7. Erosion Patterns - Getting Ready

Getting Ready
Setting up the demonstration

  1. Fill the jar 1/4 full with gravel, another 1/4 full with sand and another 1/4 full with diatomaceous earth. Mix well.
  2. Add a pea sized amount of alum, about 1/2 a teaspoon.
  3. Fill the rest of the jar with water, leaving just a little air space at the top.
  4. Seal the jar tightly.

Preparing the tubs

  1. In HALF the tubs, place 13 cups of diatomaceous earth. Diatomaceous earth may be irritating to the lungs if it is inhaled so pour diatomaceous earth slowly. (These are identical to those used in River Cutters. If you have already conducted experiments from River Cutters, leave half the tubs the way they are.)
  2. In the other HALF of the tubs, add 10 cups of diatomaceous earth, 2 cups of playground sand, and 1 cup of aquarium gravel. Mix the sediments together thoroughly. (If you have already conducted experiments from River Cutters, you can adapt half the tubs to mixed sediment without needing to discard the whole thing. Remove 4 cups of the diatomaceous earth from the existing tubs. Add 2 cups of playground sand and 1 cup of aquarium gravel. Add 2 cups of water. Mix thoroughly then adjust the moisture level until you can cut a channel.)
  3. In ALL tubs, add 12 cups of water. Mix thoroughly. It should begin to resemble that fascinating non-Newtonian fluid, cornstarch in water. In the mixed sediments tub, the gravel and sand will likely rise to the surface – that’s OK.
  4. The consistency of the mixture is very important. Check to see if there is too much water by lifting one end of the tub. If the sediment slides down to the lower end of the tub, then it is too wet. Use the sponge to soak up some extra water. Check to see if here is too little water by slowly pouring some water onto the surface. If the water soaks in before it forms a rivulet, then it is too dry and needs more water. Ideally, the water should trickle across the surface and erode a gully as it flows downhill.

Preparing the dripper systems

  1. Cut a shallow V shaped notch in each cup.
  2. Insert a piece of paper clip wire into each stir stick.
  3. Gently curve the stir stick into U shape resembling the Saint Louis Gateway Arch or the end of an egg.
  4. In each pitcher, put 3 drops of blue food coloring then fill the rest of the pitcher with water.
St Louis Gateway Arch
Saint Louis Gateway Arch
Chicken Egg

Working the dripper systems

  1. Fill the cup with water
  2. Dunk the stirrer into the cup so that the entire straw fills with water (insert the straw middle first with the ends pointing upwards). You should see bubbles come out of the ends.
  3. Carefully pick the straw out of the cup. I find that holding a finger over one end of the straw helps.
  4. Quickly turn the straw over so that the ends point downward and simultaneously stick one end (the end with your finger over the tip) into the cup. Position the straw onto one of the notches.
  5. Hopefully, the straw drips slowly and steadily, around 2 drops per second. If there is no water at all, try again. If the water flows too quickly, bend the straw straighter. If the water flows too slowly, bend the straw into a deeper U shape.