A Lake Colored by Geology
The intense turquoise color of Big Almaty Lake, located at an altitude of 2,511 meters in the Trans-Ili Alatau mountains, results directly from geology in motion. The lake occupies a basin formed by tectonic activity and later shaped by glaciers. Its water comes from the melting of glaciers that carve through the surrounding peaks, which include Sovetov Peak (4,317 m), Ozerny Peak (4,110 m), and Tourist Peak (3,954 m).
As these glaciers advance, they grind the bedrock of the Tian Shan mountains into a fine silt. This material, known as glacial flour or rock flour, consists of minute mineral particles. The particles are so small—typically between 2 and 5 micrometers—that they do not sink. Instead, they remain suspended in the water column, creating a colloidal solution. It is this suspension of rock flour that gives the lake its opaque, turquoise appearance. The lake's water volume is about 14 million cubic meters, and its depth reaches up to 40 meters.
The Physics of Turquoise Water
The specific color of the water is a function of light physics. Pure water appears blue because it absorbs longer wavelengths of light (reds, oranges, yellows) more strongly than shorter, blue wavelengths. In Big Almaty Lake, the suspended glacial flour particles dramatically alter this process.
The interaction is a form of particle scattering. While the hook refers to Rayleigh scattering—which applies to particles much smaller than the wavelength of light, like air molecules—the 2-5 micrometer particles in the lake are similar in size to the wavelengths of visible light (0.4-0.7 micrometers). This suggests that Mie scattering is the more dominant physical process. This type of scattering scatters all wavelengths of light, contributing to the water's milky opacity. The turquoise hue emerges from a combination of this scattering effect and the inherent absorption properties of water. The particles provide more surfaces to reflect the weakly-absorbed blue and green light back to an observer's eye before it can be absorbed by the water.
The color's intensity fluctuates with the seasons. During the summer melt, from June to August, the concentration of glacial flour in the water is at its highest, producing the brightest turquoise color. The water level is also highest in August and lowest in February, with fluctuations up to 20 meters. In autumn, the color may shift to a greenish-blue, and in winter, the lake freezes over completely.