Introduction
Glaciers are melting at an alarming rate. As this cold fresh water from glacier melt enters lakes and oceans, it can have a big effect on how the water behaves � and on the fish, mammals, and other animals that live there.
Safety Suggestions
- Safety goggles required
- Do not eat or drink any of the materials used in this activity
Safety First! Read the Science Safety Tips to find important practices for kids and chemists to do before, during, and after every chemistry activity.
Materials Required
- Two 10-ounce clear tall plastic cups (300 mL)
- Insulated container for cold water
- Ice cube tray
- Blue and yellow food coloring
- Ice-cold water (add ice cubes to water and pour into the insulated container when cold)
- Salt (fine salt is best because it dissolves faster)
- A teaspoon measure
- 1-cup measuring cup (8 oz or 240 mL)
- Small pipette or plastic syringe without a needle
Procedure
Before Getting Started: Create your glaciers!
- 24 hours before the activity, make some “glacier� ice cubes by adding blue food coloring to water in an ice tray. Place in the freezer until completely frozen.
Part 1: Simulating cold glacier melting into warmer freshwater
- Pour cold water into an insulated container. (Use the coldest water you can get from the tap or melt ice). Drop several drops of blue food coloring, and stir until you see a rich blue color.
- Add warm tap water to one of the 10-ounce cups, filling it at least 1/2 to 2/3 full. Add some drops of yellow food coloring and stir until you get a nice bright color.
- Fill your syringe, eye dropper or pipette with cold blue water from the container.
- Slowly place the tip of the full syringe, pipette,or eye dropper against the inside of the container with the yellow water, just above the water surface. Squeeze out all the blue water you can from the dropper. Do not stir! Make observations. If you don’t see the blue water layer from the side of the cup, add more blue water using your dropper, syringe, or pipette.
Part 2: Simulating cold glacier melting into warmer, saltier ocean water
- In the second 10-ounce cup, make a salt-water solution of 1 cup of warm water and 1 level tsp of salt. Add yellow food coloring until it is bright yellow, and stir to make sure the salt is dissolved and well-mixed. (This mimics ocean water.) Let the water cool to room temperature.
- Carefully place one blue ice cube, your “glacier,� on top of the salt water and observe it over time for the next 5 minutes, or longer if you wish. Make observations.
What did you observe?
Part 1: The cold, blue glacier water makes a layer at the bottom of the cup. The more slowly you add the cold water, the more distinct the layer will be. The longer it sits, the more mixing will occur.Â
Part 2: The ice cube “glacier� melts from the bottom and from the edges inward, forming a blue layer of water at the surface of the water in the cup. Eventually the water in the cup turns green.
How does it work?/Where’s the chemistry?
An equal volume of cold water is heavier than warm water. We say the cold water is more dense. A liquid of greater density will sink to the bottom when put in a liquid that is less dense. When cold glacial ice melts and runs into a warmer body of fresh water, it sinks. This can change the natural currents in the lake, and can harm the animals that live in and around it.Â
Salt water is more dense than fresh water. As glaciers melt, the released freshwater mixes with saltwater, lowering its overall density. This less dense water tends to stay near the surface, getting in the way of the deep ocean currents that the earth needs to distribute heat around the world. This is why changes in how fast glacial melt happens can create major problems for regional and global climate patterns.Â
As your ice cube “glacier� melted in the “seawater,� did you notice how the sides and bottom melted a little faster than the top? A similar thing can happen with real glaciers. When their edges break off and fall into the ocean, it’s known as calving. These pieces of glaciers are called icebergs.
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