At http://siberiantimes.com/science/casestudy/news/n0302-startling-changes-… … we have giant holes created when pingos erupted after filling with gas. The craters are found on the Yamal peninsular in northern Russia and indications are that not all of them were formed in the same way. They were first noticed last year and a variety of explanations have been offered. One if over 60m deep
One researcher suggest that by next year it will fill with water and become a lake. It is believed that methane gas was largely responsible for the hole as a result of a build-up under the pingo (a mound with an ice core, a relic of Arctic conditions) and pingos are common to both Canada and Russia
The first comment at the end of the piece says there is another possible caused and that is lightning strikes – another replies, if lightning was to blame there would be lots of holes. It turns out to be Wayne Burn who wrote the article in www.ncgt.org journal June issue (2015). He actually included the holes as evidence of lightning strikes and he signs his post as Wayne of Nottingham.