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Geology of the Terai zone

Short answer

The Terai is divided into Bhabar (coarse gravel, boulderes, highly permeable) and Terai proper (sand, silt, clay with high water table). It consists of unconsolidated Quaternary alluvium over a thousand meters thick.

Describe the geology (classification and lithology) of the Terai zone.

Terai zone. A flat, low plain 60-300 m in altitude, the northern edge of the Indo-Gangetic plain, formed of Quaternary alluvium brought by the Himalayan rivers.

By the nature of deposits it is divided into:

  1. Bhabar zone: a narrow belt (8-12 km wide) at the foot of the Siwalik. It consists of coarse boulders, cobbles and gravel, very permeable, so streams disappear underground.
  2. Terai proper (Terai plain): finer sand, silt and clay with high water table and springs where the Bhabar water re-emerges.

Lithology: unconsolidated gravel, sand, silt and clay; thickness is over a thousand metres.

Engineering problems: floods and shifting rivers, high water table, liquefaction in earthquakes, low bearing capacity, and shortage of rock for aggregate.

✓ Answer checked by Claude Opus 5.5 (high effort)

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