Academic journal article Science and Children

Explaining Glaciers, Accurately: A Geologist and Two Fourth-Grade Teachers Team Up to Improve Hands-On Lessons That Show How Glaciers Can Change the Earth's Landscape

Academic journal article Science and Children

Explaining Glaciers, Accurately: A Geologist and Two Fourth-Grade Teachers Team Up to Improve Hands-On Lessons That Show How Glaciers Can Change the Earth's Landscape

Article excerpt

What happens when a geology graduate student and two fourth-grade teachers collaborate on lessons for the classroom? They discover interesting and practical ways to explore geology and other scientific concepts, that's what! This collaboration was made possible by the National Science Foundation GK-12 Partnership for Reform Through Inquiry in Science and Mathematics (PRISM) program. Through the program, we participated in five weeks of summer professional development together and then coplanned and cotaught together 10-20 hours a week during the following academic year.

The glacial erosion lessons shared here grew out of the geologist's frustration at finding glacial erosion labs erroneously showing glaciers eroding by pushing rocks. Although the concept that glaciers erode a mountain or a continent by pushing the rocks is a popular explanation in numerous age-appropriate erosion labs, it is not an accurate portrayal of how glaciers transform the Earth.

Our goal was to find a way to show and explain glacial erosion more accurately in a way that elementary age students could understand. The task proved challenging; however, working as a team and relying on each others' areas of expertise, we were successful in developing geology lessons that did just that. After completing these activities, most of our students were able to explain the processes of glacial plucking and abrasion and describe how they change the shape of the Earth's surface.

Glacier Basics

So, if glaciers don't push rocks, what do they do? Glaciers erode the Earth by two mechanisms: plucking and abrasion. Plucking is when the glacier "plucks" pieces of rock from their parent rock (or a mountain). This occurs through a series of events, beginning with the glacier melting a little bit. Scientists believe that the glacier floats on the melted water. The rock then freezes to the bottom of the glacier during seasonal or global cooling. The water also seeps down into cracks in the rock, and water that was in the rock cracks is now ice, which expands the cracks (see Figures 1 and 2). The glacier itself accumulates snow and ice on its surface, and under this added weight and pressure, the glacier slides down the mountainside.

This glacial movement will cause some rocks to break off and move along with the glacier. Rocks also freeze into the glacial ice and are contained within it (until the glacier recedes or breaks off into chunks of icebergs). When the glacier recedes, the glacier will melt a bit and deposit many of the rocks that it once contained. The rocks may be deposited in perpendicular piles in relation to the glacier's movement, known as drumlins, or in parallel ridges in relation to the glacier, known as moraines.

The second form of glacial erosion is called abrasion. Abrasion basically sands and polishes the parent rock. While scientists cannot observe abrasion actively occurring, abrasion leaves "footprints" in the rocks called glacial striations. Glacial striations are typically found as elongated grooves on rock surfaces. These are created by the rocks that are attached to the base of the glacier scraping the surface rock as the glacier moves (see Figure 3, p. 24). This scraping or abrasion creates rock flour (sand, silt, or dust) and also creates grooves on the surface of the rock (glacial striations).

Due to the complex processes described above, we needed to develop an activity that accurately portrays these phenomena. Since glaciers do not simply push rocks like a bulldozer but in fact carry them within the ice and "sand down" parent rocks, we took on the challenge to demonstrate glacial erosion in an accurate way that students would understand. Our first step was to demonstrate the process of plucking.

Glacial Hitchhikers (Plucking)

We began this lesson by first asking the students what they knew about glaciers. We used pictures from websites as a springboard for opening discussion with the class (see Internet Resources). …

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