The mystery of Siberia’s exploding craters

 The mystery of Siberia's strange exploding craters may have finally been solved

Scientists offered a new explanation for the huge craters that keep appearing in Siberia. These craters, first spotted in 2012, can be more than 160 feet deep and over 65 feet wide. They may be due to hot time bombs made of natural gas building up under the frozen ground. Scientists are putting forward a new explanation for the giant exploding craters that seem to be randomly appearing in the Siberian permafrost. These craters, first spotted in 2012, have been popping up in the deserted Siberian permafrost, puzzling scientists. They can be substantial, reaching more than 160 feet in depth and 65 feet in width, and blasting chunks of debris hundreds of feet away. Researchers from the Russian Academy of Sciences discovered a new crater in Yamal during an expedition in August 2020. On a remote peninsula in the Arctic circle, enormous wounds are appearing in the permafrost, as something that is worrying scientists bursts out from underground. It appeared suddenly and explosively, leaving a ragged pockmark on the landscape. Around the crater’s edge, the earth is a torn, grey jumble of ice and clods of permafrost. The roots of plants, newly exposed around the rim, show signs of scorching. It gives some idea of just how violently this hole in the middle of the Siberian Arctic materialised.

From the air, the freshly exposed dirt stands out against the green tundra and dark lakes around it. The layers of earth and rock exposed further inside the cylindrical hole are almost black and a pool of water is already forming at the bottom by the time scientists reach it. Among them is Evgeny Chuvilin, a geologist at the Skolkovo Institute of Science and Technology, based in Moscow, Russia, who has flown out to this remote corner of the Yamal Peninsula in north-west Siberia to take a look. This 164-foot-deep (50m) hole could hold key parts of a puzzle that has been bothering him for the past six years since the first of these mysterious holes was discovered elsewhere on the Yamal Peninsula. The hole, which was around 66ft (20m) wide and up to 171ft (52m) deep, was discovered by helicopter pilots passing overhead in 2014, around 26 miles (42km) from the Bovanenkovo gas field on the Yamal Peninsula. The scientists who visited it, including Mariana Leibman, chief scientist of the Earth Cryosphere Institute, who has been studying the permafrost in Siberia for more than 40 years,  described it as an entirely new feature in permafrost. Analysis of satellite images later revealed that crater, now known as GEC-1, formed sometime between 9 October and 1 November 2013. "When climate change or atmosphere warming is weakening the other part of the permafrost, then you get these outbursts — only in Siberia," he said.

But exactly what is causing these enormous holes in the permafrost to appear and how suddenly they form is still largely a riddle. There are also unanswered questions about what they mean for the future of the Arctic, along with the people who live and work there. For many of those who study the Arctic, they are a disquieting sign that this cold, largely unpopulated landscape at the north of our planet is undergoing some radical changes. Recent research, however, is now starting to provide some clues about what might be going on. What is clear is that these holes are not forming due to some gradual subsidence as the permafrost melts and shifts below the surface. They explode into being. “As the blast occurs, blocks of soil and ice are thrown hundreds of metres from the epicenter,” says Chuvilin. “We are faced here with a colossal force, created by very high pressure. Why it is so high still remains a mystery.”

Some reports have suggested the blasts can be heard 60 miles away. Now scientists are proposing that hot natural gas seeping from underground reserves might be behind the explosive burst. The findings could explain why the craters are only appearing in specific areas in Siberia. The area is known for its vast underground reserves of natural gas. Gas makes the hole, but it comes from deep reserves. Permafrost traps a lot of organic material. As temperatures rise, it thaws, allowing that mulch to decompose. That process releases methane. So scientists had naturally proposed the methane seeping from the permafrost itself was behind the craters. This isn't a crazy thought. It's notably the process that's thought to lead to thermokarsts, lakes that appear in areas where permafrost is melting, which bubble with methane and can be lit on fire. Bubbles are shown on rising to the surface of the thermokarst. Themokarsts are full of methane, which bubbles to the surface. But that doesn't explain why the so-called exploding craters are so localized. 

Only eight of these craters have been identified so far, all within a very specific area: the Western Siberian Yamal and Gydan peninsulas in Northern Russia. Chuvilin is one of a group of Russian scientists, collaborating with colleagues from around the world, who have been visiting these craters to take samples and measurements in the hope of understanding more about what is going on beneath the tundra. Some scientists have compared the craters to cryovolcanoes, volcanoes that spew ice instead of lava,  thought to exist in some of the distant parts of our solar system on Pluto, Saturn’s moon Titan and the dwarf planet Ceres. But as more Arctic craters have been studied in various stages of their evolution, they have become known as “gas emission craters”. The name gives some clue to how they are thought to form. Exploding lakes, by contrast, are seen in a wide variety of areas where permafrost is found, including Canada.

