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<FONT SIZE=4><P ALIGN="CENTER"><A NAME="QuickMark"></A>SNOWPACK STRUCTURE</P>
</FONT><P>PURPOSE: To determine how snow temperature and density are related to heat transfer in the layers of the snowpack.</P>
<P>MATERIALS (per group): Field -- suitable winter clothing, six or more plastic bags (about 30 x 30 cm), scissors, masking tape, snow shovel, hand lens, thermometer, snow scoop, meter stick, clipboard or other firm writing surface, pencil, millimeter ruler. Lab -- balance.</P>
<P>INTRODUCTION: Although it may seem like just a mound of white, cold stuff, take another look at that snow before shoveling it away! The <U>snowpack</U> on the ground is usually made of several distinct layers. The kind and number of these layers depends on:</P>
<P>(1) how many times it has snowed,</P>
<P>(2) how long the snow has been on the ground, and</P>
<P>(3) the environmental conditions during and after snowfall.</P>
<P>Regardless of original shape, snow crystals change with time after they land on the ground. This change or <U>metamorphosis</U> depends on such factors as wind, humidity, temperature, and solar radiation. Wind breaks off the delicate parts of the crystals to form smaller rounded granules packed closer together. The high humidity inside the snowpack also causes crystals to change into rounded granules. Temperature differences between snow layers cause water vapor to move from cold snow to colder snow, so that snow granules or air spaces grow in some layers. High air temperature or solar radiation can cause the top snow layer to melt and refreeze later into crusty snow or solid ice. Different environmental conditions result in different types of layers.</P>
<P>In this activity, you will identify the snow layers in the snowpack near your school. The Snow Layer Chart summarizes the characteristics of the layers you may see. You will measure the temperature and density of each layer. With this data, you will explain how these layers might have formed.</P>
<P>PREDICTIONS: Think about the natural sources of heat in the winter environment and then make some predictions:</P>
<P>1. Will the temperature of the snowpack be warmest near the air, near the soil, or in the middle? Explain your ideas.</P>
<P>2. Will the snow density in the snowpack be greatest in the top layer, middle layer, or bottom layer? Explain your ideas.</P>
<P>FIELD PROCEDURE: Work in groups. One student in each group should record the data and keep it dry.</P>
<P>A. Use masking tape to label the plastic bags from 1 to 6. Try to make the labels the same size.</P>
<P>B. Dig a hole in the snow to the ground that is large enough for you to kneel in and work as follows:</P><DIR>
<P>(1) Select an open area where the snow is relatively level and away from trees or bushes.</P>
<P>(2) Along one edge of the hole, cut a smooth clean vertical section in the snowpack.</P>
<P> </P></DIR>
<P>C. Examine crystals from each layer in the snow using a hand lens. Identify or describe all the snow layers you find using the Snow Layer Chart. You may not find all the layers listed in the chart. Record your data.</P>
<P>D. Measure and record the thickness of each layer and the total thickness of the snowpack. </P>
<P>E. Measure and record the temperature of each snow layer as follows: </P><DIR>
<P>(1) Insert the thermometer horizontally into the middle of each layer to a depth of about 5 cm. If the snow layer is too hard to insert the thermometer easily, try making a hole with your pencil first. If a snow layer is too hard to insert the pencil, skip that layer.</P>
<P>(2) Read the thermometer <U>in</U> <U>place</U> after waiting one minute. </P></DIR>
<P>F. Measure and record the temperature of the soil using the same method as in step E. If the soil is too hard to insert the pencil, measure the temperature at the soil-snow boundary instead.</P>
<P>G. Measure and record the air temperature 1 cm from the surface of the snow after waiting two minutes.</P>
<P>H. Measure and record the air temperature l.5 m from the <U>ground</U> after waiting two minutes. This is the height at which the weather bureau measures air temperature. </P>
<P>I. To calculate snow density you must determine the weight of a known volume of snow. Use your snow scoop to put <U>two</U> scoops of snow from each snow layer into the appropriate labelled plastic bags as follows:</P><DIR>
<P>(1) Start with the top layer. Push the snow scoop horizontally into the snow and lift up to break snow free. You may have to remove snow above the scoop with the snow shovel to carefully cut the snow free. Put the snow in the labelled plastic bag. Repeat for the second sample.</P>
