Snow in Science, Culture, and Climate

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HOW MUCH WATER IS IN SNOW? Snow Density and Snow Water Equivalent

Overview

This activity may be done in conjunction with the snow pit study or as a separate lesson. Students use a snow sampling tool of established volume to explore snow density and snow-water-equivalent (SWE), the amount of water that is contained within a given volume of snow. Older students may calculate density and SWE values, whereas younger students will learn based on observation and comparison of different snow samples. 

In addition to gaining an introduction or applied context for the concept of density, students will gain an appreciation for the importance of snow as a water source.

Background/reference

What is SWE? Snow Water Equivalent. 2021. MissoulaAvalanche.org. https://missoulaavalanche.org/2021/01/what-is-swe-snow-water-equivalent/ 

What is Snow Water Equivalent? No Date. Natural Resources Conservation Service, U.S. Department of Agriculture (USDA) https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314833#:~:text=Snow%20Water%20Equivalent%2C%20or%20SWE,the%20snowpack%20when%20it%20melts

Snow Density. Avalanche Encyclopedia. 2021. American Avalanche Association and National Avalanche Center. https://avalanche.org/avalanche-encyclopedia/#density-snow-1 

Materials 

Included in kits unless otherwise noted

● snow sampling tools (black PVC tubes with handles) (2)

● foam stands for sampling tools (2)

● square wooden rulers for sampling tubes (2)

● large metal spatulas (2) – from snow pit study materials

● extendable utility shovels (2) – from snow pit study materials

● Snow density sampling how-to video clip LINKED HERE

Procedures 

1. Activity set up

At least twenty  minutes before starting the activity, place the snow sampling tubes and spatulas outdoors to cool down, so that they don’t melt the snow when they come in contact with it during the sampling process.

There are only two sets of sampling tubes. If you would like more students to be able to participate in the sampling activity at the same time, the activity can be done by collecting snow in other types of containers of known volume (e.g. plastic containers provided in the kit) with some modification in procedures. To be able to compare results from different locations, all students should use the same type of container and follow the same procedures.

2. Activity introduction and demonstration

If students have already completed the snow pit study, they will have noticed that there are differences in snow grain size and shape, how much the snow grains stick together, how much space there is in between the snow grains, and how hard or compacted the snow is among different snowpack layers. One characteristic of snow that scientists measure when doing a snow pit study is the density of the snow layers and the overall or bulk density of the snow at that location.

If students have already been exposed to the concept of density in math or science, ask a student to refresh everyone’s memory of what it means and how it is calculated. 

  • Density is equal to mass (usually measured in grams or kilograms) divided by volume (usually in cubic centimeters or cubic feet). 
  • If you have two objects of identical size and shape and one feels “heavier” than the other, it is the denser of the two objects. (It contains more mass or material within the same volume.)

You might also ask guiding questions to find out if students have an intuitive or experiential understanding of what density means and how it is different from but related to weight. 

Do students have any ideas about why someone would want to know about how dense the snow is? They are not expected to have answers in advance, but they might suggest implications for snow stability/avalanche risk/ “post-holing” in snow; determining which snow is best to melt for water; or other ideas from personal experience.

Another way we can think about density of snow is to think in terms of how much water it contains. Snow is made up of ice particles and air, so snow with more ice and less air is more dense than snow with less ice and more air. By collecting a known volume of snow and letting it melt, we can measure how much water it contained, which is related to its density. 

3. Activity procedures

If available, show the video clip of UAF snow scientist Charlie Parr demonstrating how to collect snow samples using the density sampling tool.

Note that only two students will be able to collect samples at a time if using the snow sampling tools. Designate two students to take the samples. Distinguish the tools by writing each students’ initials on a piece of tape and affixing the tape to the wooden handles of the tools.  You might suggest that the students collect samples from different layers in the snowpack or from different locations. 

Steps:

  1. Use the shovel to cut vertically into the snowpack and remove snow from the area where you want to collect your sample. (See first snow pit study video clip for a demonstration.) Expose a vertical wall of snow at least 0.5 meters wide so that you can access it. Use a whisk broom or a gloved hand to brush loose snow from the exposed vertical surface so that you can see the locations of the different snow layers.
  2. Decide which layer you want to sample. The layer must be at least as thick as the diameter of the tool opening. If it is not thick enough, choose a different layer. 
  3. Insert the tool.
    1. If you choose to sample the top layer of snow, hold the wooden handle and insert the open end of the tool horizontally into the layer exposed in the face of the snow wall, being sure to keep it horizontal. Push it into the snow gently but firmly until the bottom of the black cylinder is flush with the face of the snow wall (with just the handle sticking out). 
    2. If you choose to sample a layer that is lower in the snowpack, use the shovel or metal spatula to gently remove (by scraping away) the upper layer(s) of snow. Once you have removed the snow above the layer that you would like to sample, repeat the process described in step 3.a.
  4. Use the large metal spatula to cut down vertically into the snow at approximately the location where you expect the open end of the tube to be located. (It might be helpful to use a ruler or tape measure to find the approximate location by measuring horizontally 13 centimeters back from the exposed snow wall.) Move the spatula around or cut down from the top again to try to find the position at which the spatula will cover the open end of the tube. Be sure not to push the spatula toward the tube opening, as this will push more snow into the tube, compacting it, which will affect the results.

The spatula can be done by the student who is still holding the sampling tube or by another student if more convenient. 

  1. When the spatula is touching the open end of the tube and covering the opening, gently and slowly pull the tube out of the snow horizontally, being sure that the blade of the spatula remains fully covering the opening of the tube the whole time.
  2. Once the tube has been extracted from the snow, slowly turn it to the upright position, keeping the spatula blade over the opening.
  3. Once the tube is in the upright position and being gripped by the handle, the spatula can be removed, and the sample should be carried inside, being careful not to spill any of the sample.
  4. In the classroom, insert the handle of the tube into the foam stand so that it remains upright while the snow melts.
  5. Place the tools in their stands on a stable surface close to a heat source, if possible, to speed up melting.
  6. When the snow in the tube has completely melted, insert the square wooden ruler, with the zero mark down, vertically into the center of the tube so that it touches the bottom. Then remove it. The part of the ruler that was submerged in the water will appear darker.
  7. Measure how deep the water was by referring to the darker colored, wet portion of the ruler.

4. Calculating density and snow-water equivalent

This portion is optional and is suitable for students who are more advanced in math, including geometry.

Steps:

  1. Calculate the volume of the cylinder, which is the volume of the snow sample if collected properly. 

Volume of the cylinder in cm3 = pi x radius of the cylinder squared x height of the cylinder

Vcylinder = π x r2 x hcylinder

The number pi (π) can be abbreviated as 3.14

V = volume, r = radius, h = height

  1. Calculate the volume of liquid water contained in the snow sample.

Volume of water in the cylinder in cm3 = pi x radius of the cylinder squared x height of the water in the cylinder

Vwater= π x r2 x hwater

The number pi (π) can be abbreviated as 3.14

V = volume, r = radius, h = height

  1. Determine the mass of the water in the cylinder.

Water has a known density of 1 gram per 1 cubic centimeter (1 g/cm3). Therefore:

Mass of water in the cylinder =  volume of water in the cylinder times the density of water.

mwater= Vwater x 1 g/cm3

m = mass, V = volume, 1 g/cm3 = density of water

Density is represented by the symbol ρ (Greek letter rho)

  1. Determine the density of the original snow sample.

Density of the original snow sample = Mass of water in the cylinder divided by volume of the cylinder.

ρ snow = mwater ÷ Vcylinder

ρ = density, m = mass, V = volume

5. Comparing and discussing results

Compare the depth of water that resulted from the two different samples. Was there more water in one sample than another? Were the samples taken from the same snowpack layer or a different snowpack layer? If from different layers, which layer contained more water?

We can infer from the amounts of water that each sample contained whether one snow sample was more dense than the other. Which sample was more dense?

6. The importance of water from snow

References to help connect the activity content to critical freshwater resources from snow:

Importance of snow. 2020. Our Winter World website. http://ourwinterworld.org/importance-of-snow/ 

Importance of snow: Supplying Water. 2020. Our Winter World website. http://ourwinterworld.org/importance-of-snow/supplying-water/ 

Snow Program Overview. National Water and Climate Center,  Natural Resources Conservation Service, U.S. Department of Agriculture (USDA). https://www.nrcs.usda.gov/wps/portal/wcc/home/aboutUs/snowProgramOverview/
Program History. National Water and Climate Center,  Natural Resources Conservation Service, U.S. Department of Agriculture (USDA). https://www.nrcs.usda.gov/wps/portal/wcc/home/aboutUs/programHistory/

PAPER SNOWFLAKES

Overview

This activity reinforces the fact that snow crystals (which we often call snowflakes) have hexagonal (six-sided) symmetry. Students fold round paper and cut out their own six-sided snowflake designs. 

Recommended age/grade range: all ages!

