Lab 7 – Campus Tour: The Geology of the East Bank’s Bluffs & Buildings

Pre-Lab Activity:

Your lab instructor will assign each lab group one of five rock groups to present during the campus geology tour. This lab requires a significant amount of pre-lab preparation and coordination among lab group members, so be sure to get one another’s contact information and clearly determine ahead of time who will be responsible for each part of the presentation. Realize that you should take personalities into account. Some people relish attention and would do well taking a leading role in giving the group presentation. Others may be terrified by the idea of speaking before the class, so they could instead contribute more towards the group research or any handout materials developed. You can divide up responsibilities any way that you wish, as long as it is clear to your lab instructor that each group member ultimately made a significant contribution to the group effort.

Once you know which rock group you will be presenting, your lab group should visit the localities where those rocks are present and map out how the group will prepare for their presentation. Presentations MUST be brief! Since there will be a number of presentations, you will only have 15 minutes (at most) to present your rock group. As a consequence, your group is highly encouraged to create some type of handout that summarizes your information. The other lab groups will be relying on the information your group presents to complete the post-lab exercise and do well on the lab final, so take some time to decide what information is important and how to present it well.

The link below leads to a website which hosts a virtual tour of most of the locations visited on the campus tour, with general information on the tour’s main rock groups. This web site is an important starting point as it displays the rocks you will see on the tour, but your tour presentation should go beyond the posted information as the other lab groups will view the same site. Note that since the web site is based on location, much of the rock information is repeated on different pages.

http://www.geo.umn.edu/courses/1001/campus/pages/

Previewing Locations:

You are strongly encouraged to visit the tour’s four main stops (Walter, Northrop, Folwell and Pillsbury) before leading the tour, so you are familiar with the buildings and their stones. With the exception of Northrop Auditorium, the buildings have Internet kiosks so, if necessary, you can reference the tour website while on location. Do NOT scratch, damage, or place acid on, any of the building stones!

Be sure to read the Post-Lab Activity ahead of time, so that your presentation includes the information others will need to complete the Post-Lab Activity.

Lab 7 - 1 Lab Goal:

To gain an appreciation of the variety of building stones used in our society and practice interpreting geological history from rocks’ texture and composition.

Lab Assessment:

• Given background information on outcrops or building stones, you will be asked to present a synthesis of the geological information encoded in the rock, including their origin and subsequent geological history.

• Given a described building stone, you will be asked to identify it, and describe how and in which environment the rock most likely formed. You will also be asked to construct a plausible geological history for the rock, from the time of its formation to the point when it was quarried as building stone.

Your lab grade for the campus tour will be based on your presentation (12 points) and Post-Lab Assignment (8 points).

Lab Activity:

Suggestions for Preparing your Presentation:

You will only have fifteen (15) minutes to lead your part of the tour, but your lab group should view that limited time frame more as a challenge than a blessing. Trying to decide which information should be presented, where and how to present it can be a remarkably difficult task. If nothing else, your lab group should gain an appreciation of the task your lab instructor faces every week!

Your goal should be to try to give the rest of your lab class an understanding of which rocks are present, how they formed, and what geologic information can be interpreted from them. Remember that all of these rocks had to be taken from surface quarries, so if you are dealing with a rock that formed deep within the Earth or at the bottom of the sea, then its presence at the Earth’s surface also tells a story of uplift and erosion, the collision of ancient continents, or changes in sea level. Emphasize the story behind the rocks, not just their geologic names or compositions.

Since your classmates will be relying on the information you give them to complete the Post-Lab Activity, be sure your presentation includes any information your classmates need to complete the post-lab and do well on the final lab quiz. While the tour website is a good starting point, your presentation should also include information from other text or Internet sources.

Lab 7 - 2 Tour Structure:

The five rock groups for the tour are listed below, along with their locations on the tour. Note that the order of stops will vary between groups and your lab instructor may not know it until the day of the tour. If your rock type occurs at more than one stop, you should decide which stop(s) your lab group wishes to present at. You could choose to present different aspects of the rock at different stops or choose one stop for your main presentation and only point out the rock type out at other stops, noting that it will be covered later on or referring back to your presentation.

Marble & Limestones: Folwell Hall, Northrop Auditorium, Walter Library. (including stylolites)

Granites & Xenoliths: Northrop Plaza, Folwell Hall, Walter Library benches.

Serpentine & Greenstone: Walter Library, Folwell Hall, Pillsbury Rock Garden. (including pillow structures)

Sandstones: Pillsbury Hall only. (including cross-bedding)

Dolostones: Walter Library, Northrop Auditorium, Pillsbury Rock Garden. (including burrows)

Note that your presentation should only cover your own rock group - even if other rocks are present at the same location. Lab instructors will deduct points if you present any part of another groups’ information as part of your group’s presentation. In contrast though, you are encouraged to ask questions about other group’s rocks during or after their presentation.

Your lab group is responsible for presenting ______(Be sure to record which rock group your lab group will present before leaving class.)

Even though the bluffs are featured on the tour website, do not visit the river bluffs on your own. The bluffs are natural rock cliffs, with all the hazards such areas involve, such as twisting an ankle on the dirt paths, or being hit by falling rock. In addition, a few assaults have occurred in the lower river flats area, so wait to visit the bluffs until your lab instructor can show the class how to get to the bluffs safely.

Check with your lab instructor to find out if the river bluffs will be part of the campus tour (this will depend on the weather forecast).

Lab 7 - 3

GEO 1001 - Campus Tour Presentation Sites:

To avoid overlap and make the tour run more smoothly please make your lab groups’ main presentation at the locations below. That way they are spread out over the whole tour. You can take a moment to point out your group’s rock types at the other stops, but save the main presentation for your designated spot on the tour.

Remember not to ‘poach’ other lab groups’ material when making your presentation. Only present information on your group’s rock types.

Presentation Locations:

Marble & Limestones: Folwell Hall Granites & Xenoliths: Northrop Plaza Serpentine & Greenstone: Walter Library with greenstone at Pillsbury Rock Garden. Sandstones: Pillsbury Hall Dolostones: Northrop Auditorium with potholes at Pillsbury Rock Garden.

Notes on using the campus tour web site:

Some of the ‘zoom in’ pages on the web site contain additional information in their text. To find all of the information available for your rock type, be sure to visit all of the pages that cover your rock group (including the ‘zoom in’ pages).

• Marbles & Limestones are present at Folwell Hall (interior), Walter Library (interior), and Northrop Auditorium (interior). • Granites & Xenoliths are present at Northrop Auditorium (exterior), Folwell Hall (exterior) and Walter Library (exterior). • Serpentines & Greenstones are present at Walter Library (interior), Folwell Hall (interior) and the rock garden at Pillsbury Hall. • Sandstones are only present at Pillsbury Hall. • Dolostones are present at Northrop Auditorium (interior), Walter Library (interior) and the rock garden at Pillsbury Hall.

Since you have to have your presentation ready for next week’s lab, be sure that you get contact information from your other lab group members before leaving today’s lab. ON THE DAY OF THE CAMPUS TOUR, BE SURE TO DRESS APPROPRIATELY FOR THE WEATHER AND WEAR GOOD WALKING SHOES!

Lab 7 - 4 Post-Lab Activity: (also to be used as a guide for preparing your presentation)

At the conclusion of the class, your lab instructor will provide you with a location and description of two building stones on the East Campus. Each of these will be similar to one of the building stones or rock units you saw on the campus tour.

You should find the described building stones, choose ONE of them and try to identify which type of rock it is. From the information you gained on the campus tour, you should then write a 200-to 300-word essay describing the following:

• Briefly identify which type of rock is present, and what features of its composition or texture support your identification (such as grain or crystal size, mineral composition, presence of fossils or other features).

• More importantly, how did the rock originally form and in which type of geologic environment did it most likely originate? Include its most likely plate tectonic setting(s), realizing that these would include such settings as continent interiors or passive continental margins that lie in a plate interior, as well as active plate boundaries.

• What was the rock’s subsequent geological history after forming? In other words, what most likely happened to the rock from the time that it originally formed up to the point when the rock was quarried as building stone and what features of the rock reflect this history? If appropriate, include any periods of metamorphism or tectonic activity (including burial and uplift).

For the above, note that you only have to describe how your chosen rock type formed, not the history of a specific rock unit. For example, if the tour included a diorite rock taken from a quarry in Alberta, you would only have to explain how and where diorites in general form, not the details of that specific Alberta diorite.

Lab Deadlines:

Obviously your lab group needs to meet well ahead of the class period to prepare your presentation, so plan accordingly. Your post-lab activity essay can be submitted by email or as typed copy, but it is due at the start of the following lab period.

For the Final Lab Quiz:

• Given a sample or image of a building stone, be able to identify which type of rock is present. Also be able to construct a logical geologic history for the rock, including the environment or plate tectonic setting in which the rock most likely formed, as well as its burial and subsequent history up to the time the rock was quarried to be used as building stone.

Lab 7 - 5 Lab 7 - 6 Contrasting Cultures: Cultural differences in our use of the Earth

Parts of Labs A, B and C examine historic interactions between Upper Midwest geology and regional cultures. The goal in doing this is to understand how cultures can use and view their world in very different ways, to consider how geological processes have affected human history, and to realize that every use of the Earth involves its own benefits, costs and risks. Managing our world is a complicated endeavor and ignoring the potential impacts of a society’s actions can have disastrous consequences, as hurricane Katrina recently demonstrated.

In popular culture there is a tendency to overly simplify 18th and 19th century clashes of native and Euro-American societies. In environmental terms this plays out as a tendency to think of native cultures as having lived in complete harmony with a pristine natural world, while contemporary Euro-American societies transformed nature with little regard for the consequences of their actions. These stereotypes are not only exaggerations, but they also undercut the labs’ goal of exploring the complex interactions between geological processes and human societies.

So some often overlooked considerations to bear in mind as you complete the labs:

• During the 19th century, Euro-American society in the Upper Midwest undoubtedly had a far greater impact on the environment than native cultures, but this reflects their greater population as well as their differing resource use. Even if cultural approaches to the land are identical, large populations will have a greater impact than small ones.

• Alterations of geological systems are seldom completely negative or positive. Clear-cutting Upper Midwest pine forests nearly destroyed a natural ecosystem, but it also created new ecosystems in its wake and provided rich farmlands for crops and livestock. Draining wetland areas expanded agricultural areas and crop yield, but also greatly increased the potential for large floods. Leaving St. Anthony Falls in a natural state would have preserved the cataract’s natural beauty, but would also have forgone the power that built a city.

• Traditional native societies managed their environment on an impressive scale. They had rich agricultural traditions and used seasonal burning to expand and maintain prairie areas to attract bison herds. Coming into the Upper Midwest, Euro-American explorers did not enter a pristine wilderness, but a complex mosaic of environments that were largely modified, and in part created, by human management.

Realize that the case studies presented in the labs are not intended to show ‘right’ or ‘wrong’ approaches to natural resource management. They are simply examples of how societies used the same resource base in very different ways and the subsequent implications of those uses. The goal is to drive home the realization that every choice of how we use the Earth will have predictable consequences.

Reminder on Order of Labs A, B and C:

The order in which you complete Labs A, B and C will depend upon your lab room.

If your lab section normally meets in Ford B85: you will do Lab A first, in Ford B85. The next week, your lab section will meet in Ford 180 to complete Lab B, and the following week will meet in Ford 185 for Lab C. Your lab section will return to its original room (Ford B85) for the Lab Final.

If your lab section normally meets in Ford 180: you will do Lab B first, in Ford 180. The next week, your lab section will meet in Ford 185 to complete Lab C, and the following week will meet in Ford B85 for Lab A. Your lab section will return to its original room (Ford 180) for the Lab Final.

If your lab section normally meets in Ford 185: you will do Lab C first, in Ford 185. The next week, your lab section will meet in Ford B85 to complete Lab A, and the following week will meet in Ford 180 for Lab B. Your lab section will return to its original room (Ford 185) for the Lab Final.

Lab A – The Upper Midwest’s Glacial Legacy

Pre-Lab Activity:

At the beginning of the lab, your instructor will choose one of the following questions and you will have five minutes to write an essay response to that question. Your essay must be independent work, completed without the aid of your classmates. Be sure to read the lab before coming to class as you cannot refer to the lab manual or notes while completing this essay.

1) Briefly explain why glacial ice moves and how you can distinguish glacial deposits and valleys from those formed by flowing water. In a similar manner, how can you distinguish an older glacial landscape from one that was more recently ice covered?

2) Given any two of the following areas (your lab instructor’s choice), Canadian Shield, Driftless Area, Recent Glacial Margin, Lake Agassiz, or Older Glacial Margin, briefly describe the major differences between the areas’ geologic histories.

3) Briefly explain how glacial processes contributed to the development of the Minnesota River Valley and the Upper Midwest pine forests (the ‘Pinery’). How did 19th century Dakota, Ojibwa and Euro-American cultures differ in their use of resources in the Minnesota River Valley and Upper Midwest ‘Pinery’?

Lab A Goals and Assessment:

• Given an image of an area, be able to interpret whether glacial or non-glacial processes were primarily responsible for the present land surface. You should be able to identify specific features that support your interpretation and explain how those features formed.

• Given an image of a glacially impacted area, be able to identify and describe the origin of any glacial features present. Using the glacial features present, be able to create a reasonable interpretation of past glacial movement through the area.

• Be able to explain to someone who did not take this class how the glacial history of the Upper Midwest led to the development of the region’s pine- dominated forests and rich valley soils, as well as the different ways in which the region’s historic cultures viewed and used these glacial legacies.

Each lab group member must submit her or his answers to the lab questions.

