| OCR Text |
Show - 13 - EXPERIMENTAL RESULTS It is possible to test the validity of equation ( 20) by comparing calculated depth hoar formation times with those observed experimentally. Turning first to data reported in the literature, we note the results of laboratory experiments at the Weissf1uhjoch reported by de Quervain, in the paper previously cited. Of these studies of snow metamorphism under controlled laboratory conditions, reference is made to de Quervain's Experiment No. 10, involving depth hoar formation under very light compressive load. Data reported from this experiment are sufficient to permit calculation of formation time. Observations of depth hoar formation under controlled conditions were made at the A1ta and Berthoud Pass avalanche stations during winter of 1960/ 61. In both cases the shallow natural snow cover early in winter was dug away back to the ground, and a light plywood frame installed to support temperature- sensing elements. These were thermocouples at Alta and Weston dial thermometers at Berthoud Pass. The frames were filled to a depth of 20 cm at Alta and 30 cm at Berthoud Pass with freshly- fallen snow shovelled off the surface of the snow cover. Frequent observations were made of temperatures at various levels in the snow, and at the end of the experiments, the snow was dug up for crystal examination and density measurements. The Alta experiment was terminated after 12 days by heavy falls of fresh snow. The one at Berthoud Pass was continued for 55 days by scraping fresh snowfalls off the test layer in the frame. Data from these experiments are summarized in the following table. There are two separate entries for the Alta study, representing two separate layers in the snow. |