Time required: 20 minutes

Background/reference

Ken Libbrecht – Snowflake Science: A Snowflake Primer –  http://www.snowcrystals.com/science/science.html 

Ken Libbrecht – Types of Snowflakes chart – http://www.snowcrystals.com/guide/snowtypes4.jpg

Ken Libbrecht – Snowflake Photographs – http://www.snowcrystals.com/photos/photos.html 

Ken Libbrecht – Designer Snowflakes – http://www.snowcrystals.com/designer/designer.html 

Materials 

Included in kits unless otherwise noted

● Circular white paper 

● Snow crystal types charts – laminated

● Scissors must be provided by the school

Procedures 

1. Activity set up

Optional: You may choose to cut out a couple of snow crystals to show as examples or help provide ideas.

2. Introduction: Hexagonal symmetry

When we see these crystals falling from the sky, we usually call them snowflakes. Snowflakes can be individual snow crystals, or they can be clumps of snow crystals stuck together.

Snow crystals can be different shapes and sizes, but they all have six sides or arms. (Sometimes when we find them they are broken, so we can’t see all of the arms.)

Look at snow crystal types chart:

Practice finding and counting 6 sides & 6 arms of crystals depicted in the chart.

Introduce or remind students of the concept of symmetry. Because snow crystals have six identical sides/arms and an individual crystal looks the same no matter which side or arm is “up,” we say that snow crystals have hexagonal symmetry. (Show the shape of a hexagon.)

3. Paper snowflake activity

Today we’ll be cutting out our own hexagonally symmetrical snow crystals. 

Has anyone made a paper snowflake before? Let’s first look at some examples found online.

Optional: Look at paper snowflakes online or take a walking field trip to view paper snowflake decorations. Are there some designs that couldn’t actually be found in nature? Which ones? (Paper snowflake crafts are sometimes made with four- or eight-sides. These may be pretty, but snow crystals in nature only have six sides or arms. (Sometimes they can appear to be twelve-sided/twelve-armed when two snow crystals stick together or “aggregate” and then continue to grow as one….but their symmetry is always a multiple of six.) 

Display examples and coach kids through cutting out snow crystals.

Allow students to take their snow crystals home or use them to decorate windows or bulletin boards at school.

For students who want a challenge, show them (or encourage them to find online) photographs of specific snow crystal shapes and challenge them to create a paper snowflake that looks like the example.

Many different examples of photographs of real snow crystals can be found on Ken Libbrecht’s snowcrystals.com website. 

Step 1: use circular piece of paper

Step 2: Fold circle in half

Step 3: fold the halved circle into thirds

Step 4: figure out how you want to cut your snowflake and cut your lines

Step 5: Unfold your snowflake and see what you created!

If you run out of circular paper, see the following instructions for how to make six-sided snowflakes out of 8.5 x 11” paper:

Ken Libbrecht – Making Anatomically Correct Snowflakes: http://www.snowcrystals.com/paper/paper.html 

KarenHC, November 30, 2015. Instructions for making paper snowflakes – an easy tutorial. When Life is Good. http://www.whenlifeisgood.com/instructions-for-making-paper-snowflakes-an-easy-tutorial/ [Retrieved 8/22/2021]

TRACK SOUVENIRS: Casting plaster animal tracks

Overview

Students make plaster casts of animal tracks found outside or create plaster imprints of animal track replicas. They gain practice observing the natural world closely, and create a memento they can keep without removing any objects from the natural world. 

Background/reference

How to make plaster casts of an animal track. 2011. MyNatureApps. https://www.youtube.com/watch?v=Y4WTmgo4zeA 

Cabrera, Kim A. 2001-2007. Plaster Track Casting Procedure. Beartracker.com. https://www.michigan.gov/documents/dnr/Track_casting_382484_7.pdf 

Save Animal Tracks as Plaster Casts. https://www.startwithabook.org/content/pdfs/tracksplastercast.pdf 

Mangor, Jodie. 2021. How to make a plaster cast of animal tracks in the snow. Scout Life. Boy Scouts of America. https://scoutlife.org/hobbies-projects/funstuff/151633/make-a-plaster-cast-of-animal-tracks-in-the-snow/ 

Materials 

Included in kits unless otherwise noted

● Plaster of Paris (2-4 x 4 lb. containers)

● Jumbo craft sticks for stirring/mixing plaster

● Gallon size Ziplock bags for mixing plaster and water

● 1-2” wide strips of cardstock or manila folder material for forming a ring or collar around the track to contain the plaster

● clothespin or paperclip to secure the cardstock/paper ring

● Spray bottle 

● School provides water for mixing with plaster and for use in spray bottle to set the track in snow before pouring plaster. 32 oz. Nalgene water bottle provided in kit should hold enough water for a couple of smaller tracks; a moose or bear track might require the whole bottle.