Lab A - 1 Introduction:

Less than 21,000 years ago, glacial ice still covered much of the Upper Midwest. This ice formed the southern margin of a vast ice sheet that stretched across Canada. However, within a few thousand years this ice sheet would collapse, melted by warming Canadian summers due to natural climate change. Now only a few remnants of ice remain, scattered across the northernmost Canadian arctic islands. Although this ice sheet disappeared from the Upper Midwest over 10,000 years ago, its legacy lingers on in the region’s landscape, its natural animal and plant communities, and the history of the various cultures who have lived in the region. As a consequence, recognizing and interpreting the Upper Midwest’s varied glacial history can provide a better understanding and appreciation of the region’s landscape, ecosystems and human history.

Part A. Glacial Movements and Their Terrestrial Records:

The Movement of Glaciers & Ice Sheets

From a modern tourist’s perspective, it is easy to look at a mountain glacier and think of the ice as a solid, non-moving mass. However, people who live along glacial margins realize that the ice within a glacier is constantly, though slowly, moving. Glaciers are balanced systems of ice accumulation and loss. As snowfall accumulates in an area and is compressed into ice, its weight causes the underlying ice layers to deform and flow even though they remain solid1. If enough ice is accumulating in its headland area, a glacier can flow out into areas where snowfall is more limited and melting more pronounced. Even though there is not enough local snowfall to offset ice melting, the glacier persists because it is fed by ice flowing from its headland area. A continental ice sheet is simply a very large glacial system. The ice sheets that covered the Upper Midwest over the past few million years were fed by snowfall during periods of cool, short summers across the Canadian region. Ice accumulated to a depth of more than five kilometers in the center of this immense ice sheet but, as the ice flowed outwards from that area, the ice sheet tapered down to thickness of a few hundred meters along its margins.

It is important to understand that ice is not the only thing moving within a glacial system. Sediment, rocks and boulders are eroded by the ice and continue to move with it. As the ice reaches the glacier’s margin, it melts or changes to water vapor, leaving this eroded and transported material behind as glacial deposits. If an ice sheet’s volume increases or remains relatively constant for a time, these deposits can pile up to form long low ridges along the ice sheet’s margin. If an ice sheet’s volume decreases, its margin recedes and a thinner layer of glacial deposits covers the land surface exposed by the melting ice sheet. In both scenarios, some of the deposited material can be remobilized and sorted by melt water or wind to be deposited elsewhere. Once

1 Ice at the bottom of a glacier is under so much pressure that it does not behave like the brittle solid so familiar to us as ice from a freezer or a frozen lake surface. Under great pressure, ice behaves as a ductile solid and is capable of slowly deforming or flowing. The uppermost layer of ice a glacier remains brittle, but is carried along by the movement of ice deep within the glacier. This motion is roughly analogous to the movement of brittle lithosphere due to the convection of solid, but ductile, mantle rock deep beneath the Earth’s surface.

Lab A - 2 an ice sheet is gone, the complex pattern of glacially eroded and deposited features is usually the most obvious land-based record of the ice sheet’s past existence. Interpreting this record can be tricky though, as multiple ice sheets have formed and each one has partially erased or overprinted the record of previous ice advances. Even along the margin of a single ice advance, the patterns of erosion and deposition can be complex. Ice sheets seldom advance in a uniform line, but rather as a mosaic of shifting ice lobes that may leave complex local records.

Exercise A – Terrestrial Ice Sheet Records

Although you do not have to submit any written answers for Exercise A, keep notes of the exercise. The basic concepts of why terrestrial glacial records are so incomplete and so easily misinterpreted are fair game for lecture and lab quizzes.

Classroom Activity 1: Recording Multiple Ice Sheets

With your help, your lab instructor will orchestrate a brief chalkboard exercise to illustrate one of the most basic difficulties in interpreting the Upper Midwest’s glacial legacy, namely that each ice sheet advance can erase or modify the record of a previous advance. As a result, the land surface only provides a fairly complete record of the most recent ice advance, which is the focus of this lab.

Classroom Activity 2: Ice Movement Along Glacial Margins & Sediment Transport

How does the model you explored above change if you considered the movement of ice sheets in three dimensions? Follow along as your lab instructor takes you through a second demonstration designed to explore this idea. Again, there are no specific answers required for this activity, but its concepts are fair game for lab and lecture quizzes. You should be able to explain not only why the composite land records of glacial cycles are so incomplete, but also why they vary from one area to another, even along the margin of a single ice sheet advance.

Sidebar 1 - A Mistaken Legacy of Names

From a geologist’s perspective, our best record of previous ice advances is not preserved in the land record, but in sedimentation patterns seen in cores taken from the deep sea floor. Those patterns have not been disturbed or eroded as much as the land record. The record of glacial cycles preserved in the sediment pattern of deep sea cores suggests 30 to 40 significant ice advances occurred within the past few million years, but early geologists who only had access to the land records came up with a very different interpretation. Faced with an incomplete record, these workers underestimated its complexity and incorrectly collapsed the whole Ice Age record into four major North American glaciations called Nebraskan, Kansan, Illinoisan and Wisconsin. These terms and the interpretation they represent dominated our perception of the Ice Age for so long that they still have not been completely replaced, even though a four-stage Ice Age history has been disproved.

Lab A - 3 Glacial Erosion and Deposition

Although ice flows, it still remains a solid so it erodes and transports material in a very different manner than flowing water. Glaciers moving through resistant rock tend to erode broader valleys than rivers do, and these valleys have a characteristic U-shaped cross-section distinct from the more steeply walled, narrow, V-shaped valleys of rivers. In sediment-covered areas rivers can form broad floodplains that mimic the smooth floors of glacial valleys, but these floodplains can be distinguished from glacial valleys by the trends of their depositional features. In river floodplains, elongated features like levees and terraces tend to parallel the stream channel. In contrast, the long curved sediment ridges of glacial valleys intersect the valley’s midline almost at right angles. These low ridges, called moraines, formed during times when the glacier’s volume slowly increased or did not change significantly, allowing the continued flow of ice within the glacier to pile sediment up along the glacier’s margin.

Ice-deposited sediment can also be distinguished from water-deposited sediment by its sorting. Water is remarkably effective at sorting sediment by grain size. As the velocity of flowing water changes, pebbles, coarse sand, fine sand, silt and mud are each deposited in different areas. In contrast, ice transports all of these grain sizes together, leaving them as an unsorted mix. Grains ranging in size from fine clay to house-sized boulders are jumbled together to form distinctive deposits known as glacial till or drift.

After the Ice – Draining a Landscape

As ice sheets retreat, they leave behind an irregular, poorly drained landscape with numerous lakes, ponds and wetlands. Eventually river systems expand to claim the land once covered by ice and begin to drain the landscape of its standing water. So over time Minnesota will lose its claim to being a land of 10,000 lakes as rivers rework the land surface. Even though long gone, the vanished ice sheets themselves play a role in this process of landscape alteration. When they covered the land, the weight of these immense ice sheets caused the land surface to subside. Once the ice melted, the land began to slowly rebound. This rise in the land surface increases the slope of the area’s river systems, allowing them to more effectively drain the landscape. A recently glaciated landscape has lower relief and more lakes and ponds than the same area thousands of years later, after its slope has increased and rivers have had more time to drain its surface.

Sidebar 2 - A Mistaken Legacy of Ideas

Before geologists realized that ice ages had occurred, many of them thought the unsorted deposits that covered much of northern Eurasia and North America probably formed during a period of high sea level, as icebergs ‘drifted’ over those areas to melt and deposit their sediment load. As a consequence, early geologists called this unsorted sediment ‘drift’. The term continued in use even after the sediment’s glacial origin was established. So the Upper Midwest’s ‘Driftless Area’ (see next section) simply means an area in which no glacial deposits were found.

Lab A - 4 Part B. Interpreting the Upper Midwest Glacial Record

Even the most recent ice advance left a rich pattern of erosion and deposition features across the Upper Midwest. In Figure 1 this complex pattern is informally subdivided into five areas, each exhibiting a characteristic pattern of land features.

Figure 1. The five broad subdivisions of the Upper Midwest used in this lab. Note that the Recent Glacial Margin is further subdivided into two phases depending on whether the most recent ice advance totally dominates the landscape (areas marked by a’s) or has not completely altered the record of previous glacial advances or the pattern of the underlying bedrock (areas marked by b’s).

The Minnesota River Valley, discussed in Part D, lies in the Recent Glacial Margin (a) area just west of the Driftless Area.

• Canadian Shield: So much ice moved across this region that it eroded all the original surface deposits and planed the area down into a relatively low relief rocky surface with little soil cover. The only topography that remains is due to recent erosion of the area’s bedrock. Bedrock in this area is a complex mosaic of different rock types, some of which are more resistant to erosion than others. As erosion wore down less-resistant rocks and enlarged intersecting bedrock fractures, it created an intricately patterned landscape.

Lab A - 5 • Driftless Area: In contrast to the ice-dominated history of the Canadian Shield area, the Driftless Area of southwestern Wisconsin appears to have an ice-free history. It is the only area in the Upper Midwest region where the land surface was never directly modified by moving ice sheets. The reason for this may lie to the north, in the size and depth of the Lake Superior basin. As the Canadian ice sheets expanded, the Lake Superior basin appears to have been deep enough that the ice could not completely fill it and was forced to diverge around the basin. Although small ice lobes did squeeze around the basin’s flanks to cover parts of northern and eastern Wisconsin, these were not large enough to reach the Driftless Area. Only rivers have had a chance to erode this landscape, so the pattern and shapes of its valleys differ from those in glacially eroded areas.

• Recent Glacial Margin: These areas were the broad margin of a continental ice sheet where the records of recent ice movement, erosion, and deposition are well preserved. On Figure 1, this margin is further subdivided into areas (a) where the most recent ice advance completely dominates the record and areas (b) where older glacial records were modified, but not completely reworked, by the most recent glacial advance. The difference between these two landscapes was probably due to a combination of ice supply and surface resistance. In areas with an abundant supply of flowing ice and where the underlying surface was composed of glacial deposits or non-resistant bedrock, the most recent ice sheets had free reign to modify the landscape. In areas where ice supply was not as great, or where the underlying surface consisted of more resistant bedrock, the most recent ice sheets could not completely rework all traces of past ice advances or the area’s underlying bedrock pattern.

• Lake Agassiz: As the most recent ice sheet began to melt, the diminished ice sheet still prevented water in the Red River area from draining to the north as it does now. Instead, melt water pooled up along the margin of the ice sheet to form a large glacial lake. Mud settled out of the quiet lake water to cover the area now known as the Red River Valley. The lake rose until it eventually found an outlet to the south and its water drained to the southeast down the present Minnesota River valley. One of the more important legacies of this past glacial lake is that communities in the Red River Valley face a high risk of flood damage. If floodwaters escape their river channel, there is not enough relief on the ancient lake bottom surface to constrain them.

• Older Glacial Margin: Although previous ice sheets covered these areas, the most recent ice advance did not reach them. As a result, river processes were primarily responsible for sculpting the present land surface, just as they are in the Driftless Area. Unlike the Driftless Area though, rivers in these older glacial margin areas are cutting through glacial deposits from previous ice advances rather than solid bedrock.

Lab A - 6 Name ______

Lab A - Exercise B

Exercise B – Comparing Upper Midwest Regions

Use Figure 1, the descriptions of the five informal subdivisions, and the large regional map to answer the questions below. Do not focus on specific features or details but consider the overall pattern of the land surfaces and look for general similarities or differences between areas.

Question 1 Compare the land surface of the Recent Glacial Margin (a) area with that of the Driftless Area, paying particular attention to the valleys in the two areas. (1½ points)

1a. If you compare a single valley in the Driftless Area to one in the Recent Glacial Margin (a), how do the valleys compare in size and shape? (Consider how the profile of the valleys would look both along their long axis and in cross section.)

How do the two areas differ in terms of their river drainage patterns? (Drainage patterns are an area’s distribution of river channels as seen in map view.)

Recent Glacial Margin (a) Driftless Area

size (which area has larger valleys) Valleys

shape (briefly describe)

abundance (which area has more streams) Rivers

pattern (briefly describe)

1b. What processes or factors are most likely responsible for the differences you noted above? In other words, why do the two areas differ so much in their features?

(This page should be turned in as part of the submitted lab materials.)

Lab A - 7 Question 2 Compare the land surface of the Recent Glacial Margin (b) areas in northern Wisconsin and central Minnesota with that of the Driftless Area, paying particular attention to the patterns of lakes and rivers in the two areas. (1½ points)

2a. How do the two areas differ in terms of their relative abundance of lakes, their relative abundance of rivers and the shape of their drainage patterns?

Recent Glacial Margin (b) Driftless Area

Lakes (briefly describe any differences in size and number of lakes)

abundance (which area has more streams) Rivers

pattern (briefly describe)

2b. Why do the differences you noted above most likely occur? How might the number of rivers in the two areas help to explain the concentration of lakes?

Question 3 Compare the land surface of Recent Glacial Margin (b) areas in central Minnesota with that of the Older Glacial Margin in southern Iowa, (1 point)

3. Both of these areas have very similar types of bedrock, share a similar climate and vegetation. Glaciers have covered both areas in the past and rivers are presently eroding both areas’ land surface. So why does one area have far more lakes than the other? (Another way to think of this one is to consider why rivers have managed to drain one area more completely than the other.)

(This page should be turned in as part of the submitted lab materials.)

Lab A - 8 Question 4 Compare the land surface of the Canadian Shield area to those of the Recent Glacial Margins (a) and (b). (2 points)

4a. Since glaciers recently moved across all of these areas, why is it so much more difficult to tell the pattern of glacial movement across the Canadian Shield area? What factors control the pattern of the land surface seen in the Canadian Shield area?

4b. How could you distinguish an image of part of the Canadian Shield from images of a Recent Glacial Margin area or part of the Driftless Area? In the table below briefly describe the land surface features (including lakes and streams) that characterize each of the three areas. If someone was given a map image of an unknown area, they should be able to use your description to determine which of the three regions the image most likely came from.

