Correct Option
The correct option is (a) 1 only.
Explanation
The Northern Plains of India are a result of extensive alluvial deposition in the vast basin lying at the foothills of the Himalayas. This physiographic division is geologically young and agriculturally productive due to the nature of its soil and water availability.
Statement-wise Analysis
- Statement 1 is Correct: The Northern Plains have been formed by the interplay of the three major river systems-the Indus, the Ganga, and the Brahmaputra-along with their tributaries. Over millions of years, these rivers deposited alluvium in the depression formed between the Himalayas in the north and the Peninsular Plateau in the south.
- Statement 2 is Incorrect: The plains are formed primarily of alluvial soil, which is brought down by the rivers from the mountains. Black soil (Regur) is the characteristic soil of the Deccan Trap region in the Peninsular Plateau, formed by volcanic origin, not the Northern Plains.
- Statement 3 is Incorrect: While the Northern Plains are generally described as flat, it is factually incorrect to state they have "absolutely no variations in relief." Based on variations in relief features, the plains are divided into four distinct regions:
- Bhabar: A narrow belt of pebbles lying parallel to the slopes of the Shiwaliks.
- Terai: A wet, swampy, and marshy region south of the Bhabar.
- Bhangar: Older alluvium forming terraces above the flood plains, often containing calcareous deposits (Kankar).
- Khadar: Newer, younger deposits of the flood plains that are renewed almost every year.
Key Takeaway: The Northern Plains are depositional landforms created by the Indus, Ganga, and Brahmaputra systems comprising alluvial soil. They possess distinct relief variations classified into Bhabar, Terai, Bhangar, and Khadar belts.