Loess

Loess is a special kind of soil made mostly from tiny bits of dust carried and dropped by the wind. It covers about ten percent of the land on Earth. This soil is important because it helps plants grow well.

Loess forms in cold places, called periglacial areas, or where the wind can carry dust over long distances. It is made up of small pieces of sand and silt, with a little clay. These pieces often stick together because of a natural cement-like substance called calcium carbonate.

Because loess is loose and full of air spaces, it can break easily into tall, straight walls called bluffs. This makes the soil interesting for scientists and useful for farming in many parts of the world.

Properties

Loess is a special kind of soil that is light yellow or buff in color. It is made up of tiny, angular grains of minerals like quartz, feldspar, and mica. Because of its structure, loess can stand upright without falling over, which makes it useful for building homes, such as caves carved into the soil.

Loess deposits can be very thick—over a hundred meters in some parts of China and tens of meters in the Midwestern United States. These deposits cover large areas and often have steep sides. While loess is good for building, it can also erode easily when water gets to it.

Etymology

The word loess comes from the German word Löss. It was first used in English in 1824. The German word Löss is related to the English word loose and the German word los. People began using this word to talk about the dust-like soil near the Rhine River around 1821.

History of research

The word for loess began in Central Europe when a scientist named Karl Cäsar von Leonhard described a special kind of soil near the Rhine valley close to Heidelberg in 1823–1824. Later, Charles Lyell helped make the word well-known after seeing similar soil in the Rhine and Mississippi areas. At first, people thought this soil came from rivers, but later they learned it was carried by wind. This was especially clear after studies in China by Ferdinand von Richthofen in 1878.

Since then, many studies have looked at how loess forms and how it can help us understand past climates. In the 1980s, scientists found better ways to figure out how old loess is using special light-based dating methods. These methods have helped us learn more about Earth’s climate changes over many thousands of years.

Formation

Loess forms when four things come together: dust, wind, a place for the dust to settle, and time to build up.

One way loess forms is near big rivers that were once frozen. When these rivers melt, they carry dirt and tiny rocks. Later, when the melting stops, the land dries out and the wind blows the tiny pieces to new places. The loess along the Mississippi River alluvial valley is an example of this.

Loess can also come from deserts, sandy areas, dry lake beds, and even volcanic ash. For example, the thick layers of loess in China came from deserts, and the loess covering the Great Plains of Nebraska, Kansas, and Colorado is also from deserts. Non-glacial loess is found in many places, including Australia and Africa.

Fertility

Loess can make very rich soil that is great for farming. In the right climate, this soil is some of the most productive in the world.

The soil drains well and its tiny particles break down fast, which makes the soil rich. The fertility comes from the soil holding nutrients and having air spaces, not from lots of plant material. Even with good care, loess farmland can lose soil quickly. In China, loess has been farmed for over a thousand years, helping to feed many people. But wind can pick up loess particles, causing air pollution. In the United States, along the border of Iowa and Nebraska, loess has been farmed for about 150 years. Today, farmers use careful methods to protect the soil.

Large areas of loess deposits and soils

Central Asia

Loess deposits go from southern Tajikistan to Almaty, Kazakhstan.

East Asia

China

The Loess Plateau is a big area around the upper and middle parts of China's Yellow River. The river looks yellow because of the loess in its banks. This soil is easy to wash away and covers almost all of Shanxi, Shaanxi, and Gansu provinces, the Ningxia Hui Autonomous Region, and parts of other places.

Europe

Loess deposits are found all over Europe. In northern Europe, they go from southern England and northern France to Germany, Poland, and southern Ukraine. In south-eastern Europe, loess is mostly in plateau areas in the Danube basins. In south-western Europe, loess is mainly in the Ebro Valley and central Spain.

North America

United States

The Loess Hills in Iowa are fertile because of rich soil that built up over 10,000 years. When this topsoil is lost, the loess underneath is not good for farming and needs fertilizer to grow crops.

Loess along the Mississippi River near Vicksburg, Mississippi has three layers that formed at different times during the Pleistocene. Animal remains found here include land snails and ancient large mammals.

Oceania

New Zealand

Loess is found in many places in New Zealand, such as the Canterbury Plains and on the Banks Peninsula.

South America

Argentina

Much of Argentina has loess. There are two main types: neotropical loess north of latitude 30° S and pampean loess. The neotropical loess is made of silt or clay and has less quartz and calcium carbonate than pampean loess. Some scientists think it comes from old river deposits near the Andean foothills, while others believe volcanic material is important. The pampean loess is sandy or made of sandy silt.