Ecology Lab #1 –Aeolian ProcessDate:

Team Member Names: ______Hour: ______

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Purpose: The objective of this exercise is to demonstrate the process of wind erosion and deposition around surface features such as hills and craters in a desert biome.

State Standard:

Materials:

3-speed fan (1 per team)

tablechairdrop clothsugarsmall objects

metric rulerpenciltablestring (approx 15cm long)

Introduction

Wind is an important agent of gradation in many arid and coastal regions of the Earth and on Mars and Venus. During wind erosion, small particles are moved in suspension, saltation or traction. Very small particles can be carried by the wind without touching the ground until the wind slows and stops and drops the particles. Wind erosion and deposition of particles result in distinctive landforms, such as dunes and wind streaks. Venus and Mars have wind related features similar to those seen on Earth.

Vocabulary—define each to complete the lab.

  • Suspension
  • Saltation
  • Traction

Procedure:

  1. Place the fan on the chair, centered at the end of the table. Make sure the center of the fan is even with the surface of the table.
  2. Direct the wind by tilting the fan towards the surface on the table at an angle of 15 to 20 degrees from vertical.
  3. Tape a piece of string on the end of a pencil.
  4. Turn the fan on medium speed.
  5. Holding the pencil perpendicular to the surface on the table with the string along the table, move the pencil around the table to locate the “dead spots” produced by the fan.
  6. Locate the area near the fan where the air movement is greatest; this spot is where all “sand” piles should initially be placed.

Aeolian Process--PART ONE

1. Form a 5 cm high cone of sugar in the identified spot (procedure #6 above). Make an initial sketch of the TOP view and SIDE view of the cone

TOPSIDE

  1. After the sketch is completed, turn on the fan at the MEDIUM speed that results in moderate movement of material. Leave the fan on for three minutes. Answer the following questions while the fan is blowing:

How far down the table has the sugar traveled after one minute? ______cm

Describe the pattern the sugar has formed at the far end of the table after 2 minutes.

What is the average length of the bounce of a sugar grain leaving the cone of sugar? Is the second bound of a sugar brain longer or shorter that the first bounce?

How high above the table does the sugar rise? ______cm

  1. After three minutes turn off the fan and make a sketch of the cone. Include both a top and

side view.

TOPSIDE

4. Turn the fan back on for another TWO minutes. Be sure to note the saltation of the sugar grains at the far end of the table. Sugar from the cone will hit sugar grains on the table and make them move along in saltation or traction. After two minutes turn the fan off and make a final sketch of the top and side views of what remains of the cone of sugar.

TOPSIDE

From where has most of the sugar been eroded on the cone?

  1. Has any sugar been deposited around the cone? If so, where?
  1. Based on your three sketches of the sugar cone, diagram the effect the cone has on the wind movement. Do this by imagining you can see the wind. Draw arrows to show how you think the wind moves around the cone.

Aeolian Process--PART TWO

Clean up the sugar on the table—but keep it. Form another 5cm high cone of sugar in the spot of greatest wind movement. Place obstacles (keys, small rocks, eraser, etc) at different locations on the table downwind of the cone of sugar. Place the obstacles at different orientations to the wind. For example, with a long side parallel, perpendicular or at an angle to the wind; flat or on its side. Turn on the fan at the same speed as in PART ONE. After three minutes turn the fan off and observe the deposition and erosion of the sugar around the obstacles. Make a sketch (TOP and SIDE view) of each obstacle and the sugar surrounding it. Add arrows to indicate the movement of the wind around each obstacle.

TOPSIDE

Where does most of the deposition occur at the obstacle? Where does most of the erosion occur?

Aeolian Process--PART THREE

Remove the obstacles and clean up all the sugar on the table. Form a thin (few grains thick) layer of sugar 20cm x 20xm in size and make a 3 cm high cone of sugar in the center. Make sure the cone is in the spot of maximum wind. Use the ball to form a bowl-shaped crater on the pile. Remove the ball and make an initial sketch of the crater (TOP and SIDE view).

Initial Sketch

TOPSIDE

Turn the fan on and off for THREE ONE-MINUTE intervals to monitor the progress of erosion of the crater. Turn on the fan at the same speed used previously, producing moderate movement of the sugar. After one minute, turn off the fan and observe what changes have occurred to the crater and the surrounding area. Sketch what you have observed (TOP and SIDE view) as well as arrows indicating the wind movement over and around the crater.

Sketch after first one-minute interval

TOPSIDE

Sketch after second one-minute interval

TOPSIDE

Sketch after third one-minute interval

TOPSIDE

How is the movement of the wind around the crater different from the movement of the wind around the cone in PART ONE?