Canadian Shield Recent Glacial Margin Driftless Area

(This page should be turned in as part of the submitted lab materials.)

Lab A - 9 Question 5 Compare the land surface of the Lake Agassiz area with that of the Recent Glacial Margin (a) area straddling the Minnesota-South Dakota border. Both areas are part of a large glacial valley system that formed as glacial lobes moved to the south. (1 point)

5a. The overall size and shape of this glacial valley system remains relatively constant across the two areas, but how does the detailed surface features of the valley floor differ between the Lake Agassiz area and the part within the Recent Glacial Margin area? In other words, if you were walking across an unknown area, how could you tell whether you were walking across a part of the Lake Aggassiz area or the Recent Glacial Margin?

5b. Originally both areas formed as part of the same glacial valley and before Lake Agassiz formed, the details of the land surface in both areas were very similar. So what process associated with the lake is responsible for the two areas having such different land surfaces? (Hint for this one, think about the sequence of events in the order they occurred – glacial advance, glacial retreat and moraine development, glacial lake and lake sediments, and finally draining of lake to expose present land surface.)

(This page should be turned in as part of the submitted lab materials.)

Lab A - 10

Part C. Interpreting Local Glacial Records:

Exercise C – Creating & Presenting a Glacial Interpretation

Obviously the Upper Midwest has a rich, complex glacial history. Rather than attempt to interpret the whole region at once, your lab instructor will assign your lab group a smaller area to interpret. Answer any questions on the associated handout, then look at your area and try to develop an interpretation of its glacial history. What paths did ice take through the area? How did the present landscape features form? Once you are satisfied with your interpretation, use the erasable markers provided to annotate your interpretation on the large laminated copy of your area. Your lab group will use this map to communicate your interpretation to the rest of the class in a brief (less than five minute) presentation. If you complete this exercise before the other lab groups, work on Part D and the Post-lab Activity until your lab instructor begins the group presentations.

Lab A – Exercise C (Lab Handout 1) (3 points) Your lab instructor will assign your lab group one of five areas to interpret. Complete the questions on your copy of Lab Handout 1 and then interpret the glacial history of your area, annotating your interpretation on both the large laminated map and the small map image on your copy of Lab Handout 1.

Part D. Cultural Impacts of a Glacial Legacy:

In our society, we often think of human interactions with the land only from the perspective of how humans affect the landscape. Often overlooked is the realization that the landscape, along with its associated resources, exerts a tremendous impact on the people who live there and their culture. The ways in which a people view their landscape, as well as how they use and modify its resources, to a great extent defines their culture.

Examples of this relationship abound in the history of the Upper Midwest, but this lab will only examine two examples: the Minnesota River Valley and the pine forests of northern Minnesota and Wisconsin.

Lab A - 11 Figure 3

Figure 2. Different views of Dakota use of the Minnesota River Valley. On the left, Dakota hunters pursue buffalo in an 1868 painting by Seth Eastman. On the right, Eastman depicts Dakota women guarding their corn field from avian competitors.

Case Study 1 - Minnesota River Valley:

To the Dakota of the 17th and 18th century, the Minnesota River Valley was the physical and cultural center of their world (for reference, the valley is labeled in Figure 1 on page 5). Its broad valley floor hosted an intricate mosaic of river, wetland and grassland ecosystems in close proximity to the resources of northern forests and western prairies. The relatively small river occupying the center of this glacial valley eased trade with downstream villages and southern Mississippi River Valley cultures, while the valley floor itself was covered by remarkably thick, rich glacial soils. Buffalo could even be driven over the valley’s bluffs, providing an easy way to hunt these massive beasts long before horses were available to run them down on open plains2 (Figure 2).

Within this rich eco-system, the Dakota developed a very fluid societal structure centered about a few semi-permanent villages. The size of these villages fluctuated seasonally as small groups left to harvest resources from the many ecosystems that comprised the Dakota world. Wetlands provided wild rice, forests yielded deer and small game, prairies offered bison, while the rivers were sources for fresh water, fish and mussels. These resources alone did not support the Dakota culture however; they were supplements to a rich agricultural tradition based around corn, potatoes, squash, pumpkins, and gourds (Figure 3).

2 Perhaps the best evidence of this valley’s importance to the Dakota is that the Minnesota River Valley was where the Dakota retreated to, as they were forced into one treaty after another to cede their land. The Dakota never ceded the Minnesota River Valley by treaty; they were only driven from it by force in 1862, the start of a tragic conflict that continued through the Plains Wars to end at Wounded Knee.

Lab A - 12

Figure 5 Figure 4 . Although it is not in the Minnesota River Valley, Seth Eastman’s 1846-48 depiction of early Prairie du Chien illustrates the more intensive and permanent agricultural traditions of early 19th century Euro- Americans. Eastman painted a representation of the cultural displacement that occurred as Euro- American took over Dakota land in the sketch on the left that became the basis for Minnesota’s official state seal and state flag.

This flexible approach to their environment was in stark contrast to that of the Euro-Americans moving into Dakota lands. While the Dakota viewed the Minnesota River Valley as a rich mosaic of resources, the Euro-Americans’ attention focused primarily on one of the valley’s many resources: its soil. Although the Dakota had a diverse agricultural tradition, their farming practices were not nearly as intensive as those originally developed in densely populated European areas (Figure 4). Centuries of farming had depleted Europe’s soil horizons and to 19th century immigrants the Minnesota River Valley’s soil was almost beyond comprehension. Many had grown up in areas with extremely poor soils, a few inches thick at most. They came into a valley covered with thick glacial sediment, where even the soil’s organic-rich layer was measured in feet rather than inches.

Moreover from their perspective, this rich valley appeared to be almost deserted. Only familiar with their own cultural traditions, and with the absence of any fences or permanent structures, many early settlers did not even realize that the land they claimed was an integral part of the Dakota’s resource base. For their part, the Dakota found it nearly inconceivable that an individual, rather than a people, could claim sole use of any particular piece of land. Over centuries, these patterns of land use had become so deeply ingrained into their respective cultures that few individuals in either society could completely understand, or appreciate, the other society’s perspective (Figure 5). Cultural differences in land use would ultimately set the stage for societal conflict that erupted in the Dakota War of 1862.

Lab A - 13

Case Study 2 – The ‘Pinery’ (Upper Midwest’s Boreal Forest):

The pine-dominated forests of northern Minnesota and Wisconsin provide another example of how geologic processes produce a resource base that can greatly impact cultures living in that area and how different cultures can end up using that resource base in very different ways.

Pine forests are so familiar to Upper Midwest residents that they are often taken for granted. However these forests are actually relict survivors of a plant community that once dominated the dinosaurs’ world, but is now only found in areas with cold winters. Pine trees are gymnosperms, plants that rely on wind to fertilize and spread their seeds. Most modern trees are angiosperms, which use flowers to trick insects and animals into fertilizing and spreading their seeds. Angiosperms did not arise in large numbers until the middle Cretaceous (140 to 65 MYA) but, once they arose, they quickly replaced the slower growing gymnosperm community. Even though pine trees can thrive in tropical conditions if protected, for the past 60 million years fast-growing angiosperms have out competed them, pushing pine forests into those few areas where angiosperms are less competitive. In high latitude, or high altitude, areas cold weather restricts angiosperms and the insects they rely on for regeneration, allowing slow growing gymnosperms to dominate these environments. As ice sheets melted to reveal the land beneath them, pine trees were the first large plants to colonize the new landscape as cold harsh conditions along the margin of the remaining ice sheet prevented angiosperms from gaining a foothold. As the ice sheet continued to melt, pine forests moved north to keep pace with the receding glacial margin, while angiosperms replaced older pine forests in warming southern areas.

Geologically, the pine forests of Minnesota and Wisconsin are relative newcomers to the region, but to 19th century Ojibwa and Euro-Americans these forests appeared to be an ancient and nearly inexhaustible resource. Although the Ojibwa used wood for fuel and housing, they primarily hunted deer and small game that lived in the forests and gathered plants and berries on a seasonal basis. Wetlands, lakes and streams scattered throughout the forests were also rich sources for wild rice and other fresh water resources. Hence, the pine forests provided the whole framework within which the Ojibwa culture developed, even though it was not directly harvested in terms of large scale tree cutting or timbering operations3.

3 The indirect importance of the woodlands to the Ojibwa culture is reflected in archaeologists’ use of the term ‘Woodland Tradition’ for the cultures across northeastern North America up to the time of Euro-American arrival.

Lab A - 14

Figures 6 & 7. Differing views of woodland use: On left, Seth Eastman’s painting of an Ojibwa sugar camp provides an example of the Ojibwa’s use of the woodlands, where lumber use was secondary to the many other seasonal resources harvested over the course of the year. In contrast the wood itself was the primary resource of interest to contemporary Euro-Americans whose logging operations that cleared huge tracts of forest.

The Ojibwa use of the forests contrasted greatly with that of 19th century Euro- Americans. From the latter’s perspective, the Ojibwa had overlooked the forest ecosystem’s most valuable resource, the wood itself. This perspective even carried over into their vocabulary. Although early Euro-America explorers referred to the tree-covered landscape as forest or woodlands, those terms quickly became replaced by ‘timber’ and ‘lumber’, words that reflected the wood’s commercial value. With a larger population and a culture based on constructing permanent dwellings, Euro-Americans saw the pine forests as wealth and power. Soon the region became home to one of the most intensive, large-scale clear-cutting timber operations in human history. The forests became known as ‘The Pinery’ as lumber camps sprang up across the region. Remarkably few areas of old-growth forest survived these lumbering operations and most of our present woodlands are new growth forests that only weakly reflect the extensive pine forests of pre-lumbering time. With diameters over six feet, the old growth pine trees soared hundreds of feet into the air. These giants are gone now and the lumbering operations that destroyed them also irrevocably altered the woodland ecosystem they supported. To transport lumber to camps and mills, hundreds of dams were built to raise water levels. As a result, the wetland community and wild rice on which the Ojibwa depended were also lost as environmentally sensitive wetland areas became lumber ponds.

Both cultures placed a huge value on the Upper Midwest’s pine forests, but that value was based on very different uses of this geologic legacy. As with the Minnesota River Valley, the differing cultural perspectives were central to their respective societies and not easily changed. Cultural conflict was almost inevitable, as each society’s use of the pine forests clashed with that of the other. In the ‘Pinery’s’ case, this conflict fortunately did not flare into open warfare, but it still ended up devastating the traditional Ojibwa way of life.

Lab A - 15 Exercise D – The Cultural Legacy of Past Ice Sheets

Pollen that settled to the bottom of lakes and wetlands provide one of the best geologic records we have of past environmental change. Cores can be taken of lake bottom sediment and the pollen present in each layer of lake bottom sediment can be identified and measured. Organic matter in the layers can also be dated by means of C-14 (radiocarbon) dating to yield the age of each layer. On the desktop of the lab room computers, there should be a folder labeled Glacial Lab Visualizations.

Use the visualization within this folder to complete the questions for Exercise D on pages 17 and 18.

Upon finishing the lab, submit pages 7-10, 17-18, and your copy of Lab Handout 1. If time permits you may also complete and hand in the Post- lab Assignment (pages 19-20).

Next Lab: Before leaving, check with your lab instructor as to which lab your section will complete next week. The room location will also change, so be sure you know where to meet.

Next Pre-Lab Activity: Before you leave, check to make sure that you understand the next pre-lab assignment as it may differ from previous pre-labs.

For the Final Lab Quiz:

• Given an image of an area, be able to interpret whether glacial or non-glacial processes were primarily responsible for the present land surface. Describe any features that support your interpretation and explain how these features formed.

• Given an image of a glacially impacted area, be able to identify and describe the origin of any glacial features present. Using the glacial features present be able to create a reasonable interpretation of past glacial movement through the area.

• Be able to explain to someone who did not take this class how the glacial history of the Upper Midwest led to the development of the region’s pine- dominated forests and rich valley soils, as well as the different ways in which the region’s historic cultures viewed and used these glacial legacies.

Lab A - 16 Lab A – Exercise D

Question 6 (2 points) Look at the visualization titled Pine Pollen Records. This visualization used both the color and size of dots to display the relative importance of pine pollen in the layers of a sediment core taken from a lake or wetland area. As you run the visualization it will display the distribution of pine pollen through time across eastern North America. In the visualizations ‘ka’ refers to 1000-year intervals, so 12.5 ka means 12,500 years ago. You can manually move the bar beneath the visualization to quickly move back and forth through the record.

6a. When did pine forests first dominate the Upper Midwest area? (You can provide a range for when pine came to dominate the area, rather than pick one specific date).

6b. Once the ‘Pinery’ became established across the Upper Midwest (your time from question 6a above), what subsequently happened to the size and position of the pine range? Did it remain in place or continue to shift?

6c. What might explain the patterns you see in pine distribution both before and after the ‘Pinery’ first becomes established?

6d. What happens in the pine pollen records during the period from 300 to 100 years ago (0.3 ka to 0.1 ka) and what is the most likely cause of the changes observed?

(This page should be turned in as part of the submitted lab materials.)

Lab A - 17 Question 7 (1 point) Look at the visualization titled Ambrosia Pollen Records. ‘Ambrosia’ is simply a pretty name for ragweed, an angiosperm (flowering plant) that torments many allergy sufferers. Ragweed is a fast growing plant that takes root quickly and does well in disturbed soil. Use the visualization to run through the distribution of ragweed across eastern North America for the past 18,000 years, but be patient and run the visualization all the way to the end.

7a. How does the distribution of ragweed (ambrosia) change within the last 200 years (0.2 ka to 0.0 ka)?

7b. This change occurs are a time when there is no historic evidence of a climate change that might explain the change in pollen records. So if it wasn’t climate, what other change in the environment occurred at this time that might help explain the observed changes in ragweed distribution?

