The wondrous journey of a grain of sand

We often associate beaches with vacation, the smell of sunscreen and the warming sun in the sky. Especially we Swiss, who are geographically blessed with beach and sea. But how does a sandy beach actually arise?

Sand grains are, by definition, those pieces of rock that are between 0.063 and 2 millimeters in size. If the chunks are between 2 millimeters and 6 centimeters in size, we speak of gravel and if the chunks of stone have a diameter of 6 to 20 centimeters, they are stones.

In principle, all sandy beaches are created in the same way: over millions of years, weathered rock is broken down further and further until the grains of sand are finally carried over the water to the coast. But the path begins at a great height:

The life cycle of a grain of sand begins as part of a rock. There it is under the influence of the weather – cracks appear in the rock and little by little smaller pieces of rock separate from the larger ones. The broken boulder splintered into other, even smaller pieces and ended up in a stream or on a glacier, for example. From there, the boulders enter a larger river, where they are constantly ground up, hitting other rocks and breaking up into smaller pieces.

Depending on the slope of the river, it can take between 1,000 and a million years for a grain of sand to travel 100 kilometers, an expert explains to the “Tagesanzeiger”. Ultimately, the grain of sand ends up in the sea, where it is exposed to much harsher conditions than in the river. As it collides with other grains of sand and rocks in the sea, its corners become more rounded. Eventually, the tide carries it to the beach, where countless people can enjoy it.

The size of the grains of sand on the beach is determined by the slope of the seabed off the coast: the shallower, the smaller the grains.

The size of the waves also plays a role: when they are longer, they wash sand from lower elevations onto the beach. The length of a wave refers to the distance it travels before breaking again.

A white sand beach, as you know it from the catalog of travel agencies, consists of lime. The sand consists of dead coral and broken shells.

The yellow sand found in Egypt consists of quartz rocks. For example quartzite, gneiss, granite or rhyolite.

Red sand is also very beautiful to look at – it is found in Canada, Australia and parts of Africa, for example. It owes its color to the mineral iron. As soon as this comes into contact with oxygen, iron oxide is formed – so the iron will rust. There is also red sand in the Mediterranean – here the lime from the limestone rocks is carried away by the water. What remains is iron, which discolors in the air.

Black beaches get their distinctive hue from the volcanic rock that makes up the sand. This occurs in Hawaii and the Canary Islands, among others.

Hawaii has another special sand color to offer: green. The reason for this is again a volcano, more precisely the volcanic mineral with the beautiful name olivine, which is responsible for the green color.

(ann)