🏜️ Sand and deserts

Sand feels tiny and grainy, and it can slip right through your fingers like water.

Sand is made of countless tiny grains of rock and mineral, broken down and worn smooth over a very long time by water, wind, or waves crashing again and again. Most sand grains are made of a hard, glassy mineral called quartz, which is exactly why sand often feels gritty but rarely crumbles apart. Not all sand looks the same, some is pale yellow, some is black, and some is even pink or white, depending on what kind of rock it came from.

Wet sand sticks together, so you can pack it into a bucket and build a sandcastle.

Sand heats up quickly in sunlight because the tiny grains are dark or dry enough to soak up heat fast, and unlike water, sand cannot spread that heat around or cool itself down easily. With so little water or plants around a desert to help hold onto moisture, the ground has almost nothing to slow down how fast it heats up under a strong sun. That same sand loses its heat just as quickly once the sun goes down, which is exactly why deserts can feel scorching by day and surprisingly cold at night.

Some deserts sit right next to tall mountains. The mountains squeeze all the rain out of the clouds before the clouds ever reach the other side, the same way an umbrella keeps rain off you. Other deserts simply sit far from any ocean, so the clouds run out of rain long before they get there. A desert is not always hot either, some deserts get bitterly cold, since what makes a place a desert is how little rain falls each year, not the temperature.

A desert has very little water and few clouds, so the sun beats down and heats the sand all day long.

Sand dunes form when wind picks up loose grains of sand and piles them up wherever something slows the wind down, like a rock or a bush. Once a dune starts to grow, wind keeps blowing sand up its gentler slope and dropping it just over the top. This means the whole dune creeps forward, grain by grain, over months and years. The tallest sand dunes in the world can grow taller than many buildings, built up entirely by countless tiny grains moved one gust at a time.

Wind slowly pushes sand into big piles called dunes, which can look just like small, soft hills.