<P>(2) Make a firm knot in the top of each bag. </P></DIR>
<P>J. Place a few crystals from the bottom layer of snow on your sleeve. Use a hand lens to examine the crystals. Sketch the crystals on the back of your data sheet. Estimate and record the size of the crystals using a millimeter ruler. Repeat for each layer.</P>
<P>LAB PROCEDURE:</P>
<P>K. Mass each bag of snow. (You can ignore the weight of the labelled plastic bag because it is constant and small compared to the weight of the snow.) Record your data.</P>
<P>L. Calculate the snow density (g/cm<SUP>3</SUP>) by dividing the weight of the snow (g) by the <U>twice</U> the volume of the can (cm<SUP>3</SUP>). Record your data. </P>
<P>M. Use your data to make a scale drawing of your snowpack. Label each layer.</P>
<P>N. Construct a bar graph of your data, plotting snow temperature on the horizontal axis and snow depth on the vertical axis on the snow temperature graph.</P>
<P>O. Construct a bar graph of your data, plotting snow density on the horizontal axis and snow depth on the vertical axis on the snow density graph.</P>
<P>CONCLUSIONS:</P>
<P>3. Which layer in the snowpack was the warmest according to your data? Which layer was coldest? How does your prediction compare to these results.</P>
<P>4. Which layer in the snowpack was the most dense according to your data? Which layer was the least dense? How does your prediction compare to these results?</P>
<P>DISCUSSION:</P>
<P>5. Use the air and soil temperatures you measured to explain the temperature pattern within the snowpack.</P>
<P>6. Why is the bottom layer of snow next to the soil (pukak) usually <U>less</U> dense (more air spaces) than the layer above it? Consider your graph of temperature in the various layers of snow and how water vapor moves in snow of different temperatures.</P>
<P>7. Sketch a line on your snow density graph to show how a layer of ice in the middle of the snowpack would affect the density pattern of the snowpack.</P>
<P>8. Was the air temperature 1 cm above the snow closer to the top snow layer temperature or to the air temperature 1.5 m above the snow? Give one possible explanation for your results. </P>
<P>GOING FURTHER: Use weather data provided by your teacher to explain how the layers in your snowpack may have formed.</P>
<P>====================================================================</P>
<P>	SNOW LAYER CHART</P>
<P>------------------------------------------------------------------------------------------------------</P>
<U><P>Frost</U>: A thin layer of crystals which form on top of the snowpack by sublimation of water vapor from the air.</P>
<U><P>Powder snow</U>: Cloud-formed crystals or parts of broken crystals. Layer is light and fluffy and makes terrible snowballs.</P>
<U><P>Wet snow</U>: Snow with high water content, ranging from good snowball snow to slush.</P>
<U><P>Ice Pellets</U>: Sleet or hail.</P>
<U><P>Wind-blown snow (Upsik)</U>: Small snow grains, rounded by tumbling in the wind. An upsik layer usually has been packed hard by the wind.</P>
<U><P>Granular Snow (Corn Snow)</U>: Old snow in which the original crystal structure has broken down by moving water vapor, leaving rounded grains. </P>
<U><P>Crust</U>: Snow grains fused together at various spots by liquid water moving down into the snowpack and refreezing.</P>
<U><P>Ice</U>: Ice layers are formed by freezing rain, or snow melting and refreezing at the surface of the snowpack. Ice or crust layers can be buried by subsequent snow storms.</P>
<U><P>Depth hoar (Pukak, Sugar Snow)</U>: Large crystals at the bottom of the snowpack with much air space between them. This layer is formed near the ground as water vapor moves from cold snow to colder snow.</P>
<P>====================================================================</P>
<P>	SNOW LAYER DATA SHEET (EXAMPLE)</P>
<P>====================================================================</P>
<TABLE BORDER CELLSPACING=1 CELLPADDING=7 WIDTH=571>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">Layer</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P ALIGN="CENTER">Snow Layer Name or Description</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P ALIGN="CENTER">Thickness (cm)</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P ALIGN="CENTER">Temperature (C)</TD>
<TD WIDTH="16%" VALIGN="TOP">
<P ALIGN="CENTER">Snow Weight (g)</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P ALIGN="CENTER">Snow Density (g/cm<SUP>3</SUP>)</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">Air</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> \\\\\\\\\\\\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P ALIGN="CENTER">-10.0</TD>
