The mountain's plumbing
The Cangshan Mountain range is a dramatic geological feature, a wall of rock rising to the west of Erhai Lake. This compact range, part of the larger Hengduan Mountains, stretches approximately 50 kilometers from north to south and is defined by its distinct structure: nineteen peaks separated by eighteen streams. Nearly all of the peaks exceed 3,500 meters in elevation, with the highest, Malong Peak, reaching 4,122 meters (13,524 feet). The year-round snowmelt and rainfall collected by this massive landform are channeled through the eighteen streams, which are the primary source of fresh water for Erhai Lake.
The mountain itself is a metamorphic core complex, the result of immense geological pressure from the collision of the Indian and Eurasian tectonic plates that also formed the Himalayas. This process created a landscape of ancient metamorphic rocks, including the famous Dali Marble, a stone prized for centuries and the reason the Chinese word for marble is "dali shi". The mountain also holds relics from the Quaternary Period's "Dali Glacial Period," providing an important reference point for studying past climate change in the region. This complex geology gives each of the eighteen streams a unique character as they carve their way down to the lake.
Tracing the water's origin
The consistent flow of water from the nineteen peaks is important for the health of Erhai Lake, but the specific contribution of each part of the watershed changes throughout the year. To understand this dynamic system, scientists use stable isotope hydrology. This technique analyzes the ratios of heavy to light isotopes of hydrogen (Deuterium, ²H) and oxygen (¹⁸O) in water molecules. Water originating from different sources—such as high-elevation snowmelt versus lower-elevation rainfall—has a distinct isotopic "fingerprint."
Studies in similar high-altitude basins show that precipitation and meltwater have characteristic isotopic values that shift with the seasons. Water from summer monsoons, for example, has a different isotopic signature than winter snowpack. By sampling the water in the eighteen streams and in Erhai Lake at different times of the year, researchers can trace the water back to its source. This allows them to quantify how much of the lake's water comes from high-altitude snow melting in the spring versus direct rainfall runoff during the summer wet season. This data is important for managing the water resources of the Dali basin, predicting the effects of climate change on the lake's water supply, and protecting the ecosystem from pollutants that can enter via these streams.