Loess is a type of soil composed mainly of:

Loess is a fine, yellowish-brown, loosely packed soil (sediment) made up mainly of silt-sized particles and dust, carried and deposited by the wind. It is a classic example of an aeolian (wind-formed) deposit.

How loess forms:

• Strong winds pick up fine particles of silt and dust from deserts, dry river beds and glacial outwash plains (areas where meltwater from glaciers deposited fine sediment at the end of the Ice Ages).
• The winds carry the dust for long distances and deposit it in thick layers over large areas, sometimes many tens of metres deep.

Characteristics of loess:

• It is yellowish or buff in colour.
• It is very fine-grained, uniform and porous.
• It usually has no clear layers (it is unstratified).
• It can stand in vertical cliffs, but erodes very easily when wet and forms deep gullies and ravines.
• It is highly fertile, because it is rich in minerals, and it is easy to plough.

Major loess regions of the world:

The Loess Plateau of northern China: the largest and thickest loess deposits in the world, in places over 300 metres thick. The fine dust is believed to have been blown from the Gobi and other deserts of Central Asia. The Huang He picks up this loess, which gives the river its yellow colour.

The Great Plains and the Mississippi valley in the USA.

Central and eastern Europe, including parts of Ukraine, Hungary and Germany.

The Pampas of Argentina.

Importance:

• Loess regions are among the most fertile farming areas of the world, producing wheat, maize and other crops.
• However, loess areas suffer from severe soil erosion, which adds large amounts of sediment to rivers.

Wind deposits in India:

Wind-formed features in India include the sand dunes of the Thar Desert.

Why not the other options?

• ✗Boulders and gravel are deposited mainly by fast rivers and glaciers (for example, moraines).
• ✗Peat and plant remains form organic soils in waterlogged areas.
• ✗Coral fragments form calcareous sands on coral islands, such as Lakshadweep.