I heard about these and mapped the location some years back. Stories about large upside down cauldrons and I will leave it at that. There was an actual expedition aa few years back and some of the members got very sick. They are northwest of Yakutsk which is on the Lena River.
I hope you can look at these, they seem to be what you talk about. May I ask where in England you saw a crop circle being made? Just curious.