Shifting sand dune swallows lighthouse

In the north of Jutland, a huge dune has gone wandering. Its masses of sand have now buried the local lighthouse. Its operation was abandoned years ago. Now the Museum of Flying Sand, which was located in one of its outbuildings, is also closing.

The lighthouse sent out its first signal to the open sea on 27 December 1900. But a huge dune grew on the rock at its feet: Rubjerg Knude. Over time, the sea moved closer and the wind blew large amounts of sand up the cliff. To stop the drifting sand, beach grass was planted, but the dune remained unimpressed and grew larger and larger. When the light of the lighthouse could no longer be seen from the sea, the 23-metre high tower was shut down on 1 August 1968.

In contrast, a museum opened in an outbuilding of the tower to provide information about drifting sand. When the fight against the sand drift around the tower was abandoned in 1994, the dune’s wanderings began. Now it moves forward about 10 metres per year. And the museum is now itself a victim of the quicksand. Three of the tower’s outbuildings have already sunk, and now the museum must also close. But the dune continues to move and will eventually release the buildings. However, in the not too distant future they will fall victim to the erosion on the coast and tumble into the sea.

An entire village blown away by the wind

The worst of the sand drift is long behind the inhabitants of Rubjerg: more than 300 years ago, it is very cold here, as in all of northern Europe, the “little ice age” prevails. The sea level is about one metre lower, the beaches are wide. Their sand can easily be blown away by the stormy winds. For the inhabitants of the area, the devastating sandstorms make it more than uncomfortable: they flee. What remains is a lonely church in a desert-like environment. The faithful continue to come to worship, but the path through the dunes eventually becomes too arduous for them. In 1904, they completely demolish the church and rebuild it two kilometres away in their new community.

Erosion by wind – Of shifting sand dunes and mushroom rocks

Wherever wind sweeps over sandy dry ground, it carries fine grains with it and later lets them fall again. In this way, sand hills pile up – the dunes. Such sand dunes are mainly found in dry deserts such as the Sahara, the Gobi Desert or the Namib Desert. Their dunes can be over 200 metres high and many kilometres long.

But you don’t have to go to the desert to see a dune: There are also dunes on the coasts, in Germany for example on the North Sea or Baltic Sea coast. The sand that is blown off the beach by the wind piles up inland to form dunes. If you want to go to the beach, you often have to find a way through or over the dunes.

Some dunes hardly move at all, for example when they are overgrown with beach grass. Others, however, roll forward in the direction of the wind, similar to the waves of the sea, the shifting dunes. A particularly migratory dune is the “Rubjerg Knude” on the coast of Denmark. This almost 100-metre-high dune moves in a north-easterly direction and has even rolled over a lighthouse on its journey.

Dunes have different shapes. Some are curved like crescents or sickles – the sickle dunes. Others form a wall across the wind direction, the transverse dunes. Both rise slightly on the windward side. On the side away from the wind, they drop steeply downwards. And some dunes even sing their own song: When sand avalanches break loose from the dune and the grains of sand collide, they make humming or buzzing noises: the dune “sings”!

But wind and sand do not only shape dunes. Flying grains of sand can abrade rocks in the landscape like sandpaper. Even hard rock can be given a new shape by this wind abrasion: Rising rocks are scraped and hollowed out at their base over time. Finally, they rise up like mushrooms – a mushroom rock has been created.

From rock to grain of sand – weathering

Today, northern Canada is a gently undulating landscape. Many millions of years ago, however, a mountain range stood here. In fact, over a very long time, even high mountains can turn into small hills.

The reason for this transformation: the rock on the earth’s surface is constantly exposed to wind and weather. If, for example, water penetrates into cracks in the rock and freezes, it blasts the stone apart. This process is called frost blasting. Changes in temperature between day and night and the force of water and wind also cause the rock to become friable. In other words, it weathers. This process can also be observed on buildings or stone figures. During weathering, the rock breaks down into smaller and smaller components down to fine grains of sand and dust. Different rocks weather at different rates: granite, for example, is much more resistant than the comparatively loose sandstone.

