Learn how to: Perform A Rutschblock Test
The Rutschblock, like the Compression Test, uses increasing impact forces to test snow stability. The Rutschblock tests a larger area than the Compression Test and it uses a person's actual weight for the test. This most likely gives testers a more accurate indication of stability; however, Rutschblocks take longer to perform and people typically perform fewer of them than Compression Tests. So the trade off is that the actual test is probably more reliable but typically people will get information from fewer locations.
To perform a Rutschblock, the slope angle should be at least 25 degrees and preferably 30 degrees or steeper.
Dig the front wall out about two meters wide (six feet) and at least one and one half meters (four and one half feet) deep. Dig it deeper if you are concerned about deeper weak layers.
Be careful not to disturb the snow uphill of the front wall of your block. Next, fully isolate a block 2 meters wide by 1.5 meters deep. Cut or trench the sides with a shovel, saw, or skis, then cut the back of the block with a snow saw on a pole, ski, or length of cord. If you do not trench the sides, be sure the isolated block is trapazoidal so the sides do not bind (see video above).
Cut and isolated on all four sides and then have the biggest skier in your group with his or her pack on approach the block from the uphill side of the back cut. Now you will load the block in 7 steps and the score (1-7) is the loading step at which the block slides. (Watch the video above and see the interpreting results table below.)
• Rutschblocks can be adapted by non-skiers, using the same standards.
|Mark width of pit with your ski and dig front wall about six feet wide.
||Measure the slope angle of your Rutchsblock.
||Mark the sides of the Block one pole length uphill. Next cut along those marks to the same depth as the front of the Block. You can use a snow saw or ski to cut the sides.
||Move to the back of the Block and make a straight line that connects the side cuts. Next use a saw or a ski to cut the back to the same depth as the front. The back of block should be slightly narrower than front.
|Step onto upper third of block.
||Downweight with feet in place.
||Jump hard once in place.
||In this instance, the Block fractured after a single hard jump.
|Loading Steps That Cause Block to Move
||What Do These Scores Mean?
RB1 The Block fractures when you are digging or isolating the Block
RB2 The Block fractures when skier is approaching the Block or gently stepping onto the upper third of block.
RB3 The Block fractures when skier downweights with feet in place.
|Indicates Poor Stability
Similar slopes should be considered very unstable and avoided.
RB4 The Block fractures when skier vigorously jumps once in the same spot.
RB5 The Block fractures when skier vigorously jumps a second time in the same spot.
Indicates Fair Stability
Similar slopes should be considered “unstable” or “suspicious.”
Making conservative route selections and following Low Risk Travel protocols are essential.
RB6 The Block fractures after repeated vigorous jumps or after jumping onto bottom half of block.
RB7 The Block does not fracture even after repeated vigorous jumps or the Block does not slide cleanly.
|May indicate Good Stability
Continue collecting data and proceed with caution.
SHEAR QUALITY: The fractures or shears defined above are divided into three types:
Quality 1: Very clean, planar, smooth and fast shear surface. The slab slides quickly and easily off the isolated column and into the snow pit and occasionally makes a "popping" noise when the test is conducted on slopes 35 degrees or steeper (and occasionally on slopes as low as 25 degrees). (Q1)
Quality 2: Mostly smooth and planar shear surface but the slab either does not slide off the isolated column or only partially slides off the column. (Q2)
Quality 3: Non-planar, uneven, irregular and rough shear surface. Typically the slab does not move off the isolated column even on slopes steeper than 35 degrees. (Q3)
INTREPRETING RESULTS: Stability tests only test stability in the location the test is performed; consequently, it is important to perform several stability tests in several locations to get a more accurate test sample.
Stability is judged relative to the amount and rate of stress exerted on the snowpack. The more force required to make a layer fail, the better the stability. The location and the quality of the failures is also very important. For example, an RB 3 fracture two feet deep indicates a much more dangerous situation than a fracture four inches deep.
And a Quality 1 (Q1) shear is typically indicative of much more dangerous conditions than a Q2 shear and certainly a Q3 shear. Be warely of Q1 shears even when they require a force of RB6; Q1 shears indicate poor bonding and often very poor stability.
Stability Tests only test the immediate area of the test; stability may be entirely different just a short distance away. The more tests you perform, the more apt you are to get an accurate assessment. PERFORM LOTS OF STABILITY TESTS AND USE THEM IN CONJUNCTION WITH YOUR OBSERVATIONS WHEN YOU ARE FORMULATING A STABILITY EVALUATION.
One sign of instability trumps all signs of stability!
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