Do sand dunes have life?

While crossing the vast Gobi Desert in the 13th century, Marco Polo began hearing strange sounds that seemed to come from the sand. Unable to explain the whistling, humming, and booming noises, he attributed them to evil spirits. Who else could it be?

Polo's ears weren't deceiving him. Sand dunes do sing, and they also grow, migrate, and even reproduce. These dynamic behaviors give what would otherwise be a simple pile of sand a lifelike quality.

A sand dune forms when wind blows loose sand onto an obstacle such as a rock or tree. The heavier grains settle against the obstacle, starting to create a small ridge. The lighter grains drift to the other side of the obstacle, forming the slip face. As long as the wind persists, the sand ridge grows, eventually becoming a full dune. To understand this process in detail, read How Sand Dunes Work.

Sand originates from rocks. Over time, as rocks erode, their fragments are transported by wind, water, or ice (such as in the case of glaciers). Quartz, or silica, is the most common component of sand, though the specific makeup can vary depending on the local rock sources.

So, how does sand – broken down rock – come to life in the desert? Discover more on the next page.

Sand Dune Singing, Breeding and Migrating

Just like living creatures, sand dunes grow too. A dune can begin as little more than a handful of sand grains nestled against a rock. With the right wind conditions, it can grow to heights of several hundred feet. The wind’s speed and direction also shape the dune into beautiful ripples and patterns across its surface.

Wind also causes some dunes to migrate. Yes, a sand dune can actually move. To transport sand grains, the wind must blow at a minimum speed of 15 miles per hour (24 kph). As the sand grains bounce and collide with one another, they slowly shift along. As the dune’s sand piles up, the slope eventually becomes too steep and the dune collapses under its weight. The sand cascades down the slip face, accumulating on the opposite side. In this way, the dune can move while keeping its original shape. These are known as migrating dunes, and scientists are still studying the physics behind them. Migrating dunes can sometimes move toward and engulf entire villages, which is why understanding them is important.

Like humans, sand dunes can also reproduce. They don't need flowers or romantic dinners – all they require is wind. As sand dunes move, sometimes they meet and merge in a slow collision. And by 'slow,' we mean it – these collisions can take as long as a year to happen. When a smaller crescent-shaped dune runs into a larger one, it may pass through and break into two smaller dunes on the other side. This process is known as breeding. It occurs when the dune becomes unstable, causing the horns of the crescent-shaped dune to break off, forming new baby dunes.

Still wondering why people think sand dunes are alive? Take a look at the strange phenomenon of booming dunes. People have reported hearing dunes sing, croak, burp, bark, and even moan. How does this happen? It’s simple: the sound comes from the grains of sand rubbing together. The quality of the sound depends on the size and texture of the grains.

For sand to make loud booming or humming sounds, the grains need to be uniform in size, rounded, dry, and free from other particles. As mentioned earlier, when sand gathers at the top of a dune, it eventually reaches a tipping point and slides down the dune’s face in a sand avalanche. The dune's surface acts as a speaker, amplifying the sound of the grains crashing together. As the sand moves, it creates vibrations that produce sounds similar to a cello or didgeridoo. Some dunes have been measured at up to 110 decibels – as loud as a snow blower or motorcycle!

A sand dune can produce its own song as these avalanches happen, but you can also make a desert dune sing by sliding down its slope. You may have even heard sand squeaking underfoot while walking on the beach – that’s the same process, just on a smaller scale.

For more details on sand dunes and other geological formations, explore the links on the next page.

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