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<FONT SIZE=4><P ALIGN="CENTER"><A NAME="QuickMark"></A>SNOW LAYERS</P>
</FONT><P>PURPOSE: To identify snow layers and investigate heat transfer in the snowpack.</P>
<P>MATERIALS: Suitable winter clothing, shovel, thermometer, meter stick, clipboard, pencil, hand lens, millimeter ruler.</P>
<P>INTRODUCTION: Although it may seem like just a mound of cold, white stuff, take another look at that snow before you shovel it away! The snow on the ground is called the <U>snowpack</U>. As you dig down into it, you will see that the snow is usually not the same from top to bottom. The snowpack is actually composed of various layers. The kind and number of these layers depends on three things:</P>
<P>(1) how many times it has snowed</P>
<P>(2) how long the snow has been on the ground</P>
<P>(3) the environmental conditions before and after snowfall.</P>
<P>Changes in air temperature, wind, sunlight and humidity can make old layers disappear and create new ones in their place. The Snow Layer Chart describes some of the layers you might see in the snowpack near your school.</P>
<P>The chart also shows that the movement of water vapor inside the snowpack is very important in changing and creating snow layers. Water vapor tends to move from cold snow to colder snow. In this activity, you will find the different layers in the snow and measure the temperature of each layer. You will use this information to help explain how snow layers form.</P>
<P>PREDICTION: Think about the natural sources of heat in the winter environment and then make a prediction: </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>
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<P>SNOW LAYER CHART</P>
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<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 with much air space between them. This layer is formed near the ground as water vapor moves from cold snow to colder snow in the snowpack.</P>
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<P>PROCEDURE: Work in groups. One student in each group should record the data and keep it dry.</P>
<P>A. 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 shrubs.</P>
<P>(2) Along one edge of the hole, cut a smooth, clean vertical section in the snowpack.</P></DIR>
<P>B. Examine the crystal structure from each layer using the hand lens as follows:</P><DIR>
<P>(1) Identify all the snow layers you find in the snowpack using the Snow Layer Chart. All layers listed may not be present in your sample. Record your data on the data sheet. </P>
<P>(2) Put a star (*) next to the snow layer on your data sheet which seems to have the biggest air spaces between the ice crystals.</P></DIR>
<P>C. Measure the thickness of each layer and the total thickness of the snowpack. Record your data on the data sheet.</P>
<P>D. Measure and record the temperature of each snow layer as follows:</P><DIR>
<P>(1) Insert the thermometer horizontally 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>E. Measure and record the temperature of the soil using the same method as in step D. If soil is too hard to insert the pencil, measure the temperature at the soil-snow boundary instead.</P>
<P>F. Measure the air temperature 1 cm above the snow, after waiting two minutes. Record the air temperature on the data sheet.</P>
<P>G. Place a few crystals from the bottom snow layer on your sleeve. Sketch the crystals on the back of your data sheet. Estimate and record the size of the crystals using a millimeter ruler. Do the same for crystals from the top layer.</P>
<P>	</P>
<P>H. In the lab, use your data to make a scale drawing of the snowpack. Label each snow layer, the air, and the soil with its name and temperature.</P>
<P>CONCLUSIONS:</P>
<P>2. How many layers did you identify in the snowpack. What evidence, if any, did you find that snow had melted and refrozen?</P>
<P>3. How did the crystals in the bottom snow layer compare to the crystals in the top layer?</P>
<P>4. Which layer in the snowpack is the warmest according to your data? Which layer is the coldest? Was your prediction correct?</P>
<P>5. How did the soil temperature compare to the air temperature?</P>
<P>DISCUSSION:</P>
<P>6. Using the air and soil temperatures, how can you explain the temperature differences within the snowpack?</P>
<P>7. Use your snow temperature data to explain why the bottom layer of snow often has larger air spaces than the layer above it (Hint: Remember that water vapor in snow moves from cold to colder snow.)</P>
<P>8. Since the sun is the source of heat for the air and soil, why are air and soil temperatures different?</P>
<P>9. What characteristics of the snowpack make the bottom layer a favorable habitat for small animals?</P>
<P>10. What characteristics of the bottom layer of the snowpack can be used to explain the occurrence of avalanches?</P>
<P>	SNOW LAYER DATA SHEET</P>
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<TABLE BORDER CELLSPACING=1 CELLPADDING=7 WIDTH=529>
<TR><TD WIDTH="13%" VALIGN="TOP">
<P ALIGN="CENTER">Layer</TD>
<TD WIDTH="42%" VALIGN="TOP">
<P ALIGN="CENTER">Snow Layer</P>
<P ALIGN="CENTER">Name or Description</TD>
<TD WIDTH="22%" VALIGN="TOP">
<P ALIGN="CENTER">Thickness (cm)</TD>
<TD WIDTH="24%" VALIGN="TOP">
<P ALIGN="CENTER">Temperature (C)</TD>
</TR>
<TR><TD WIDTH="13%" VALIGN="TOP">
<P>Air</TD>
<TD WIDTH="42%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\</TD>
<TD WIDTH="22%" VALIGN="TOP">
<P>\\\\\\\\\\\\\\\\\\\\\\\</TD>
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<P> </TD>
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<P>10</TD>
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<P>Soil</TD>
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<P>\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\</TD>
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<P> </TD>
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</TABLE><P> </P>
<IMG SRC="snow-ch-b.jpg" alt="snow chart example" ALIGN="LEFT" HSPACE=12 WIDTH=308 HEIGHT=552>
<IMG SRC="snow-ch.jpg" alt="snow chart" ALIGN="RIGHT" HSPACE=12 WIDTH=339 HEIGHT=571>
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<font size=4><b>
<pre> Your Chart Example
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