- Glacier velocity in the Zanskar Himalayas dropped 16% between 1992 and 2023, with the slowdown accompanied by accelerated ice thinning.
- Glaciers at lower elevations lost speed faster than those higher up.
- The slowdown signals reduced water security for the rain-shadow region of Ladakh, which relies heavily on glacier and snowmelt for its water supply amid broader Himalayan ice loss.
The phrase “moving at glacial pace” is inspired by the slow, inching motion of glaciers as they flow downwards. But new research suggests glaciers in the Zanskar Himalayas in Ladakh are moving even slower than before, with implications for water availability in the region over the long term.
Centuries-old glaciers blanketing mountaintops may appear to be stationary, but their mass is slowly pulled down by gravitational forces over time. The speed at which glaciers descend can be used as an indicator of their health, explained Manish Mehta, a scientist and glaciologist at the Wadia Institute of Himalayan Geology.
“Glaciers have two parts. The crown at the top is where ice and snow is accumulated from solid precipitation at higher elevations, and the snout or toe is at the bottom. The accumulation of ice at the crown is what pushes the glacier down, increasing its velocity,” he explained, adding, “But in recent times, glaciers are losing their mass in both the upper and lower zones. With less mass, there is less movement.”
In the Zanskar Himalayas in Ladakh, glacier velocity decreased by 16% from 1992 to 2023, a study published in The Cryosphere journal found. The study is among the few long-term observational analyses of glacier velocity from the region, and adds to existing evidence of unprecedented glacier retreat in the world’s third pole.
Region-wide slowdown
The Zanskar Himalayas cover an area of 7,000 square kilometres, with elevations ranging from 3,500 to 7,135 metres above sea level. These mountain ranges are home to around 1,755 glaciers, but to observe their changing velocity, the researchers selected just 12 glaciers.
Despite being a major contributor to the Indus river basin, long term observational studies from the Zanskar Himalayas have been lacking, said Tirthankar Ghosh, a PhD student at IIT-Bombay and Monash University, and the study’s author. The study relied primarily on satellite imagery to calculate glacier velocity and determine glacier thickness.
It found that between 1992 and 2000, all observed glaciers showed an increase in glacier velocity, indicating a healthy mass balance. Between 2001 and 2023, however, the velocity of most glaciers slowed.
Glaciers at lower elevations (less than 5000 metres) slowed at a faster rate than those at higher elevations. Slower glacier velocity was also accompanied by glacier thinning, with average thinning at a rate of 0.22 metres per year from 2000 to 2005, accelerating to 0.57 metres per year from 2015 to 2020.
“The slope, length and thickness of the glaciers all influence how it will respond to varying climatic factors. A glacier on a northern facing slope may be exposed to less solar radiation than a glacier on a southern facing slope, for example,” said Ghosh.
Other factors that complicate the movement of a glacier include the amount of debris it collects as it moves, as well as whether it terminates in a lake. The study finds that debris does not protect against thinning, and that lake-terminating glaciers gain velocity as they thin down, although this could be due to their sheer size.
According to Mehta, who was not part of the IIT Bombay-Monash University study, changing precipitation patterns due to global warming are a significant driver of glacier velocity loss and thinning. Annual temperatures in Leh increased by 0.02°C every year from 1901-2019.
“The Zanskar region is much more glacier rich compared to Leh or the Karkoram regions, for example, because it receives the most precipitation by both weather systems, the southwest monsoon and western disturbances. Global warming is causing the area of snowfall and precipitation, which feeds these glaciers, to decrease,” he said.
A water crisis in the making
The thinning of glaciers has been reported across the Karakoram, Zanskar, and Hindu Kush Himalayan (HKH) ranges which stretch across India, Pakistan, and Afghanistan. A 2026 report by the International Centre for Integrated Mountain Development found that the HKH range experienced a 12% reduction in glacier area between 1990 and 2020.
Glacier retreat has a direct impact on water availability to the region, because of the water they store. All but one of the sub-basins supplying the Indus river system with water were found to have depleted glacier mass in a 2024 study.
“Ladakh is a rain shadow area which is mostly dependent on the snow and glacier melt for water supply. So if we can understand the dynamics of how these ice bodies are flowing, we can make better predictions of how they will evolve in the future,” said Ghosh.
Banner image: Drang Drung glacier in the Zanskar Himalayas. Image by Andrew Mackintosh.
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