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 is very fertile, which means it helps plants grow well.

Loess forms in places where the weather is very cold, called periglacial areas, or where the wind can carry dust over long distances. It is made up of small particles of sand and silt, with just a little bit of clay. These particles 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 both interesting for scientists and very 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 started using this word to describe the dust-like soil along the Rhine River around 1821.

History of research

The word for loess started in Central Europe when a scientist named Karl Cäsar von Leonhard described yellowish brown, silty soil near the Rhine valley close to Heidelberg in 1823–1824. Later, Charles Lyell popularised the term after seeing similar soil in the Rhine and Mississippi areas. People first thought this soil came from rivers, but later learned it was actually carried by wind, especially after studies in China by Ferdinand von Richthofen in 1878.

Since then, many studies have explored how loess forms and how it helps us understand past climates. In the 1980s, scientists developed 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 thousands of years.

Formation

For loess to form, four important things are needed: a place where dust comes from, strong winds to carry the dust, a spot where the dust can settle, and enough time for it to build up.

One way loess forms is near big rivers that used to be frozen. When these rivers melt in the spring and summer, they carry lots of dirt and tiny pieces of rock. But when the melting stops in the fall and winter, the land dries out and the wind can blow away the tiny pieces, dropping them somewhere else. The loess along the Mississippi River alluvial valley is a good 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 create very rich soils that are great for farming. In the right climate, these soils are some of the most productive in the world.

These soils drain well and their tiny particles break down quickly, making the soil rich. The fertility comes from the soil's ability to hold nutrients and its 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, feeding many people. However, 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 stretch from southern Tajikistan up to Almaty, Kazakhstan.

East Asia

China

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

Europe

Loess deposits of different thicknesses are found all over Europe. In northern Europe, they stretch from southern England and northern France to Germany, Poland, and southern Ukraine. In south-eastern Europe, loess is mostly found 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 built up over 10,000 years. When this topsoil is lost, the loess underneath is poor 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.