loess

Loess is an aeolian sediment composed primarily of silt-sized particles, typically about 20 to 60 micrometres in diameter. It is usually well sorted, highly cohesive when dry, and forms extensive, nearly horizonless blankets over bedrock or older deposits. The color ranges from yellow to light brown, reflecting its mineral content and low organic matter.

Loess accumulates where strong winds transport fine dust from glacial outwash plains, deserts, or eroded surfaces and deposit it over large areas. Deposition is favored by cold, arid, or steppe climates with limited vegetation. In many regions loess sheets are thick enough to host extensive soil development, creating loess-paleosol sequences that record alternating periods of dust input and soil formation.

Loess deposits occur in several major mid-latitude regions of the Northern Hemisphere, most notably the Chinese Loess Plateau in East Asia, large belts across central and eastern Europe, and portions of the North American Great Plains. Thicknesses vary from a few meters to several tens of meters, with some regions exhibiting even thicker accumulations.

Loess soils are among the most fertile temperate soils, offering a fine texture, high nutrient content, and good water-holding capacity. However, they are typically well drained and susceptible to erosion when vegetation is removed, making land management and conservation important. Calcareous loess can feature prominent carbonate nodules and horizon development related to soil weathering.

Loess records are valuable for paleoclimatology and archaeology, providing archives of past climate, monsoon variations, and patterns of human settlement. Their agricultural value is balanced by erosion risk, shaping land-use practices in regions where loess is prevalent.