<TD WIDTH="16%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\\\\\</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">8</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">7</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">6</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">5</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P ALIGN="CENTER">POWDER</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P ALIGN="CENTER">2</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P ALIGN="CENTER">-10.0</TD>
<TD WIDTH="16%" VALIGN="TOP">
<P ALIGN="CENTER">75</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P ALIGN="CENTER">0.1</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">4</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P ALIGN="CENTER">GRANULAR</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P ALIGN="CENTER">7</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P ALIGN="CENTER">-4.5</TD>
<TD WIDTH="16%" VALIGN="TOP">
<P ALIGN="CENTER">440</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P ALIGN="CENTER">0.6</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">3</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P ALIGN="CENTER">ICE</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P ALIGN="CENTER">2</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P ALIGN="CENTER">TOO HARD</TD>
<TD WIDTH="16%" VALIGN="TOP">
<P ALIGN="CENTER">660</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P ALIGN="CENTER">0.9</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">2</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P ALIGN="CENTER">GRANULAR</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P ALIGN="CENTER">10</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P ALIGN="CENTER">-2,0</TD>
<TD WIDTH="16%" VALIGN="TOP">
<P ALIGN="CENTER">435</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P ALIGN="CENTER">0.6</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">1</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P ALIGN="CENTER">PUKAK</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P ALIGN="CENTER">2</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P ALIGN="CENTER">-1.5</TD>
<TD WIDTH="16%" VALIGN="TOP">
<P ALIGN="CENTER">290</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P ALIGN="CENTER">0.4</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">Soil</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> \\\\\\\\\\\\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\\\\\</TD>
</TR>
</TABLE>
<P>Volume (cm<SUP>3</SUP>) of Snow Scoop ____<U>730</U>_______</P>
<P>====================================================================</P>
<P>	SNOW LAYER DATA SHEET (YOURS)</P>
<P>====================================================================</P>
<TABLE BORDER CELLSPACING=1 CELLPADDING=7 WIDTH=571>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">Layer</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P ALIGN="CENTER">Snow Layer Name or Description</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P ALIGN="CENTER">Thickness (cm)</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P ALIGN="CENTER">Temperature (C)</TD>
<TD WIDTH="16%" VALIGN="TOP">
<P ALIGN="CENTER">Snow Weight (g)</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P ALIGN="CENTER">Snow Density (g/cm<SUP>3</SUP>)</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">Air</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> \\\\\\\\\\\\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\\\\\</TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">8</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">7</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">6</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">5</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">4</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">3</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">2</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">1</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="14%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="19%" VALIGN="TOP">
<P> </TD>
</TR>
<TR><TD WIDTH="10%" VALIGN="TOP">
<P ALIGN="CENTER">Soil</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P> \\\\\\\\\\\\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="14%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="18%" VALIGN="TOP">
<P> </TD>
<TD WIDTH="16%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="19%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\\\\\</TD>
</TR>
</TABLE>
<P>Volume (cm<SUP>3</SUP>) of Snow Scoop ___________</P>
<P ALIGN="CENTER"><IMG SRC="sn-le.jpg" alt="blank chart" WIDTH=606 HEIGHT=405></P>
</HTML>
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