The stone forest of Tin Alkoum, Tassili n' Ajjer (Algeria), is a sight to behold in the Sahara. It is the result of erosion, which is not unusual in itself. Here, however, the factors determining the attack on the minerals are quite peculiar. First of all, there is the abrasion caused by the Saharan storms, which hurl the sand against every obstacle in a manner comparable to a sandblaster. Then there is the difference between the daily temperature maxima and the nightly minima of such magnitude that it causes veritable rock explosions. And finally, although this has practically ceased, the attack by water at a time when the rains fell mainly in the form of thundery and heavy downpours. Witnesses to the violent thunderstorms are the numerous fulgurites or thunderbolts that formed in the sand as a result of lightning strikes by melting it around the impact hole. These hardened tubes were then exposed by erosion. - Algeria - 1969
