~THE INEXACT SCIENCE OF AVALANCHE FORECASTING~
Counting the four skiers killed in Washington State over the 2012 Presidents Day long weekend, 17 skiers, snowboarders, and snowmobilers died in backcountry avalanches as of February 20th in this winter of 2011-2012. In an average season, about 30 people die nationally in avalanches. At this point in the season, 17 is just slightly higher than normal.
“Only” 17 deaths is somewhat of a miracle, given the once-in-a-century avalanche conditions which have lurked in most of the American West all winter. A forecaster from the Utah Avalanche Center wrote early in the season “we’ve got conditions none of our forecasters have seen before”. Another wrote “the snowpack is like a fleet of Oldsmobiles parked on a layer of champagne glasses”.
Interestingly, of the four victims from last weekend’s tragedies, three of them were ski industry professionals trained in avalanche analysis. They weren’t drunked-up snowmobilers out for a yahoo hill climb. They were experienced backcountry skiers trained to recognize, and mitigate, exactly what killed them. And yet they died anyway.
What has caused the US snowpack to be so unstable this season? Why are people who should know better out in the backcountry rather than skiing inbounds, where highly trained professionals pre-emptively blow down unstable terrain with explosives? What are the basic terms I need know to understand avalanche terminology? (see below!)
A lot of different factors can cause avalanches. Ideally, a snowpack is densest at the bottom. The weight of layer after layer of snow presses down, solidifying the one below it. Analyzing the solidity from layer to layer is why backcountry travelers and avalanche forecasters dig snow pits. They dig all the way down to the ground, carefully exposing a smooth vertical wall of snow which reveals every snowfall since winter started, much like the growth rings of a tree. They then can analyze the various layers below the surface, observing the composition of each and the level of adhesion between them. Various standard tests can be performed on the lower layers, yielding a coefficient of cohesion for the entire snowpack.
It’s a general guide, at best. A snow pit analyzed at, say, at 8,000 feet on a Southeast-facing slope may or may not have relevance to one dug only 200 feet higher, or on a different aspect. The two pits may yield completely different results.
One of the most common villains disrupting a stable snowpack is a phenomenon called “surface hoar”. Snow sitting out in the cold too long before another, subsequent snowfall buries it (therefore insulating it against the cold) develops hoar, a dried-out layer of snowflakes combined with smoothing of the rough edges which normally makes snowflakes stick together (“faceting”). Surface hoar looks a little like freezer burn. It makes the surface snow sugary and dry. You can’t make a snowball with it. When more snow falls on top of a hoar layer, the buried hoar becomes “depth hoar”, and it begins to behave like a layer of ball-bearings. The layer above it can crack and slide in pieces as large as an airport. No matter how much snow falls on top of it, depth hoar does not go away. It can stabilize somewhat, depending on weather and subsequent snowfall, but it more or less remains until the snowpack melts in the spring. And snow is heavy stuff. A one-foot-square column of snow, six feet high, weighs well over 100 pounds. Multiply that by an area the size of a college campus, and you have a rough picture of an unstable ski slope, or, as that Utah forecaster wrote, a huge parking lot full of Oldsmobiles parked on a few million champagne glasses. Add a few layers of snow on top of the depth hoar, bake it in the sun on a few warm afternoons until the top layer fuses, and you wind up with something experts refer to as a “deep slab”. Imagine a piece of glass the size of the deck of an aircraft carrier sitting on the side of a mountain, atop a layer of billiard balls. Nudge the deck with your foot, and the whole thing starts to slide, explodes into a trillion pieces, and cascades into a violent river of kinetic energy akin to a Niagara Falls full of ice cubes.
