| OCR Text |
Show 10 types of new snow appear to be scarce, presumably even the incipient forms of graupel associated with partial riming must exhibit a heightened viscosity serving to forestal1 stress reflef through plastic deformation. Conclusions. On the basis of empirical field experience, there i appears to be a definite Relationship between snow crystal riming and stability of the deposited snow layers. Rime- free crystals form highly unstable snow which sluffs readily and does not generate dangerous soft slabs. As the degree of riming increases, a pseudo- stability allows accretion of layers capable of sustaining stresses and forming large slab avalanches. Numerous illustrative examples of this relationship are available from the cl imate* of northern Utah. There appears to be a rational explanation of the relationship in terms of sintering phenomena, but it has not been rigorously proved. The acquisition of a sufficiently large sample of data collected by reliable observers will probably require a number of years before a meaningful statistical comparison can be obtained. In the meantime, tests of mechanical properties of newly- fallen snow could either confirm or deny the validity of present speculation about reasons for the effects of riming. This type of snow is difficult to manipulate in the laboratory, but it should be possible to devise in s i tu f ield tests for instance, large cone pentrometers or shear vanes which would yield information on the relative strength properties of low- density new snow. Viscosity measurements would be more difficult. |
