Formation of the Siberian Yamal gas emission crater via accumulation and explosive release of gas within permafrost

Abstract

AbstractThe Arctic landscape has experienced many dramatic forms of change due to anthropogenic warming. Large crater‐like forms surrounded by fragmented blocks scattered outward to great distances with precursor mounds appeared in the continuous permafrost zone of the Yamal and Gydan peninsulas of Western Siberia. The morphologies of these craters, in addition to the abundant evidence of active and intense gas emissions across the region, indicate that they formed due the subsurface accumulation, pressurization, and explosive release of gasses trapped within the permafrost. Therefore, these craters were termed “gas emission craters” (GEC). However, some have suggested that in addition to gas accumulation, these features form in a manner similar to ice‐cored pingos and require pressurization due to the freezing of subsurface ice. This is despite the fact that not all GECs form in areas conducive to pingo‐like ice accumulation. Here, we test whether the pressurization and explosive release of methane gas alone can reproduce the observed morphology of the first‐discovered and most intensely studied GEC, Yamal crater. We use the available field and satellite data to constrain the initial dimension parameters of a model of the explosion process and consider several plausible configurations for the unknown interior cavity shape, the overlying permafrost cap thickness, and gas chamber volume. The explosion process is modeled in phases: gas migrates upward and accumulates in the subsurface until the gas pressure fractures the overlying cap, the expanding gas and cap blocks are initially accelerated outward together, and then the blocks are launched as projectiles. The sizes and locations of the ejected blocks found at Yamal crater are used to determine the initial gas pressures required to launch those projectiles to the observed locations. Finally, we estimate the amount of gas released in each of the multiple model runs testing different plausible internal cavity geometries. For the range of plausible block sizes and densities, and a subset of gas chamber volumes considered, we find that the gas pressure (0.6–2.6 MPa) required to launch the Yamal crater blocks to their observed distances was within the range of the sum of the ice/permafrost tensile strength and the lithostatic pressure (0.22–2.87 MPa). Thus, the observed blocks could have been launched by the energy required to fracture and displace the overlying permafrost cap. We show that the mechanism of formation of this GEC does not require pressure from the freezing of ice in the subsurface to crack and explode the overlying permafrost—gas pressure alone can produce these GECs. We expect that as our planet warms, the Siberian permafrost will continue to warm, weaken, and release gasses such as the greenhouse gas methane, and contribute to a permafrost carbon‐positive feedback cycle that would lead to the formation of even more explosive GECs.