How destructive is an avalanche? Avalanche forecasters often talk in terms of two codes preceded by the letter “R” and the letter “D”, i.e. “D3 R4”. The “D” represents destructive force. The “D” scale goes up to 5. An avalanche of D3 will destroy a house. D5 will destroy an entire town. The “R” factor is Run Length. An avalanche described as “R4” thunders down a mountainside with so much kinetic energy that it continues across the flat terrain at the bottom and continues uphill on the other side of whatever flats or drainage exists in the valley until gravity eventually overcomes its kinetic energy.
In the US, Colorado, Montana and Wyoming generally have the most dangerous snow packs. The mountains there are rocky and steep, the snow pack is relatively thin, and the weather is cold. Conditions are favorable for development of surface hoar. Utah is generally more stable than Colorado. Utah averages more than twice Colorado’s snowfall, and Utah’s temperatures are milder. Surface snow is exposed to the elements for shorter durations, and the exposure isn’t as cold. The Pacific snowpack tends to be more stable than either Utah or Colorado, as the snow there tends to fall in gloppy layers, like Play-Dough, known as “Sierra Cement”. Sierra snow layers tend to stick to the layers below extremely well. However, the Pacific snowpack usually goes through multiple freeze-thaw cycles, which can cause an entirely different set of problems. Layers at ground level can melt, and the snowpack can rot from beneath. Meanwhile, the top layer melts and the re-freezes into a crust resembling a layer of glass. Freeze-thaw can turn huge, neighborhood-sized slopes into what amounts to a frozen lake sitting on a hillside. Puncture the frozen layer in a critical place, and the entire mountainside can break away.
What happened to make this season so much more dangerous than normal? It started when several robust early storms dumped about 50 inches of snow across the West prior to Thanksgiving. How early was this? A snowboarder was killed in an avalanche at Snowbird, Utah, almost a month before the resort opened for the season. The boarder hiked up to Hidden Peak (the top of Snowbird’s tram) and launched into terrain he considered familiar. The snowboarder didn’t connect the dots: although Snowbird is extraordinarily steep, rocky, dangerous, and avalanche-prone, the slope he died on never slides not because it’s safe, but because Snowbird hires some of the best avi-patrollers in the world to keep it safe by setting off explosive charges when nobody is around. The explosions bring unstable areas down, in a carefully controlled way, before a skier can. But this snowboarder was up there so early in the winter, Snowbird’s world-class ski and avalanche patrolmen hadn’t even been hired yet. For two months after the initial promising snowfall, the weather stayed cold yet almost no snow fell. The pre-Thanksgiving snows sat out in the cold developing hoar for almost 10 weeks. The hoar reached from the snow surface clear down to the ground. Then, after January 1, it started to snow for real.
That sugary layer of hoar became the Depth Hoar From Hell. Analysis pits show the depth hoar still remains in February, except now it has 150 inches of snow on top of it. Billions of tons of snow sits on ball-bearings, just waiting for small disturbances to release.
In general, snowmobilers are much more vulnerable to backcountry avalanches than skiers or snowboarders. First of all, snowmobiles have a lot more range. A novice snowmobiler who smokes and is 100 lbs overweight can easily cover 50 miles in a day. An extremely fit and experienced backcountry skier on telemark or Alpine Touring gear can only cover a fraction of that. The ‘bile goes so deep in the backcountry that it may reach slopes that have not been otherwise disturbed all season. Second of all, snowmobiling has few entry barriers. An enthusiast does not need more than a few bucks for a tank of gas to enjoy a day in the backcountry on a snowmobile. Skill is optional, as is avalanche expertise. Thirdly, snowmobiles disturb the snowpack much more than a skier, because the vehicle/rider combination weigh much more than a skier, and the machines vibrate violently. Think of an unstable snowpack like a piece of glass holding an SUV suspended in mid-air. A skier will scratch the glass like, say, a razor blade. A snowmobile will score the glass much deeper, like a glass cutter, and will vibrate the glass like someone tapping on it with a hammer. At a certain point…..ka-blammo.