Some types of rock even dissolve completely when they come into contact with water, for example rock salt and lime. Rock salt is chemically the same as table salt – and that already dissolves in ordinary water. Lime is somewhat more resistant, but limestone also dissolves in acidic water. Acid is formed, for example, when rainwater in the air reacts with the gas carbon dioxide. This “acid rain” attacks the limestone and dissolves it over time. On the earth’s surface, weathering leaves behind fissured limestone landscapes, while caves form underground.

But it is not only solution weathering, but also heat and pressure that wear down and crumble rock beneath the earth’s surface. Where plants grow, roots dig in, blast the rock apart piece by piece and also ensure that it is eroded millimetre by millimetre.

In this way, weathering not only works on individual rocks, it gnaws away at entire mountain ranges. But it will take a few million years before the Black Forest is as flat as northern Canada.

What causes erosion?

When rock weathers, it rarely stays in its original place. Often, rock debris rolls down the slope, is washed away by water or pushed away by ice masses. Fine rock dust or sand can also be carried by the wind. Whether the rock is carried away by water, ice, wind or gravity, all these processes are called erosion.

The erosion caused by flowing water is particularly drastic. Streams and rivers dig a bed in the ground, rock slides down and a valley forms. If a glacier rolls down the valley, it planes the valley wider by dragging debris with it. Such trough valleys show that there was a glacier here long after the ice has melted. The surf of the sea, on the other hand, attacks the coast. Steep cliffs are eroded and collapse, sandy beaches are washed away by the waves. In deserts, the wind sweeps away large areas of sand. The harder it blows, the more sand it can carry away. A sandstorm gradually grinds away obstacles made of solid rock like a sandblaster.

When rain and wind wash or blow away the soil cover on large areas, this is called soil erosion. Landslides on slopes are also referred to as soil erosion. The problem is that the fertile upper layer of the soil disappears. In the worst case, it can no longer be used for agriculture.

If the soil is overgrown with plants, this slows down erosion. The roots of the plants hold the soil in place and prevent wind and water from carrying it away. However, if the plant cover is destroyed, for example by deforestation, the soil lacks this hold and is eroded away.

Bottom formation

Plants rarely grow on bare rock. They need a soil from which they can draw nutrients and in which they can form roots. For such soil to develop, weathering is necessary: rain and oxygen, heat and cold, water and wind grind the rock and thus grind even hard granite into smaller and smaller grains. What emerges is the so-called weathering debris.

But thousands of years pass before it becomes living soil. Bacteria, fungi and lichens are the first to settle on the rock; the first soil animals are attracted to them. Dead plant remains, animal carcasses and faeces gradually mix with the crushed rock. From this mix, with the help of fungi and bacteria, the upper soil layer of fertile soil develops, on which plants can thrive. Below that are other layers, for example of sand or clay. At the very bottom is the rock from which the soil develops.

In our temperate latitudes, brown earths are common. They develop on rock with little or no limestone in a humid climate. Dark coloured is the rendzina, a soil that forms on limestone. Because it is so stony, it is difficult to cultivate crops on it. And on the Italian island of Stromboli there are very special sandy soils: because the lava rock that comes from the Stromboli volcano is dark, the sandy beaches on the volcanic island are also pitch black.

Why does it look different on Earth than on the Moon?

It doesn’t look very inviting on the moon: The surface is dry and covered with a grey layer of dust. Meteorite impacts have torn huge craters into the ground, which filled with lava from the interior of the moon. Around these lava basins, kilometre-high crater rims tower up as mountain rings.

Our blue planet is completely different – if only because three quarters of it is covered by water. But water not only covers a large part of the earth, it also shapes its land mass: rivers, glaciers and the surf of the sea work the rock, break it up and rearrange it. This is how valleys, coasts and ever new layers of rock are formed.

The interior of the moon today is solid and rigid. The Earth, on the other hand, has a liquid mantle on which movable plates float. The movement of the Earth’s plates causes mountains to fold up, deep-sea trenches to form and volcanoes to spew fire and ash.

