A 300-million-year-old fire
The landscape around the city of Karaganda is dotted with conical hills known as terrikons. These are not natural formations, but massive spoil tips—mountains of waste rock and low-grade coal piled up over a century of intensive mining. The coal within these man-made mountains dates back to the Carboniferous Period, and today, it is releasing its ancient, stored energy. Deep inside many terrikons, slow-burning fires, often invisible from the surface, smolder for decades.
This process is spontaneous combustion. It begins when pyrite (iron sulfide), present in the coal and shale, is exposed to air and moisture. This triggers an exothermic oxidation reaction, generating heat. Inside the densely packed terrikons, this heat cannot easily escape, causing the internal temperature to rise steadily. Once the temperature reaches the ignition point of coal, around 300–350°C, the Carboniferous fuel begins to burn. Deprived of ample oxygen, the coal doesn't burst into open flame but instead combusts slowly, creating a persistent, hidden furnace. Internal temperatures can reach intense levels, sometimes exceeding 1,200°C.
A landscape of industrial alchemy
The Karaganda Coal Basin is one of the largest in the world, with total resources estimated at over 41 billion tons. Industrial-scale mining began here in the early 1930s when the Soviet Union designated the region as its "third coal base". This rapid industrialization led to the creation of the terrikons that now define the local topography.
The intense heat from the subterranean fires is a geological forge, altering the surrounding rocks and even creating new, exotic minerals. As hot gases, rich in chemical compounds, rise through fissures, they cool and deposit these minerals near surface vents. This process, similar to volcanic fumaroles, produces a colorful crust of crystalline substances.
The burning also releases a cocktail of gases into the atmosphere, including carbon monoxide, hydrogen sulfide, and sulfur dioxide. These emissions contribute to local air pollution and present hazards to anyone venturing too close. The ground around active vents can be unstable and extremely hot, with the smell of sulfur hanging in the air. This phenomenon transforms these industrial ruins into active geological laboratories.