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Show They perform satisfactorily in soft snow, but are not recommended for prolonged use in hard, dense snow. For examination of pit profiles at avalanche fracture lines or at distant study plots, a portable snow density kit ( Ak) is convenient. ( Figure 9-) This kit provides a single aluminum 500 cc sample tube, a suspension cradle, and a precision spring balance. Density profiles will be slower to obtain with a single tube, but this disadvantage may be worth the compactness and light weight of the kit when it has to be transported in a rucksack. The aluminum tube must be handled carefully to avoid damage to the cutting edge., especially in hard, icy snow. A steel tube cannot be substituted, for its tare weight will exceed the capacity of the balance, unless the snow sample is emptied into a plastic bag and weighed separately. Standard density tubes normally are weighed with a triple-beam balance ( Alia). This is a standard laboratory instrument of adequate accuracy which is reasonably sturdy for use in the field. Use of the 500- gram auxiliary weight may be necessary in dense snow { py 500 kg m" 3) . A plywood case should be constructed for field transport of this instrument. The case also provides a convenient base for setting the balance on a snow surface. it is important to keep the spacing spring under the balance pan at all times except when the balance is set up on a firm base and in use. This spacer keeps the knife edges from contacting the agate bearings, which otherwise would be damaged during transport. A more compact spring platform balance is also available for weighing snow tubes ( Alib). A key instrument for pit observations and for determining snow structure without pit excavation is the rarn penetrometer. It was introduced in Switzerland by R. Maefeli 30 years ago and has since become a standard instrument for testing snow strength and stratigraphy. Construction of various models differs in details, but the essential dimensions and mode of operation are identical for all. A firm in Chicago can supply ram penetrometers from stock ( Alb). The ram penetrometer is also available from a mechanical fabricator in Zurich, Switzerland ( Ala). The penetrometer furnished by the Chicago firm is built largely of stainless steel; the other has a body of aluminum. The manner of locking sections together is more convenient in the Swiss model, expecially for the mittened hand, but it is not entirely secure against unlocking while the penetrometer is deep in the snow. The stainless steel model has a more secure, though less convenient lock, but it tends to deform slightly at the joints after prolonged use in dense, hard snow. - Metallic dial thermometers with a long, slender stem are customary for snow temperature measurements in pit wails. None is available with an entirely satisfactory temperature range to give 26 |
