Glacier Travel - Probing Techniques
It is important to keep a studied eye on the terrain and snow in front of you, searching for clues of danger as you travel along the glacier. Depending on what time of year you are crossing the glacier the risk may be more, or less. In the early season, when snowcover is thin, many potential hazards may be barely masked making them difficult to detect. Later in the season, snowbridges begin to form and strengthen, offering a quick and potentially safe crossing. Snowbridges can be a very useful means of travel if proven trustworthy. Early morning travel after a hard freeze is especially encouraging. It’s a good idea to test the strength of the bridge with a shovel or ice ax before crossing, especially if you are getting accustom to the conditions.
In the instance a crevasse is discovered, it’s good to remember they often run parallel and may have hidden arms. A lightly covered crevasse gives off certain visual hints. Snow typically sags over a crevasse due to the pull of gravity, and you can spot these linear sags. The linear nature of the sag helps to differentiate from a sun cup which is typically round. The sag snow may have a different sheen, texture, or color. It may look flat white and have a finer texture because it is newer than the old neive. It may look dirtier from dust or it may look chalky like a wind slab. These subtleties are easiest to see in low angle light such as in the early morning or late afternoon when more shadows are cast.
In the case that the snow is more than a light covering over a crevasse, crevasses may give no hints to their location and it becomes necessary to probe the surface for safety. It is important for every member of a roped team to be on high alert in this scenario, at the ready to arrest in case any member falls. The leader of the rope team can probe suspicious areas in front of them with their ice ax, probe or ski pole. Some experience is important when taking these measures so that a true hole can be identified verses simply a softer layer. Uniform resistance indicates the snow is solid. If your probe plunges through and seems to be able to move freely, you have probably found a crevasse as well as a snow bridge. When probing, there are a few techniques to keep in mind: be sure to probe well in advance of your weight, use a smooth motion, and keep the angle of your probe as vertical as possible. If a hole is found, use the probe to find its limitations. Can it be stepped over? Is there a snow bridge? Or perhaps you may have to do you best to find the end of the crevasse and walk around. If a bridge has been found but its stability is in question, your rope partner can anchor themselves and belay you across the bridge or any other questionable terrain. When a crevasse is found, try to find the lip and break open the hole, marking its extent with wands. This is important for the rest of the party who may not have come to the hole yet and is also helpful in the case that you return the way you came.
Route finding on a glacier can be a tedious procedure. Give yourself plenty of time. Be thorough and attentive. And most of all, have fun!