(This page should be turned in as part of the submitted lab materials.)

Lab A - 18 Name ______Post-Lab A Activity

The answers to these Post-lab questions are due at the start of the next lab. If time permits, however, they can be completed and handed in during class.

Question 8 If 19th century Dakota and Euro-Americans had first encountered one another in a Canadian Shield area rather than the Minnesota River Valley, would their differing agricultural traditions have posed more or less potential for cultural conflict? Briefly explain the geological reasoning behind your answer. (1 point)

Question 9 How did 19th century Ojibwa and Euro-American uses of woodland areas differ in terms of the woodland ecosystem’s ability to quickly recover from its exploitation? (1 point)

Question 10 is on next page.

Lab A - 19

Question 10 In 1850, the combined Indian population of the Minnesota Territory was estimated to be slightly over 30,000. By comparison, Minnesota’s Euro-American population exploded from just over 6,000 in 1850 to well over 170,000 by 1860. How might differences in their approach to the natural world help to explain the difference in population size between these cultures? In other words, do you think it likely that the Dakota and Ojibwa lifestyles could have supported a population as large as that of the incoming Euro-American community? (1 point)

Lab A - 20 Lab B – A River Through Time: ‘Managing’ the Upper Mississippi River

Pre-Lab Activity: At the beginning of the lab, your lab instructor will choose one of the following questions and you will have five minutes to write an essay answer for that question. Your essay must be independent work, completed without the aid of your classmates. Be sure to read the lab before coming to class, as you are also not allowed to refer to the lab manual or notes while completing the essay.

1) Briefly describe how the two river management schemes of channel restriction and lock/dam construction differ in their approach to creating a deeper, more continuous channel for river transport.

2) Briefly describe how the two river management schemes of channel restriction and lock/dam construction differ in their impact on the surrounding river valley system.

3) What roles do wetlands play in river systems and how did 18th to 19th century Dakota and Euro-American views of wetlands differ? How did the two river management schemes of channel constriction and lock/dam construction affect wetland areas?

Lab B Goals:

• Understand how river processes work by manipulating those processes to achieve a desired goal, such as a forming a deeper, more continuous river channel.

• Place river processes in an historic context of different cultural perspectives and the human societies using, and manipulating, those processes.

• Understand the goals and design of various river channel management systems, as well as the implications of those modifications on the broader river system.

Lab B Assessment:

• Given an image of part of a river system, be able to identify evidence of any recent changes in the river channel.

• Given an image of part of a river system, be able to predict where the river’s flow is fastest or slowest, and where its velocity changes significantly. In other words, be able to predict where erosion is most likely to occur along the river channel and where sediment is most likely to be deposited.

• Given an image of part of a river system, be able to predict the probable consequences of any given natural or human alteration of the river channel.

Each lab group member must submit her or his answers to the lab questions.

Lab B - 1

Corps of Engineers’ snagboat J. G. (Photographed by Henry Peter Bosse in 1885.)

Part A: Life along the Upper Mississippi River:

Resources & Cultures:

Cultures differ in their use of Earth’s resources. The differences may be so ingrained within a culture that they even determine the ways in which people view their world. When Euro-American settlers first moved into the Upper Midwest, they entered the same landscape that the Dakota had lived in for centuries, yet they viewed it from a very different perspective. As they took over the land, they not only displaced a native society, but also transformed the reigning cultural definitions of the land itself.

“With the signing of these treaties a subtle but profound change had already taken place. Prairie and oak openings had become acres; forests had become timber stands; tumbling rivers had become water rights.”4

As a consequence, eighteenth and nineteenth century Dakota and Euro-Americans saw river systems in very different ways (Figure 1). Viewed through Dakota eyes, the whole of the river valley was a closely integrated, resource-rich environment upon which their culture depended. In contrast, the contemporary Euro-Americans considered river systems almost exclusively in terms of flowing water. Although they would redefine the importance of rivers over the years in terms of the fur trade, regional commerce, and hydropower, the movement of water in river channels remained the crucial resource for Euro-American society.

4 Rhonda Gilman, ‘Territorial Imperative: How Minnesota Became the 32nd State’, in ‘Making Minnesota Territory 1849-1858’, Anne R. Kaplan and Marilyn Ziebarth editors Minnesota Historical Society Press, 1999

Lab B - 2 These differing cultural perspectives extended down to each part of the Mississippi River and Minnesota River systems.

• Wetlands: Wetland areas provide a rich mosaic of integrated environments that host a wide array of plants and animals, many of which can only survive in a wetlands habitat. Surprisingly, this diverse ecosystem is as vulnerable to too much water as it is to too little water. Although drought may damage a wetland area, many of the plants and trees that form the wetland community’s base are also damaged or killed by high water. If flooded for extended periods of time, a wetland community will collapse.

Nowhere was the contrast between Dakota and Euro-American perspectives greater than in wetland areas. To the Dakota, wetland areas were valuable resources rich in plants and animals, of which wild rice was arguably the most important. In contrast, during Euro-American settlement, half of Minnesota’s wetland areas were purposely destroyed. Too wet to easily cross or plow, too dry to navigate or transport goods, wetlands were viewed by Euro-Americans as nuisance areas that would only be useful if they were drained for agriculture or flooded to float logs or goods downstream. The sole aspect both groups shared was a tendency to overlook the crucial role wetlands play in flood control. During cloudbursts and spring thaws, wetland areas absorb tremendous amounts of water and slowly release it over time, decreasing the chance of catastrophic flooding. Without wetlands, floods are larger and more frequent.

Figure 1. Differing views of river use: On left, Dakota harvest wild rice in a painting by Seth Eastman, 1867.On right, a steamboat pushes a log raft through St. Paul in 1878, highlighting the river’s commercial importance to 19th century Euro-American society. (Photo on right from Minnesota Historical Society)

• River Bluffs: Even the bluffs along the river valleys were resources for the Dakota, who harvested bison by driving them over the bluffs’ edge. From an Euro-American perspective though, the bluffs were obstacles that hindered the movement of people and goods from the river to the plains above. Euro- Americans did recognize two benefits of the bluffs however. Along most rivers, homes and buildings erected even miles from the riverbank might be within the reach of floodwaters, but the bluffs here protected most of Minneapolis and Saint Paul from flooding. Even more importantly, the bluffs were indirectly linked to the existence of waterfalls, and falling water was a source of power that would transform Minneapolis into a leading milling and industrial center.

Lab B - 3

• River Flow: The Dakota used the river as a source of water, freshwater plants fish, mollusks, birds and mammals, as well as a means of easy transportation. Early Euro-American river use mirrored that of the Dakota, but this changed as Euro-Americans came to dominate the region. Commerce overshadowed all other uses for the river, until the mills of St. Anthony Falls made hydropower an even more important resource. This emphasis on flowing water may have been the most significant difference between nineteenth century Euro-American and Dakota perspectives. When the Dakota spoke of the Mississippi, they often meant the whole Mississippi River valley system, but when Euro-Americans used the term they were usually speaking specifically of the river’s channel.

A Natural River:

Naturally flowing rivers are remarkably sensitive to changes in water movement. When a river speeds up, it can erode and carry more sediment. Where it slows down, a river no longer can carry all of the sediment it was moving, so some is deposited. In general, the fastest flowing water tends to be in the center of the channel, as friction along the channel floor and sides slows the flow. At any bend though, the swift moving water is forced towards the outer riverbank, leaving the inner bank an area of particularly slow flow. As a consequence, the outer bank of a river bend erodes while the inner bank builds up as sediment is deposited (Figure 2).

Figure 2. In a flowing river, the fastest current (shown by arrows) is forced towards the outer bank at river bends, leaving the inner bank an area of slowly moving water. Because of the differences in water velocity the outer riverbank tends to erode, while the inner riverbank is built up by sediment deposition.

Exercise A – The Minnesota River Valley: An example of Channelization as a River Management Strategy (2 points)

The course of the Minnesota River below Fort Snelling is an example of channelization, an extreme form of river management in which the whole path of the river channel is reconstructed to better fit human uses of the river, whether flood control or improved navigation. Below Fort Snelling the goal was to convert a meandering river system into a more effective transportation corridor. Straightening and deepening the channel allowed barges to move goods more quickly to the Mississippi River. Reconstruction of the river system was not limited to the main river channel. Secondary streams were closed off and surrounding wetland areas drained and converted to agricultural fields.

Lab B - 4 Name ______

Lab B - Exercise A (2 points total) Note - If your lab group completed Exercise B first, do not confuse 'channelization' (straightening a river channel) with 'channel constriction' (narrowing a river channel).

Question 1 Using the aerial photograph mosaic, draw the path of the Minnesota River prior to its channelization on the image below. Circle the three areas where channel’s path was most significantly changed by channelization.

Question 2 Look at the map which shows the path of the river back in 1878. Comparing that path to the one you drew in Question 1, how did the natural river's path change from 1878 until shortly before the Army Corp of Engineers channelized the river?

a) The river's path had not significantly changed in the century between 1878 and its reworking by the Army Corps of Engineers.

b) The river's curves had become more pronounced in the century between 1878 and its reworking by the Army Corps of Engineers.

c) The river's path had already begun to straighten itself out in the century between 1878 and its reworking by the Army Corps of Engineers.

Question 3 In the decades since the Minnesota River was channelized there has been a dramatic increase in both the number and size of flood events, even though the region’s amount of precipitation has not significantly increased. What change in the river valley system is most likely responsible for this increased flooding?

(This page should be turned in as part of the submitted lab materials.)

Lab B - 5 Lab B - 6 Part B: A Brief History of Travel on the Upper Mississippi

Prior to the late nineteenth century, the Upper Mississippi was a natural river system that differed markedly from the river we know today. The natural river system was not a single channel, but a mosaic of shallow channels that wound around numerous ephemeral islands and were often choked by shifting sand bars. Expansive wetlands covered much of the bluff-lined valley floor.

The channels were so shallow that the only crafts that could easily ply their waters were birch bark and dugout canoes. During late summer and early fall, river levels fell so low that even young children could wade the Mississippi’s width. Even when water levels were high, shifting sandbars and sunken trees made navigation a dangerous enterprise for large boats. Euro-Americans turned to rafts and flatboats to transport goods downstream, but only the shallow keelboat could transport cargo upstream. To move upstream, crews had to pull the craft from shore or pole it upstream, both painfully slow processes. Averaging less than ten miles a day, keelboats soon proved incapable of fulfilling the growing demand of upstream communities for goods.

By 1820, the development of the Upper Mississippi steamboat transformed river commerce. The Upper Mississippi steamboats were specially modified steamboats built on a very shallow base. The engine was placed on the deck, rather than in the hull, and upper decks were added for passengers and cargo. Although the largest of these boats soared to more than seventy feet above the river, they only drew four feet of water fully loaded and small steamboats could move in only eighteen inches of water.

Even with the new steamboats, shifting sandbars and channels still posed a significant risk to river commerce, and during low water the river simply was not navigable. By 1854, railroads began to reach the Upper Midwest. The railroads though held a near monopoly on bulk transportation and charged exorbitant shipping fees. Businesses and communities looked to the river as an alternative that might be able to curb the railroads’ influence, but only if the river channel was improved so ships could transport goods through more of the year, instead of being restricted to high water spring and early summer months.5 Recognizing the importance of river traffic to their future, communities all along the upper river began to call on Congress to improve the river’s natural channel.

5 Agricultural concerns, in particular, hoped for improved river transport as their bulk goods fared the worst under the railroads’ monopoly. The rise of the Grange, a national agriculture-based social movement founded by Oliver Hudson Kelly of Coon Rapids played a prominent role gaining Congressional support for river improvement projects. Started in 1868, within six years the Grange claimed nearly a million members. (John O. Anfinson)

Kelly’s Coon Rapids farm is now owned and operated by the Minnesota Historical Society as a historical site.

Lab B - 7 Exercise B – Mimicking Early River Management Schemes: (3 points)

Using the Stream Table Before using the stream table, take a moment to examine how the table and pump system works. There are electric plugs in the surrounding floor so it is critical that you do not allow the tub beneath the table to overflow. Be sure that you know how to turn the pump on and off, and NEVER leave the table with water running.

Start by using the tools to move the sand into the two-thirds of the table furthest from the table’s drain. Smooth the sand into a uniform surface that gently slopes towards the drain. Then dig a shallow, roughly one-inch deep channel from the upper part of this slope towards the drain end of the table. This channel should include at least one or two gentle curves but avoid tight bends, as the water flow cannot follow them. A gentle S-shaped channel works well.

Your lab instructor should help you to set the water supply up so the direction of river flow is not determined by the hose’s water pressure.

Before starting the water flow, use vertical toothpicks to mark your channel’s edge, spacing them roughly every ten centimeters along the riverbank. Each lab group member can then opt to place one of the cows along the stream bank. Depending on your lab group's personality, the last cow standing or first swept away wins!

If you haven’t already done so, be sure to read Part C: Mississippi River Management – Early Years to understand the idea behind wing dams before completing Exercise B.

Complete the questions on the following page.

Lab B - 8 Lab B - Exercise B

Question 4 – An Unmanaged Stream

Before you start the water flow: 1) Draw a simple sketch of your river channel below. 2) Use dots to show areas where you expect deposition will occur. 3) Use x's to show areas where you expect erosion will occur.

O Drain

4a. Turn the water on and let it flow for several minutes. How did you predictions hold up? If there were any significant differences, try to figure out why they occurred.

4b. While the water is flowing, set the wooden ‘boats’ adrift and time how long the fastest boat takes to travel a meter downstream. If a boat is beached, push it back into the river flow.

Travel time: ______

(This page should be turned in as part of the submitted lab materials.)

Lab B - 9 Question 5 – Wing Dams

Turn the water off and, as a group, decide where to place the small metal pieces as wing dams. Your goal should be to use wing dams to narrow the river flow and force it to erode a deeper channel. Draw the channel and your wing dams’ positions below.

