A long, brilliantly blue lake on the Ladakh plateau, with no outlet to the sea.
Pangong Tso is a long, thin ribbon of brilliant blue water lying at about 4,350 m on the cold Changthang plateau of eastern Ladakh, and stretching east onto the high Tibetan Plateau.
It is an endorheic lake, which means water flows in from snow and glacier-fed streams but no river carries it out to the sea. In a closed basin like this, the only way water leaves is by evaporating, and evaporation takes the water but leaves the dissolved salts behind. Those salts slowly build up, which is why a lake fed by fresh mountain snow ends up brackish and slightly alkaline. The thin, clear air at this altitude is part of why the water looks such an intense blue.
The lake sits in a trough opened by the Karakoram Fault, one of the great strike-slip faults of the region. A strike-slip fault is one where the ground on either side slides horizontally past itself, rather than one side riding up over the other. Where such a fault bends or steps sideways, the crust caught in the bend is pulled apart and sinks, forming a long, straight, narrow basin. Pangong’s shape, a sliver of water more than 130 km long, traces that fault-controlled trough, and its northwestern end is bounded by two branches of the fault, the Pangong and Tangtse strands.
The ranges flanking the lake are built of old, hard rocks (migmatitic gneiss and granite) that were squeezed and heated deep within the same fault zone. So the basin the water sits in and the mountains that wall it are really two expressions of one sliding-fault system.
Pangong has not always stood at today’s level. Old shorelines, called strandlines, are preserved as faint benches above the water, roughly 1 to 6 m higher, each marking a time when the lake was fuller. Salt and sediment recovered from the lake bed show the climate here has swung between wetter and drier over the last few thousand years: a warmer, wetter spell a few thousand years ago kept the lake high, and later a turn toward drier conditions dropped its level and concentrated its salts.
Today Pangong still freezes solid in winter despite being salty, and its level keeps rising and falling with the balance between meltwater coming in and water evaporating away. Its length and straightness are the signature of the fault it lies along; its saltiness is the signature of a basin with no way out. Both trace back to the same thing: this is a closed trough torn open by a sliding fault, sitting high on an arid plateau.
Sources
- Geological Survey of India
- Sagwal et al. (2023), Late-Holocene hydrological variability from the NW Himalaya and southwestern Tibetan Plateau: Paleo-salinity records from Pangong Tso, The Holocene
- Rapid lake level fall in Pangong Tso (lake) in Ladakh, NW Himalaya: a response of Late Holocene aridity (2020)
- Catastrophic partial drainage of Pangong Tso, northern India and Tibet, Geomorphology