Unlike the moon, the earth has an air envelope, the atmosphere. It is in this envelope of air that the weather is created. Wind, rain and snow have worked and shaped the earth’s surface over millions of years. The atmosphere also acts as a protective shield, slowing down meteorites and preventing them from burning up.

Because the moon has no such atmosphere, meteorites strike its surface unchecked and suddenly crumble the rock to dust. But meteorites are the only forces that shape the lunar landscape. Because there is no water, no atmosphere and no plate tectonics, the influences that make our Earth’s surface so varied are missing.

The first humans to set foot on the barren lunar landscape were astronaut Neil Armstrong and his colleague Edwin E. Aldrin. The footprints they left behind when they landed on the moon in 1969 can still be seen today – because neither wind nor water can erase the traces on the moon.

Earth on the move – landslides, mudflows and landslides

Suddenly the earth starts to move: tons of rock, mud and debris slide or tumble down the mountain into the valley. Destructive and unstoppable, the earth’s masses sweep away everything in their path.

Erosion can proceed very slowly, but sometimes it happens suddenly. If, after a heavy downpour, the soil softens considerably and is heavy enough, an entire slope can start to slide. Such a landslide transports large amounts of earth and debris down into the valley. At the foot of the slope, the loosened rock collects in debris cones and heaps.

Whether a landslide occurs depends on the slope: The steeper the slope, the more likely the earth is to slide. How firmly the layers of earth hold together also plays a role. If the slope is overgrown with plants, the roots provide more grip. If nothing grows on the slope or trees have been cleared, the roots that hold the soil in place are missing. Then it is easier for a landslide to occur.

A landslide can look different: The whole slope can slide downwards over a large area. Or earth and mud flow like a river through a valley or carve one out, then it is called a mudflow.

In the shortest possible time, huge masses of rock go down in a landslide. Debris and rocks tumble down within a few seconds. Mostly, landslides happen at places where different rock layers meet. Heavy precipitation, the alternation of heat and cold or earthquakes can cause these layers to separate. In a landslide, large blocks of rock break off. Due to global warming, layers of rock that used to be held together by ice are thawing today. As a result, such landslides are occurring more and more frequently.

Dubai opens “The Palm Jumeirah

At midnight, Dubai welcomed its island “The Palm Jumeirah” with the largest fireworks display in the world. It took seven years to build the artificial island, which juts into the sea like a giant palm tree. Now the “eighth wonder of the world” is finished – in the middle of the Persian Gulf.

With the branching palm island, Dubai wanted one thing above all: to gain large beaches and many plots of land that lie directly on the sea. The shape of the palm tree was made for this. By all appearances, the developers’ plan has succeeded: Dubai’s coastline is now a hundred kilometres longer. How the island construction will affect the environment and how stable it will be in the long run remains to be seen: New roads, villas and luxury hotels – everything here is built on sand.

It is a project of superlatives: in order to heave the fantastic island out of the water, 100 million cubic metres of sand were moved from the sandbanks off the coast and piled up. A wall of stones is to protect the artificial beaches from erosion. At peak times, 40,000 construction workers were at work every day. Thirty luxury hotels were built, over 1,500 villas with their own access to the beach. The construction of the island complex cost a whole 1.5 billion dollars.

“The Palm Jumeirah” is not the last construction project of its kind. The Emirate of Dubai is planning and building four more large-scale art islands. Their names: “The Palm Jebel Ali”, “The Palm Deira”, “The World” and “The Universe”.

New territory for the Maldives

Nowhere else do the inhabitants of Malé live so closely together. The capital of the Maldives is the most densely populated city in the world. To create space, the government began reclaiming new land as early as 1975. But the area was not enough. Therefore, sand was piled up on the neighbouring island from 1997 and a new city was founded: Hulhumalé. The island is at least two metres above sea level. That is a lot for the Maldives, because on average the coral islands in the Indian Ocean rise just one metre out of the water. Their low height poses a great danger: because of the expected rise in sea level, one metre more or less could become essential for survival.