Chapter 2: North America S Environmental Setting

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Chapter 2: North America’s Environmental Setting

Overview

Chapter 2 will likely be one of the most difficult chapters for students to fully comprehend, unless they have taken coursework in physical geography. Many students may be unfamiliar with the basic physical processes that shape North America’s landscapes. A helpful way to approach teaching Chapter 2 is to think of this as an opportunity to introduce them to these basic processes, using examples from North America. This will give students a broad overview that can form the basis for in-depth coverage of these processes and patterns in the regional chapters.

Outline

Landforms, Hydrology, Soils
Landforms and Geomorphic Processes in North America
Hydrologic Patterns
North America’s Physiographic Provinces
Weather and Climate
North American Climate Zones
Biogeography and Ecology
Forests
Tundra
Grasslands and Steppes
Deserts and Steppes
Mediterranean Scrub
Subtropical Wetland
Ecosystems and Watersheds
Conclusion

Student Learning Outcomes

Explain the difference between physical geography and human geography.
Identify the major geomorphic processes that shaped the Appalachian Mountains as compared to the Rocky Mountains through time.
List and describe North America’s 12 major physiographic provinces.
Compare and contrast a shield volcano and a composite cone volcano in North America.
Distinguish between an ecosystem and a biome.
Explain why environmental planners often prefer to use a map showing an area’s watershed instead of a map based on political boundaries.
List and discuss the impacts of four climate controls on weather and climate in North America.
Compare and contrast the different kinds of landforms created by continental glaciers as compared to alpine glaciers.
Differentiate between North America’s five major river drainage systems according to the general direction of their flow outward to the sea.
Describe the major temperature and moisture properties of a Polar continental air mass and a Tropical maritime air mass.
Differentiate between North America’s Mediterranean, Continental Midlatitude, and West Coast Marine climate zones.
Explain why a comparison of maps showing (1) general climate zones, (2) landforms, (3) soil types, and (4) vegetation biomes may prove useful for geographic analysis.

Teaching Strategies for Chapter 2: North America’s Environmental Setting

1. Human versus Physical Geography

Since many students will be unfamiliar with the discipline of geography, Chapter 2 provides an opportunity to introduce them to geography’s subdisciplines. When explaining the differences between human geography and physical geography, it is important to emphasize the ways that the physical and cultural landscapes interact. The physical landscape has had significant impacts on people’s settlement patterns and activities, so understanding the dynamics of the physical landscape allows us to make sense of settlement patterns and the distribution of economic activities. An obvious example of this can be seen in the distribution of the major cities of North America. Almost all large cities in North America are located near a port or on a major waterway. Although people are less likely to travel by boat than they were in previous centuries, even today shipping of goods is still a major part of North America’s political economy.

Human activities have also had a major impact on the physical landscapes of North America. We can see this impact in the way that humans have reworked the land through our economic activities: logging, mining, and agriculture, which have produced environmental problems such as habitat destruction and pollution. In some parts of North America, hydrologic systems have also been reworked through damming, draining, and canal building.

2. Landforms and Geomorphic Processes in North America

An easy way to approach teaching basic geomorphic processes is to split them into two groups: mountain-building processes and processes of erosion and deposition. Mountain building happens through a variety of tectonic processes such as the movement of tectonic plates and volcanism. Today the most tectonically active part of North America is the far western coastal portion of the continent. Fault lines extend from California to Alaska, where the North American plate is rubbing up against Juan De Fuca Plate and the Pacific Plate. The U.S. Geological Survey Earthquake Hazards program website (http://earthquake.usgs.gov/) is a great place to look for additional information on tectonic processes, including animated graphics, photos, and Google Earth files.

Most of North America’s active volcanoes are located near this tectonically active zone as well. The Cascade Range in the Pacific Northwest includes some active volcanoes, such as Mount St. Helens, which erupted in 1980 and again in 2004. However, two of the most famous areas of volcanism in North America are associated with hot spots in the mantle. Both the Yellowstone caldera and the Hawaiian Islands are being formed by hotspots. Composite cone volcanoes such as those in the Cascades erupt explosively, shooting out pyroclastic debris and poisonous gases. The 1980 eruption of Mount St. Helens killed 57 people in the blast zone. In contrast, shield volcanoes, such as the Hawaiian volcanoes, produce a less viscose type of lava that is able to flow across the landscape. Shield volcanoes are generally much less dangerous because their eruptions are considerably less violent, although active lava flows do sometimes destroy homes and property.

