Stability In The Snow Pack example essay topic

Introduction I have chosen the topic: " Avalanche" as I am interested in the outdoors and am an enthusiastic skier, who would like to do back country skiing. To do this safely I have to learn about the avalanche danger. The following questions I have chosen and researched: Who is affected by avalanches? What different avalanches do we know? Where and why do avalanches occur? How do you keep safe? and How do you recognise avalanche terrain?

I also watched a video produced for the NZ Mountain Safety Council, called Avalanche Awareness! A guide to snow safety in the New Zealand Mountains. As my oral component I interviewed a friend, who was actually involved in an avalanche. General facts Avalanches are one of the great hazards facing winter travellers in the mountains these are mainly skiers, snowboarders, trampers, climbers, people who are using the backcountry for recreation or passing through in cars, buses etc. (e.g. on the Milford Road). Every year appr 250 people are buried and the majority of the victims trigger the slide themselves. More than half (180) of all buried victims will die if they are not rescued within 30 minutes.

Many are killed during or within minutes of the avalanche from suffocation, the severe trauma of being buried alive, by hitting boulders, trees during the slide, or having been crushed by massive blocks of snow. If the victims are still alive the only realistic hope for survival is a fast and organised rescue from the rest of the party. What are the different types of avalanches? There are two types of avalanches, loose snow and slab avalanches. Loose snow avalanches begin from a single point and expand as they move downhill accumulating more snow as it flows down. Slab avalanche starts when a large mass of snow breaks away, leaving an obvious fracture line at the top, the crown wall with the avalanche path ending in the run out zone.

Why and when do avalanches occur? For avalanches to happen three factors are required: 1. snow 2. sufficient slope angle 3. instability within the snow pack Unless all of these conditions exist, there is no risk of an avalanche. Avalanche danger is greatest during and after a storm with new snow, rain or big changes in the temperature. The stability in the snow pack weakens through surface hoar (hoar is the formation of big crystals on the snow surface) through melt- freeze Cycle (snow melts over day, then refreeze over night).

When the stress within the snow layers exceeds the strength of the cohesion. The trigger for a collapse of the snow pack can be the added weight of snow, rain, wind, icefall or a person. The greatest danger from avalanches is during or immediately after the storm". (Tony Daffern, 1992). Snow can fall in many different forms, but in general it is usually some variation of the classic six-arm flake. It usually snows in fairly mild temperatures, which helps promote settlement.

Snow changes over time through a process called sublimation. Sublimation is the change of a solid directly into a gas without first becoming a liquid. At mild temperatures the water vapour travels from the arms of the crystal to refreeze in the centre. This produces a rounding of the snowflake.

These rounds will often begin to form necks and bond to each other. This is sometimes called destructive metamorphosis. This will generally produce a good cohesive layer of snow. The colder the temperature, the longer this process takes.

In a cold shallow snow pack, like early season in the Rockies another process is a work changing the crystals. When it's cold and the snow pack is thin (a change of 10 degrees Celsius or more per metre of snow) a different form of re-crystallization occurs. Water vapour recrystallizes at the bottom of the snow pack where it is warmest, into sharp angular faceted crystals. The longer and more severe the temperature gradient, the more extensive the faceting. Facets will further recrystallize into striated crystals of depth hoar. Facets and depth hoar tend to be less cohesive and more un-supportive within a snow pack.

In short facets tend to weaken the strength of the snow pack from the bottom up. How to keep safe? In my opinion one of the most important facts about keeping safe in backcountry snow is the recognition and observation of avalanche terrain. As Tony Daffern points out: "Only by recognising risk can you use your knowledge and experience to reduce that risk to an acceptable level". (Page 11) This allows the skier, climber to either avoid potentially dangerous areas completely or pick a route to minimise the risk by not moving near terrain traps; ie an avalanche could sweep the person over a cliff, into a crevasse or into a gully. Wind direction plays a major role, as it can transport large amounts of snow.

Particularly during and after storms, loose snow is taken from the windward slopes and accumulated on the lee slopes, in gullies or corniced ridges. This adds weight to the snow pack and increases the avalanche danger on lee slopes. The snow pack profile (a vertical pit dug into the snow) gives detailed information about the stability of slope and the likelihood of an avalanche. If the surface formed a smooth sun or wind crust, it would indicate that there might be similar layers down in the snow pack and this could cause it to slide. Cracking of the snow is a sure sign, that the snow is unstable and could potentially release a slab avalanche. If the snow gives way under you with a whumpfing sound, as I have personally experienced in the Canadian Rockies.

It indicates a hard layer of snow over a soft layer and an extremely unstable situation. If a person decides to travel through terrain traps or avalanche paths, they can minimise the danger by travelling in single file about 20 meters apart or one at a time through questionable slopes. It is recommended practise to remove pole and ski straps before entering the slope, and travel as quickly as safely possible from a safe spot to another safe spot. Someone in the group should be watching each person cross. Should an avalanche occur only one person is exposed, and the rest of the party can begin a rescue.

