Fig. 3.

Photographs representing different surfaces present in the tunnel and their differential sublimation features. a The main tunnel showing the walls 52.5 years since excavation. Note the dark shadowy regions are where massive ice wedge features have retreated more than a meter into the wall. The roof and upper wall material represent pristine 52.5-year exposures. b Differential sublimation of ice wedge ice (dark color) and ice cemented silt (dark tan) in a wall exposed to sublimation for 5 years. c Reticulate-chaotic ice cryostructure with areas of ice (angular dark features retreated inward) in ice cemented silt. This exposure is three years old. d A 5 year old exposure exhibiting differential sublimation of segregated, lenticular-layered, and lens ice features