In this lesson students explore weatherization (physical and chemical) by doing a series of short experiments that demonstrate how rocks and minerals are broken down into soil. Expand this lesson further by taking students on a field trip to look for rocks breaking down into soil.
Here are two ways to approach the five short demonstrations of how rocks become soil.
Option 1: Set up five experiment stations based on the activities below. Cut apart each station directions and set with corresponding station materials. Have students work in small groups, record their findings at each station, then complete the Weatherization worksheet. Plan for about 10 minutes per station. When everyone has done all the experiments, assign each group one of the activities to present and explain to the class.
Option 2: Break students into groups. Assign each group one of the activities below. After completing the experiment once on their own, each group will then demonstrate their activity for the class and explain what is happening and how it relates to soil formation.
For teachers, the directions include explanations of what is being seen and where in Oregon you can find this type of weatherization. You may wish to remove this information from the directions you give students to follow.
Beginning Activity: Forces of Nature
(Instructor demonstrate to class)
Materials – Several small rocks, cloth, hammer, safety glasses
Directions: Show students the rocks. Then wrap the rocks in a sturdy piece of cloth. Wearing safety glasses, hit the rocks with a hammer. Ask the students what they think they will see when the rocks are unwrapped. Unwrap the cloth and show the students how the rocks look.
Have students guess what forces in nature, if any, could cause this much change in a short time.
Answer: Earthquakes, severe freezing, hurricanes, or other violent forces can break up rocks.
Where can we find examples of this in Oregon?
Activity I: Roots, Heaving & Uplifting
Materials – Large balloon, small stack of lightweight books
1) Place a large flattened balloon between two light weight books.
2) Blow the balloon up while it is between the books. See image.
3) As you inflate the balloon, observe what happens to the books.
What is happening: The expanding balloon shifts and lifts the books. In this experiment the balloon represents both the roots of plants that, over time, can split rocks. The expanding balloon can also be used to represent water that freezes in the cracks in rocks, expands, and breaks rocks when it turns into ice. Finally, the balloon example can also represent the uplift of mountains.
Oregon example: In high mountainous places with freezing and thawing temperatures roads shift and buckle, and rocks on cliffs “pop” off on to roadways. You may have seen road signs that say, “Watch for falling rock,” and “Frost Heaves.” These are warnings to motorist about road hazards created by this type of weathering.
This exercise also demonstrates uplift. The Steen Mountains in NE Oregon are one of the largest single fault uplifts in North America and an excellent example of uplift.
Activity II: Wind Erosion
Materials – Soft rock, medium grade sandpaper, white sheet of paper
1) Over a white sheet of paper, briskly rub the surface of a soft rock with a piece of medium grade sandpaper.
2) Observe how much of the rock rubs off onto the paper.
What is happening: This experiment illustrates the influence of sandy winds on rock. It is one way rocks can be eroded. Wind erosion is also a problem in farmland. The greatest historical example is the Dust Bowl of the 1930s that literally blew away the soil of Midwestern farms.
Oregon example: On the Oregon coast sandy winds erode and reshape the coastline sandstone cliffs.
Activity III: Glaciation
Materials – Two sedimentary rocks, white sheet of paper.
1) Grind two sedimentary rocks together over a piece of white paper.
2) Observe how much of either rock falls onto the paper.
What is happening: This experiment illustrates the abrasive force of glaciers. Glaciers not only transport material as they move, but they also cut and carve the land beneath them. A glacier’s weight, combined with its gradual movement, can drastically reshape the landscape, shearing away mountainsides and creating deep valleys with vertical walls. Much of the Midwest’s rich, flat farmland was formed by glacial activity.
Oregon example: During the Pleistocene era (2.5 million – 12,000 years ago) scientists believe the entire Oregon Cascade Range may have been covered by glaciers, forming an ice cap over the region. Today, there is much less glacial activity. Glaciers can still be found on the stratovolcanoes of Oregon’s Cascade Range and in the Wallowa Mountains of northeastern Oregon. These glaciers are important shapers of the landscape, as well as important sources of water to downstream ecosystems, farms and human infrastructure.
Activity IV: Speleogenesis
Materials – white vinegar, eyedropper, Tums or some other type of calcium carbonate tablet.
1) Place a few drops of vinegar on a piece of calcium carbonate tablet.
What is happening: This experiment demonstrates Speleogenesis. That’s the scientific term for the (natural) chemical break down of rocks to form caves. Rainwater seeping into soil turns into a natural acid, carbonic acid, that dissolves away at rock underground to create caves. In this experiment the vinegar represents carbonic acid and the TUMS represents limestone. Note how the tablet quickly dissolves and even bubbles.
Oregon example: The Oregon Caves National Monument near Cave Junction is an excellent example of rock being carved away over millions of years. Deep inside the Siskiyou Mountains the caves formed when acidic rainwater dissolved the surrounding marble, creating one of the few marble caves in the world. Most caves are limestone.
Activity V: Water Erosion
Materials – pan or paper plate, sand, 1/4 cup of water
1) Cover the bottom of a pan or paper plate with sand.
2) From about 2-4 feet above the pan, slowly drop the water onto the surface of the sand and observe what happens to the sand.
What is happening: This experiment shows how water erodes soil and rock.
Oregon examples: Oregon’s landscape is full of examples of water erosion large and small. Examples can be found at river banks, farm fields, backyards, plus memorable features like the monoliths at Cannon Beach, waterfalls and deep canyons.
For full instructions and worksheets, please download our PDF.