Procedures 

Refer to instructions in reference materials listed above. Note that different sources have different opinions and preferences for materials and methods. Try an approach that appeals to you! One thing to note is that if you are making plaster tracks in snow, it is worth lightly spraying the track with a fine spray of cold water before adding the plaster to help set the track. Also, mix some snow in with the water when mixing your plaster so that the plaster mixture doesn’t melt the track.

In case you aren’t able to find any good tracks to cast outdoors, you can make negative track imprints using the flexible track replicas provided in your kit. Your kit will contain either a) two caribou tracks and two wolf tracks or b) two wolverine tracks and two snowshoe hare tracks. 

Follow these steps to make negative impressions of the replica tracks provided:

  1. Use the paper bowls provided to mix individual portions of plaster and water. A mixture of two parts plaster to one part water is generally recommended.
  2. Fill the bowl about two thirds full with plaster-water mixture and continue to stir using a craft stick.
  3. When your plaster and water mixture is a good consistency (like thick pancake batter), smooth the top of it with a craft stick. 
  4. If you have access to cooking spray, you might choose to lightly spray the surface of the track replica before inserting it into the plaster. 
  5. Then, firmly press the track replica face-down into the bowl of plaster. Allow it to sit, undisturbed, for approximately twenty minutes. 
  6. After twenty-five minutes, lightly touch the plaster with your finger to test how dry it is. If it is fairly dry and stiff, attempt to remove the track replica from the plaster. 
  7. Your result should be an imprint of the track – just like what you might find in the snow or mud if you found an animal track outdoors. 
  8. Ideally there will be enough bowls that each student can make an imprint and take a bowl home; there is no need to remove the plaster from the bowl. They may choose to decorate the final product with paint or glitter or to add their initials, the date, and the name of the animal whose track they have cast.

Albedo Experiment

Overview:

Students conduct a simple experiment to investigate reflection and absorption of visible light by dark and light materials. They learn that the term albedo refers to the ratio of how much incoming light is reflected by a substance and explore the albedo values of different types of surfaces on Earth. Based on the results of the experiment, they make inferences about the important role that snow plays in regulating Earth’s climate. 

Background/reference:

Importance of snow: Cooling the planet. 2020. Our Winter World website. http://ourwinterworld.org/importance-of-snow/ 

Snow science: Optical properties of snow. 2020. Our Winter World website. http://ourwinterworld.org/snow-science/properties-of-snow/#optical-properties 

Changing Albedo Values. My NASA Data. https://mynasadata.larc.nasa.gov/basic-page/changing-albedo-values. Includes links to:

  • Earth’s Energy Budget Includes Albedo (Why does the Sun Matter for Earth’s Energy Budget? video)
  • When do albedo values change? (Climate Bits: Albedo video)
  • Why does NASA study albedo? (Global temperature anomalies from 1880 to 2018 video)

Albedo – Terrestrial Albedo. 09.03.2021. Wikipedia. https://en.wikipedia.org/w/index.php?title=Albedo&oldid=1042141005 

Earth’s Energy Balance (online interactive simulation). 2021. University Corporation for Atmospheric Research (UCAR) Center for Science Education. https://scied.ucar.edu/interactive/earths-energy-balance 

Materials:

Included in kits unless otherwise noted

Kits include enough materials so that four groups of students can do the experiment at the same time.

● Black felt pockets (4)

● White felt pockets (4)

● Dial stem thermometers (8)

● Clamp on lamps with reflector shades (4)

● 60 Watt Incandescent light bulbs (4)

● Schools might need to provide extension cords and/or power strips for lamps.

Procedures:

1. Experiment set up

Set up four stations. For each station, you will need a desk, table, or other flat surface; 1 black felt pocket; 1 white felt pocket; and 1 clamp lamp with light bulb. 

Lamps should be positioned so that they shed light on the surface below them, upon which the two felt pockets will be placed side by side. The lamps should be centered over the surface so that each pocket receives the same amount and intensity of light. If there are no good options for affixing the clamp lights above desk/table height, you can clip them to the edge of the desk and set up the felt pockets on the seat of a chair underneath. 

Felt pockets should be oriented so that the thermometer dial can be read easily while the thermometer stem is inserted into the pockets. 