O Drain

Before turning on the river flow, decide whether you expect boats to (circle one):

a) travel slower b) travel the same speed c) travel faster

than they did in the unmanaged stream.

5a. Turn the water flow on. After it has run for a few minutes set the wooden ‘boats’ adrift and time how long the fastest boat takes to travel a meter downstream. If a boat is beached, push it back into the river flow.

Travel time: ______

5b. Is this faster or slower than the travel time for the original unmanaged river system?

a) faster b) slower

Circle one and briefly explain why the difference in travel time occurred.

5c. If you needed a still deeper river channel, what further changes to the river system might be needed to attain that goal? (Hint - Consider what else the Army Corps of Engineers did that is not matched in your simpler model.)

(This page should be turned in as part of the submitted lab materials.)

Lab B - 10

Question 6 – Dams & Dikes Turn the water off and use the longer metal pieces to construct a dam across the river channel close to its downstream end. The dam’s goal should be to raise the river level and create a deeper channel. To achieve this, you will also need to pile sand up in thin ridges (called dikes) along the channel’s banks. Try to design the dam and dikes so the water upstream of the dam will be close to, but still below, the top of the dikes.

Start the water flow. Once the pool behind the dam is filled, water should spill over the dam’s top into the downstream channel. Do not let water break through the dike system to flood the surrounding low areas.

6a. Compared to the wing dam program, how much upkeep is required to maintain this dike and dam river management system to prevent flooding? In a real-life situation, do you think your observations would also hold true?

6b. When the dam is filled, keep the water flowing and set the wooden ‘boats’ adrift close to the start of the dike-lined channel. Time how long it takes the boats to travel a meter downstream.

Travel time: ______

6c. Is this faster or slower than the travel time for the original unmanaged river system?

a) faster b) slower

Circle one and briefly explain why the difference in travel time occurred.

6d. Is this faster or slower than the travel time for the wing dam managed river system?

a) faster b) slower

Circle one and briefly explain why the difference in travel time occurred.

(This page should be turned in as part of the submitted lab materials.)

Lab B - 11 Lab B - 12 Part C: Mississippi River Management – Early Years6 Channel Constriction (1867-1907)

The Civil War delayed initial efforts to improve navigation on the upper Mississippi River, but beginning in 1866 Congress charged the Army Corps of Engineers with a series of channel ‘improvement’ projects. In quick succession, projects for a three-foot, a four-foot, a four-and-one-half-foot and a five-foot channel followed one another. In each of these, the goal was to create a continuous channel the length of the river that, even during periods of low water, would respectively be at least 3, 4, 4.5 or 5 feet deep at its shallowest points. The Corps quickly learned that trying to achieve this channel by dredging was impossible. Almost as fast as a section could be dredged the river’s shifting sands would begin to infill the channel. Impressed by the river’s efficiency, the Corps decided to manipulate the river’s natural processes to erode and maintain a deep continuous channel.

To do this, the Corps adopted a policy of channel constriction. Its goal was to increase the river’s depth by narrowing and constricting its main channel. With the resulting increase in velocity, it was hoped that the river could erode and maintain its own deeper channel. The Corps’ early channel constriction efforts primarily involved three types of structures: closing dams, wing dams, and riprap.

• Closing Dams – Closing dams were low dams built to close off smaller channels diverting their water flow into the main channel to increase the size and velocity of the main channel’s water flow (Figures 3 and 4).

• Wing Dams – Wing dams were low dams built perpendicular to the riverbanks. They were designed to subtly alter and augment natural river processes in order to achieve a deeper channel. Sets of wing dams were placed in areas where the river’s velocity naturally slowed and deposited sediment, like the inner banks of river bends. Building wing dams in these areas further slowed water movement, allowing even more sediment to be deposited behind the wing dam. The result was a narrower, swifter flowing river channel that could erode a deeper channel (Figures 3 and 5).

• Riprap – If closing dams and wing dams succeeded in creating a narrower, faster moving main channel, this channel might end up eroding its other riverbank, rather than scouring a deeper channel. If this occurred, then the channel would widen, its velocity would drop and the whole goal of the dam construction project would be lost. To avoid this, layers of brush and rock called riprap were used to protect riverbanks that were vulnerable to erosion, like the outer banks of river bends (Figures 3 and 6).

6 The history of the Corps’ efforts to manage the Mississippi is outlined by John O. Anfinson in River of History: A Historical Resources Study of the Mississippi National River and Recreation Area (U.S. Army Corps of Engineers, St. Paul District, 2003), and described in more detail in The River We Have Wrought: A History of the Upper Mississippi (University of Minnesota Press, 2003).

Lab B - 13

Figure 3. The effects of channel constriction structures on a river channel. On the left, the river channel is shown just after construction. A closing dam cuts off the secondary channel, diverting its water flow to the main channel (shown by arrows). Wing dams built on the inner bank of river curves eventually trap sediment to constrict or narrow the river channel. An apron of riprap on the opposite bank guards against the channel widening itself by eroding the riverbank.

Figure 4. A closing dam at Pigs Eye Island marked the Corps’ first attempt at channel constriction. Built in 1874 to test the concept, the Pigs Eye closing dam succeeded in creating a continuous 3-foot channel through the area.

(Top) Prior to the closing dam’s construction, the Mississippi channel at low water consisted of deeper pools, isolated from one another by shallow sand shoals. Shoals are areas where the water is shallow because sediment has built up on the river floor.

(Bottom) By cutting off the side channel, the closing dam redirected its water flow to the main channel. The increased flow allowed the main channel to scour a deeper, more continuous channel.

Lab B - 14

Figure 5. Wing and closing dams on the Mississippi River at Pine Bend in the Grey Cloud Island area. (Photographed by Henry Peter Bosse in 1891.)

Note that the wing dams were built in sets on the inner bank of a river curve. In the background, deposition associated with the wing dams has already filled in much of the channel’s right side.

A closing dam blocks the secondary channel on the center right, which will eventually completely fill in.

Figure 6. Pigs Eye Island seen from the Mississippi River bank south of St. Paul (same area shown in Figure 4). (Photographed by Henry Peter Bosse in 1885.)

A layer of broken rock covers the sloping riverbank in the foreground. The rock layer, called riprap, was part of the Corps’ channel constriction effort. This area of riverbank lay on the outer curve of a river bend. Wing dams and a closing dam on the opposite bank narrowed the river channel and increased the water flow along this bank. To protect the riverbank from erosion the Corps armored this outer bank with riprap.

Lab B - 15 Lab B - 16 Lab B - Exercise C

Exercise C – River Management by Channel Constriction (4 points)

Your lab instructor will assign each lab group a section of the Mississippi River. Your Lab B Handout 1 shows that section of the river as it appeared during the Corps early attempts to constrict its channel (1878-79 Farquhar Survey – Map 10, 11, 12, 13 or 14).

Question 7 Develop a plan of channel constriction for your section of the river, choosing locations for closing dams, wing dams, and riprap. In doing this, realize that although closing dams were single structures, wing dams needed to be built in sets in order to effectively narrow a river stretch. Also consider that your plan for channel constriction has to be economically feasible. Riprap was expensive. It would be economically prohibitive to continuously line both sides of the river with riprap, so only use it in those areas that would be the most vulnerable to erosion once your dam construction begins to constrict the channel.

Draw your channel constriction plan directly on your copy of Lab Handout 1 using the colored pens provided.

Question 8 Once you have finished your channel constriction plan, ask your lab instructor for the plan that was adopted by the Corps for your section of the river (1915 Hoffman Survey – Map 10, 11, 12, 13 or 14).

Compare the two plans and note any important differences between them. For this part of the exercise, do not worry about the details of individual dam locations or the length of riprap cover. Just concentrate on significant differences between your scheme and that implemented by the Army Corps of Engineers.

Examples of significant differences include:

• If closing dams were used to shut off channels, did the two schemes choose the same channel to close? • Are there bank areas protected by riprap in one scheme that were left unguarded in the other? • Did one scheme place a set of wing dams along the bank of a river curve while the other scheme ignored that area or placed wing dams on the opposite bank?

Use the back of this page to discuss the two plans.

You do not have to assume that the Corps’ plan was correct. If you think your plan would have been more effective, simply explain why that would be the case.

(This page should be turned in as part of the submitted lab materials.)

Lab B - 17 Briefly discuss the overall differences between your proposed plan and the plan implemented by Army Corps of Engineers. You can use numbers or letters to tie discussion below to specific localities on the handout if needed.

• If closing dams were used to shut off channels, did the two schemes choose the same channel to close? (This one may not apply to all map sections)

• Are there bank areas protected by riprap in one scheme that were left unguarded in the other?

• Did one scheme place a set of wing dams along the bank of a river curve while the other scheme ignored that area or placed wing dams on the opposite bank?

(This page should be turned in as part of the submitted lab materials.)

Lab B - 18 Part D: Mississippi River Management – Later Years Locks & Dams (1907-present)

The Corp’s efforts at channel constriction were not sufficient to keep up with the increased demand for a deeper river channel. Calls for deeper channels, combined with the development of hydroelectric power as a commercial industry, led the Corps to switch strategies. Abandoning a policy of channel constriction, the Corps instead began an ambitious campaign of building massive lock and dam structures. These lock and dam structures created a nine-foot channel7 for commerce, but in doing so transformed the river into its present form.

In contrast to earlier channel constriction projects, lock and dam construction is an attempt to overwhelm and control natural river processes, rather than to work with them. A dam pools water behind it, raising water levels for navigation but also flooding vast areas of the river valley. The lock allows boats to move past the dam. Locks are rectangular chambers with two doors. Once ships enter, the doors are closed and water can be let into or out of the lock to raise or lower the water level within the lock. Essentially, the lock acts as an elevator, lifting or lowering the boat between the high water behind the dam and the lower water in front of it. Benefits of lock and dam construction include higher water levels for shipping and, if the dam is tall enough, water falling over the dam can generate hydroelectric power. On the other hand, as a result of their construction, large areas of the valley floor are flooded and the river is broken up into separate pools rather than flowing as a single stream. At present, the only way freshwater animals can go from pool to pool is to move through the locks as they open and close for boats and barges.

The first of the lock and dam structures was built at Meeker Island in 1907, but within five years the Corps dynamited the top of this structure in favor of building an even larger lock and dam near the Ford plant that could generate hydroelectric power as well as aid navigation. A second lock and dam complex was built at Hastings in 1930 and a third just above Redwing in 1938. Twenty-two more Upper Mississippi River lock and dams between Redwing, Minnesota and Alton, Illinois would follow during the 1930’s. It wasn’t until 1963 though, that a lock at St. Anthony Falls finally extended navigation upstream of the cataract.

Exercise D – River Management by Lock and Dam Construction

Ask your lab instructor for a copy of the present navigation charts for your section of the Mississippi River. (2001 Navigation Charts – Map 10, 11, 12, 13 or 14).

Complete the questions for Exercise D on page B-19.

7 As with the earlier channels, the nine-foot channel project’s goal was that the Mississippi River channel would have a minimum depth of 9’, even during periods of low water. The standard used to define ‘low water’ is the river’s depth in 1864, a year of pronounced drought.

Lab B - 19

Lab B - 20 Lab B - Exercise D (3 points total)

Question 9 Compare your section of the river under channel constriction (1915 Hoffman Survey – Map 10, 11, 12, 13 or 14) to its present form as shown on the 2001 navigation chart. Briefly describe any significant changes in water volume or channel path that have occurred as a result of lock and dam construction.

Ask your lab instructor for the large maps that show the whole river system through time.

Question 10 Although the wing dams and closing dams were originally built to help river traffic, what role do you think they currently play with river commerce? Are they an aid or potential hazard? If they still help river traffic, what help do they supply? If they are a hazard, what would have to be done to offset or decrease that hazard? (As a hint, realize that although the wing dams are now submerged, canoeists and the U's crew teams still have to take them into account!)

Question 11 In the decades since lock and dam construction was completed, the Army Corps of Engineers has had to substantially increase dredging operations to keep the channel open. So much sand is dredged up from the channel floor that its disposal poses a significant environmental problem. Why would dredging operations increase under lock and dam management of the river system, compared to the older channel constriction management efforts?

(This page should be turned in as part of the submitted lab materials.)

Lab B - 21

Lab B - 22 Part E: Summing Things Up

Use the large maps to compare the river system over the last 125 years. The 1878-79 Farquhar Survey mapped a largely natural channel. Less than forty years later, the 1917 Hoffman Survey maps show the complete channel constriction effort at a time shortly after the Corps abandoned that strategy in favor of higher dams and locks. Lock and dam construction transformed the river to its present form shown on the Corps 2001 navigation charts.

Exercise E – Post-Lab Essay Outlines

The Post-Lab Activity requires you to write two half-page essays. Before leaving the lab, it may help to have your lab group compose a preliminary outline or ‘bullet-list’ of the main points each essay should cover. If you have enough time, you can complete the Post-Lab Activity in class, but remember that while you can share ideas, the essays themselves must be completed as independent work.

Upon finishing the lab, submit pages 5, 9-11, 17-18 and 21, along with your copy of Lab Handout 1. The Post-Lab Activity is due at the start of the next lab.

Post-Lab Activity (4 points) Imagine that you were trying to explain to a friend or family member what you have learned about the historical efforts to ‘manage’ the Mississippi River. With that goal in mind, write a half page essay for both of the questions given on page 25.

Your completed essays are due at the start of the next lab.

Next Lab: Before leaving, check with your lab instructor as to which lab your section will complete next week. The room location will also change, so be sure you know where to meet.

Next Pre-Lab Activity: Before you leave, check to make sure that you understand the next pre-lab assignment as it may differ from previous pre-labs.

