Starting from 2013 mysterious craters have appeared on the surface of the permafrost of the Siberian tundra, the first of which on the peninsula of Yamala northwestern region of Siberia. A recent study published in the journal Geophysical Research Letters led by researchers from the University of Cambridge proposes a new hypothesis to explain the formation of these structures: at the basis of the phenomenon there would be a osmosis process between the melt waters that infiltrate the subsoil and the layers of salt water present in the cryopeg (saltwater lenses) at a depth of approx 50 meters. The pressure variations in the subsoil would cause the fracturing of the frozen ground and the rapid decomposition of the methane gas hydrates present in the permafrost, whose release into the atmosphere occurs with a violent explosion.
The first crater, which you can see in the photo at the top of this article, appeared in autumn 2013 and immediately received considerable media coverage worldwide. It had a diameter of approx 30 meterswith one band of debris 20 meters wide extended around the edge. There were no signs of human activity or traces of a possible meteor impact. In the following years, numerous other craters were found on the Yamal Peninsula, all having the same characteristics.
The presence of traces of methane on the bottom of the craters suggested that their formation was associated with the release of this hydrocarbon from the gas hydrates present in the subsoil of the Siberian permafrost. THE hydrated gases they are solid compounds formed by water and gases that are found in conditions of high pressure and low temperaturessuch as on the ocean floor and in permafrost. Rising temperatures in the tundra and the resulting partial melting of the permafrost would have destabilized the gas hydrates, causing the release of methane and the formation of craters. However, according to researchers at the University of Cambridge, the melting of the permafrost alone would not be sufficient to cause an explosion and explain the formation of the craters.
The absence of traces of high temperatures in the craters suggests a physical, rather than chemical, origin of the explosive phenomenon. Through laboratory simulations, researchers have identified the cause the process of osmosis, that is, the movement of fluids across a semipermeable membrane from a less concentrated solution to a more concentrated one.
In the Yamal Peninsula, permafrost consists of frozen clay soils that they reach locally thicknesses exceeding 300 metres. Inside them, at a depth of less than 50 metres, are found i cryopeg (or cryopegs), that is, salt water lenses dating back to Pleistocene which prevent portions of the food from freezing cryotic medium (which is part of the permafrost). In fact, dissolved salts lower the freezing point of the aqueous solution. These saltwater lenses sit immediately above methane gas hydrates, stable at high pressures and low temperatures.
Due to theincrease in temperaturesa larger portion of surface permafrost melts seasonally, the so-called superficial active level. The produced water moves downwards, for osmosisuntil reaching the cryopegs, which occupy a relatively small volume of land. This influx of water causes an increase in pore pressures, leading to permafrost fracturing overlying the cryopegs. The pressure gradient then reverses when the fractures reach the surface, causing a drop in subsurface pressures and destabilization of the gas hydrates, resulting in sudden release of methane accompanied by an explosion. The entire process can last several decades and seems to coincide with the worsening conditions of increasing average temperatures in the area since the 1980s.
According to the authors, explosions themselves are a local and infrequent phenomenon; however, the release of methane into the atmosphere can have a significant impact by contributing to global warming.
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