Environment · 13 Aug 2026
Assertion (A): A study of 12 glaciers in Ladakh's Zanskar Himalaya found that average glacier flow velocity slowed by 2.4 metres per year per decade between 1992 and 2023.
Reason (R): A slowing glacier necessarily means reduced immediate river runoff, since slower ice flow directly translates into less meltwater reaching downstream rivers.
Select the correct answer:
Researchers including IIT-Bombay's Tirthankar Ghosh published findings in The Cryosphere showing Zanskar Himalaya glaciers have slowed measurably over three decades due to surface thinning, a mechanism also seen in the Alps, Alaska, the Andes and the Tibetan plateau.
UPSC frequently uses assertion-reasoning to test whether aspirants conflate two related-sounding but distinct environmental indicators - here, glacier flow slowdown versus immediate water availability - which is exactly the kind of nuance the exam rewards.
A 1992-2023 satellite study found Zanskar Himalaya glaciers slowing by 2.4 m/year/decade due to surface thinning, but a slowing glacier does not necessarily mean reduced immediate river runoff - current flow and long-term ice health can diverge.
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