The metaphor of a piece of glass holding up an SUV also illustrates a common misconception which often kills the inexperienced: slopes with prior tracks on them must be safe. Counterintuitively, the opposite is often the case. Each skier or snowmobiler scores a hard slab, again, like a glass cutter. The breakable layer gets progressively weaker, until the Nth track releases the entire hillside. And down it goes. Aerial photographs of the aftermath of avalanches often show fracture lines, sometimes as long as a mile, precisely along a cut made by a traversing skier or snowmobile.
Another deadly misconception illustrated by the glass metaphor: look down for danger. More often than not, a disturbance will trigger an avalanche below it. But frightfully often, a disturbance can trigger a slide above. Imagine skiing or snowshoeing on a flat at the bottom of a steep slope. Seems safe. But under the wrong circumstances, it can bring the whole mountain down on your head.
Standard avalanche avoidance procedures are similar to military tactics for avoiding snipers. Travel in groups. Cross dangerous terrain one by one, leap-frogging from safe zone to safe zone. If an individual goes down, attack in force. And travel well-equipped. Standard avalanche safety equipment consists of three things: probe, beacon, shovel.
Avalanche shovels bear little resemblance to the shovels you see at Home Depot. They are compact. light, strong, and collapsible. Their handles are about 18 inches in length, and the disassembled shovel is designed to fit into a backpack. Probes, when stored in their pouches, are about the size and weight of a rolled-up magazine. When deployed with a flick of the wrist, an avalanche probe resembles an 8-foot-long #2 pencil.
And then there are beacons. Invented in 1968, avalanche beacons are about the size and weight of an original Palm Pilot. They are transceivers. They both transmit a rescue signal and are capable of homing in on the signal of another beacon. Their effective range is about 50 yards. Beacons are available from about a dozen different manufacturers with a variety of features, and come in pouches with a sturdy array of web straps so that the device can be securely attached to one’s body beneath clothing. It’s a bad idea to put a beacon in one’s jacket pocket, because avalanches powerful enough to bury a person frequently rip much of the clothing off the victim’s body.
In the event of an avalanche, the remaining and hopefully safe backcountry travelers in the group immediately snap their beacons into “search” mode and head for the pile of rubble, spaced about 20 meters apart. As they get close to the victim, hopefully one of the searchers’ trackers will start to pick up a signal from the victim’s beacon. When the searchers’ beacons indicate they are standing over the buried victim, they get out their probes and try to locate him beneath the snow. Once found with the probe, they get out their shovels and start digging. Again, it seems counterintuitive, but sometimes a victim is difficult to find, even if rescuers are standing right on top of him. The reason: victims often are buried vertically, like a lawn dart. If that’s is the case, rescuers are digging down attempting to find something about the size of a dinner plate.
They’d better be quick. A human buried by an avalanche, if not already dead from trauma, has about 15 minutes to live. This also seems counterintuitive, as snow is very porous and impregnated with air. One would think a buried human could breathe indefinitely. But what happens is the moisture and heat from the victim’s exhalation quickly glazes the snow around his face into an icy, airtight shroud resembling a frozen garbage bag. It becomes airtight. And the snow burying him is so heavy that the victim can’t move an inch. The victim quickly suffocates.
In the past decade or so, technology has added two significant devices designed to tip the odds in the victim’s favor. Both have limited effectiveness and neither is a magic bullet, but both are accumulating long track records of saving lives. One is a device called “Avalung”. The other is a device not unlike a car airbag, built into a backpack.
The Avalung, invented in 2001 by Utah’s Black Diamond, essentially solved the problem of asphyxiation during burial. An Avalung is a tubular ventilation system built into a backpack frame. Extending from the top of the frame is a flexible hose with a mouthpiece, not unlike the ones used by scuba divers. If an avalanche victim is alive, conscious, and has the presence of mind to stuff the mouthpiece into his mouth during an avalanche, the victim can then survive burial almost indefinitely. Drawn air comes from the snow surrounding the buried victim’s face, as there is plenty of it. The Avalung routes exhalation through the backpack frame and expels it at the bottom of the victim’s back. This keeps the otherwise deadly ice layer from forming in front of the victim’s mouth. Tests and real-world incidents have shown Avalung users can survive hours, even days, fully buried.