Much of North America has been shaped by glaciation. Glacial activity produces a number of distinctive landforms. There are two different types of glaciation: continental glaciers and alpine glaciers. Continental glaciers covered virtually all of what is now Canada and much of the Great Lakes region and New England during the last ice age. These continental glaciers carved out the basins of the Great Lakes and left much of this region scraped to the bedrock. In some places continental glaciers deposited sediments in distinctive patterns called drumlins and moraines.

While continental glaciers have virtually disappeared from the North American continent, alpine glaciers still exist, particularly in the Rocky Mountains and the Cascades. These alpine glaciers form dramatic landscape features such as horns, arêtes, tarns, and cirques. The best way to fix these features in students’ minds is to show contrasting photos of landscapes shaped by glacial ice versus those shaped by fluvial processes. In particular, the difference between V-shaped river valleys and U-shaped glacial valleys is easy to visually distinguish. Additionally, arêtes and horns formed by glaciers are distinctively thin, sharp peaks when viewed in contrast to mountain tops shaped by rainfall and fluvial processes. This can be easily seen by contrasting the much weathered forms of the Appalachians with the glacial peaks of the Rockies. The website Teaching Geomorphology in the 21st Century (http://serc.carleton.edu/NAGTWorkshops/geomorph/index.html) has a large number of resources related to teaching geomorphic processes. With regard to glacial processes and climate change, there are a number of Google Earth files showing glacial changes over the last 50 years.

Another easy contrast to make is between coastlines mainly shaped by erosional processes versus depositional processes. In general, eroded coastlines can be seen on the Pacific Coast of North America and depositional coastlines along the Atlantic Coast. Photos of narrow erosional coastlines with features such as sea cliffs, wave-cut platforms, and sea stacks can be contrasted with the wide beaches, spits, bay barriers, and lagoons of the East Coast.

3. Hydrologic Patterns

Understanding North America’s major drainage systems and continental divides will help students make sense of settlement and transportation patterns. Relating drainage and transportation systems will help students remember the patterns of both. For example, the Mississippi–Missouri Basin served as a major transportation system for much of the central United States. The Great Lakes–St. Lawrence system provided a transportation network for settlement and trade in Quebec and the Great Lakes region. With the building of the Erie Canal, the Great Lakes became connected to the East Coast. Similarly, the Illinois and Michigan Canal was built near Chicago to form a navigable link between the Great Lakes and the Mississippi drainage. This linkage was a key factor in the development of Chicago as a regional trading hub, promoting the city’s growth beyond that of others in the region.

Some drainage patterns can be easily associated with major mountain ranges that form continental divides. East of the Appalachians, river systems flow into the Atlantic, and west of the Sierras and Cascades, major river systems flow into the Pacific. Between the Rockies and the Appalachians, the great Mississippi–Missouri Basin drains into the Gulf of Mexico. A portion of the region in between the Sierras and the Rockies forms the Great Basin, a large internal drainage system. If students can associate the relationships between the major mountain ranges and the drainage (or early transportation) patterns, they will have a better grasp of the basic geography of North America.

4. North America’s Physiographic Provinces

North America’s landform regions (or physiographic provinces) can be seen in Figure 1.9. These landform regions give students an understanding of the physical context of the regional divisions discussed in the following regional chapters. A physiographic province is defined by its geomorphic features and underlying structural elements. So, for example, both the Appalachian and Rocky Mountains form their own physiographic provinces.

It should be noted that map reading and interpretation is a cognitive skill that is better developed in some people than others. One way to help students develop these skills is to give them an exercise that asks them to read a map and translate the features on the map into a journey. So, for example, the exercise might ask them to list the major physical features or physiographic provinces they would encounter during a journey from New York to San Francisco. They would be expected to list them in the order they would be encountered. Of course, what the students list would depend on the level of detail on the map and the exact route they choose. It may seem like this is a rather easy task, but this type of exercise helps students develop their mental map of the region.

5. Weather and Climate

Understanding the difference between weather and climate is key to students’ comprehension of climate change and its impacts. This difference may seem obvious, but it is important that students understand that while day-to-day variations in weather conditions are highly variable and difficult to predict, long-term patterns (climate) are much more stable and predictable. While students will be familiar with climatic variables such as temperature, atmospheric pressure, wind, and precipitation, many students will have little understanding of the physical processes that produce climatic differences.