Scientists suggest there's another mechanism at play: hot natural gas, seeping up through some kind of geological fault, is building up under the frozen layer of soil and heating the permafrost from below. Those hot gas plumes would help thaw the permafrost from the bottom, making it weaker and more likely to collapse. A diagram explains the process by which the exploding craters could be formed. "This explosion can only happen if the permafrost is thin and weak enough to break," said Hellenvang. Rising temperatures melt the upper layer of the permafrost at the same time. This creates the perfect conditions for the gas to be freed suddenly, triggering either an explosion or a "mechanical collapse" caused by the gas, which is under pressure. That creates the crater, Hellevang and colleagues are suggesting. The area is rife with natural gas reserves, which lines up with Hellevang and colleagues' theory, per the study. "This area is one of the largest petroleum provinces in the world," he said. According to the scientist's model, more of these craters could have been created and have since disappeared as nearby water and soil fell in to fill the gap. "This is a very remote area, so we don't really know the true number," he said. "If you look at the satellite image of the Yamal Peninsula, there are thousands of these round plate-like depressions. Most or all of them could have been thermokarsts, but potentially they could also be earlier craters that have formed," he said.

There is evidence that the life cycle of gas emission crater can be very short, ranging from 3-5 years. It is clear that the mounds in north-west Siberia are behaving differently. They swell “very fast, rising to several metres” before they blow their top suddenly. And instead of freezing water, the uplift appears to be caused by a build-up of gas beneath the ground. One study of tree rings in willow shrubs found among the debris thrown out by the explosion that created the first crater discovered in 2014 suggests the plants had been experiencing stress since the 1940s. The researchers say this could have been due to deformation of the ground. One crater that formed in the early summer of 2017, known as SeYkhGEC, was found in satellite images to have first begun deforming the ground in 2015. To understand more about how the craters form, scientists have lowered themselves into the deep holes to take samples.  

Similar scars and mounds related to gas pocket emissions have been found on the floor of the Kara Sea, just off the Yamal Peninsula, and others have been found in the Barents Sea. But so far, nothing similar has been found on land elsewhere in the Arctic. Something about the permafrost in Yamal and Gydan makes them prone to these exploding mounds. “There are some characteristic features of the landscape there,” she says. “It is an area where there is a very thick layer of ice, called tabular ice, which forms a cap across the permafrost. It is also an area where there’s a lot of features known as cryopeg, which are areas of unfrozen ground surrounded by permafrost – a kind of permafrost sandwich. The third feature is very deep deposits of gas and oil.” Qne crater recently examined,  a 66ft-wide (20m) hole known as the Erkuta crater after the river whose flood plain it appeared on, appears to have formed on the spot of a dried up oxbow lake. When the lake vanished, it left behind an unfrozen patch of soil beneath it known as a talik, where gas then built up. But the exact source is still largely unclear. “The key issue in crater research is identifying the source of gas that builds up under the permafrost surface,” says Chuvilin. “Once the crater is there, the gas is already gone.” Local reindeer herders reported seeing flames and smoke after one crater explosion in June 2017. Retracing the evolution of these mounds and how the gas gets there is now an intense source of study. “It is intriguing that there could be a new or previously unknown geochemical process happening that we would never have imagined,” says researchers.

Researchers brave enough to abseil down into the craters have found elevated levels of methane in the water pooling at the bottom, suggesting the gas may be bubbling up from below. One leading theory is that these deep deposits of methane gas under the permafrost find their way up to the unfrozen pocket of ground beneath the icy cap. Another idea is that high levels of carbon dioxide dissolved in the water in these unfrozen pockets begins to bubble out as the water starts to freeze, and the remaining water cannot hold onto the dissolved gas. An alternative source of both methane and carbon dioxide could be microorganisms thriving in the unfrozen pocket of ground breaking down organic material and releasing the gases. Isotopic analysis of methane at one particularly dramatic crater appeared to confirm this, but the activity of methane-producing microbes, however, has been found to be particularly low in the lakes at the bottom of recently formed craters, even for the cold conditions where they are found.

