The Rocky Mountains rising up and the Grand Canyon cutting down through the Colorado Plateau seem like opposing processes: one builds, the other excavates. In reality they are two sides of the same phenomenon, because all relief results from a permanent tug-of-war between forces that uplift and forces that wear away.
Relief: a balance between internal and external processes
When we look at a mountain range, we see rugged peaks thousands of meters high alongside deep ravines and slopes covered in fallen blocks, like the Rocky Mountains. What forces are capable of lifting millions of tons of rock up to the clouds while the atmosphere and water relentlessly try to break them down?
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Name four external geological agents that shape the landscape and give an example of a landform created by each one.
Name four external geological agents that shape the landscape and give an example of a landform created by each one.
Two regions with the same climate have very different landscapes because one consists of limestone rock and the other of granite. Explain how lithology (rock type)…
Two regions with the same climate have very different landscapes because one consists of limestone rock and the other of granite. Explain how lithology (rock type) influences landform development and what characteristic relief limestone typically creates.
In Yosemite Valley we find a wide, flat-bottomed valley with sheer walls, while in other parts of the Rockies rivers run through narrow canyons where there is barely room for the channel. Why do two agents shaping the same mountain produce such radically different valley forms?
Erosion, transport and deposition
Shaping happens in order: erosion wears material away, transport carries it (water, ice, wind or gravity), and deposition drops it where the agent loses energy, building deltas, dunes and moraines. Four external agents: water (river canyons), ice (U-shaped valleys), wind (dunes) and gravity (landslides).
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State whether these landforms were mainly shaped by water, ice, or wind: a U-shaped valley, a dune, a river canyon, and a moraine.
State whether these landforms were mainly shaped by water, ice, or wind: a U-shaped valley, a dune, a river canyon, and a moraine.
The value of relief: scientific, scenic and economic
Every use of relief also carries a risk. Farming in a fertile valley risks flooding and soil erosion. Geotourism can damage trails and fragile rock formations through overuse. Quarrying leaves unstable slopes.
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Relief is also a resource. Describe two economic uses of relief (for example, tourism or agriculture) and a risk associated with each.
Relief is also a resource. Describe two economic uses of relief (for example, tourism or agriculture) and a risk associated with each.
Relief of the United States and managing it sustainably
If you drive west from Chicago to California, you cross the flat Great Plains, climb the Rocky Mountains, and cross deserts before reaching the Sierra Nevada. Why does the relief of one country change so much?
Summary
Biodiversity: why it matters
Biodiversity is the variety of life at three levels: genes, species and ecosystems. It matters because it gives us food, clean water and pollination, and because a varied ecosystem is more stable: if one species declines, others can fill its role. Main threats: habitat loss, invasive species (like kudzu or Burmese pythons in the Everglades), overharvesting and pollution. Losing a species can disrupt a food web, because energy no longer flows the same way between producers and consumers. Conserving it means protecting habitats, as in national parks and wildlife refuges.
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Look at the cross-sectional profiles of the two valleys in the diagram, marked with ?. Identify which is a river valley and which is a glacial valley, explain which…
Look at the cross-sectional profiles of the two valleys in the diagram, marked with ?. Identify which is a river valley and which is a glacial valley, explain which agent shaped each one, and what differences in shape allow them to be distinguished.