Lab B - 23

For the Final Lab Quiz:

• Be able to explain how the Corps’ attempts at channel constriction and lock/dam construction differed from one another in their approach to creating a deeper, more navigable river channel.

• Be able to explain the role wetlands play in river systems and how the Corps’ river management schemes (channel constriction, lock/dam construction, and channelization) affected the river valley system, including wetland areas.

• Given an image of part of a river system, be able to choose appropriate sites for wing dams and riprap construction to force the river to cut a deeper, more continuous channel by means of channel constriction.

Lab B - 24 Post-Lab B Activity

Imagine that you were trying to explain to a friend or family member what you have learned about the historical efforts to ‘manage’ the Mississippi River. With that goal in mind, for each of the questions below, write a half page essay covering all parts of the question. Completed essays are due at the start of the next lab.

You can use the space below each question to compose an outline of the main points your essay should cover before leaving the lab.

The essays can be completed on a separate sheet or on the back of this page.

Question A (2 points) a) Briefly explain the basic idea behind the Corps’ early attempts to ‘improve’ the Mississippi River channel by ‘channel constriction’. In other words, what was the goal of channel constriction and what methods did the Corps use to achieve that goal? b) What were some of the subsequent impacts of channel constriction efforts on the overall river system? In particular, what was lost from the river valley system the Dakota originally knew?

Main points:

Question B (2 points) a) In a similar fashion, explain the main idea behind the Corps’ later attempts to ‘improve’ the Mississippi River channel by lock and dam construction. b) What were some of the subsequent impacts of lock and dam construction on the overall river system? Again, how does the present river system differ from the one that the Dakota used? c) What are the pros and cons of river management by dam and lock construction compared to earlier channel constriction efforts?

Main points:

Do NOT turn this page as part of your submitted lab materials. (Unless you finish essays during class.)

Lab B - 25 Post-Lab B Essays Name ______Or complete on separate page…

Lab B - 26

Lab C – In the Wake of a Waterfall The Geology Behind the Founding of Minneapolis & St. Paul

Pre-Lab Activity:

At the beginning of the lab, your instructor will choose one of the following questions and you will have five minutes to write an essay response to that question. Your essay must be independent work, completed without the aid of your classmates. Be sure to read the lab before coming to class as you cannot refer to the lab manual or notes while completing this essay.

1) Briefly describe the geologic background behind the waterfalls of the Twin Cities area. In other words, which features of the regional bedrock were necessary for waterfalls to form?

2) Briefly explain the geologic history of Saint Anthony Falls. How and where did the falls begin, why did their location change over time, and how did human use of the falls ultimately lead to their change from a natural cataract to their present form?

3) Briefly explain the reasoning behind Winchell’s estimate for the time it took Saint Anthony Falls to retreat from the Fort Snelling area to its present position. How did a fossil beaver skeleton provide a means to check the accuracy of this estimate?

Lab C Goals and Assessments:

• Understand the geologic background behind the origin of Twin Cities’ area waterfalls and how they have evolved over time. Given a set of geological conditions, be able to predict the probability of having a waterfall develop and the waterfall’s subsequent behavior if one does form.

• Given an actual or hypothetical change in geological conditions, be able to predict that change’s probable impact on the evolution of a waterfall system.

• Understand how different cultures can view and use waterfalls in very different ways. Be able to explain to someone who did not take this class how the evolution of present and past waterfall systems affected the history of the Twin Cities area, as well as how human activity in turn altered Saint Anthony Falls.

Each lab group member must submit her or his answers to the lab questions.

Lab C - 1

Figure 1. Saint Anthony Falls in downtown Minneapolis. Once a natural cataract, water now flows down an artificial apron. The original apron was constructed in 1871 to prevent the falls from retreating north.

Introduction:

Exceeded only by Niagara Falls, Saint Anthony Falls (Figure 1) is the second largest waterfall in the Upper Midwest region and the only cataract along the entire length of the Mississippi River. A natural obstacle to river travel, the falls forced early visitors to portage boats and cargo around the cataract, giving them ample opportunity to view the falls up close. Perhaps for no other Upper Midwest surface feature though, was this observation so subject to the viewer’s cultural perspective. To the Dakota, the falls may have been a place of spiritual power, but in practical terms their main impact was a forced detour for river travel. Euro-Americans, however, saw an invaluable source of physical power, falling water that could drive mills and build a city.

Water is heavy, so falling water can be harnessed to drive machinery and mills. On the East Coast, cities like Lowell, Massachusetts8 provided examples of how mills, textile plants and other industries could be built around waterfall-based hydropower. Although early Euro-Americans explorers in the Upper Midwest initially concentrated on the regions fur and timber, from the beginning they also recognized that Saint Anthony Falls would one day form the hub of a major metropolitan area (Figure 2).

8 The textile industry at Lowell, Massachusetts was such a powerful model for early Euro-American investors in the Upper Midwest that New Lowell was one of the names originally proposed for the city of Minneapolis.

Lab C - 2

Figure 2. Differing cultural perspectives of Saint Anthony Falls. Above is a painting of the falls in 1842 by an Alexander Loemans, a rare image of the natural waterfall known to the Dakota. On the right is a photograph of the falls taken less than forty years later, during the height of lumbering operations at the falls. Mills were built out over the falls to harness the rushing water.

Although early Euro-American travelers remarked on the falls’ natural beauty, its power proved to be of paramount importance to their society.

(Minnesota Historical Society photographs)

Early on, the easiest way to tap the water’s power was to simply build platforms out over the falls so the water flowing beneath the platform could drive the mills. This was relatively easy to do since the water level above the falls was shallow enough that the river could be crossed much of the year on horseback or in carriages. Platforms were built across the east channel and the western half of the larger west channel. An upstream horseshoe-shaped barrier was constructed between the western platform and Hennepin Island to concentrate water flow beneath the two platforms (Figure 3). To guard against periods of dangerously high water, spillways were added to the central area. In theory these spillways and the falls’ area below the horseshoe-shaped barrier would allow floodwaters to safely bypass the platforms. Reality proved to be a bit more difficult however, as many floods damaged or swept away structures.

Figure 3. The map shows the locations of Saint Anthony Falls’ mill platforms and riverbank mills during the height of early milling operations. One of the early platform mills (circa 1860) is shown on the right.

Lab C - 3 Classroom Activity 1: Views from the Past – Stereopticon Images of the Falls

Minneapolis’ early days overlapped with the heyday of stereopticon photography, leaving a legacy of stereo images from a time when lumber mills dominated the falls. Use the GeoWall to view the falls as they existed before their reconstruction by the Army Corps of Engineers.

Sidebar 1 - Spirit Island: A Beginning

Although the custom was seldom followed, a Dakota man could take more than one wife, provided that he could support this extended family. The custom’s existence, however, did not necessarily mean that every Dakota woman accepted it. One woman was so opposed to her husband’s decision to take a second wife that as her tribe traveled downstream she took advantage of the falls to negate it. Instead of landing to portage around the cataract, she propped her child up in the canoe’s front. Ignoring the frantic calls of her husband, friends and relatives, she paddled directly over the falls while singing to her child. Their bodies were never recovered and many Dakota believed that their spirits came to inhabit a small mist- covered island that lay at the foot of the cascade. This isolated spot became known as Spirit Island and it was said that at times the voices and songs of mother and child could still be heard above the roar of rushing water (Figure 4).

Figure 4

View of Saint Anthony Falls taken about 1865. Spirit Island is in the foreground on the left.

Some of the mills on the west channel mill platform can be seen behind Spirit Island, while the buildings on the right margin are mills on Hennepin Island.

(Minnesota Historical Society photograph)

Sidebar 2 – Lies at the Falls, Part 1

Father Louis Hennepin was one of the first Europeans to visit the falls and named them after his patron saint, Saint Anthony of Padua. In his account of the visit, Hennepin described how a Dakota warrior climbed a tree to offer a decorated beaver robe to a spirit who lived in the falls. The warrior prayed for his people’s safety and asked for aid to destroy their enemies, promising human sacrifices in return for the spirit’s aid. This bloodthirsty prayer is widely credited as being the first historical record of Dakota religion, but it never actually occurred! By his own admission, Hennepin could not understand the Dakota language well enough to follow a simple conversation. Although he may have witnessed some sort of ritual at the falls, his account of the prayer was a complete fabrication. It only reflected Hennepin’s worldview and overly active imagination, not any Dakota beliefs or customs.

Lab C - 4 Part A. The Geology Behind Saint Anthony Falls:

Saint Anthony Falls is the Twin Cities area’s largest and best-known waterfall, but smaller waterfalls are scattered through the metro area (Figure 5). While a variety of processes can produce cataracts, the Twin Cities area waterfalls all share a common origin that lies in the character and geometry of the area’s surface bedrock geology.

Besides the obvious necessity of flowing streams, three other geologic conditions were necessary to explain the origin of Twin Cities’ area waterfalls.

• The area’s soil and sediment cover is thin enough that streams cut down through the unconsolidated surface sediment to flow across the solid rock (bedrock) beneath. Streams that flow across bedrock are influenced by the rock’s composition and texture. In contrast, streams that only flow through unconsolidated sediment cannot form waterfalls.

Figure 5. These photos show two of the many waterfalls in the Twin Cities area. On the left is Bridal Veil Falls, just south of the Minneapolis campus. On the right is Minnehaha Falls on Minnehaha Creek, a small tributary of the Mississippi River. At both these falls, as at Saint Anthony Falls, the Platteville Formation forms the waterfalls’ resistant ledge, overlying the more easily eroded St. Peter Sandstone.

Figure 6. A schematic view of the bedrock geology covering much of the Twin Cities area. The Glenwood Formation is less than a meter thick so it only plays a limited role in the formation of the area’s many waterfalls.

At first glance it appears as if the sandstone is only being eroded from beneath the waterfall itself. At Saint Anthony Falls though, most of the sandstone was excavated by water moving down vertical fractures through the Platteville, well behind the waterfall’s edge.

(Figure from ‘Minnesota’s Geology’, by Ojakangas & Matsch, 1982)

Lab C - 5 • Through much of the Twin Cities area two rock units, the Platteville Formation and underlying St. Peter Sandstone, dominate the surface bedrock (Figs. 5 & 6). A carbonate unit, the Platteville is composed of rock layers that are physically stronger than the weakly cemented St. Peter Sandstone. When a hard rock unit overlies a more easily eroded unit, the setting favors waterfall development. As streams cut through the resistant rock, they can quickly erode the underlying weaker rock to create waterfalls.

• Although often overlooked, even by geologists, the surfaces that bound and subdivide rock units are often as important as their host rock. The Platteville Formation is cut by intersecting sets of fractures that break the rock layers up into a mosaic of fitted blocks (Fig. 7). These fractures not only reduce the rock unit’s physical integrity, but they provide flowing water access to the underlying St. Peter Sandstone. As the sandstone is eroded and excavated by water flowing down fractures through the Platteville, whole blocks of Platteville rock are undercut at the waterfall’s edge. So a waterfall retreats upstream through time. In the case of the Twin Cities area waterfalls, this retreat did not take place as a slow, continuous, millimeter-by-millimeter retreat. Instead it occurred by leaps measured in meters, as undercut Platteville blocks episodically broke loose to collapse into the downstream channel.

Figure 7. Vertical fractures through the Platteville Formation as seen in cross-section and map views. A vertical line on the boy’s right marks a fracture in the river bluff above. The boy rests his back on one of two vertical faces that formed as a large block broke off along fracture planes. The exposed surface of the Mississippi River above Saint Anthony Falls is shown on the right, when river water was diverted to allow repairs to the falls’ edge. Fractures appear as a mosaic of cracks in the rock surface, while the loose polygonal blocks were separated from this broken surface by water rushing over the falls.

Lab C - 6 Exercise A – Maps & Rocks

Look at the anaglyph map of the Twin Cities area, being sure to wear the glasses properly for your view of the map. Remember to only view the map from the bottom or top, not from the two sides.

Even a brief inspection of the Mississippi River valley in the Twin Cities area reveals that the valley has three distinct segments. North of Saint Anthony Falls, the river flows across a gentle surface, with low banks on both sides of the stream. At the falls, the Mississippi drops down into a narrow gorge lined by steep bluffs. Eight and a half miles south, at Fort Snelling, this narrow gorge joins the much wider, bluff-lined valley of the Minnesota River. The Mississippi then flows down this larger valley, past downtown Saint Paul where it turns to the south. Although this larger valley dwarfs the narrow gorge between Fort Snelling and Saint Anthony Falls, the surrounding landscape hold clues that the river valley in this area was once even larger than it is now. How did this three-stage river valley come about? Somewhat surprisingly, its origin did not arise within the valley itself, but far to the west in the history of an immense, now-vanished glacial lake.

Nearly 21,000 years ago, a vast ice sheet covered most of Canada and extended down across the northern half of Minnesota. As the climate warmed, this ice sheet started to melt, releasing huge amounts of water. In the area now known as the Red River Valley, this released melt water could not drain away. Ice still remained to the north, blocking the valley’s natural drainage to Hudson Bay, so the melt water simply pooled up in front of the ice sheet to form an immense glacial lake called Lake Agassiz (Figure 8). As the lake level rose, it eventually found an outlet to the southeast. Erosion quickly enlarged this outlet to allow the lake water to catastrophically flood down a large glacial valley and carve what we now call the Minnesota River Valley.

Figure 8. The gray shading indicates areas that were, at one time or another, part of Glacial Lake Agassiz. Black areas highlight large lakes that still remain in parts of what was once the Glacial Lake Agassiz basin.

At the time Glacial Lake Agassiz formed, vast ice sheets still lay to the north of the gray area, blocking the area’s natural drainage into Hudson Bay. Hence the lake rose until it found an outlet to the south, down the present Minnesota River Valley.

