Scientists were baffled last July when they discovered three giant holes in the ground in the Yamal Peninsula in northern Siberia. 
 
 Now, with the help of satellite imagery, researchers have located four additional craters--and they believe there may be dozens more in the region. That has them calling for an urgent investigation to protect residents living in the area. 
 
 "I am sure that there are more craters on Yamal, we just need to search for them... I suppose there could be 20 to 30 craters more," Prof. Vasily Bogoyavlensky, a corresponding member of the Russian Academy of Sciences and deputy director of the Moscow-based Oil and Gas Research Institute, told The Siberian Times. "It is important not to scare people, but to understand that it is a very serious problem and we must research this." 
 
 Researchers ventured deep inside one of the holes last November, collecting data in an effort to learn why the holes formed. The leading theory is that the holes were created by gas explosions triggered by underground heat or by rising air temperatures associated with climate change, the Siberian Times reported last December. 
 
 Since scientists can't predict when or where gas explosions will occur, it's dangerous to study them, according to Bogoyavlensky. But he said his team is planning to launch a new expedition, and to put stations in the area to detect earthquakes that might strike when the craters open up. 
 
 "We need to answer now the basic questions: what areas and under what conditions are the most dangerous?" he told the Siberian Times. "These questions are important for safe operation of the northern cities and infrastructure of oil and gas complexes." 
 
 Experts in the U.S. echoed that sentiment. 
 
 Dr. Carolyn Ruppel, a research geophysicist at the Woods Hole Field Center in Massachusetts and chief of the U.S. Geological Survey's Gas Hydrates Project, told The Huffington Post in an email that she was not surprised that new holes had been found. 
 
 Ruppel, who is not involved in the Siberian research effort, called for more research on the holes. 
 
 "The processes that are causing them to form likely occur over a wide area of the continuous permafrost in this part of Siberia," she said in the email. "Scientists should definitely conduct more research on these features to determine the processes that cause their formation, how they evolve with time, and whether it is possible to predict where new ones will occur." 
 
 See below for photos from the November's expedition into one of the craters. 
 
 PHOTO GALLERY BEFORE YOU GO Experts Explore Mysterious Siberian Crater PHOTO GALLERY Experts Explore Mysterious Siberian Crater ||||| A trio of mysterious gaping holes in northern Siberia has spawned many theories about the craters' origin, but scientists have suggested some concrete explanations. 
 
 In mid-July, reindeer herders stumbled across a crater that was approximately 260 feet (80 meters) wide, on the Yamal Peninsula, whose name means "end of the world," The Siberian Times reported. Since then, two new chasms — a 50-foot (15 m) crater in the Taz district and a 200- to 330-foot (60 to 100 m) crater in the Taymyr Peninsula — have also been reported. 
 
 Neither aliens nor meteorites caused the strange cavities, as some had speculated, but the true explanation could be exciting nonetheless. Russian scientists have launched an investigation to find out more. [How Weird! The Top 10 Unexplained Phenomena] 
 
 Helicopter video footage of the first hole shows it is surrounded by a mound of loose dirt that appears to have been thrown out of the hole. 
 
 "My personal opinion is it's some type of sinkhole," said Vladimir Romanovsky, a geophysicist who studies permafrost at the University of Alaska Fairbanks. Sinkholes are pits in the ground formed when water fails to drain away. 
 
 The water likely came from melting permafrost or ice, said Romanovsky, who has spoken with the Russian scientists investigating the site. But whereas most sinkholes suck collapsed material inside, "this one actually erupted outside," he told Live Science. "It's not even in the [scientific] literature. It's pretty new what we're dealing with," he added. 
 
 Early on, polar scientist Chris Fogwill of the University of New South Wales, in Australia, suggested the first hole was created by the collapse of a pingo, a large, earth-covered mound of ice that usually forms in Arctic and subarctic regions. 
 
 Large holes have been showing up in Siberia, and scientists believe weather is the cause: http://t.co/4mExye7BR9 pic.twitter.com/bix07TBEka — Sean Breslin (@Sean_Breslin) July 29, 2014 
 
 Kenji Yoshikawa, an environmental scientist also at the University of Alaska Fairbanks, said he also thinks that a drained, collapsed pingo pond is the most likely explanation for the Yamal Peninsula pit. In Alaska, similar pingos exist in the Northern Seward Peninsula and near the city of Nuiqsut. 
 
 But Romanovsky said the hole doesn't look like a typical collapsed pingo; such features usually form from larger mounds that slowly cave in over a period of decades, with all the material falling inside. 
 
 From the photo of the Yamal crater, "it's obvious that some material was ejected from the hole," Romanovsky said. His Russian colleagues who visited the site told him the dirt was piled more than 3 feet (1 m) high around the hole's edges. 
 
 The crater's formation probably began in a similar way to that of a sinkhole, where water (in this case, melted ice or permafrost) collects in an underground cavity, Romanovsky said. But instead of the roof of the cavity collapsing, something different occurred. Pressure built up, possibly from natural gas (methane), eventually spewing out a slurry of dirt as the ground sunk away. Anna Kurchatova, a scientist at the Sub-Arctic Scientific Research Center in Russia, made a similar observation to The Siberian Times. 
 
 The photo of the crater rim shows some vegetation that does not appear freshly grown, which suggests the hole may be several years old, Yoshikawa said. Romanovsky said it might be more recent, but investigators will need to look at archived high-resolution satellite images to pin down exactly when the crater appeared. 
 
 And many other questions remain: If a sinkhole erupted material, why is the hole's border so round and even? Would there be enough gas to fuel such an eruption, and where did such gas come from? 
 
 This part of Siberia contains deep gas fields, and it also contains a lot of small lakes, which formed between 4,000 and 10,000 years ago when the climate was warmer, Romanovsky said. Perhaps these odd holes developed in the same way that sinkholes did, but later expanded. 
 
 Domes of natural gas also exist in the United States, located east ofthe Sagavanirktok River in Alaska's North Slope Borough. 
 
 The development of permafrost sinkholes could be one indication of global warming, Romanovsky. "If so, we will probably see this happen more often now." 
 
 Editor's Note: If you have an amazing Earth science photo you'd like to share for a possible story or image gallery, please contact managing editor Jeanna Bryner at LSphotos@livescience.com. 
 
 Follow Tanya Lewis on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.
– When a mysterious crater was discovered this past summer on the Yamal Peninsula in northern Siberia, origin theories abounded, including it being the work of extraterrestrials, a man-made hoax, a meteorite, or the result of a stray missile colliding with the surface of the Earth. Now that it's cold enough to venture in, a team of scientists organized by the Russian Centre of Arctic Exploration lowered themselves into the crater last week and began the hunt for answers, reports National Geographic. "Yamal" means "end of the world" in Russian. The current working theory is that the crater, which is 260 feet wide and 54 feet deep, formed after the release of gas hydrates, and scientists will begin testing that theory now. Researchers performed radiolocation tests as deep as 650 feet and took samples of ice, earth, gases, and air from the largest of three known holes, all of which appear to have formed recently. Once they've processed the information from the expedition, the scientists "plan to explore the surrounding area, comparing images from space, and even those taken in the 1980s, to understand if there are—or were—some similar objects," one researcher tells the Siberian Times. (One geophysicist in Alaska thinks climate change plays a role in the formation of these holes.)