Erg Chebbi, the dunes themselves

The numbers

An erg is a sea of wind-blown sand. Erg Chebbi is one of only two large ergs in Morocco — the other is Erg Chigaga, further west — and it is the more dramatic of the two, because its dunes are considerably taller.

You will see heights of "500 feet" quoted a lot. That is about 150 metres, and it refers to the tallest ridges, not the average. It is still enough that the erg is visible from a long way out on the approach road, sitting on the horizon like a mountain range that someone poured.

Where the sand came from

There are two explanations you will hear locally. The geological one is that the sand is the product of ancient lake beds and river systems, moved and piled by prevailing winds over a very long time — the same process that builds every erg in the Sahara.

The other is the story people here tell: that a family in a village once turned away a woman and her child in a sandstorm, and God buried the village in sand as a punishment. Both accounts have been passed down for generations. Only one is testable, but you will understand the second one better once you have stood in a real sandstorm.

The colour

The reddish-orange comes from iron oxide coating the grains, and it is why the dunes look so different at different times of day. Around sunrise the sand goes pink and then a deep orange, with very long shadows that pick out every ridge. At midday it flattens to pale gold and the shadows disappear — the least interesting light of the day. Then in the last hour before sunset it deepens again, and you get about twenty minutes after the sun is down when the whole erg glows without any direct light on it. That last window is the one photographers come for.

Sunrise or sunset?

Both, if you stay the night at a bivouac — that is rather the point of doing so. If you can only pick one, pick sunrise. Fewer people, unmarked sand, cooler air for the climb, and the colours are arguably better because you are looking at the lit faces rather than into the sun.

Photographing Erg Chebbi without ruining your camera

• Do not change lenses out there. Fine sand in a sensor chamber is a repair bill. Choose a lens at the hotel and commit.
• Bag everything. A zip-lock bag around the body between shots is genuinely enough.
• Include something for scale — a person, a camel, a tent. Dunes photograph as abstract shapes and lose all sense of size without a reference.
• Shoot along the ridges rather than straight at them, so the sidelight separates the planes.
• Underexpose slightly. Bright sand fools meters and blown highlights cannot be recovered.

Walking on the dunes

Take shoes off. Soft sand and shoes are a bad combination and every local walks barefoot. Go up the ridgeline rather than the face — the sand is more compacted there and you sink less. Take water even for a short climb; it is more effort than it appears and the air is extremely dry.

And do not go far alone. Dunes look identical from the top of the next one, there are no landmarks, and phones do not work out there.