Check to make sure the two thermometers at each station read within a degree or two of each other. If they don’t, refer to the instructions on the packaging to calibrate them so that they start at the same temperature.

2. Experiment introduction and hypothesis development

Introduce what the experiment will entail without presenting too much information about the underlying science. 

Ask students to develop a hypothesis based on their everyday life experience as to whether and in which direction they think that the temperatures will change (go up, go down, or don’t change) and whether and how the temperature changes will be different between the black and white felt pockets (e.g. one will go up, one will go down; both will go up but the black one more so than the white one, etc.). 

Ask students to write down their hypotheses in a notebook or data sheet and to including their rationale, whether based on life experience, knowledge of underlying scientific concepts, or intuition. 

3. Experiment steps

Students at each station should follow these steps in sequence:

1. Before turning the lights on, insert a thermometer into each pocket (one black, one white) so that the dial is facing them and the stem is fully covered by the felt. Ensure that the thermometers are placed in such a way that the lamp is centered over them, providing an equal amount of light to each pocket.

2. Read the initial temperature of both thermometers and record them in a notebook or data sheet.

3. Turn on the light. Without touching the materials, watch the thermometers for changes in temperatures.

4. After five minutes, check the temperatures, being sure not to touch the thermometers or remove them from the pockets. Record the temperatures in a notebook or data sheet, being careful to note which temperature is for the black felt pocket and which is for the white felt pocket.

5. If there is a substantial temperature difference between the two thermometers after five minutes, you can end the experiment. However, if there has only been a small change in temperature and/or if the temperature of one or both thermometers seems to be continuing to change rapidly, wait another three to five minutes and record the temperatures again.

3. Share and discuss results

Ask each group to calculate how much the temperature of the white pocket and the black pocket changed during the experiment by subtracting the starting temperature from the ending temperature for each. 

Compile results from all groups by having a representative of each group enter their temperatures in a whole class chart (e.g. created by the teacher on a white board) or by sharing aloud the starting and ending temperatures that they recorded for the white and black pockets. Note any discrepancies in results and check to find out if everyone followed the same experimental protocols.

Did the results support or conflict with their hypotheses? If so, do they have any thoughts about what might account for the results that they had not considered in developing their hypotheses?

If they haven’t already done so, ask students to share examples from their life experience that relate to the experiment. For example, if they have ever worn black or dark clothing versus white or light-colored clothing on a hot, sunny day, which color of clothing made them feel warmer? Has anyone had the experience of walking barefoot on black asphalt or lighter colored surfaces? 

4. Connecting scientific concepts: Explaining absorption and reflection

Refer to background/reference information.

Light is either reflected or absorbed by an object or substance. 

The word albedo refers to how much of the incoming light that an object receives is reflected by that object. More reflective objects have higher albedo values, and less reflective objects have lower albedo values.

Albedo values range from 0 to 1. An object that absorbs all incoming light and reflects none of it has an albedo value of 0. An object that reflects all incoming light and absorbs none of it has an albedo value of 1. 

5. Applying what we’ve learned: Albedo, snow, and Earth’s climate

Display an aerial photograph or photograph of the Earth from space and notice the different colors of Earth surfaces. Which areas would the students expect to have high albedo values and which would have low albedo values?

Table

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6. Optional extension for advanced learners

A. Earth’s Energy Budget

Earth’s albedo is an important part of Earth’s energy budget, which describes the net amount of energy absorbed by the Earth based on its incoming energy and outgoing energy flows. Earth’s energy budget determines the temperature of the Earth.

This online interactive from UCAR Center for Science Education allows you to manipulate amount and brightness of incoming solar energy and the albedo of Earth’s surface and see how changes to those values affect Earth’s temperature: https://scied.ucar.edu/interactive/earths-energy-balance 

B. The electromagnetic spectrum and visible light

Teaching references:

NASA Science. 2021. Introduction to the Electromagnetic Spectrum (video). National Aeronautics and Space Administration (NASA). https://science.nasa.gov/ems/01_intro 

NASA Science. 2021. Visible Light (video). National Aeronautics and Space Administration (NASA). https://science.nasa.gov/ems/09_visiblelight 

Butcher, G., Mottar, J., Parkinson, C.L., and Wollack, E.J. 2016. Tour of the Electromagnetic Spectrum. National Aeronautics and Space Administration (NASA). https://smd-prod.s3.amazonaws.com/science-pink/s3fs-public/atoms/files/Tour-of-the-EMS-TAGGED-v7_0.pdf