From Mammoths to Methane

The helicopter ride to Cherskii affords a schematic view of a battlefield where earth, air, water and fire (and fire's inverse, photosynthesis) struggle for supremacy. The field is churned, scarred, pitted—no wonder the study of landforms there has reached its apotheosis. This is a landscape for connoisseurs of form: line, dimension and color and their arrangement with each other all have meaning and give insight into the battle between the elements, both contemporary and ancient. On the horizon is a collection of lakes, thousands of them, all triangular and pointed in the same direction. Below us, adjacent to the Kolyma River, defunct channels form long, narrow oxbow lakes. These eventually drain and give way to long stripes of mosses or trees that reveal the pace of the river's meander. The river itself is the least interesting part of the braided skein.

Most bizarre are the polygons. Like the storming of a citadel, water finds a small chink in the armor of the earth and exploits this crack, expanding it as it freezes so as to allow more water to penetrate after the next year's thaw. This process is amplified over years until the soil becomes filled with ice wedges and it is unfair to still call it soil; it is now an ice-complex, or yedoma. From above, this can look like polygons—quadrangular, hexagonal, with straight sides and distinct corners.

It would appear ice rules this landscape. But no: enter fire. As it burns off the insulating layer of moss, the black soil warms, melting the ice below. In a couple of summers the ground will collapse, one meter, two meters, 10 meters. What was once a tranquil, tussocky but flat landscape is shattered into giant mounds and pits owing to the now-absent ice. Like walking on the beach, any violation of the tranquil surface leaves a wet depression. The wetness absorbs the sun, and warms. The puddle now makes a small pond, now a lake, as the ground below it collapses, and it collects more and more runoff from the surrounding landscape.

As the lake expands and grows deeper, the surrounding landscape starts to melt, collapse into the lake and slide to the bottom. The yedoma sediments are particularly high in organic matter, containing not just soil humus but frozen roots, leaves and bones from tens of thousands of years ago. Once they settle at the bottom of the lake, there is a small family of microbes that makes its meager living exploiting the stored energy in this matter, creating methane in the process. This methane bubbles up from the lake bottom and into the atmosphere, where it is invisible but very effective at trapping the long-wave radiation emitted from Earth. The greenhouse effect heats the world atmosphere. One theory holds that the methane from these lakes is partly responsible for the runaway warming that happens at the end of an ice age, accelerating the melting of permafrost.