Snow Pit Graph Explained

Many of you will be familiar with this stuff already, but Aunt Tilley (Margo) wanted a more thorough explanation of the graph in my last post, so I wrote it out for her and figured I might as well put it up here, too.

The whole graph shows the results of a snow pit that we dug and the temperature, depth, hardness and snow crystal type that we found. Let's take the left half first, with all the blue bars.


The right hand axis of that section is the overall depth of the pit, starting with 0 cm at the top and going down to 132, which is as deep as we dug.

The bottom axis represents the hardness -- from left to right, I (impenetrable), K (knife), P (pencil), 1F (1 finger), 4F (4 finger), F (fist). As you might guess, if it rates a "P" hardness, that means the snow is fairly easily penetrated with a pencil (but is too hard for 1 finger), at that depth. You can see a couple of examples of that at the 43-44 cm depth and the 55-70 cm depth. You can also see a number of different layers of "F" and "1F" snow -- fist and 1 finger hardness.

The top axis of the left side is Temperature of the snowpack. I didn't take a lot of readings on this pit, so the red line in the graph (which represents T) only shows three data points, ranging from -3 C at the bottom to -1.5 C at 43 cm.

The right half of the graph isn't as populated in the example, because I didn't look at everything in detail.

The "Form" column uses symbols to show what kind of snow crystals are present at different depths in the pit -- the "+" means new snow, the bold "-" means an ice layer. There are many other symbols.

The only other column that has data is the Stability Tests -- these are test we've done in the pit to assess the likelihood of avalanche activity on similar slopes. In this example, we dug a 6 foot wide, 4 foot deep block (a Rutschblock), placed a skier on top of it and had them do a series of knee bends, hops and jumps, to get our result. "RB4" means Rutschblock, score of 4, which tells us that the skier was able to approach the block (score 1), step onto it (score 2), do a knee bend (score 3), and then do a small jump (score 4) before the block failed. The higher the number, the less likely there is to be avalanche activity on slopes of similar shape, elevation and angle.