Issues in Earth Science

“Eww, There’s Some Geology in my Fiction!”

Issue 12, Nov 2019

Teacher Resources

Suggestions for Activities and Discussions to accompany Readings of

The Crease presents a story that bridges the time between the ice ages and today. Consequently, the story offers an opportunity to consider change in either climate or landscape as well as to consider the nature and behavior of glaciers. Authentic investigation in the classroom might go in any of these directions based on inspiration from the story. However, the teacher as mentor and practitioner of science may not have the resources or time to pursue all possible investigations. For example, our first thought on a direction to take with the teacher resources for this story was to examine glacial movement. The dangerous crevasses in The Crease requires that the ice be flowing plastically at depth but yet deform in a brittle fashion at the surface of the ice where the cracks form. It would be interesting to study this transition from plastic to brittle behavior in ice to understand better how glaciers can both flow like a liquid and also create dangerous cracks by breaking open like a solid. However, we were not able to figure out any way to reliably reproduce in the classroom the high lithostatic pressures that are required to make the ice behave plastically.

Thus, we have instead decided to offer a few seed ideas for a spatial reasoning activity that considers the landscape of the Yosemite Valley where they story is set and to compare the valley landscape formed by glaciers with other types of valleys. This activity requires that students have computer access to Google Earth Pro (a free program as of this writing) or a similar spatial data visualization tool.

What underlying change in the valley topography might have created the Crease (dangerous cracks in the ice) of the story?

Cracks tend to form in glacial ice where the ice flows over a sharp change in slope, causing the ice to flex and the brittle ice at the top of the glacier to break.

By using Google Earth Pro, students can look at the modern topography of the area near Half Dome in Yosemite Valley, CA and think about where Tara was climbing the rock wall in modern times and where Aztl was negotiating the Crease during the ice ages.

1) In Google Earth Pro, navigate to (or search on) the Half Dome in Yosemite Valley

2) Click on the line-drawing tool in the top menu bar (see Fig. 1)

3) Click on several points starting upstream from Half Dome and continuing downstream to make a curved line that follows the bottom of the valley floor.

4) Right-click on the line down the valley that you've just drawn (see Fig. 2) and select "Show elevation profile"

5) Consider bumps in the valley floor and sharp changes in slope that might have caused the glacier to flex during flow to cause the Crease to form. What location is the best match for the story? Where was Tara climbing?

6) The objective is for students to gain a better sense of spatial relationships, especially the relationship between a map view of a region and the cross-sectional view of that region, and to think about what those relationships imply about glacial flow.

Three Types of Valleys.

Different valleys have different topographic expressions reflecting the different processes by which they formed. Valleys formed by glaciers appear different from valleys formed by liquid water. Valleys formed by liquid water flowing well above base level (where the gradient of the river is very steep and the river erodes downwards creating a canyon) appear different from valleys formed by water flowing very close to base level (where the gradient is shallow and the river meanders sideways, creating a wide flood plain).

By using Google Earth Pro, students can explore the topographic expression of these different types of valleys, starting with the glacially formed valley in Yosemite where The Crease is set.

1) In Google Earth Pro, navigate to (or search on) the Half Dome in Yosemite Valley

2) Click on the line-drawing tool in the top menu bar (see Fig. 3)

3) Draw a path across the valley, right-click on the path and select "Show elevation profile" (see Fig. 4.

4) Students might draw several profiles across the valley in different locations to get a feel for how much variation there is in the appearance of the profile. Of particular note is the distinctive "U" shape to the valley, a characteristic of valleys formed by glaciers.

5) Repeat the steps above for two different types of valley, for example, in Google Earth Pro, navigate to (or search on) the Grand Canyon of the Yellowstone River just downstream from the Lower Falls in Yellowstone National Park. Do several profiles across the canyon (see Fig 5). Then navigate to the Missouri River valley just south of Sioux City Iowa and do profiles across the valley (see Fig. 6). Think about how the profiles are different from each other and from the profile in Yosemite.

6) Notice that the profiles of these valleys are quite different from the glacial Yosemite Valley and different from each other. The distinctive "V" shape to the profile across the Yellowstone Canyon is characteristic of a 'youthful' river that is well above its base level and eroding downwards rapidly. In contrast, the Missouri River Valley is a wide, flat plain between bluffs on either side. This valley is formed by the migration of the river over time, meandering back and forth across the valley, gradually widening it and leveling it to a level consistent with the river's base level. Notice the relatively small channel in the much broader Missouri river plain. Also, take note of the different vertical and horizontal scales on the topographic profiles for each valley, and think about their real-world difference in size.

7) The objective is for students to gain a better sense of what different types of topography imply about the processes that have formed different types of valleys. The geomorphology of these three types of valleys is addressed in most earth science text books, but exploring real data through Google Earth can help students understand the idea and see the connection to real landscapes. It also helps them realize that the topography at Yosemite is indeed consistent with the icy story in The Crease. Students also get experience with scale and three-dimensional spatial thinking.

Connecting to the Next Generation Science Standards.

Students can exercise skills in the practices of science including:

1) Analyzing and Interpreting Data – in both activities, students use Google Earth’s spatial data to construct topographic profiles. In the first activity, students pinpoint the underlying cause of ‘the crease’ by connecting topography’s effect on the behavior of glacial ice. And in the second activity, students compare elevation profiles of three valleys with different shapes and origins.

2) Constructing Explanations – in the Three Types of Valleys activity, students use the scientific ideas of erosion (by running water or glaciers) and base level to explain how different processes formed the U-shaped valley of Yosemite, the V-shaped valley of the Yellowstone and the broad flood plain of the Missouri River.

Students use the crosscutting concepts of

1) Cause and Effect – in the first activity, students consider topography’s effect on the behavior of glacial ice.

2) Scale, Proportion and Quantity – in the second activity, students deal with spatial data (topographic profiles) that show significant landscape patterns that are seeable at different scales.

The investigative activities above support the following NGSS performance expectations:

5-ESS2-1 Develop a model using an example to describe ways in which the geosphere, biosphere, hydrosphere and/or atmosphere interact.

MS-ESS2-2 Construct an explanation based on evidence for how geoscience processes have changed Earth’s surface at varying time and spatial scales.

HS-ESS2-1 Develop a model to illustrate how Earth’s internal and surface processes operate at different spatial and temporal scales to form continental and ocean-floor features.

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The Teacher Resources for The Crease are written by Russ and Mary Colson, authors of Learning to Read the Earth and Sky.

Return to The Crease by Jeanne Panek

Return to “Eww, There’s Some Geology in My Fiction.”

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