Aerial view of greenery along the Kuiseb River in the Namib desert. This river separates the gravel desert from the sand desert. Namib Naukluft National Park, Namibia. [Getty Images]

Aerial view of greenery along the Kuiseb River in the Namib desert. This river separates the gravel desert from the sand desert. Namib Naukluft National Park, Namibia.

Photolibrary Martin Harvey