In 1985, German firm ABS invented a backpack with a balloon similar to a car airbag in it. Although it took almost 20 years for the idea to catch on, airbag packs are getting quite popular and are now manufactured by a variety of companies, including Colorado’s BCA and Switzerland’s Mammut. Airbags work on a principle known as The Brazil Nut Theory. Put 3 lbs of Peanut M&Ms into a big salad bowl, shake the bowl for a while, and you will find that the biggest M & Ms are on top, while the smallest ones have sunk to the bottom. A skier in an avalanche can remain close to, or on, the surface simply by being larger than the chunks of snow falling with him. The larger the skier, the better his chances of surviving. An avalanche victim, again, providing he is alive and conscious, can pull a rip cord located on one of the backpack’s shoulder straps, which inflates the bag as he is engulfed. The bags, when inflated, look like a giant pair of water-wings. If the victim doesn’t slide off a cliff or die of trauma from colliding with a tree, odds are he will remain on top of the debris pile.
Recent innovations by BCA, Swiss manufacturer Snowpulse, and others have attempted to address the trauma problem as well. Many of the more recent airbag designs are now shaped, not like water wings, but rather like a giant life jacket – the yellow ones you see airline flight attendants wearing during in-flight safety demonstrations. The top part of the bag now attempts to shield the victim’s head from blunt trauma.
The airbag concept clearly works. But again, it’s not a panacea. Two of the four victims in Washington on Presidents weekend had airbags, and deployed them. But both died of trauma nonetheless.
Another problem with airbags is, like pretty much everything (including baby formula and toothpaste) they are extremely difficult to get onto an airplane. They must be checked, and prior to checking, the air reservoirs must be emptied and dismantled. Only when the device arrives at its destination can the reservoir be re-assembled and pressurized at a dealer or dive shop. Good luck finding one of those in many parts of the country. But clearly, the track record of airbags and Avalungs are tipping the odds toward avalanche victims, despite the pain-in-the ass factor, the additional weight, and their cost. An airbag costs about $1,000. An Avalung costs about $200.
Basic Avalanche Terminology:
- avalanche: a large mass of snow, ice, soil or rock, which detaches from a mountain slope and slides or falls suddenly downward; the sliding or falling of rocks, snow or other materials down the side of a mountain
- avalauncher: a cannon, powered by compressed nitrogen, that can hurl a two-pound projectile 2,000 yards. It is used to break up unstable snow, allowing it to avalanche and leaving more stable snow in place
- Bannwalder: an area of woodland in an avalanche zone, which cannot be cut or disturbed because it is a natural barrier to avalanches
- banned woods: an area of woodland in an avalanche zone, which cannot be cut or disturbed because it is a natural barrier to avalanches
- breakaway zone: the area where an avalanche is most likely to start or break away
- depth hoar: a layer of snow made up of round or cup-shaped crystals that act like ball bearings, allowing the layer of snow on top to slide of easily; also known as sugar snow
- gallery: a wooden, steel or concrete barrier or bridge built in known avalanche paths; a gallery allows cascading snow to pass over highways and railroad racks
- metamorphose: scientific term to describe the change in snow as it settles
- probe line: a line of 20 to 30 people, standing elbow to elbow, who advanced up a slope, poking into the snow with long poles in an effort to find victims buried by an avalanche
- slab: a layer of snow that breaks loose and avalanches
- sleet: falling snow or hail that has partly melted; partly frozen rain
- stabilized snow: a layer of snow that has metamorphosed; snow that has been packed down so that it will not avalanche; rangers stabilize a ski run, for example, by blowing up an unstable layer of snow, leaving only packed, safe snow for skiing