The orange dunes frosted with snow look at first as though they could be images from a frozen moon circling some distant planet.

In fact, the rolling hills with the alien-looking white peaks were formed by a more earthly — if unusual — phenomenon: snow in the Sahara.

According to news reports in Algeria, about 15 inches of snow fell on Sunday in the region of Aïn Séfra, in the northwest of the country.

Unforgivingly hot in the day, but freezing during the night, the Sahara is renowned for its extreme temperatures. Experts said snowfall was rare — though nobody knows quite how rare, because the desert is so vast and there are comparatively few monitoring facilities.