http://cavingnews.com/20120713-experts-discover-cause-behind-deep-sinkhole-next-to-colorado-highway-us-route-24-tennessee-pass?utm_source=cavingnewswidget&utm_medium=widget&utm_campaign=cavingnewswidget
Could someone help me understand this particular quote?
engineers, maintenance supervisors, and geological experts examining the hole, now estimated at 30 meters (100 feet) deep, discovered that it was caused by a century-old railroad tunnel that collapsed decades ago.....Experts suspect that the decade long delay in the appearance of the hole is due to the soil deep down remaining frozen until very recently.
Does deep soil freeze? And is this article suggesting that the soil between surface and tunnel has been frozen for decades?