Two more mysterious craters of unknown origin have been spotted in Russia's Siberia, just weeks after a similar-looking hole was discovered in the isolated area, according to The Siberian Times.
The paper published pictures of two new giant holes discovered by reindeer herders.
One of them was located in the Yamal and other in the Taymyr peninsula, both of which are above the Article circle.
Theories of their origin have ranged from stray missiles, aliens, meteorites, or an underground gas explosion.
Another theory is that the crater formed because of global warming.
"Could it be linked to the global warming? Well, we have to continue our research to answer this question," said Andrey Plekhanov, senior researcher at the Russian Scientific Centre of Arctic Research, according to The Daily Mail.
Russian state TV reported earlier this month that a giant hole appeared in the gas-rich Yamal peninsula where temperatures drop below -50 degrees Celsius.
A Russian scientific expedition reached the site to inspect the first crater earlier this month. They collected samples of soil, air, and water from the scene and named the spot the "Yamal black hole, according to a recent report by state-run website Vesti.ru.
"They found the crater, around up to 300 feet deep, has an icy lake at its bottom, and water is cascading down its eroding permafrost walls," said The Siberian Times. "It is not as wide as aerial estimates which earlier suggested between 164 feet and 328 feet."
Yamal is considered one of Russia's richest regions in natural gas.
A meteorite did hit central Russia in 2013, injuring more than 1,000 people.
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