| OCR Text |
Show 5 dynamiting cornices for control purposes. Using time- lapse photography, we were able to demonstrate that some deformation is contemporaneous with cornice growth. When this happens, the bedding layers in the accretion wedge tend to diverge toward the upper and outer edge. Slightly below freezing temperatures seem to be prerequisite for such contemporaneous deformation to occur. Bedding. Under relatively cold conditions, contemporaneous deformation is minimal and divergent bedding does not form during accretion. Thus, by analyzing the nature of the bedding, it is possible to estimate the temperature conditions under which the cornice wedge formed. Welzenbach and Paulke ( 1928) originally had observed that involution of the growth wedge could be contemporaneous with deposition, as described above. They suggested that the amount and rate of deformation depended upon the infiltration of water in the cornice. To date, no relation between rate of deformation and infiltration of water has been noted on Bridger Ridge. It is hoped that experiments with dyes may indicate the true nature of intergranular movement involved with cornice deformation. Creep and Glide. The entire cornice mass creeps and/ or glides continuously. Such movement is well known for snow in general ( see, for instance, in der Gand and Zupancic, 1965)- As creep or glide progresses, tension fractures tend to develop between the cornice mass and ridgeline bedrock. During the winter of 1967- 68 at Bridger Ridge, the cornice root moved away from the ridgeline leaving a tension fracture 1 m. in width near the surface. Bits of bedrock embedded in the icy wall of the cornice mass proved that the wall was once in contact with the rock. In order to determine the nature of deformation within the main cornice mass, vertical rods emplaced in the cornice roof behind the |
