Try swimming in the Dead Sea and you can’t help but float. This salt lake, bordered by Jordan, Israel and the West Bank, is nearly 10 times as salty as the oceans. In recent decades diversion of freshwater streams has made it even saltier, and since 1979 scientists have observed salt crystals “snowing” down, depositing up to 10cm on the sea floor every year. It’s the only place in the world where this happens and now scientists think they know why.

During summer the Dead Sea separates into two layers: a warm super-salty layer sitting above a cooler less-salty layer. The research, published in Water Resources Research , shows that when small waves break this boundary they encourage salty fingers to penetrate into the lower layer. Warm water holds more salt than cool water, so as the fingers cool they produce salt crystals which then rain down on the sea floor.

The mechanism helps explain the mystery of some of the massive ancient salt deposits found in the Earth’s crust, such as the thick salt layer underneath the Mediterranean Sea. During a period when the Strait of Gibraltar closed (about 6m years ago) the Med would have had similar properties to the Dead Sea.