A habitat carved from ancient rock
The Marble Caves, or Capillas de Mármol, are a geological formation composed of marble that is more than 94% calcium carbonate. This rock began as limestone sediment at the bottom of a sea during the Carboniferous period, roughly 320 million years ago. Tectonic pressure and heat associated with the formation of the Andes mountains metamorphosed this limestone into marble. The caves themselves are a much more recent feature, formed over the last 6,200 years. The relentless wave action of General Carrera Lake, fed by glacial meltwater, has physically and chemically eroded the marble into the smooth, swirling structures seen today.
The water of the lake is an agent in this process. Its turquoise color comes from fine particles of glacial rock, known as rock flour, suspended in the water. This "glacial milk" scatters sunlight, reflecting blue and green wavelengths. The water, slightly acidic from dissolved carbon dioxide, reacts with the calcium carbonate of the marble, slowly dissolving it and carving the complex network of tunnels and caverns that line the shore for about 300 meters.
An ecosystem defined by water levels
The constant fluctuation of General Carrera Lake's water level creates a vertically zoned ecosystem on the cave walls. These changes, driven by seasonal snowmelt, expose and submerge different sections of the marble, creating distinct bands of life. The mineral-rich marble, consistently wetted by waves and spray, provides an ideal substrate for specific types of algae, mosses, and lichens that can tolerate the periodic inundation and exposure.
The upper zones, which remain dry for longer periods, support certain hardy lichens. Below this, a zone of frequent splashing allows for the growth of specialized mosses that cling to the smooth, calcium-rich surfaces. The lowest zone, almost always submerged, is dominated by aquatic algae. The unique turquoise light that filters through the glacial water influences which photosynthetic organisms can thrive beneath the surface. This interaction of geology, light, and fluctuating water levels results in a microhabitat specifically adapted to the unique conditions of the marble caves.
The area is part of a transition zone between the Valdivian temperate rainforest and the Patagonian steppe, meaning the surrounding shores support forests of coihues and lengas, contrasting with the aquatic ecosystem within the caves.