Methane is a powerful greenhouse gas, and the abrupt degassing events that recently have formed large craters on the Russian Arctic Yamal and Gydan Peninsulas have caused major concern. Here we present field data on cover sediments and evolution of a gas-emission crater discovered in the Erkuta–Yakha River valley in the southern Yamal Peninsula in June 2017. The crater is located south of other similar craters discovered over the past decade in northern West Siberia. Data were collected during a field trip to the Erkuta crater in December 2017 which included field observations and sampling of permafrost soil and ground ice from the rim of the crater. All soil and ice samples were measured for contents of methane and its homologs (ethane and propane) and carbon dioxide. The contents of carbon dioxide in some samples are notably higher than methane. The strongly negative δ13С of methane from ground ice samples (−72‰) is typical of biogenic hydrocarbons. The ratio of methane to the total amount of its homologs indicate a component of gases that have migrated from a deeper, thermogenic source. Based on obtained results, a potential formation model for Erkuta gas-emission crater is proposed, which considers the combined effect of deep-seated (deep gas migration) and shallow (oxbow lake evolution and closed talik freezing) causes. This model includes several stages from geological prerequisites to the lake formation.

Gas accumulation and pressurized unfrozen rocks under lakes (sublake taliks) subject to freezing in shallow permafrost may lead to explosive gas emissions and the formation of craters. Gas inputs into taliks may have several sources: microbially-mediated recycling of organic matter, dissociation of intrapermafrost gas hydrates, and migration of subpermafrost and deep gases through permeable zones in a deformed crust. The cryogenic concentration of gas increases the pore pressure in the freezing gas-saturated talik. The gradual pressure buildup within the confined talik causes creep (ductile) deformation of the overlying permafrost and produces a mound on the surface. As the pore pressure in the freezing talik surpasses the permafrost strength, the gas-water-soil mixture of the talik erupts explosively and a crater forms where the mound was. The critical pressure in the confined gas-saturated talik (2–2.5 MPa for methane) corresponds to the onset of gas hydrate formation. The conditions of gas accumulation and excess pressure in freezing closed taliks in shallow permafrost, which may be responsible for explosive gas emissions and the formation of craters, are described by several models.