| OCR Text |
Show - 3 - but follows a very similar pattern. This upward displacement can in part be attributed to a rise in bulk density due to the retention of percolated free water by the snow layers in question. This can be only a partial explanation because the density increase, 3% to 6%, is greater than usually associated with the amount of free water retained in all but surface layers or meltwater flow channels in isothermal snow. Some rise in density due to accelerated metamorphism at the freezing point must also be assumed. Snow layer densification at the Berthoud Pass study plot, in the high alpine zone, is shown in Figures 3 and 4. Here the initial densification during the normal course of destructive metamorphism ( Figure 3) is considerably slower than at Alta. Approximately 34 days are required to achieve a mean density of 0.30 g/ cm^, in contrast to 18 days in the middle alpine zone. After about 60 days there is practically no further density increase, the value remaining constant presumably until intrusion of meltwater in the spring, for which data are at present unfortunately lacking. Both of these differences in the high alpine zone are probably due in large measure to the lower prevailing temperatures. Differences in compressive load of the overlying snow layers must also be important, as discussed below. The ( high alpine) snow layers in which depth hoar formation ( constructive metamorphism) takes place show a distinctly different densification pattern, depicted in Figure 4. The density increases very slowly ( reflecting the common observation that depth hoar layers undergb little settlement), and requires over 100 days to reach a value of 0.30g/ cm3. This phenomenon will be treated in more detail in a progress report on depth hoar studies currently in preparation. The curves of Figures 1 through 4 are compared on a single graph in Figure 5 » together with the snow layer densification curve for a siligle |
