach about 3,700 m.

UNESCO lists the Barbary macaque (Macaca sylvanus), Cuvier's gazelle (Gazella cuvieri) and the lesser kestrel (Falco naumanni) among its animals, and the reserve includes the Ramsar sites Lake Afennourir, Aguelmams Sidi Ali-Tifounassine and Lacs Isly-Tislite.

High up in the mountains, the air is thin. Go up slowly.

Tell a grown-up if your head hurts.

UNESCO notes Atlas peaks reaching about 3,700 meters. Up high, the air pressure is lower, so each breath brings in less oxygen. The US Centers for Disease Control and Prevention (CDC) says children can get altitude sickness just as adults can, and that going up gradually gives the body time to adjust.

Headache is the main sign of altitude sickness. If you feel worse at the same height, the CDC's advice is to go back down.

The CDC's Yellow Book advises ascending gradually: avoid going from low altitude to a sleeping altitude above 2,750 m (9,000 ft) in one day, and above 3,000 m raise sleeping altitude by no more than 500 m per day. Children are as susceptible as adults. Acute mountain sickness usually begins 2-12 hours after arrival and generally resolves within 12-48 hours if travelers go no higher; if symptoms worsen at the same altitude, descent is mandatory.

PlayOwl's own advice: in snowy months, check the weather and go with someone who knows the mountains.