GEOL151 Fall 2016: Lab for Week #9 Glacial Erosion, Sediment Transport, and Deposition in the Champlain Valley

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Ralf Ward
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1 GEOL151 Fall 2016: Lab for Week #9 Glacial Erosion, Sediment Transport, and Deposition in the Champlain Valley Overview This week, we will delve into glacial processes and landforms. Glaciers are generally very effective agents of both erosion and sediment transport, and produce many distinctive landforms through both erosion and deposition. We will use our study of these landforms to contemplate how glaciers move sediment and shape landscapes by visiting three different areas in the Shelburne area, just south of Burlington (Figs. 1 and 2). Our goals are to study glacial erosion and glacial deposition, to think about how sediments are cycled through the glacial system, and to contemplate how glaciers shape landscapes. Gear As always, you should come prepared to take notes and sketch. Additionally, in order to conduct this week s field exercise, your group will have access to the following: Shovel Two compasses Acid bottle Bedrock map (provided in Fig. 3) Historical air photograph and LiDAR image (provided in Figs. 4&5) Stops and Field Plan Below, I provide a list of the three stops (Fig. 2) as well as observations, measurements, and inferences to make at each. Note that we will be visiting three very different features, so your field procedures will vary from site to site. Stop #1: Glacial sediments along Route 7 south of Shelburne Village Measurement of striation directions on the bedrock exposed in the stream (more measurements = more robust data set!) Characterization of the exposed sediments (color, density, grain size, sorting, layering) Characterization of the rocks contained within the sediments (size, shape, angularity, presence/absence of striations) Lithologic descriptions of rocks contained in the sediments (identify the rock type or unit if you can, see Fig. 3, but most importantly try to put them into groups) Determination of what the sediments are, how they formed, and where the material was sourced 1

2 Stop #2: Exposed bedrock in Shelburne Bay Measurement of striation directions (more measurements = more robust data set!) Detailed study of cross-cutting striations (including photographs or sketches, measurements of the two directions, and observations regarding relative age) Descriptions of any erratic boulders you find Determination of how the striations formed and why there are numerous directions Comparison between these striations and the ones exposed at the first stop Stop #3: Glacial depositional landform at Shelburne Farms (Fig. 4) Creation of a detailed map-view sketch of the landform Creation of two detailed cross-sectional sketches of the landform, one along its long axis and one along its short axis Characterization of the sediments that make up the landform Determination of what this landform is and how it formed Big Questions As we progress through the field trip, I encourage you to consider the following big-picture questions. You should return to these questions in the interpretations/conclusions sections of your field reports. 1.) What are each of the features we observed and how did you arrive at those conclusions? Focus on building a logical, evidence-based argument and eliminating certain possibilities to arrive at a unique solution. 2.) In what direction(s) did ice flow? 3.) Was the direction of ice flow constant over time, or did it change? If it changed, what evidence causes you to think this? Why might flow direction change over time? 4.) What was the direction of sediment transport and what was the source material? How is this manifested in the type of sediments and erratics you see? Refer to the bedrock map shown in Fig. 3 for inspiration. 5.) What can you learn about the history of glaciation in the Champlain Valley? Try to piece together a sequence of events. Data Reduction Working with your group, you will collect numerous different datasets throughout the field trip. You will need to decide how you will reduce, assess, and eventually present your data. Please come see us with any questions about calculations, Excel, etc. You should think about the most effective way to visualize each dataset; for example, a rose diagram is a good way of showing directional measurements (like your striation measurements) while a pie chart may be more appropriate for depicting percentage data (like the lithology of rocks embedded in the sediments). 2

3 Field Report Present your data and interpretations in a professional field report focused on glacial erosion, glacial deposition, sediment flux, and landscape development in the Champlain Valley. Refer to the How to Prepare a Successful Field Report handout for more ideas on organization, content, and presentation. You should consider each stop individually (both results and discussion) as well as interpreting what you can conclude from the trip as a whole. As will be the case with many of our investigations, there is no right answer. I am looking for you to present your data clearly, then make logical, supported interpretations. You may work together to develop ideas; however, each student must turn in his/her own field report. These reports are due at the beginning of the lab period on Wednesday next week (11/2). 3

4 Figure 1. Satellite image of the Champlain Valley, with the study area shown in the green box. The study area includes three stops and is located just south of Shelburne Bay. Specific locations are shown in Fig. 2. 4

Figure 2. Satellite image of the three stops in the Shelburne area. Stop 1 location: 44.

5 Figure 2. Satellite image of the three stops in the Shelburne area. Stop 1 location: N, E Stop 2 location: N, E Stop 3 location: N, E 5

6 Figure 3. Bedrock map of a portion of the Champlain Valley; relevant units are described below. 6

7 Figure 4. Historic photograph of the landform at Shelburne Farms (Stop #3) from when the area was still deforested. 7

8 Figure 5. LiDAR hillshade map of the Shelburne Area. Green oval shows the feature we will investigate at Stop 3. 8

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