Wednesday, July 23, 2014

Excessive snowfall heightens the dangers of avalanches

From page B5 | April 19, 2011 |

MONTE HENRICKS of the El Dorado Nordic Ski Patrol measures the snow's height while teaching about snow conditions. Photo courtesy of El Dorado Nordic Ski Patrol

El Dorado County is fortunate to have many opportunities for downhill and cross country skiing. From late fall through late spring, snow falls on the eastern side of the county. Sometimes it snows just a bit and other times, the snowpack measures 50 feet or more. This is one of those years.

Snow started falling in November and except for a short break in January, it has continued to fall. The ski resorts get a little giddy when this pattern of constant, heavy snow shows up.

Sierra-at-Tahoe is the closest downhill resort for skiers on the West Slope. Heavenly Valley is further up the road in the Tahoe Basin and Kirkwood on Highway 88 is another favorite. Other resorts scattered around Lake Tahoe include Squaw Valley, Northstar-at-Tahoe, Homewood, Alpine Meadows, Granlibakken and Mt. Rose.

All have one thing in common — their ski areas are clearly marked and constantly patrolled by qualified National Ski Patrol members. There is a vast variety of terrain and safety for skiers is always stressed.

Safety measures start each day long before any skiers show up. The ski patrol checks with the Sierra Avalanche Center for current conditions and cautions, and then heads to the slopes to assess avalanche dangers. It is a complicated business.

Avalanches are relatively common in the mountains and the danger increases when there is a lot of snowfall. Avalanche science boils down to this: snow slides off steep slopes — how and when and the conditions that promote it are important to know.

Avalanches are more likely to occur during and after a significant snowfall but the conditions prior to the snowfall are important as well. New snow adds additional stress on the existing snow pack. The period of time before the old and new layers bond is when the danger is greatest.

Ted Lenzie of the El Dorado Nordic Ski Patrol calls this unconsolidated snow.

Warm days followed by freezing nights causes the new snow to bond with the old snow. Without the melting from warmer days, the snow pack remains unconsolidated. This is especially true when temperatures stay below freezing. A new layer of snow on top of a harder, frozen layer will simply slide off more easily.

Oddly though, longer periods of melting within the snow pack, such as when a warm front moves through, can cause the upper layers of snow to become more prone to avalanches because they lose the bond with the layers just under it. In addition to the freeze-thaw cycle, the actual shape of the snow crystals is an additional factor in whether the snows will bond together or fail, causing an avalanche.

Coarse, grainy snow, known as depth hoar, which typically falls early in the season, is granular like dry sand and is more prone to fail than snow that has melted into a round shape. The round shape is caused by the freeze-thaw cycle and it compresses into a more solid snow pack. A layer of unconsolidated snow under well consolidated snow can fail and cause the entire upper layers of the snow pack to slide.

Wind plays an important role in avalanches as well. Wind blows upslope on the windward side. It blows downslope on the leeward side. When the winds blows upslope, it picks up snow and can blow it over the ridge to the leeward side of the mountain. This snow is generally powdery and creates an uneven and unstable layer of snow on the leeward side. It can pile up quickly in a heavy wind.

Here in California, storms generally blow in from the west and head east. The northeast-, east- and southeast-facing slopes are the leeward slopes, and the most likely to have windblown snow on them. Looking at the ridges in our part of the Sierra, it is easy to spot cornices, or snow overhangs, at the top of ridges and on the leeward side of the mountains. These are inherently unstable and prone to failure.

Avalanches can and will run on just about any slope. Those that are 30 degrees to about 45 degrees in steepness are more likely to produce an avalanche, but it is important to understand that a 20-degree slope is also capable of unleashing an avalanche.

Almost all of the ski runs at the resorts are on north and northeast facing slopes. They get the least amount of sun, especially in the early part of the season. The ski patrol’s job is to understand the snow conditions on all of the slopes and make them safe before the resorts open.

When they have questions about an area they ski across the top of the slope, called a ski cut, to see if that triggers any kind of slide. They also carry small explosive charges with them. If they don’t get a reaction from a ski cut, or the conditions are too iffy for a ski cut, they throw the explosives onto the slopes.

The goal is to trigger an avalanche and make the area safe for skiing. These are not by any means controlled avalanches. There is no such thing as a controlled avalanche. Once started, an avalanche runs until it’s over.

When skiers venture outside of the ski area boundaries, they are on their own. Backcountry skiers typically ski in areas that have no one assessing the conditions or tossing hand charges onto slopes to trigger avalanches to make the area safer.

Cross country skiers have to rely on themselves for safety. It is important for anyone heading into the backcountry to understand the avalanche risks.

Cross country skiers should check the Sierra Avalanche Center’s Website for current information regarding the area they are going to ski ( The Website is updated about 6:30 a.m. each day, listing recent avalanche activity and often including photos and video of the area where the slide occurred. The conditions of the day are rated from low to extreme. Any rating above low is cause for concern.

Monte Hendricks and Rich Platt of the El Dorado Nordic Ski Patrol are expert backcountry skiers. They have 30+ years worth of experience. They teach winter safety classes each year and avalanche awareness classes every other year.

A big part of the class is the outdoor component, generally held at Loon Lake. Participants learn several methods to determine snow conditions and what to be aware of in the backcountry.

They agree that awareness and preparation are key to safe backcountry skiing. Cross country skiers who Telemark along with those who enjoy touring flatter areas need to be very cautious and aware. Avalanches may start on high ground but they can run onto flat areas before they stop.

At a minimum, Platt said that cross country skiers need to have a shovel and poles that double as avalanche probes. Additionally, it is best that everyone in the group have avalanche transceivers, which send signals and communicate with each other.

A skier with a transceiver who is buried in an avalanche, has a better chance of being found by another skier in the group who also has one. The chances of being located without a transceiver are not very good. Hendricks said that skiers should look for evidence of recent avalanche activity. Avoid any area that is questionable and always ski with a partner.

Avalanches can happen anytime. Knowing the conditions, what to look for and when to stay off the steeper slopes is critical for backcountry skiers. There are plenty of days to ski.

Hendricks reminds everyone that there are old backcountry skiers and bold backcountry skiers but there aren’t any old, bold, backcountry skiers. As Hendricks, Platt and the National Ski Patrol, point out, safety is the best part of a great day skiing.



Charlie Ferris



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