EAPS 112 Earth History - Purdue University. LAB 13 Pleistocene glaciations EAPS 112 Fall 2022. Q&A

EAPS 112 Earth History - Purdue University. LAB 13 Pleistocene glaciations EAPS 112 Fall 2022. Q&A LAB 13 (Exercise 19 of the Lab Manual) – Pleistocene Glaciation • To be able to recognize and interpret landforms associ ...

EAPS 112 Earth History - Purdue University. LAB 13 Pleistocene glaciations EAPS 112 Fall 2022. Q&A LAB 13 (Exercise 19 of the Lab Manual) – Pleistocene Glaciation • To be able to recognize and interpret landforms associated with continental and valley glaciation Source Acknowledgments: National Snow and Ice Data Center, https://nsidc.org/cryosphere/glaciers/gallery/drumlins.html, Accessed 4/25/2020. Koslowski, A., http://www.nysm.nysed.gov/research-collections/geology/research/subglaciallandforms-and-processes, Accessed 4/25/2020. Ritter, S. and Petersen, M. 2015. Interpreting Earth History, 8th Edition. Waveland Press Inc., Long Grove, IL. Total Points: 20 pts PART 1 – CONTINENTAL GLACIATIONS A – Glacial geology of the Upper Midwestern United States Figure 1 - Glacial geologic map of North America (Figure 19.1 from Ritter-Petersen lab manual), with location shown in inset. Key to figure below. Note the color change in the Wisconsin-age deposits in the northern portion of the map, from pinks to browns - consider them to be the same age for both colors. 1. [1.5 pt] Refer to Figure 1 above. In the past, 4 main glaciations were recognized in the geologic deposits of North America. These are shown in the key to Figure 1 (however, the Wicander and Monroe text notes that there up to 13 recognized now). On the basis of the principle of cross-cutting relationships, what are the relative ages of the four main Pleistocene till deposits? 2. [1.5 pt] What was the direction of ice movement in the vicinity of Chicago, Illinois; Fort Wayne, Indiana; and Mankato, Minnesota. (Note the latitude/longitude lines on the map for reference as to N, S, E, and W) 3. [1 pt] What were the likely controlling factors that determined the present position of the Missouri and Ohio Rivers? 4. [1 pt] Explain the lack of glacial deposits in the southwestern corner of Wisconsin. 5. [1 pt] Pleistocene lake deposits are illustrated on the map by a horizontal pattern. What is the origin of the Pleistocene lake basin approximately 50 miles south of Chicago? 6. [1 pt] What types of isostatic forces are likely to be affecting this area at the present time? Explain your answer. B – More Google Earth and LIDAR... This section will familiarize you with two types of landforms associated with continental glaciation: drumlins and eskers (Figure 2). Refer to slides 38 in Lecture 19 for more examples. Drumlins are streamlined deposits formed subglacially by ice flow over basal till, often occurring in clusters. They are laterally symmetrical, but asymmetrical front to back - the steeper, higher portions form on the upstream side of glacial flow. Eskers are sinuous ridges of sand and gravel deposited by subglacial streams that flow within ice-walled tunnels within and under continental glaciers. Figure 2 – A. Diagram of a drumlin. https://nsidc.org/cryosphere/glaciers/gallery/drumlins.html. B. Photo of an esker from western Sweden. https://en.wikipedia.org/wiki/Esker Figure 3 - LIDAR view of drumlin field at Duck Lake, New York and surroundings. Note the eskers at the sites labeled C. A is a paleo-shoreline from Lake Ontario; sites labeled B are fans of sediment deposited at the margin of the ice sheet. LIDAR makes such a huge difference in being able to recognize and study landforms in vegetated areas! 7. [1 pt] Is there a preferred orientation to the drumlins in the LIDAR view? If so, what is it? Yes, Vertical 8. [1 pt] Based on this LIDAR view, from what direction (approximately) did the ice flow here? Now, let's move closer to home here in Indiana. Figure 4 presents a nice summary of glacial vs. non-glacial landforms in the state. Compare this map to the map in Figure 1, and see if you can identify topographic features that correspond to geologic deposits. (Refer to the background reading if needed 9. [1 pt] Note the Wisconsin and pre-Wisconsin glacial boundaries on Figure 4, represented as solid and dashed blue lines, respectively. What correlation do you see between the distribution of glacial deposits in Figure 1 and the boundaries shown on Figure 4? PART II – VALLEY GLACIATION (Refer to slides 36-37 in Lecture 19 for more examples) Yosemite Valley, California 10. [4 pt] Construct topographic profiles along lines A to A′ and B to B′ in the spaces provided on figures 19.3 and 19.4. The technique for constructing topographic profiles is explained in exercise 13 (figure 13.7) 11. [1 pt] Compare and contrast the shape of the Merced River valley in the two topographic profiles and briefly explain what you observed. 12. [1 pt] Based on your observations, explain which of the sections of the Merced River Valley that you've explored here were modified by glaciers. 13. [1 pt] What is the gradient (elevation loss per mile; feet/mile) of the Merced River in figure 19.3? 14. [1 pt] What is the gradient (feet/mile) of the Merced River in the area depicted in figure 19.4? 15. [1 pt] Name a map feature in figure 19.3 that represents a hanging valley. (A hanging valley is a valley that formerly contained a smaller tributary glacier that fed into the main valley glacier. Being a smaller glacier it was unable to cut as deeply into its valley, thus when the glaciers receded the hanging valley was left stranded high up the valley wall.) 16. [1 pt] Based on the comparison of the glaciated and unglaciated stretches of the Merced River valley, discuss how valley glaciers modify the valleys through which they flow.