Wet Slab Avalanche in the Lip, 4-19-2013

There was an unexpected avalanche in the Lip area today. In all honesty, I’m more than a little humbled by what happened, so I thought I’d do a quick post to let you know what happened, but also to provide some insight from my own perspective. I’m always amazed by the dynamics of avalanches, and this was no exception.

The avalanche took place at about 12:30 in the afternoon. We’re classifying it as a D2, R2 wet slab triggered naturally. We spoke with a couple guys who were above the avalanche when it released. They reported seeing a block of ice fall into the waterfall hole, and then water began flowing over the ice and more onto the surface snow just prior to the slide. For you SWAG junkies, this might be the elusive “NO” classification–an unclassified natural trigger. For the record, no one was in the runout at the time of the slide. Nobody was involved with the slide, it was purely natural.

Before

Before

Avalanche danger was rated Low today. We frequently say “Low danger does not mean No danger,” but this one definitely caught me off-guard. I’d been in the ravine three of the last four days. Stability had been very good. I went so far as to write in advisories this week “…drop the avalanche hazard to the low end of low” and “…we’re about as low as low can go right now.” I had such a high degree of confidence in the stability that I’m left wondering what I missed this morning that should have clued me in to the danger in the Lip.

After

After

Earlier this week, on Tuesday night, about 0.45″ of rain fell on the mountain, followed by freezing temperatures that were  just cold enough to freeze the surface, but not put the ravine into a deep freeze. Wednesday was a nice sunny day, and Thursday was warm during the day and had a very small amount of rain in the afternoon (0.03″ on the summit.) You can see in this graph how the temperatures began to rise on the 18th. They didn’t freeze up overnight before being heated more today.

32F is the black line, the colored lines represent different Auto Road temperature sensors over time.

32F is the black line, the colored lines represent different Auto Road temperature sensors over time.

It was impressive to see the water levels in the streams rising this morning. At the time when we were writing the advisory, I actually looked at the waterfall just to see how much water was flowing. Avalanche potential was not a priority in my mind. The Little Headwall had more water flowing in it this morning than on Thursday, but again, not enough to raise red flags. When I got to the bowl at about 10am, one thing I’d never seen before was the stream in the floor of the ravine had percolated up and was running over the snow for 50-75 yards before going down beneath the snow again. That raised my eyebrows, but again, not enough to make me think there was an increasing avalanche potential in the Lip. In hindsight, perhaps I should have been a little more concerned at this point.

After working with FOTR to set the course for tomorrow’s race, I descended Left Gully and met up with Joe in the floor of the ravine. We stood not too far from where the debris would eventually run to–maybe 100 yards downhill of the terminus. I then headed to the cabin, along the way stopping to admire how much water was moving through the Little Headwall. A few minutes after arriving at the cabin, the call came in that the avalanche just happened.

This location for this type of avalanche is not unheard of. Historically, it’s been rain that has been the trigger, such as in these two photos. I think part of why this avalanche was not an expected event was due to the lack of rain. It was a result of increased runoff pouring down into the ravine, and part of this may have been rain, but the last significant rain event ended over 48 hours earlier. (Ironically, Mark Sauer, patrol director for Park City Mountain Resort, just had an article published in The Avalanche Review on the relationship between wet slab avalanches and stream flow measurements.)

A previous wet slide triggered by rain

A previous wet slide triggered by rain

The "TexasSlide" from about 10 years ago (?)

The “Texas Slide” from about 10 years ago (?)

Personally, I think this event should be seen as a wake up call for anyone who has ever looked at a Low forecast with a cavalier attitude. At least that’s how I’m taking it, as a learning experience. There are so many ways that we can be blinded to some seemingly obvious clues. It’s incredibly important when traveling into avalanche terrain to give careful consideration to all the information at hand. Not that you want to get bogged down in the details, but you can at least try to keep your awareness up.

One good way to combat the natural process of taking mental shortcuts is to look for information that DISproves what you think to be the case, rather than focusing on information that confirms what you think to be the case. In this event, I thought there was little avalanche danger. Rapidly increasing stream flow rates contradict this conclusion, so this is the type of data that I should have been seeking out. Instead, I relied more heavily on data from several previous days in the ravine. In other words, I ignored something that might have alerted me to increasing hazard.

Another point that’s driven home for me is the idea of always treating avalanche terrain as if there is avalanche hazard. Why would I abandon my safe travel habits, such as not lingering in the runout of an avalanche path, when it requires very little extra effort to travel safely? In this case, continuing farther down the floor until I was completely out of the runout path would have been wise. Similarly, it’s all-too-frequent that I see someone hiking right up the center of the floor of the ravine while I’m doing stability tests up in the headwall area. This puts that person at risk if I should trigger an avalanche, and to get out of the runout would only require hiking up about 50 feet to the side of their current path. It’s these little things that increase our chances of not being involved in an incident, so why not always do them? If we do them every time, we can free up mental capacity for being alert to changing conditions or for making smart decisions.

