By Ashley Klassen
One of the greatest challenges of crossing glaciated terrain is navigating its crevasses. There are several methods to employ in order to facilitate a safe crossing. You should be aware of areas of a glacier that are more likely to have crevasses than others, such as the sides of the glacier, near icefalls, or any bends or drops in the terrain around the glacier. Photographs of the area can be very helpful as well if you can find any. If you have the chance to see the glacier beforehand, by flying over or hiking up it, sometimes it’s helpful to sketch or note a possible route, major crevasses, or other landmarks. Although, what the glacier looked like from far away and what it will look like while walking on it are likely to be very different.
It’s important to keep a studied eye on the terrain and snow in front of you, searching for clues of hazard as you travel along the glacier. Generally, the time of year when you are crossing the glacier may increase or lessen the risk of crevasse falls. In the early season, when snow cover is thin, many potential hazards may be barely masked making them difficult to detect. Later in the season, snow bridges begin to form and strengthen, offering a quick and potentially safe crossing. In late season, those same bridges can begin to melt, sag and lose strength.
For West Buttress climbers, the generalizations above will hold true about one year in three. The most crevasse falls we have seen in a season occurred in May of 2008, the result of an ice lens that formed on the surface of the Kahiltna Glacier after rain fell on the glacier in January. On the other end of the spectrum, in 2021 the Kahiltna was very filled in and travel was easy in mid-July due to lots of snow falling in June. Be suspicious until you discover that conditions are solid as you hike up glacier. And then, be suspicious again when you descend a couple of weeks later.
If the Kahiltna is suspect, travel through the areas of highest risk in the early morning when bridges will be stronger. Night travel is commonly discussed as a means of mitigating crevasse risk, but keep in mind that in Alaska the sun might leave a stretch of route at 10 p.m., so bridges will be more solid in the hours before the sun hits again than they will be at midnight. Regardless of when you travel, it’s a good idea to test the strength of the bridge with a ski pole, ice axe, probe or the center pole from your pyramid shaped kitchen tent 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 one another 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 as bridges are pulled into the void, and you can often 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’s newer than the old névé. 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. Polarized sunglasses or goggles can sometimes make it harder to see the subtle differences in snow cover.
Often, crevasses may give no hints to their location, and it might be necessary to probe the surface of the snow to find them. This is especially the case when establishing a camp on a glacier. It’s 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. On the Kahiltna, we really recommend probing suspicious areas in front of you with an avalanche probe. 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 poked through a snow bridge and found a crevasse. 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, as finding the edges with your probe will probably be obvious. If you are on the trail, can it be stepped over? Is the snow bridge relatively thick and does it feel consolidated as your probe passes through it? Or perhaps you may have to do your best to find the end of the crevasse and walk around it? If you encounter a bridge, but its stability is in question, you might need a belay from your partner to cross it. If you find a suspect bridge, try to find the lip of the crack and break open the hole, marking its edges 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.
When probing a camp, approach your selected site keeping the rope taught. You might probe a “safe zone” and bring your team into it, or the lead person on a rope can start probing the camp after disconnecting their sled from the system and dropping their pack in a safe zone. Belay the person as they probe ahead of themselves. The goal is to probe every one to two feet around the perimeter of the area where you plan to camp. Wand the perimeter well. After probing the outside of camp, make a grid pattern within the perimeter, probing every 203 feet. Once the area is deemed free of cracks, bring your team in and generously wand the perimeter, taking care to not step outside the probed area.
The 7,800′ Camp zone at the base of Ski Hill can have cracks running across the glacier, and teams that establish camps down glacier even a few hundred meters can find increasingly large crevasses when the glacier melts out. The 11,000′ Camp is notorious for having cracks run through camps, so you might not wander around that camp without a rope. Years ago, a friend probed their camp at 11,000 feet and wanded it well. A climber on his team took one step outside the probed area and plunged to his armpits in a completely hidden crevasse. After excavating the hole, they rappelled in to see how deep it was, and 80 feet down they could not see the bottom. Be highly suspicious!
Route finding on a glacier can be a tedious procedure, and probing a camp well when everyone is tired and thirsty can build frustrations. Give yourself plenty of time. Be thorough and attentive. And most of all, have fun!