The spotter watches the victim and remembers the last seen point. Before the rescue begins, a look out is established to watch for another avalanche, and the party decides if it is safe enough to proceed with the rescue. If it is safe to continue, everyone then switches his or her avalanche transceiver to receive. One person skis to the last seen point and begins the search, while another assembles the shovel and probe. When the searcher is very close to the buried skier's location, the second rescuer skis down to the site with the probe and shovel to probe and dig out the victim. All of this must occur within a matter of minutes if the victim is to have a good chance of survival.

(This is a very simplified search and rescue description). Only with good training, practice, and experience is it safe to travel in avalanche terrain. A friends account of being trapped I found it very interesting and informative to talk to a friend's brother and hear his first hand observations about being in an avalanche in the Craigieburn's. Luckily my friend ended up only half submerged after the standstill of the snow slide.

But he said it was very quick and an awful, scary feeling of "drowning", when submerged in the snow. Finding a safe route is easier said than done and " choosing the best route through avalanche country is best gained in the company of others, who have greater experience, and a kinder heart". (Buck Stilton 1992 page 36). Observation of the terrain you intend to travel into can tell you about the snow condition, like evidence of recent avalanches in the area.

This is one of the most important signs of snow instability. Storms Recent precipitation and changes in temperature are equally crucial. Stability Tests A snow stability test is one of the most reliable tests that can be done, to give you a good idea about the avalanche danger on a slope. The test should be dug in a safe area that represents the aspect and angle of the slope in question. Snow in the area should not be disturbed, or have any rocks, or vegetation interfering with the profile. The names of different tests are compression test, shovel-shear test, rutschblock test and the loaded column test.

The intention with all these tests is to locate and identify the weak bonding of layers of snow and ice within the snow pack. An easy method of collecting information about the snow pack is to dig a snow profile. Snow temperatures and crystal forms in the different snow layers will give vital information, to determine and identify the cohesion in the of the total snow pack. The pit for the profile should be dug to the bottom of the snow pack or at least 2 metres deep, with the front wall 1/2 metre wide.

The front wall is in the shade, cut vertical and brushed with a glove or mitten to help define the various layers. A plastic card run vertically through the profile will help to gauge the hardness of each layer. Fist, finger or pen is used to probe the hardness too. The 'Shovel Shear Test' is used to identify potentially weak layers and their location in the snow pack. Cut an Isolate column up to 1.5 metres deep in undisturbed snow by 0.5 metres across. Remove soft and very soft snow from the top of the column (fist and four-finger snow).

Cut the back of the column with a snow saw, but do not cut deeper than 0.7 metres from the top of the column. Insert the shovel at the back of the column, and with both hands pull the shovel towards you in an even, increasingly stronger pull. If the column breaks in a clean smooth manner, record the height of the failure, force required, and observe the crystals at that site. If the column fails to break, or produces an uneven shear, level the column above the height of the 0.7 metre back cut, saw to 0.7 metres from the new top and repeat. All these techniques and many more helpful tips and hints were described in the video and I enjoyed actually seeing these procedures, rather than just reading about them. You can improve your safety by having the right equipment and knowing how to use it like a transceiver, snow probe, shovel and first aid kit, as well as knowing the weather forecast and the current level of avalanche danger.

Conclusion Avalanches may not be unavoidable, but your ability to survive an avalanche, if you should be so unlucky to be involved, is greatly improved by having the right equipment, the right company and by coming prepared into this potentially dangerous environment. As I pointed out before there is a lot of information to be gathered for the interested person. This includes survival facts of victims and why and when avalanches occur. Simple rules can be observed and put into practice, such as the danger being greatest after storms. Fascinating, scientific facts can be gained from studying snow, ice and crystals. Avalanche terrain also can be studied and recognised as unsuitable for skiing or traversing.

Again many common practices could potentially help save lives and they include such common sense ideas as removing pole and ski straps before entering a slope or one person only to cross at a time and the others watching. To have the right equipment is vital for survival and of course one needs practice and experience to use it. Stability tests have been described as well as finding the right route and being super observant about weather and avalanche forecast. Reference to study material Books Erick, B. (1998) The New Zealand Weather book.

Nelson: Craig Pott on. Tilton, B. (1992) The Basic Essentials of Avalanche Safety. U.S. A: ICS Books, Inc. Daffern, T. (1992) Avalanche Safety for Skiers & Climbers. Canada, Rocky Mountain Books. Internet Avalanche web Avalanche web Eight Steps to Reducing Your Avalanche Risk web Avalanche Awareness web Avalanche safety web Video Avalanche Awareness! A Guide to snow safety in the Mountains Produced for: NZ Mountain Safety Council (2002).