But methane could also be leaking out from the ice itself. Gases can become trapped inside the water crystals in permafrost to form a strange frozen material known as a gas hydrate. As it melts, the gas is liberated. Regardless of the source, it is thought that the gas builds up in the unfrozen pocket of ground, pushing the solid tabular ice cap upwards by 16-19ft (5-6m) until it ruptures like a boil. (While graphic, the furuncle analogy is not a bad one – much like internet users are fascinated by videos of pimple popping, so some scientists find themselves drawn to the Yamal craters. When they finally burst, they certainly appear to be spectacular. Mud and ice above the gas-filled pocket, along with much of the material in the unfrozen section itself, is flung outwards up to 980ft (300m) away. The force is so great that blocks of earth up to 3ft (1m) across are thrown outwards, leaving a crater with a raised parapet, a wide mouth and a narrower cylindrical hole – thought to be the unfrozen pocket – is left behind. Local reindeer herders reported seeing flames and smoke after one crater explosion in June 2017 along the banks of the Myudriyakha River. Villagers in nearby Seyakha – a settlement about 20.5 miles (33km) south of the crater – claimed the gas kept burning for about 90 minutes and the flames reached 13-16ft (4-5m) high. Over a year or two the edges of the dark, angry wound erode and they fill with water. In this sparsely populated region of the world, for one to occur so close to a settlement has led to concern. The region is also splattered with pipelines for the oil and gas infrastructure trying to get at the fossil fuel deposits buried beneath the permafrost.

Gas and oil infrastructure dot the landscape in north-west Siberia – the Bovanenkovo gas field was just 26 miles from one of the craters. Unravelling exactly how common these craters are is currently a slow process. After their violent birth, most seem to disappear into the landscape almost as quickly – the void left by the explosion near Seyakha – which measured 70m (230ft) wide in places and more than 50m (164ft) deep – flooded with water in just four days due to its proximity to the river. This transition from hole to lake seems to be a rather innocuous end to a dramatic event. Other craters take longer to flood, but over a year or two the edges of the dark, angry wound erode and they fill with water to become almost indistinguishable from the thousands of other small round lakes – known as thermokarst lakes – that dot the landscape. Exactly how many of these lakes are the scars of gas emission craters is still unclear.

Some researchers have tried to identify former gas emission craters by measuring the chemicals dissolved in characteristic lakes, but have been unable to identify any patterns. The craters are a very shocking indicator of what is happening in the Arctic more widely. Finding out just how common these events are is driven by more than simple curiosity. There are growing concerns that the appearance of the craters in north-west Siberia might be related to wider changes taking place in the Arctic due to climate change. Surface air temperatures in the Arctic are warming at twice the rate of the global average, which is increasing the amount of permafrost thaw during the summer months. This in itself is transforming the Arctic landscape, leading to subsidence and landslides known as thaw slumps. Siberia boasts perhaps the largest thaw slump on the planet – the Batagaika megaslump, which has grown from being just a gully in the 1960s to being nearly 3,000ft (900m) wide. 

Trapped inside the Arctic permafrost are huge amounts of carbon, about twice as much as the amount currently in the atmosphere. It is mostly in the form of the frozen remains of plants and other organic material, along with methane that has become trapped inside ice crystals, the gas hydrates. As the ground thaws, it allows microorganisms to break down the organic matter, releasing methane and carbon dioxide as by products, while the methane trapped in the ice also breaks free. When they first appear, the craters are a spectacular sight as the explosion hurls out earth and ice to leave a deep cylindrical void.  As a potent greenhouse gas, this methane leaking out of permafrost has the potential to accelerate global warming and so drive even more melting. But in Yamal, the craters have raised the prospect of another process that is adding even more uncertainty to the complex feedback loop between rising temperatures, permafrost thaw and the release of greenhouse gases. If it turns out that methane deposits trapped deep underground by the permafrost are starting to seep upwards through the normally impenetrable permafrost layers, it could be a sign that the frozen ice cap over the tundra is becoming more permeable. This could introduce new levels of uncertainty over how changes in the Arctic are likely to impact wider global warming on the planet.

Still, if the hypothesis is found to be correct, this could spell trouble for climate models. Natural gas is full of methane, a potent greenhouse gas. This could mean the craters are acting like huge chimneys through which the damaging chemical could be freed suddenly into the atmosphere. "If that's the standard way that large accumulations fail then you're dumping a lot of methane in a very short time," Scientists suggest. Hellenvang, however, exercised caution. If this phenomenon only exists in this very limited area, it may be that the impact is minute on a global scale. While there is likely a large amount of methane stored in underground reserves, it's not clear how much of that could get out. "I think what we need to do is understand first and foremost how much methane is naturally leaking from these kind of systems, and then compare that to how much methane that is actually within the permafrost for organic matter," Hellenvang said. "Then we can have a more realistic budget on how much can be released because of atmospheric heating or climate change," he said.