Students will know that temperatures are generally warmer near the equator and cooler towards the poles and that temperature generally decreases at higher elevations. However, many will not have considered the differences between heating and cooling potential of land and water. Because water heats and cools more slowly than land, places near oceans tend to have less temperature variations than places further inland. Another important concept that many students struggle with is the relationship between topography and precipitation patterns. Understanding orographic precipitation and rain shadows will help students make educated guesses about differences in precipitation across the region. Students should know that the windward sides of mountain ranges generally get large amounts of orographic precipitation and that the leeward sides get very little precipitation because of the rain shadow effect. Since westerly winds move weather patterns across the continent in generally a west to east pattern, this means that in most parts of North America the western sides of mountain ranges will get significantly more precipitation than the eastern sides.

One helpful way to help students become familiar with North American climate zones and weather patterns is to teach them to read and understand climographs. In addition to the charts that are presented in Figure 2.13, you can find additional climographs online. The National Drought Mitigation Center at the University of Nebraska Lincoln has a page of climographs for many major cities in the United States(http://drought.unl.edu/DroughtBasics/WhatisClimatology/ClimographsforSelectedUSCities.aspx). Once students become familiar with the climate zones of North America, you might give them a climograph without identifying information and have them make an educated guess about what climate zone it is located in.

6. Biogeography and Ecology

Students should understand that patterns of natural vegetation are closely related to underlying soils and climate patterns. On a very basic level the presence or absence of forests can be related to moisture levels. Trees need higher levels of soil moisture during the growing season than other types of vegetation. The six major biome types can be seen in Figure 2.17. Again, particular biomes are associated with particular climate types. Once students are familiar with these biomes, they should be able to associate them with example climographs.

7. Geographic Information Systems and Ecosystem Management

The physical landscape of North America has been significantly modified since the beginning of European settlement. Today government agencies such as the U.S. EPA use management tools like geographic information systems to assist in the management of the regions’ natural resources. Rather than managing natural resources based on arbitrary political boundaries, regions based on physical geography such as the ecoregions shown in Figure 2.18 or the watersheds shown in Figure 2.5 are used.

8. Conclusion

Chapter 2 is organized around the three main subdisciplines of physical geography: geomorphology, climatology, and biogeography. Understanding the regional geomorphic, climatic, and biological patterns will set the stage for understanding how natural systems and humans have interacted in the following chapters.

Conceptual Checkpoints

2.1 Develop a presentation based on a set of comparative maps of your local region (e.g., landforms, vegetation, climate, and soils maps) that defends some of the reasons why many of the patterns shown on these maps look the same.

2.2 Develop a promotional brochure to advertise one of North America’s physiographic provinces as an appropriate site for development of a new ecotourism resort.

2.3 Speculate on some of the impacts of global climate change on a group of local indigenous residents who live in a small village located on edge of the Hudson Bay in the Canadian Arctic region.

Climate change in arctic regions has melted permafrost, producing unstable foundations for buildings and making difficult travel through wetland areas. In addition, melting ice flows have negatively impacted wildlife populations in the region, making traditional hunting more difficult.

2.4 Develop a list of recommendations for preserving the natural vegetation and streamflow patterns of an ecosystem located near your hometown that is slated for development.

Answers to Review Questions

1. How are the location patterns of earthquakes, volcanoes, and fault lines in North America related to its tectonic plate boundaries?

Fault lines generally mark the edges of tectonic plates or exist very close to these boundaries. Earthquakes most often take place near these boundaries as well. Volcanoes are often located within a few hundred miles of these boundaries and are formed as one plate is forced under the edge of another. However, volcanoes and tectonic activities are not always associated with plate boundaries; for example, the Hawaiian volcanoes and the Yellowstone caldera are both located far from plate boundaries and associated with hotspots in the Earth’s crust.

2. What have been some of the different erosional impacts of glaciers, running water, wind, and wave action on the geomorphology of the American and Canadian West?

Glaciers, water, wind, and waves are each associated with distinctive landforms. Continental glaciers scoured much of Canada and the northern United States, leaving behind distinctive hills and ridges of sediment. Alpine glaciers create sharp mountain peaks and U-shaped valleys in contrast to V-shaped valleys formed by running water. In some parts of North America wind has deposited sediment to form highly fertile but erodible soils called loess, and, in other places, wind-blown soil forms large dune complexes. The western coast of North America features many dramatic landforms shaped by wave action such as sea cliffs, wavecut platforms, and sea stacks.