Geologic Stories: retreating waterfalls and fossils

Kate Rosok, Burnsville High School & Metcalf Junior High, Burnsville, MN.
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Summary

In this geology field investigation, students investigate fossiliferous limestone, the local stratigraphy, and understand how glaciers and rivers have shaped our community. Students draw topography at three locations, and compare river valley sizes with the rivers that occupy them. Students create geologic sketches from far away and from close up, then develop a new, experimental question from observations of the fossiliferous limestone, propose a method to answer their question, and complete their investigation.

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Learning Goals

This activity is designed to have students:
-Draw the landforms they see and visualize the glacial river that carved them.
-Learn to make geologic sketches and sketch a rock outcrop
-Conduct an investigation and answer their own scientific question.

Context for Use

This field trip is used in my Earth Science class which is taught at the ninth grade level. I use it in the beginning of the year to connect students with their local landscape, and to introduce Minnesota's geologic history in a concrete way. Along with the geology, I tell stories of how people have used the area over time. Others in the Minneapolis & St Paul metropolitan area could adapt this field trip to their class level, or instructors in other areas could use the format. The attachments describe methods from other instructors for teaching the student-directed inquiry, and for teaching students how to make geologic sketches, but do not include information on the cultural or geologic history of this area.

Description and Teaching Materials

During this field investigation, students learn the short and long term geologic history of the Minneapolis-St. Paul area, and hear about how that geology has shaped the human community today. Stop 1 at Dayton's Bluff overlook allows a wide view of downtown St. Paul and the surrounding bluffs, where students visualize the glacial River Warren falls that were in St. Paul 12,000 years ago. Stop 2 at Lilydale Brickyards allows for a student-directed inquiry activity, fossil hunting, a close-up view of a waterfall, and lunch. Stop 3 at Crosby Farm overlook gives a view of the Minnesota and Mississippi confluence, where students draw the valley shapes and the rivers within them, and connect what they have seen at Lilydale and Dayton's Bluff to a comprehensive picture of how this area has changed through time.

Schedule: 30 minutes at Dayton's Bluff: travel to Lilydale Brickyards, 3 hours at Lilydale, travel to Crosby Farm overlook, 30 minutes at Crosby, return to school.
Materials:
Dayton's Bluff: Topographic map of Minnesota, map of the Mississippi between St Paul and Minneapolis.
Lilydale Brickyards: pails for collecting rocks, Inquiry Box (tape measures, rulers, plastic graduated cylinders, electronic scale, chalk, scissors, dental tools, toothbrushes), fossil hunting permit (City of St Paul, http://www.stpaul.gov/index.asp?NID=1560), geologic column, Fossil Collecting in the Twin Cities area and Quaternary Glacial Geology documents (MN Geologic Survey),
Crosby Farm Road Overlook materials: same as Dayton's Bluff

Materials:

-Clipboards

-Science notebooks

-Pencils

-Full waterbottle

-Lunch

Procedure:

At Dayton's Bluff stop, show students the topographic map of Minnesota. Point out landmarks such as school, cities, surrounding states and provinces. Show students the local map, and point out our stops. Point out features on the map and in the distance. Have students "sketch what they see" between the bluffs on the west and east banks of the Mississippi. They will sketch the large U shape of the horizon. Point out the path of the Minnesota and Mississippi on the maps and from the overlook. Tell students about glacial Lake Agassiz, and glacial River Warren, and its falls. Describe how the waterfall retreated upstream, the interactions of the Platteville limestone and the soft St Peter sandstone, the glacial till that covers the landscape.
At Lilydale stop, hand out materials for collecting fossils at the bus, so that everyone shares the load. Have students take lunch for picnic. Walk up to first (east) fossil pit. From a ways away, have students sketch the slope in their journals, and then walk up close to it and have students sketch it in greater detail. See attachment of geologic sketching. Go down hill a little, and find the small water fall on the east side of the trail. Before beginning fossil activity, have students sketch the small waterfall there, and note the resistant rock above it, with softer rock below, breaking off in chunks. Caution: Poison Ivy. Caution: students working above/below each other on the slope can be dangerous. Caution students not to stand above/below others, and if something tumbles, to yell rock!
Walk over to middle fossil bed. At middles fossil bed, have students assigned to small 1m x 1m areas in which to make their observations. Groups of 2-4. Begin student-directed inquiry activity, see attachment.
Connect fossils with previous seas, that underwater environments often are preserved as rocks, and how humans used those rocks and the landscape they formed. That if this environment had been different half a million years ago, then this area would have a different landscape.
Have lunch, time for fossil hunting. Walk back to parking lot takes approximately 15 minutes.
At Crosby Farm Overlook: Overview of human history of the area. Look at the two river valleys at the confluence. Note the different colors of the water. Ask students to "draw what you see" while looking at the two river valleys. Discuss the known timeline for the retreat of glacial River Warren Falls, connect the large shape of the Minnesota River valley with the narrow shape of the Mississippi River to their previous river size, discuss that the Minnesota River could never have carved such a large valley. On the topographic map of Minnesota, trace the Minnesota River Valley back to Brown's Valley. Connect the retreating waterfalls with the small waterfall we saw at Lilydale. Connect the rocks at Lilydale with Minnesota's previous location near the equator, and shallow seas that covered this area where the fossils once lived. Now high above sea level, those rocks control the topography of this area along with the glaciers which carved and covered the area with glacial till.


This activity draws heavily on a field trip led by Karen Campbell at the National Center for Earth-surface Dynamics, an open-ended inquiry activity taught by Lee Schmitt at Hamline University, and an introductory geology exercise from Larry Krissek at Ohio State University.

Teaching Notes and Tips

Common areas of confusions can be with the geologic timeline of Minnesota, the ability to interpret formation environment from features in rocks,
Caution: there is a lot of Poison Ivy.
Caution: students working above/below each other on the slope can be dangerous. Caution students not to stand above/below others, and if something tumbles, to yell "Rock!".

Assessment

Student work: assess oral description of the outcome of their inquiry investigation, assess their geologic sketches in their science notebooks.

Standards

9-12.III.A. ongoing change over geologic time

References and Resources