Which of the following soils is formed by lava?

Soils are classified partly by the process and parent material from which they originate. A soil that forms in place through the weathering of a specific type of rock is called a residual soil, and its genetic identity is tied directly to that parent rock.

Black soil (also called Regur soil) is the classic example of a soil that originates from lava: it develops through the long-term chemical weathering of basaltic lava flows, most notably the Deccan Trap that covers large parts of Maharashtra, Madhya Pradesh, Gujarat, and northern Karnataka, Andhra Pradesh, and Telangana.

• Black soil forms directly from the weathering of basaltic lava of the Deccan Trap, which gives it its dark colour, high clay content, and calcium-magnesium carbonate richness.

• Red soil develops from the weathering of ancient crystalline and metamorphic rocks such as granite and gneiss; its colour comes from iron oxide in those rocks, not from any lava source.

• Alluvial soil is a transported soil, deposited as river-borne silt by systems such as the Ganga-Brahmaputra-Indus; it has no residual parent-rock origin at all, let alone a lava origin.

• Laterite soil forms through intense leaching (laterization) of a variety of parent rocks under high rainfall and humid tropical conditions; the process, not a lava source, defines it.

This matches the well-documented geological record of the Deccan Trap as a Cretaceous-Paleocene lava plateau, and explains why black soil is also known as black cotton soil for its high moisture retention and characteristic cracking in the dry season, properties that come from clay minerals in weathered basalt.

Hence, the soil formed by lava is Black soil.