The dunes are all wavy? Is this a bug?

Audit expert: Zhan Mingjin

PhD, Chinese Academy of Meteorological Sciences

The desert is one of the most hostile environments on Earth, and sand dunes are one of the most famous landforms in the desert.

Sand dunes can be found all over the world and come in all shapes and sizes, but they all have an undulating shape.

Why are sand dunes wavy? Let's find out!

1

How are sand dunes formed?

Sand dunes are landforms formed by the accumulation of sand and gravel under the action of wind. The sand and gravel come from many sources, including sediments from rivers and oceans, and debris from the erosion of rocks and minerals. The sand and gravel are blown and moved by the wind and eventually deposited in one place to form sand dunes.

Sand dunes are hilly in appearance, ranging in height from a few meters to hundreds of meters. They are most widely distributed in deserts or semi-deserts, and are also distributed in small quantities on the beaches of coasts, lakesides and riverbanks.

dune source | hippopx

How are sand dunes formed? The process can generally be divided into two stages: movement and deposition of sand.

In the sand movement phase, the wind blows the sand up, causing it to jump and roll in the wind. When it encounters an obstacle or the wind cannot drive the sand forward, the sand stops moving. As more and more sand stays in one place, a small sand pile is formed , and the sedimentation phase begins. In this phase, the sand slides down the slope of the small sand pile and settles at its bottom . As this process repeats, the sand continues to accumulate, the size of the small sand pile continues to grow, and eventually a sand dune is formed.

2

Why are sand dunes wavy?

The wavy appearance of the dunes is the result of the interaction of sand migration, accumulation and wind during the dune formation process. Wind plays a key role in shaping the dunes and creating this unique landscape.

The process can be described in a few simple steps: First, the wind can blow sand and gravel into the air, causing them to flow in the air. As the wind weakens, the sand gradually falls back to the ground and begins to form a preliminary slope. Over time, the accumulated sand makes the slope gradually steeper. However, when the slope angle exceeds the maximum stable angle of the sand, the dune will collapse, forming a concave area , which is what we call a trough.

The wind continues to move the sand from one side of the trough to the other, gradually forming a new slope . This slope gradually becomes steeper until it reaches the maximum stable angle of the sand again, then collapses, forming a new trough. This cycle repeats over and over, causing the surface of the dune to gradually form a wave-like feature.
It is important to note that the direction and strength of the wind also play an important role in this process. If the wind direction is relatively constant, the dunes may present a more symmetrical and regular wave shape. On the contrary, if the wind direction varies greatly or the wind is strong, the shape of the dunes may be more irregular and complex .

In short, the wavy shape of sand dunes is the result of the migration, accumulation and reshaping of sand particles under the action of wind. The interaction of this process creates a unique and beautiful landscape in nature.

3

What shapes and types of sand dunes come in?

The shape and size of sand dunes are determined by many factors, including the type of sand and gravel, the stability of the dunes, the strength and direction of wind, precipitation and temperature. The most common dune shapes include crescent dunes, pyramid dunes and lattice dunes .

As a typical wind erosion landform, the crescent dune shows a unique shape. Its characteristic is that the slopes on both sides of the longitudinal section are asymmetrical, namely the windward slope and the leeward slope . The windward slope is convex and relatively gentle, with a slope of generally 5° to 20°, while the leeward slope is concave and relatively steep, with a slope of 28° to 34°. This symmetry allows the two wings of the dune to be formed when the wind extends, stabilizing the shape of the dune and preventing its lateral movement and destruction.

The formation of barchan dunes is closely dependent on the action of wind. They are usually formed under the influence of wind in one or opposite directions. The wind blows up the sand and gradually deposits it on the windward slope, accumulating into dunes. The leeward slope has a steep slope and cannot hold the sand, so it forms a concave surface. This process gradually gives the barchan dunes their unique appearance.

These dunes are mainly found at the edge of deserts, where winds are strong, steady, and usually come from only one or two opposite directions . This climate and wind environment encourages the formation and persistence of crescent-shaped dunes at the edge of deserts, such as the Sahara Desert in Egypt, the Simpson Desert in Australia, and the Nevada Desert in the United States.

Crescent dunes source | pexels

In contrast, pyramidal dunes are named for their pyramid-like appearance and are usually formed by stable winds . Pyramidal dunes taper upwards, with steep, straight sides and a relatively wide overall width. They are highly significant, exceeding 100 meters or even hundreds of meters . Pyramidal dunes are formed by the combined effects of wind and sedimentation, with the wind moving sand to one side and gradually accumulating it, causing the dune to gradually expand and rise.

The grid dunes are in the form of a regularly arranged grid , consisting of parallel and intersecting ridges. The slope angle is generally 20° to 30°, which is relatively steep. The height is between 10 and 20 meters, which is lower than other dunes.

In addition to crescent, pyramid, and grid shapes, these dune shapes also include other types, such as feather, star, and horseshoe . These different types of sand dunes are the result of the combined effects of factors such as terrain, climate, and wind.

Wavy sand dunes source | hippopx

Sand dunes are one of the most amazing natural wonders on Earth, demonstrating the power of wind and the amazing process of landform evolution. They come in all shapes and sizes, from the graceful curves of crescent dunes to the majestic heights of pyramid dunes to the regular grids of lattice dunes, each of which demonstrates the interaction of wind, sedimentation, topography and other factors. While we explore the mysteries of sand dunes, we should also respect and protect these natural treasures. Through scientific research, environmental protection and sustainable development, let us live in harmony with nature and protect this unique and beautiful desert land together.