Montenegro

High in Montenegro’s mountains there is a hollow full of sand from the Sahara.

The mountains in one of the country’s national parks are made almost entirely of limestone and are full of deep hollows. At almost 2,400 metres, one of them is nearly filled with fine-grained sand. Researchers dug almost three metres down, and the sand looked the same all the way.

The sand did not belong there. Almost all the grains were quartz, a mineral missing from the surrounding rock. Under a microscope they were polished smooth and covered in tiny marks from hitting other grains in the wind.

The sand cannot have rolled there, because the mountain rises hundreds of metres above its surroundings. Wind carried it high through the air, all the way from the northern Sahara, and the hollow caught it like a trap.

Saharan dust often reaches Europe, but it is mostly finer than sand. Here there are no layers from single storms. The sand came in a steady, powerful flow, at a time when the Sahara sent out huge amounts of sand.