I know that I’ll sit back and reflect on what happened today, and hopefully learn from it. I hope you will also take the time to think about how you interact with the terrain, and perhaps you’ll be a little more alert or cautious when you come to Tucks. On a recent online forum post, I saw someone say that it’s easier to come to Tucks because there is someone here who does the thinking for you. I whole-heartedly disagree with that concept. We all need to be able to think for ourselves. Our products are simply pieces of information that can lead you to make decisions.

So, was the forecasted rating of Low danger wrong? I’m not sure, but I’m leaning toward saying it was the right call given the conditions today, but I can see the arguments on both sides.  On the one hand, just because something actually happened doesn’t mean that it was more than “unlikely.” It just means that the chances were slim. Second, despite the depth of the crown, it was a rather small avalanche and it was a slow moving wet slide. Every Low danger definition comes along with caveats such as “watch for unstable snow on isolated terrain features” or ” small avalanches in isolated or extreme terrain.” The size and location of the slide fit these criteria, but since we forecast on a slope-scale basis we have a harder time using the size and distribution column of the danger scale chart. The point that I’d make against it being Low danger is that the definition says “generally safe avalanche conditions.” This certainly wasn’t the type  of slide that we usually see here, but it is anything but safe for someone who might be involved in it. I’m sure if someone happened to be caught in the slide, he or she would make the case that it wasn’t Low danger.

Jeff

 

 

 

 

 

 

 

 

 

 

 

 

Avalanche Advisory for Friday, 4-19-2013

This advisory expires at 12:00 midnight.

Tuckerman Ravine has LOW avalanche danger. Natural and human triggered avalanches are unlikely.

A General Advisory is currently issued for Huntington Ravine. We are done issuing daily avalanche forecasts for Huntington for the remainder of the season. You will need to do your own snow stability assessments when using avalanche terrain. A danger of falling ice exists and will persist until it all comes down.

Clearing but windy conditions will dominate the daylight hours with SW winds in the 55-75 mph (90-120 kph) range diminishing slightly in the early afternoon.  Gusty conditions through the day and possibly thunderstorms in the evening due to a cold front passing will challenge those camping or caught out late. Rain will accompany this cold front and may be heavy at times. Though recent warm weather with sporadic refreezing has yielded a snowpack resistant to avalanching, there are many other hazards to be aware of including the following:

  1. Factor the possibility of FALLING ICE into your travel plans. The annual process where all the ice that formed during the winter crashes down has begun. Rain and warm temperatures make the problem worse.  We know it will happen, the question is exactly when. Don’t fool yourself into thinking that you are faster than  chunks of ice sliding and bouncing erratically down the snow. Lunch Rocks and the floor of the ravines are directly in the path of falling ice. There have been many significant injuries, as well as at least one fatality, due to this hazard. Creative planning can keep you safer by giving ice fall runouts a wide berth. The waterfall at the Lip is now melted out and flowing a significant volume of water which creates a deep and dangerous slot.
  2. Stay clear of CREVASSES. We have yet to see much of this problem yet, but they have begun to form in the upper Lip area as well as a couple of other isolated locations. Warm temperatures will cause the snowpack to creep downslope, which opens up deep cracks in the snowpack. These grow large enough for a climber or skier to fall into, and often they can’t be seen from above. The best way to know about this hazard is to climb up your intended descent route. If you see cracks in the snow, stay well away from the edges. Be aware of slots opening at the bases of cliffs as well as beneath frozen waterfalls which will continue to run water due to rain and warm weather. Probing ledges of snow near rocks with your ski pole is often a good idea.
  3. Avoid UNDERMINED SNOW and the Little Headwall. Right now this issue is mostly found in the streambed leading out of the ravine and on the Little Headwall. The Little Headwall has a large open hole in the steepest part of the route.  This hole has grown in the last couple days, and is threatening to collapse further. The same can be said for the snow bridges in the streambed above the Little Headwall.  We don’t recommend skiing out from the bowl. Hiking out on the trail is a faster and safer option.

Tomorrow marks the day of the Inferno Race. Tomorrow’s weather will create a new set of hazards due to falling temperatures. Be sure to check weather forecasts at the Mount Washington Observatory and National Weather Service as well as our Weekend Advisory, which we will post later this afternoon, for further details. Remember that there are no facilities open on the summit and no other option for descent other than traveling under your own power.

Please Remember:

  • Safe travel in avalanche terrain requires training and experience. This advisory is just one tool to help you make your own decisions in avalanche terrain. You control your own risk by choosing where, when, and how you travel.
  • Anticipate a changing avalanche danger when actual weather differs from the higher summits forecast.
  • For more information contact the Forest Service Snow Rangers, the AMC at the Pinkham Notch Visitor Center, or the caretakers at Hermit Lake Shelters or the Harvard Cabin.
  • Posted at 8:00 a.m., April 19, 2013. A new advisory will be issued tomorrow.

Frank Carus, Snow Ranger
USDA Forest Service
White Mountain National Forest
(603) 466-2713  TTY (603) 466-2856

2013-04-19 Print friendly