A slow-motion geological engine
In the Karkaraly mountains, an unusual process carves the ancient bedrock. Scattered across exposed granite surfaces are bowl-shaped weathering pits, known to geologists as gnammas. These depressions are the result of a relentless physical process: frost weathering. The continental climate of central Kazakhstan produces frequent temperature shifts around the freezing point. Water from rain and snowmelt collects in slight natural indentations in the rock. As temperatures drop below 0°C, this trapped water freezes.
When water turns to ice, its volume expands by about 9%. Trapped within the confines of the rock, this expansion exerts immense pressure, widening microscopic fissures from the inside. This cycle of freezing and thawing happens more than 50 times each year. Each cycle acts like a tiny hydraulic jack, progressively weakening and fracturing the granite. Over thousands of years, this steady process of disintegration enlarges the initial depressions into the bowls seen today, some reaching up to two meters in depth. The broken-down mineral fragments are then cleared away by wind and water, allowing the cycle to continue and deepen the pit.
Islands of life on ancient stone
The granite of Karkaraly National Park is ancient, part of a massif that formed over 300 million years ago during the Paleozoic Era. This rock, primarily composed of durable minerals like quartz and feldspar, weathers very slowly. The weathering pits, therefore, represent a significant acceleration of erosion in very localized spots.
These water-filled basins create unique, isolated micro-ecosystems on the otherwise bare rock surfaces. They become temporary wetlands, providing an important water source in a dry landscape. While some water is lost to evaporation, a significant amount can also seep slowly through the weathered bedrock beneath the pit, promoting further chemical weathering deep within the rock. The pits can support communities of algae, mosses, lichens, and microscopic invertebrates. The process begins with chemical weathering, where water and acids from lichen break down feldspar minerals into clay, which is then removed, initiating the small depression. Over deep time, the combination of chemical decay and the powerful physical force of repeated freezing carves these remarkable features into one of Kazakhstan’s most unique landscapes.