(Figure from ‘Minnesota’s Geology’ by Ojakangas & Matsch, 1982)

Because this glacial river’ flow was so much larger than the present Minnesota River, geologists refer to it by a different name as Glacial River Warren. The floodwaters of Glacial River Warren quickly scoured through surface deposits and underlying soft bedrock to carve a channel down to the more resistant Platteville rock layer. It then flowed across the Platteville until it reached the downtown St. Paul area. There the

Lab C - 7 river intersected the path of an ancient sediment-filled river channel. Although long gone and its channel filled by sediment, this previous stream had managed to cut through the Platteville rock. Consequently as Glacial River Warren’s floodwaters reached the previous stream’s sediment-filled channel the flowing water quickly removed the older channel’s sediment fill, exposing the edge of the Platteville rock and creating an immense waterfall. With its rushing Glacial River Warren flow this waterfall rapidly retreated upstream, incising a deeper gorge and abandoning part of its older channel floor as a perched flat surface where downtown St. Paul sits today. When this receding waterfall reached the area where Fort Snelling now stands, a smaller waterfall broke off from the main cataract. This smaller waterfall slowly retreated north leaving a narrow, bluff-lined gorge in its wake until it arrived at its present position and came to be known as Saint Anthony Falls.

What happened to the rest of the Glacial River Warren waterfall? As it retreated up the present Minnesota River Valley, it quickly reached the edge of the Platteville rock unit. Without a resistant rock layer to form a waterfall, the cataract ceased to exist. The river also changed, as the remaining ice sheets melted to allow water in the Red River Valley area to flow north into Hudson Bay. Lake Aggasiz drained away, eliminating most of the Glacial River Warren’s water supply. Without Lake Aggasiz as a source, Glacial River Warren decreased in size and flow to become a much smaller stream, the present Minnesota River.

Classroom Activity 2: Modeling a Waterfall

Rock samples:

Start by comparing the rock samples of the Platteville Formation and St. Peter Sandstone to one another. There are no samples of the Glenwood Shale as the shale is simply weakly compressed mud that, if handled, quickly becomes a muddy mess.

Constructing a waterfall:

Then use the Plexiglas tank, sand and tiles to model the retreat of Saint Anthony Falls. A laminated guide should be in the lab room that outlines the model’s construction. Once your waterfall has retreated though, do not dismantle the model until after you have completed all of the questions for Exercise A and compared your model to the Twin Cities’ area map.

Modeling a waterfall’s behavior:

As you start the flow of water, carefully watch how the sand is eroded and the edge of the waterfall retreats. Does the whole edge retreat uniformly? Does the water only remove the sand from the front of the waterfall’s vertical face or does water flow down spaces between the tiles to erode the sand from behind? In the case of Saint Anthony Falls, most erosion of the St. Peter Sandstone and subsequent waterfall retreat actually occurred as a result of water flowing down Platteville fractures well upstream of the waterfall, not at the waterfall’s edge.

Lab C - 8 Name ______

Lab C - Exercise A (4 points)

Question 1 Look at the samples of Saint Peter Sandstone and Platteville Formation, noting their relative hardness. While the Saint Peter Sandstone originally formed as beach and coastal sands deposited along the shores of a tropical sea, the Platteville Formation formed from carbonate sediment deposited on a shallow seafloor. The Platteville was originally limestone but, after its burial, magnesium-rich fluids moved through the rock altering it to dolostone and destroying much of the rock’s original texture. Despite this loss of texture, what features still exist that suggest the rock originally formed in a marine setting?

Question 2 Which part of Saint Anthony Falls’ natural waterfall system does each part of the physical model represent?

Ceramic Tiles –

White Sand –

Boundaries between Tiles –

Question 3 If the order of bedrock units in the Twin Cities area were reversed so the St. Peter Sandstone lay on top of the Platteville Formation rather than underneath it, would waterfalls still be likely to occur? Briefly explain the reasoning behind your answer.

(This page should be turned in as part of the submitted lab materials.)

Lab C - 9 Question 4 If the Platteville Formation lacked fractures, could waterfalls still form? If not, then briefly explain why waterfalls could not form. If they could still form, then briefly explain how their behavior would differ from that of the present waterfalls.

Looking at the model again, did the whole edge of the waterfall recede uniformly or did the waterfall incise a channel along one side of the model, leaving a flat tiled area along the other side as a perched abandoned river channel? If it did retreat uniformly, then imagine what a perched surface might look like. Then examine the anaglyph map of the Twin Cities area, looking for surface features that might represent an abandoned perched river channel surface.

Question 5 Annotate the black and white copy of the map on Lab C Handout 1 to show the probable boundary of the Glacial River Warren channel prior to its waterfall’s retreat. (You might want to annotate the map in pencil first before using markers to highlight your final interpretation.)

Assuming that pens are available, use: Blue to draw in the path of the present Minnesota and Mississippi Rivers; Blacklack to outline the edges of the deeper gorge that was cut by the waterfall retreat; Green to outline the boundaries of the original Glacial River Warren valley before the waterfall cut a deeper narrower gorge. Realize that some of the green and black boundaries will coincide through parts of the area.

(This page should be turned in as part of the submitted lab materials along with your copy of Lab C Handout 1.)

Lab C - 10 Part B. Calculating the Retreat of a Migrating Waterfall

In 1878, Horace Winchell, Minnesota’s first State Geologist, published one of the earliest quantitative estimates of the timing of the last ice age. Although others had proposed the idea earlier, Winchell was the first to compile a detailed analysis of Saint Anthony Falls’ historic retreat, and extrapolate the observed rates back in time to determine when Saint Anthony Falls first split off from Glacial River Warren’s larger waterfall. Winchell was working at a time when most geologists adhered to a rather strict version of Uniformitarianism, the idea that present and past processes were very similar. Although this basic idea is still used, this older stricter interpretation of Uniformitarianism assumed that not only were past processes the same as present processes but that the rates at which they occur have been constant through time. We now know that rates have varied, but in Winchell’s time the idea of extrapolating present rates into the past seemed well founded.

Winchell based his estimates of the fall’s retreat on a variety of reports dating back to the first historical account of the waterfall made by Father Hennepin in 1680. Only a few of the reports included actual measurements of the Fall’s locations, so for the early records Winchell often had to estimate the Falls’ position based from written descriptions. After the start of milling operations at Saint Anthony Falls there were far more accurate measurements to work from, including carefully surveyed maps.

So what? Why was Winchell’s estimate of waterfall retreat considered to be of any importance at the time? Only nineteen years earlier, Charles Darwin had published the Origin of Species, and in the decade that followed, the question of the Earth’s age became of paramount interest to both sides of the debate over evolution. At the time almost all naturalists accepted that the Earth was very old, but how old? It would be almost a century before radioactive decay rates would provide a chronology for Earth events, so in Winchell’s time there was no way to calculate the age of past events in years. If correct, Winchell’s estimate of waterfall retreat would provide a minimum estimate for how much time had elapsed since the most recent ice sheets began to recede. This was one of the first attempts to date a specific past geological event with any accuracy. So let’s see how well he fared…

Exercise B – Establishing a Time Line for a Waterfall’s Retreat

Use the large aerial photograph of Saint Anthony Falls that shows Winchell’s compilation of the waterfalls’ retreat to complete Exercise B. Along each line of the waterfalls’ historic positions selected points are circled for use in calculating the average, minimum, and maximum rates of waterfall retreat.

Use these to reproduce Winchell’s estimates of Waterfall retreat (Exercise B). Exercise C will then follow the evolution of this idea as additional information was recognized that altered Winchell’s original estimate.

Lab C - 11 Lab C - 12 Name ______Lab C - Exercise B (4 points)

Question 6 Calculate the rate of the waterfalls’ retreat from the time that Father Hennepin first described it in 1680 until the Army Corps of Engineers stabilized it in its present position (shown by the 1870 line on the map).

• Measure the distance between the average point of the 1680 line and the average point of the 1870 waterfall edge. Record this distance in Table 1 on the next page.

• Then divide that distance by the number of years between the two fronts. This will be the average distance the waterfall retreated each year during this time interval. Record this average rate of waterfall retreat in Table 1. With all the possible errors involved in measuring the distances, just round your rate off to the nearest half-foot per year.

• If Saint Anthony Falls had retreated at this same rate all the way from Fort Snelling eight and a half miles to the south, how long would it have taken for the waterfall to retreat to its present position? Record your answer in Table 1, again rounding it off (to the nearest 500 years).

(Although 8.5 miles equals 44,880’, use 45,000’ as an average distance between Saint Anthony Falls and the Fort Snelling junction. Do not worry about the minor differences between waterfall positions in making your calculations of the total time interval of waterfall retreat.)

Question 7 A closer look at Winchell’s map suggests that the rate of waterfall retreat was not constant, but varied through time, speeding up as the waterfall moved towards the edge of the Platteville rock. Winchell and other geologists of his time attributed the increased rate of retreat to the thinning of the Platteville Formation as the waterfall approached the edge of the rock unit. Their idea was that with a thinned carbonate capping layer, water could more easily make its way down fractures to erode the underlying sandstone. Using the selected average points, calculate the rate of the waterfall retreat during the periods from 1680 to 1766, from 1766 to 1856, and from 1856 to 1870.

For the earlier two intervals, also use the selected minimum and maximum points for each interval to fill out the remainder of Table 1.

Question 8 Based on your measurements and calculations above, what are the minimum and maximum estimates for the amount of time it would take Saint Anthony Falls to retreat from the Fort Snelling area to downtown Minneapolis based on its historic retreat rates? (In other words, choose the slowest and quickest rates you calculated for Table 1 and record them in the space below Table 1.)

(This page should be turned in as part of the submitted lab materials.)

Lab C - 13 Table 1 – Calculation of waterfall retreat rates from Fort Snelling area.

If the falls had retreated at this rate, Distance Distance Distance R ate of waterfall retreat in feet/year. how long would it have taken the falls to retreat between between between from Fort Snelling to their current position?* Time Period selected selected (rounded off to the nearest 0.5’/yr) minimum average maximum (round time off to the nearest 500 years) points. points. points. Minimum Average Maximum Minimum Average Maximum

1680 – 1766 (86 years)

1766 – 1856 (90 years)

1856 – 1870 NA NA NA NA NA NA (14 years)

Inclusive: 1680 – 1870 NA NA NA NA NA NA (190 years)

* For the purposes of this exercise, ignore the small difference between waterfall positions when calculating the total time interval for the retreat from Fort Snelling and use 45,000 (~8.5 miles) as the distance for all your calculations of the time interval of retreat.

Taking all of the above into account what is the:

Minimum estimate of the amount of time needed for Saint Anthony Falls to retreat from the Fort Snelling area to its present position: ______

Maximum estimate of the amount of time needed for Saint Anthony Falls to retreat from the Fort Snelling area to its present position: ______

Obviously this is quite a range, so lets see how it changes as more data emerged (move on to Exercise C).

(This page should be turned in as part of the submitted lab materials.)

Lab C - 14 Part C: Re-interpreting a Waterfall’s Retreat

Reinterpretation 1:

Unrecognized by Winchell and his contemporaries, a non-geologic factor may have been responsible for Saint Anthony Falls’ accelerated rate of retreat. Starting in the 1840’s, lumbering operations north of the Twin Cities area began to send countless logs floating downstream to Saint Anthony Falls’ sawmills. Many of these logs escaped the mills to cascade over the falls. As they tumbled over the falls, these logs caught in crevasses along the front of the falls and acted as giant levers to pry rock blocks off the falls’ face (Figure 9). Hence lumbering operations ended up threatening the very falls the logging industry relied upon.

At the time, hardly anyone realized how greatly human activities could affect natural processes. So although the phenomena was observed at the time and reported in the general news (see article text below) Winchell did not recognize the tie between logging operations and the accelerated rate of waterfall retreat.

Falls Of Saint Anthony: It has been ascertained by actual measure -- that within the two last years the Falls of St. Anthony on the east side have receded eighty feet. The water of the Mississippi has been unusually high during these two years, and the thousands of pine logs which have descended the falls, have assisted the water materially in prying over the immense rocks over which the water leaps. As the logs plunge over, the ends are driven deep into the fissures of rock and serve as levers, the water and other logs being the weights, thus wrenching them from their beds to be rolled and tumbled and ground to atoms in the mad rushing torrent below. It is said that the water has already in places worn entirely through the limestone and is working on the sandstone beneath.

Text of article published in The Dakota Friend, G.H. Pond, Editor, St. Paul, Minnesota Territory, February 1, 1852.

Figure 9. Photograph of Saint Anthony Falls showing logs at the falls’ edge. At the time, relatively few people realized the extent to which human activities affected geological processes, Consequently, Winchell never recognized that logs tumbling over the falls may have been responsible for an increased rate of waterfall retreat.

(Minnesota Historical Society photographs)

Lab C - 15 Exercise C – Reinterpreting a Waterfall’s Retreat

Use the information above and below to reinterpret Winchell’s estimate for the time frame of Saint Anthony Falls’ retreat.

Answer Question 9 of Exercise C

Reinterpretation 2:

In 1938, sixty years after Winchell published his estimate of St. Anthony Falls’ retreat, the discovery of the skeleton of a giant beaver, Castoriodes ohioenesis, at Hidden Falls provided an indirect check of his estimate’s accuracy. The beaver’s skeleton is still on display in the Science Museum of Minnesota. Since a falling block of Platteville Limestone killed the beaver, Saint Anthony Falls must have passed the Hidden Falls’ area by, or before, the beaver’s death.

How do we know when the beaver died? Every living creature incorporates some radioactive carbon in its body tissues, including bones. The ratio of radioactive and non-radioactive carbon in its tissues reflects the ratio of radioactive and non- radioactive carbon in the atmosphere. However, once an organism dies the ratio of radioactive carbon to non-radioactive carbon in its body decreases as the radioactive carbon decays without being replenished. Hence the ratio of radioactive to non- radioactive carbon in an organism’s remains can be used to measure the time since the organism’s death, but only up to a point. After 70,000 years, so little radiocarbon remains that it cannot be accurately measured.

