Given below are two statements, one is labelled as Assertion (A) and other as Reason (R): Assertion (A): Teesta river was earlier a tributary of Ganga now it is a tributary of Brahmaputra. Reason (R): River capturing is a major feature of Himalayan rivers. Select the correct answer using the codes given below.
- (a)Both (A) and (R) are true and (R) is correct explanation of (A)
- (b)Both (A) and (R) are true, but (R) is not correct explanation of (A)
- (c)(A) is true, but (R) is false
- (d)(A) is false, but (R) is true
Correct — A, both statements are true and R correctly explains A. Historically the Teesta drained southward into the Ganga/Bengal-delta system through channels such as the Karatoya, Atrai and Punarbhaba. After the great flood of 1787 the river shifted its course southeastward and joined the Brahmaputra (Jamuna), which is where it flows today — so Assertion A is true. River capture (also called river piracy or course diversion) is indeed characteristic of youthful, actively down-cutting Himalayan rivers, so Reason R is true. Because standard geography teaching presents the Teesta's Ganga-to-Brahmaputra switch as exactly such a capture/diversion, R is the correct explanation of A, giving option (a).
- (b)Both (A) and (R) are true, but (R) is not correct explanation of (A) — Both statements are true, but R is not an unrelated fact — the Teesta's diversion from the Ganga system to the Brahmaputra is treated as a case of river capture/course change, so R directly explains A.
- (c)(A) is true, but (R) is false — R is not false. River capture/piracy is a genuine, recognised feature of youthful Himalayan drainage, so treating R as false is incorrect.
- (d)(A) is false, but (R) is true — A is not false. The documented shift of the Teesta from the Ganga system to the Brahmaputra (after the 1787 flood) makes the assertion true.
River capture (river piracy) is the diversion of one river's headwaters or course into an adjacent, more actively eroding channel. It is common in the young, steep Himalayan drainage, where rivers cut down rapidly and antecedent/consequent streams jostle for catchment. The Teesta is a classic Indian illustration: once part of the Ganga-side drainage of north Bengal, it swung east to become a tributary of the Brahmaputra.
In an Assertion–Reason item, verify each statement independently, then ask whether the reason is the actual cause. Here the historical course change (A) is true and the Himalayan tendency to capture/divert (R) is the very mechanism invoked to explain it, so the two are cause-and-effect — answer (a), not (b).
- Teesta earlier drained into the Ganga/Bengal-delta system; it now joins the Brahmaputra (Jamuna)
- The shift is dated to the catastrophic flood of 1787
- River capture/piracy is a recognised feature of youthful, actively eroding Himalayan rivers
- The Teesta rises from the Pauhunri/Teesta Kangse glacier in Sikkim (source differs from the Brahmaputra's)
- Marking (b) when R actually is the mechanism that explains A
- Confusing the Teesta's source with the Brahmaputra's — they are different glaciers
UPSC and UPPSC test the Teesta either through statement-based items on its source, tributaries and outfall, or as an Assertion–Reason on its historical course change and river capture.
With reference to river Teesta, consider the following statements: 1. The source of river Teesta is the same as that of Brahmaputra but it flows through Sikkim. 2. River Rangeet originates in Sikkim and it is a tributary of river Teesta. 3. River Teesta flows into Bay of Bengal on the border of India and Bangladesh. Which of the statements given above is/are correct?
- (a) 1 and 3 only
- (b) 2 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer(b) 2 only
Same river — tests the Teesta's source, its Rangeet tributary and where it drains, complementing this item's focus on its course change.
- practice — not a real PYQ
'River capture' is most characteristic of which stage/type of rivers?
- (a)old, mature rivers of the peninsular plateau
- (b)youthful, actively down-cutting Himalayan rivers
- (c)deltaic distributaries near the sea
- (d)inland drainage of arid basins
Answer(b) youthful, actively down-cutting Himalayan rivers — where headward erosion lets one stream divert another.
- practice — not a real PYQ
The Teesta river finally joins which river before entering the Bay of Bengal drainage?
- (a)Ganga
- (b)Brahmaputra (Jamuna)
- (c)Mahananda
- (d)Subarnarekha
Answer(b) Brahmaputra (Jamuna) — inside Bangladesh, after its post-1787 course change.