Vail Daily column: A lifetime of stories in the snow
February 22, 2016
You can't be in the Rocky Mountains in the winter without interacting with snow. Snow facilitates all kinds of winter recreation. Snow makes it challenging to drive on the roads. Snow provides excellent ammunition for winter battles. But did you know that snow also records history? That's right, in some ways, snow is like a book that can tell us stories about the past.
Let's start with the snowpack. The snowpack includes all the snow and ice on the ground. As snow accumulates, it forms layers — the oldest on the bottom, the newest on the top. To read the stories that snow records, people dig snow pits — holes that are dug to expose the layers of snow. Many people dig snow pits to determine avalanche danger, but by looking at the size and shape of the snow crystals in each layer, much more information can be gathered. The layers of snow and how they have changed reflect the conditions at the time of deposition as well as the weather events that occurred after deposition.
Since atmospheric conditions affect how snow forms, scientists can look at the snow and tell what these conditions were like. For instance, graupel, pellet-like snow that falls as rounded balls signifies that the ice crystals fell through super-cooled clouds. Hoar frost, or surface frost, forms as ice crystals on surfaces overnight via sublimation, indicating that the temperature of the surface is lower than the frost point of the air. As snow persists on the ground, the texture, size and shape of the individual grains changes. Strong winds can break snow crystals into smaller crystals resulting in more densely packed snow. Warmer temperatures can lead to the melting of snow and the formation of crusts — hardened layers that sit on top of softer layers. Temperature gradients between the ground and the air create depth hoar — snow crystals that have metamorphosed into faceted, square grains.
Window to Distant Past
Layers of the snow and ice can also tell us about more distant pasts. In places where snow remains year round, the snow from one year is preserved by the snow from the next. When snow falls, it captures characteristics of the atmosphere around it. As the snow builds up over time, it compresses the layers beneath, turning them to ice and sealing in the information it collected.
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These layers are collected by drilling ice cores and removing an intact cylinder of ice. Ice cores can be anywhere from 100 to 3,000 meters deep and allow scientists to sample snow accumulation, air temperature and air chemistry from up to 800,000 years ago. Each characteristic of the layers provide different information. The thickness of each layer can be used to determine precipitation rates. Bubble free ice layers, called melt layers, are related to summer temperatures. Debris found in layers can mark when volcanic eruptions occurred or indicate the degree of atmospheric circulation. Samples of ancient atmospheres, preserved by bubbles in the ice, provide the most influential measurements. By relating the levels of carbon dioxide and methane in these bubbles to today's climate, scientists can model past climates. This is valuable information as humans attempt to identify how our word is changing and prepare for future changes.
As mountain inhabitants, snow is a part of our everyday lives. We drive through it, we soar over its surface on slices of wood and fiberglass, and we laugh at those places paralyzed by mere inches of white flakiness coating the ground. Snow provides our water, too, which opens up a whole new range of playgrounds and possibilities. But let's not get ahead of ourselves. For right now, let's just see what kind of stories of our own we can write in the snow.
Laura Robison is a naturalist at Walking Mountains Science Center who is always in awe of the beauty of snow. Join her on a snowshoe hike to learn about ways that snow is crucial for the survival of our world.
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