Geography · Ch 2 — Structure and Physiography
The Northern Plains
The Northern Plains
The photograph shows a flat, open expanse of paddy field, saturated with water — the kind of scene you’d expect in the heart of the alluvial plain during the monsoon. Farmers are at work in the field, bent over the crop, while a line of trees runs along the background, marking the edge of the cultivated land. There is nothing dramatic in the frame: no hills, no steep slopes, no rocky outcrops. That flatness is the point.
What the image captures is the very character of the northern plain — a surface built entirely by river-borne sediment. The waterlogged field is not a flaw in the picture; it is the signature of the region. The plain is young, low-lying, and barely elevated above sea level (roughly 50–150 m), so drainage is sluggish and floodwaters linger. The green paddy and the farmers tending it speak to the other half of the story: this is some of the most fertile soil on Earth, and it supports an intensely agricultural way of life. Wheat, rice, sugarcane, and jute all thrive here because the alluvium is renewed again and again by the Indus, the Ganga, and the Brahmaputra. …
The Northern Plains are the product of millions of years of sediment deposition. The Indus, the Ganga and the Brahmaputra, along with their tributaries, carried vast quantities of alluvium down from the mountains and laid it down in the foredeep basin at the foot of the Himalayas. Over time, this accumulated material built up one of the most extensive and fertile plains on Earth.
The plains stretch roughly 3,200 km from east to west. Their average width varies between 150 and 300 km, and the alluvium beneath them reaches a maximum depth of 1,000 to 2,000 m. From north to south, the region divides into three major zones: the Bhabar, the Tarai and the alluvial plains. The alluvial plains themselves split further into the Bhangar (older deposits) and the Khadar (newer deposits).
The Bhabar is a narrow belt, 8 to 10 km wide, running parallel to the Shiwalik foothills at the point where the slope breaks. When mountain streams and rivers hit this sudden drop in gradient, they lose velocity and dump their heaviest load — rocks and boulders — right here. In fact, many streams simply disappear into this porous, pebble-strewn zone.
The Tarai lies immediately south of the Bhabar and is roughly 10 to 20 km wide. The streams and rivers that vanished underground in the Bhabar re-emerge here, but without any properly demarcated channel. The result is a marshy, swampy tract known as the Tarai. This waterlogged belt supports a luxurious growth of natural vegetation and shelters a varied wildlife.
South of the Tarai lie the alluvial plains proper, made up of old and new alluvium — the Bhangar and the Khadar. These plains display the classic landforms of a mature stage of fluvial erosion and deposition: sand bars, meanders, ox-bow lakes and braided channels.
The Brahmaputra plains are especially known for their riverine islands and sand bars. Much of this area is prone to periodic floods, and the river frequently shifts its course, creating braided streams. Where these mighty rivers meet the sea, they have built some of the largest deltas in the world — the famous Sunderbans delta being the prime example.
| Zone | Position | Width | Key Characteristic |
|---|---|---|---|
| Bhabar | Parallel to Shiwalik foothills, at slope break | 8–10 km | Deposition of rocks and boulders; streams often disappear |
| Tarai | South of Bhabar | 10–20 km | Streams re-emerge, creating marshy, swampy conditions; dense vegetation and wildlife |
| Alluvial plains (Bhangar & Khadar) | South of Tarai | — | Old and new alluvium; mature fluvial landforms like meanders and ox-bow lakes |