Loess

Wind blows dust across the land.

This dust makes a special soil. It is pale yellow.

The soil is very soft and light. It can form tall, steep walls.

People can even dig caves into these walls to live in. This soil is also very good for farms. It helps many plants grow well. This is why the soil is so special.

Loess is a special kind of soil. It is made of dust.

The wind carries this dust over long distances. Then, the dust settles in new places. This process covers ten percent of Earth's land.

Loess is mostly made of silt. Silt is a tiny grain of rock. It is bigger than clay but smaller than sand. The grains are often angular. This means they have sharp edges. Because of these edges, loess can stand in tall, steep walls. These walls are called bluffs.

In China, people dig caves into these walls to live in.

This soil is very good for farming. It is porous. This means it has tiny holes for air. It also holds onto nutrients well. Nutrients are the food that plants need to grow.

In China, the Yellow River gets its color from this dust. The loess makes the water look light yellow. Loess can be very thick. In parts of China, it is over one hundred meters deep.

Loess is a special kind of sediment made of wind-blown dust.

It covers about ten percent of the Earth's land area. This material is mostly made of silt, which is a tiny grain of rock. Most loess has about 20% or less clay. The rest is a balance of sand and silt. The grains are often angular, meaning they have sharp edges. This helps the soil stay together in unique ways.

There are a few ways this dust forms. One way is called periglacial formation. This happens near ice sheets. In the spring and summer, melting ice creates rivers. These rivers carry silt and clay across floodplains. In the winter, the water stops flowing. The dry floodplains are then exposed to the wind. The wind picks up the fine silt and carries it away.

Another way is non-glacial. This happens when wind blows dust from deserts or volcanic ash. This dust travels until it settles in a new place.

People have studied loess for a long time. The name comes from the German word "Löß." A man named Karl Cäsar von Leonhard first described it. He found yellowish brown deposits near the Rhine River. Later, Charles Lyell used the term more widely. He saw similar soil in Mississippi. For a while, people thought rivers moved this silt. Later, scientists realized the wind was the main cause.

Loess can be found in many different places. In China, the deposits are huge. They can be more than 100 meters thick. This dust flows into the Yellow River. This makes the river look light yellow.

In the United States, loess is found in the Midwest. The Loess Hills are on the border of Iowa and Nebraska. These hills have survived many years of farming. In Europe, loess can be found across the whole continent. It can be many meters thick in some areas.

This soil is very important for living things. It is highly porous, which means it has many tiny holes for air. It also has a high cation exchange capacity. This is a way the soil holds onto nutrients for plants. Because of this, loess makes very rich and productive farmland.

In some parts of China, people even dig cave dwellings into the steep loess walls. The angular grains help the walls stay upright. This makes the loess a very useful part of the natural world.

Loess is a unique type of clastic sediment made mostly of silt-sized particles. It is formed through the accumulation of dust that has been blown by the wind.

This material covers approximately ten percent of the Earth's total land area. Loess is defined by its specific composition of minerals. It contains 20% or less clay, with a balance of roughly equal parts sand and silt. The typical grain size ranges from 20 to 50 micrometers. These grains are often angular, meaning they have sharp edges rather than being rounded. This angularity, often combined with calcium carbonate, helps the sediment stay together in interesting ways.

To form loess, four specific requirements must be met. First, there must be a source of dust. Second, there must be enough wind energy to move that dust. Third, there must be a suitable area where the dust can settle. Finally, there must be enough time for the layers to build up.

One way this happens is through periglacial processes. This occurs near melting ice sheets. In the spring and summer, glacial meltwater carries silt and clay across floodplains. When the ice stops melting in winter, these floodplains dry out. The wind then picks up the fine particles and carries them downwind to create deposits.

Another method of formation is non-glacial. This type of loess can come from many different sources. It can originate from deserts, dune fields, or even volcanic ash.

There are many specific types of non-glacial loess found around the world. For example, volcanic loess is found in Ecuador and Argentina. Desert loess is produced by the wind wearing down quartz grains. There is also tropical loess in South America and gypsum loess in Spain. These different sources change the specific characteristics of the resulting sediment.

Scientists have a long history of studying these deposits. The term "loess" was introduced into English from the German word "Löß." Karl Cäsar von Leonhard first described these yellowish-brown silty deposits near the Rhine River between 1823 and 1824.

Later, Charles Lyell brought the term into widespread use in 1834. He noticed similarities between the loess in the Rhine and the loess in Mississippi. At that time, many researchers incorrectly believed the sediment was fluvial, or moved by rivers. It was not until 1857 that the aeolian, or windborne, origin was recognized. Ferdinand von Richthofen later provided convincing evidence through his observations of loess in China in 1878.

Loess deposits can reach massive sizes and thicknesses. In parts of Northwestern China, the deposits can be more than 100 meters thick. In the Midwestern United States, they are often tens of meters thick.

These deposits often appear as large blankets covering hundreds of square kilometers. Because the grains are angular, loess can form steep or vertical faces. This is known as vertical cleavage. In some parts of China, this property allows people to excavate the sediment to create cave dwellings for homes. In America, certain wind-aligned loess ridges are called paha ridges. In Europe, these same types of formations are called greda ridges.

This sediment is incredibly important for agriculture because it creates very rich soil. Loess is highly porous, meaning it has many air-filled spaces. It also has a high cation exchange capacity, which is the ability of the soil to retain nutrients.

Unlike tropical soils, the fertility of loess does not come from organic matter. Instead, the fine grains weather rapidly due to their large surface area. This makes the soil very productive for farming. In China, the loess on the Loess Plateau has supported farming for over one thousand years. This dust even gives the Yellow River its distinctive light yellow color.

However, loess is also very sensitive to erosion. Even well-managed farmland can lose over 2.5 kg of soil per square meter every year. In the Loess Hills of Iowa and Nebraska, intensive farming once caused erosion rates of over 10 kilograms per square meter annually. Today, farmers use techniques like no-till farming and terracing to protect the soil. Scientists also use loess to study the history of our planet. By using methods like luminescence dating, they can determine when dust was last exposed to daylight. This helps researchers understand ancient wind systems, temperature changes, and how the climate has shifted over time.