In the case of our unlucky giant beaver, radiocarbon dating of its skeleton yields a date of 10,230 radiocarbon years.

Answer Question 10 of Exercise C

Reinterpretation 3:

In the decades since the beaver skeleton was originally radiocarbon dated, scientists have recognized that although the rate at which radioactive C-14 decays does not change, the ratio of radioactive carbon to non-radioactive carbon in the atmosphere has changed slightly through time. This means that radiocarbon years and calendar years do not have the same duration, and that the length of radiocarbon years has varied slightly through time.

Use Graph 1 to recalibrate the beaver skeleton’s radiocarbon date to estimate its age in calendar years.

Answer Question 11 of Exercise C

Lab C - 16 Name ______Lab C - Exercise C (3 points)

Do NOT try to answer these questions without also going through the supporting text on pages 15 and 16.

Question 9 How does the realization that logging operations may have accelerated the rate of waterfall retreat change your interpretation of the estimates calculated in Exercise B? Since large scale logging operations started at the falls around 1840, which of the four time periods used in Table 1 is the only one NOT affected by logging activities that increased the rate of waterfall retreat?

a) 1680-1766 b) 1766-1856 c) 1856-1870 d) 1680-1870 (inclusive)

With this in mind, which of the rates (feet/year) you calculated for Table 1 are probably the best estimates for Saint Anthony Falls’ natural rate of retreat?

Minimum Rate ______Average Rate ______Maximum Rate ______

Question 10 Using the rates of waterfall retreat you choose in Question 9, how long would it have taken for Saint Anthony Falls to retreat the 39,500 feet from the site of Hidden Falls to its location when Father Hennepin visited the falls?

Number of Years for waterfall to retreat the 39,500 feet from site of beaver’s death to the falls present position based on:

Minumum rate of retreat ______years

Average rate of retreat ______years

Maximum rate of retreat ______years

Which of the above best matches the original estimate of 10,230 years for the beaver’s death? (Circle your answer above.) Even Winchell realized that his estimate of the timing was at best only a rough estimate; so do not expect an exact match.

Question 11 We now know that radiocarbon years are not exactly the same as true calendar years. So using Graph 1 on the following page, what is the beaver skeleton’s age in calendar years rather than radiocarbon years? ______calendar years

(This page should be turned in as part of the submitted lab materials.)

Lab C - 17 Question 12 Taking your answer to Question 11 into account, which of the rate and time estimates from Questions 9 and 10 are most likely to best reflect the actual rate and time frame of Saint Anthony Falls’ retreat from the Fort Snelling area to downtown Minneapolis?

Rate of waterfall retreat: ______feet/year

Total time interval for retreat of falls: ______years

Chart 1.

Corrected Radiocarbon Dates

16000

15500

15000

14500

14000

13500

13000

12500

12000

11500

11000

Radiocarbon Years 10500

10000

9500

9000

8500

8000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 19000 20000 Calendar Years

Use this chart to recalibrate the beaver skeleton’s age from radiocarbon years to calendar years. To do this, find the beaver’s age in radiocarbon years along the chart’s vertical scale, move horizontally over to the plotted slope and then drop down to the horizontal scale to find the equivalent age in calendar years.

(This page should be turned in as part of the submitted lab materials.)

Lab C - 18 Part D: The End of a Natural Waterfall

As the city’s milling operations expanded, the platforms built over the falls did not provide enough space for every business that wanted access to the falls’ waterpower, so tunnels and chutes were excavated to divert water from the natural channel into artificial runs along both banks that could power riverbank mills. Eventually the greed for even more waterpower precipitated a crisis that jeopardized the existence of the falls themselves. In 1869, a tunnel was dug beneath the river channel to tap into the upstream channel to provide waterpower for a new mill. Named the Eastman tunnel after one of its owners, the tunnel was dug upstream to take advantage of the height difference an upstream inlet provided (Figure 11). Unfortunately, the Platteville Formation ends less than twelve hundred feet upstream of Saint Anthony Falls. As this tunnel neared the Platteville’s thinning edge, water began to flood in along fractures in its roof. Soon the whole tunnel roof collapsed and the river flowed down into the resulting chasm. If unchecked, this breach would allow the river to bypass the falls, dealing a deathblow to Minneapolis’ milling industry and jeopardizing the regional economy. After local efforts to save the falls failed, the Army Corps of Engineers was brought in to reconstruct the falls. The Corps filled the breach at the Eastman Tunnel collapse and constructed a sloping apron for the falls itself, changing the falls from a natural cataract into an artificial slope. To guard against future erosion threatening the falls, the Corps also excavated a tunnel through the Saint Peter sandstone beneath the river upstream of Saint Anthony Falls and constructed a large underground wall as a barrier to further waterfall retreat. Minneapolis’ waterpower had been saved, but the natural cataract that captured the imagination of early Dakota and Euro-American visitors was lost.

Figure 11. Map of Saint Anthony Falls showing route of Eastman Tunnel and its collapse areas. Also shown is the location of the wall built beneath the Platteville Formation to guard against further retreat of the falls. On right is an image of the Eastman Tunnel collapse in 1869. (Minnesota Historical Society photo)

As lumbering operations declined, flourmills took the sawmills’ place in the regional economy and Minneapolis became the largest milling center in North America. On September 5, 1882, Saint Anthony Falls achieved another milestone as it became the site of the nation’s first commercial hydroelectric power generation.9 Saint Anthony Falls also played a pivotal role in St. Paul’s growth as a transportation center. Although the milling industry was located at the falls, Minneapolis lacked any easy way to transport goods produced at the mills. Fallen blocks from the falls’ retreat lay

9 The nation’s first generation of hydroelectric power occurred shortly before at Green Bay, Wisconsin, but was not a commercial operation.

Lab C - 19 scattered throughout the river channel making steamboat travel treacherous, while the river gorge bluffs prevented the railroad from climbing out of the river valley. At Saint Paul an older river had once cut through the river bluffs, its channel sediment now providing a gentle slope for railroads to climb from the river valley floor to the highlands above and then cross country to the milling center at Saint Anthony Falls. Indirectly both Twin Cities owed their economic well being to the falls.

Sidebar 3 – Lies at the Falls, Part 2

Minneapolis citizens’ efforts to save their falls faced many hurdles. Citizens and local businesses lacked the expertise or resources to restore the falls. Although the Army Corps of Engineers had both, involving the Corps meant overcoming a serious legal obstacle. The Corps’ involvement with the Mississippi River, as charged by Congress, was limited to improving the river’s commercial navigation. Since the falls themselves had always precluded the possibility of commercial traffic upstream of downtown Minneapolis, the Corps had no legal right to intervene in the falls’ reconstruction. To get around this, the city and Corps successfully pleaded the case that constructing a lock and dam at the falls would improve future upstream commercial navigation, even if no current traffic existed at the time. On paper it seemed like a reasonable proposition, but in reality everyone knew that any upstream commercial navigation would never justify the cost of the falls’ reconstruction. Nevertheless, the legal ploy saved the falls’ milling industries and ensured Minneapolis’ future growth.

Figure 12. Spirit Island being quarried away for building stone (about 1895).

In the foreground is a railroad spur that was built out to the island to transport the stone to shore.

(Minnesota Historical Society photograph)

Sidebar 4 - Spirit Island: An Ending

For years, Spirit Island had remained an isolated natural oasis in the midst of a bustling city. Too small to be developed, Spirit Island escaped the initial rounds of building at the falls. As the city about the falls grew though, Spirit Island held one resource that led to its destruction. The island could provide low cost building stone, without sacrificing land area that could be more valuably used for housing or industry. As the century drew to a close, a railroad bridge was built out to the island and Spirit Island, a sacred site of the Dakota, was quarried away to satisfy the demand for building stones in neighboring river bluff communities (Figure 12). Any ghostly maternal songs that may have haunted the island were finally silenced.

Lab C - 20 Name ______Lab C - Exercise D (2 points)

Question 13 Why did the Corps build their underground wall upstream of the falls, rather than at the face of the falls themselves? (Hint: consider the processes responsible for the falls retreat and how the wall might prevent these from occurring.)

Question 14 The edge of the Platteville Formation lies just upstream of the falls. If your chosen rate of waterfall retreat from Question 12 was correct, then how much longer would it have taken the falls to reach the edge of the Platteville, even if the Eastman tunnel had not hastened their demise?

Assume that the practical limit of the Platteville layer is roughly 1500’ upstream of the falls, since the waterfall system would undoubtedly collapse before reaching the final edge of the Platteville. Also recognize that your calculated answer is most likely a maximum estimate of the fall’s remaining natural lifespan, since the rate of waterfall retreat would have most likely increased as the Platteville unit became thinner close to its edge.

Based on the rate of retreat chosen in Question 12, it would have taken ______years for the falls to retreat the 1,500’ from where they presently are to the edge of the Platteville.

Another way of thinking of this is that if Euro-Americans had not come into the area until this many years later, Minneapolis would have never been built!

If time permits, you may choose to complete the Post-lab Activity in class.

(This page should be turned in as part of the submitted lab materials.)

Lab C - 21 Lab C - 22

Upon finishing the lab, submit pages 9-10, 13-14, 17-18, 21 and your copy of Lab Handout 1.

Post-Lab Activity The answers to the Post-lab questions are due at the start of the next lab. If time permits, however, they can be completed and handed in during class.

Next Pre-Lab Activity – due before the start of next lab.

Read the Pre-Lab for the next lab well ahead of time. It consists of a set of essay questions, one of which will be chosen by your instructor for you to answer as a brief (five minute) essay at the start of the next lab. There will be no time in class to prepare for this essay, so you will need to read the lab before coming to class.

For the Final Lab Quiz:

• Be able to explain the geology behind Saint Anthony Falls and how or why the falls retreated through time. Given an actual or hypothetical change in geological conditions, be able to predict that change’s probable impact on the evolution of a waterfall system.

• Be able to explain the reasoning behind Winchell’s estimate for the time it took Saint Anthony Falls to retreat from the Fort Snelling area to its present position, as well as the subsequent revisions to that estimate as new information became known.

• Be able to explain to someone who did not take this class how the evolution of present and past waterfall systems affected the history of the Twin Cities area, as well as how human activity in turn altered Saint Anthony Falls.

Lab C - 23 Lab C - 24 Name ______Post-Lab C Activity

The answers to these Post-lab questions are due at the start of the next lab. If time permits, however, they can be completed and handed in during class.

The essays can be completed on a separate sheet or on the back of this page.

Question 15 In the space below, or on a separate sheet, write a short summary essay (one to two paragraphs) covering the following points. If time is limited, this can be completed as a Post-Lab Activity. (3 points total)

15a. What would have been the impact on regional history if either Saint Anthony Falls had retreated more quickly or if Euro-Americans had not come into the region until after the falls had reached the Platteville’s limit. In other words: a) Would a city still exist at the falls and if it did, how would it differ from the present Minneapolis? b) What would have been the impact on Saint Paul if Saint Anthony Falls had ceased to exist before Euro-Americans came into the region?

15b. The lab focused on the falls’ many positive economic benefits, but what economic costs did the falls also represent? In other words, if the falls had not existed, which areas in the Twin Cities area or surrounding region might have seen an economic benefit that did not materialize because of the falls? (Hint: Think of who might have benefited in terms of regional commerce and transportation, even if these benefits were minimal compared to the falls historic contribution to the regional economy.)

Lab C - 25

Lab C - 26 Study Guide – GEO 1001 Lab Final

The final lab quiz will cover topics from Labs 7, A, B & C. Unless your lab instructor indicates others, the quiz should start at the beginning of the lab period. Topics below may be covered on the final quiz.

Lab 7 – Campus Tour (The Geology of the East Bank’s Bluffs & Buildings):

• Given a sample or image of a building stone, be able to identify which type of rock is present. Also be able to construct a logical geologic history for the rock, including the environment or plate tectonic setting in which the rock most likely formed, as well as its burial and subsequent history up to the time the rock was quarried to be used as building stone.

Lab A –The Upper Midwest’s Glacial Legacy:

• Given an image of an area, be able to interpret whether glacial or non-glacial processes were primarily responsible for the present land surface. Describe any features that support your interpretation and explain how these features formed.

• Given an image of a glacially impacted area, be able to identify and describe the origin of any glacial features present. Using the glacial features present be able to create a reasonable interpretation of past glacial movement through the area.

• Be able to explain to someone who did not take this class how the glacial history of the Upper Midwest led to the development of the region’s pine-dominated forests and rich valley soils, as well as the different ways in which the region’s historic cultures viewed and used these glacial legacies.

Lab B – A River Through Time (Managing the Upper Mississippi River):

• Be able to explain how the Corps’ attempts at channel constriction and lock/dam construction differed from one another in their approach to creating a deeper, more navigable river channel.

• Be able to explain the role wetlands play in river systems and how the Corps’ river management schemes (channel constriction, lock/dam construction, and channelization) affected the river valley system, including wetland areas.

• Given an image of part of a river system, be able to choose appropriate sites for wing dams and riprap construction to force the river to cut a deeper, more continuous channel by means of channel constriction.

Lab C – In the Wake of a Waterfall (The Geology Behind the Founding of Minneapolis & St. Paul):

• Be able to explain the geology behind Saint Anthony Falls and how or why the falls retreated through time. Given an actual or hypothetical change in geological conditions, be able to predict that change’s probable impact on the evolution of a waterfall system.

• Be able to explain the reasoning behind Winchell’s estimate for the time it took Saint Anthony Falls to retreat from the Fort Snelling area to its present position, as well as the subsequent revisions to that estimate as new information became known.

• Be able to explain to someone who did not take this class how the evolution of present and past waterfall systems affected the history of the Twin Cities area, as well as how human activity in turn altered Saint Anthony Falls.