Landform shaping
The walls of the Grand Canyon, the dunes at White Sands, and the U-shaped valley of Yosemite all tell the same story: over thousands of years, water, wind, or ice have been wearing away, carrying off, and depositing materials until they have shaped the landscape you see today.
The stages of landform shaping
If you hike along a summit in the Rocky Mountains, you will see large blocks of sharp-edged rock split apart beside the cliff walls, while at the mouth of the Mississippi you find only fine grains of rounded silt: how does solid rock change and travel from the mountain to the sea?
What is weathering? Give an example related to the action of frost on rocks (freeze-thaw weathering).
What is weathering? Give an example related to the action of frost on rocks (freeze-thaw weathering).
Order the stages of landscape shaping — deposition, erosion, weathering, and transport — and define each with a single sentence.
Order the stages of landscape shaping — deposition, erosion, weathering, and transport — and define each with a single sentence.
State whether each of these processes is weathering, erosion, or deposition: a rock cracks due to the action of ice; a river wears away its channel; the wind deposits…
State whether each of these processes is weathering, erosion, or deposition: a rock cracks due to the action of ice; a river wears away its channel; the wind deposits sand and forms a dune.
Weathering can also be biological. Explain what it consists of and give two examples, one related to roots and one to lichens.
Weathering can also be biological. Explain what it consists of and give two examples, one related to roots and one to lichens.
The agents of landform shaping
Match each agent with the landform it produces: a river, wind, a glacier, and the sea, with dunes, a river valley, a cliff, and a glacial cirque.
Match each agent with the landform it produces: a river, wind, a glacier, and the sea, with dunes, a river valley, a cliff, and a glacial cirque.
Match each landform with the agent that shapes it: a sea stack, a river canyon, a dune field, and a moraine, with the sea, a river, the wind, and a glacier.
Match each landform with the agent that shapes it: a sea stack, a river canyon, a dune field, and a moraine, with the sea, a river, the wind, and a glacier.
The biosphere also shapes landforms. Explain two examples: the action of tree roots on rocks and the building of reefs by corals.
The biosphere also shapes landforms. Explain two examples: the action of tree roots on rocks and the building of reefs by corals.
A glacier drags blocks of rock along its base and deposits them as it melts, forming moraines. Explain how the same agent carries out erosion, transport, and deposition…
A glacier drags blocks of rock along its base and deposits them as it melts, forming moraines. Explain how the same agent carries out erosion, transport, and deposition at the same time.
The river, from mountain to sea
Near its source in the Rockies, a river is a fast torrent that smashes boulders along its bed, but near its mouth the lower Mississippi flows slowly, wide and muddy over a bed of silt: why do the behavior and force of the water change so much along a river's course?
Explain the difference between erosion and transport using the work of a river as an example.
Explain the difference between erosion and transport using the work of a river as an example.
The diagram shows a river from its source in the mountains to its mouth at the sea. State in which of the labeled zones (A, B, or C) erosion, transport, and deposition…
The diagram shows a river from its source in the mountains to its mouth at the sea. State in which of the labeled zones (A, B, or C) erosion, transport, and deposition predominate, and justify your answers.
In the upper course of a mountain river, erosion predominates, whereas at its mouth, deposition predominates. Relate this change to the gradient and the speed of the…
In the upper course of a mountain river, erosion predominates, whereas at its mouth, deposition predominates. Relate this change to the gradient and the speed of the water.
The shaping of the coast
From the sea stacks of Oregon's Haystack Rock to the barrier islands of the Gulf Coast, waves shape much of the US shoreline.
What is deposition? Give an example of a place where a river deposits the materials it transports.
What is deposition? Give an example of a place where a river deposits the materials it transports.
Name two coastal landforms produced by the action of the sea and briefly explain how one of them forms.
Name two coastal landforms produced by the action of the sea and briefly explain how one of them forms.
On a rocky coast, isolated sea stacks, rock arches, and cracks in the cliff walls can be seen. Order the stages this shaping goes through and cite the agent responsible.
On a rocky coast, isolated sea stacks, rock arches, and cracks in the cliff walls can be seen. Order the stages this shaping goes through and cite the agent responsible.
Landforms and human action
Dams and levees on the Mississippi hold back sediment, and the Louisiana coast at the river's mouth has been losing land to the Gulf of Mexico: how can a dam far upstream make a coastline shrink?
The terraces of traditional farms slow down erosion on hillsides. Explain how they act on runoff and what happens when they are abandoned.
The terraces of traditional farms slow down erosion on hillsides. Explain how they act on runoff and what happens when they are abandoned.
Before the construction of a dam, a river contributed $120\,000\ \text{t}/\text{year}$ of sediment to its delta. After the dam was built, the input was reduced to…
Before the construction of a dam, a river contributed $120\,000\ \text{t}/\text{year}$ of sediment to its delta. After the dam was built, the input was reduced to $30\,000\ \text{t}/\text{year}$. At the same time, coastal marine dynamics (waves and longshore currents) remove $75\,000\ \text{t}$ of sand each year from the delta's coast.
- a) Calculate the net annual sediment balance of the deltaic coast (sediments supplied minus sediments removed) before and after the dam was built.
- b) Based on the result, predict what will happen in the medium term to the coastline and the adjacent dune ecosystems.
- c) The local city council proposes dredging sand from the nearby seabed and periodically dumping it onto the beach. Critically evaluate this proposal: justify why it does not solve the root problem and what unexpected negative impact it could cause on the marine seabed.
The beaches of a coast are fed by the sand carried by the longshore current. If a port is built that interrupts this current, predict what will happen to the beaches…
The beaches of a coast are fed by the sand carried by the longshore current. If a port is built that interrupts this current, predict what will happen to the beaches located on either side of the port and justify your answer.
Summary
Topic Challenge. Imagine that you work as an environmental consultant and the city council asks you to evaluate the vulnerability of the local terrain. Prepare a brief…
Topic Challenge. Imagine that you work as an environmental consultant and the city council asks you to evaluate the vulnerability of the local terrain. Prepare a brief technical proposal by completing these phases:
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Climate data and landforms: Check the precipitation values from the nearest station on the National Weather Service website (note the monthly record in $\text{l/m}^2$, for example $55.4\text{ l/m}^2$). Observe a nearby slope or embankment in your surroundings and identify the visible landforms (gullies, rills) and the dominant geological agent.
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Soil study: Collect a small surface sample ($50\text{ g}$ to $100\text{ g}$) in a park or open field. Determine its texture by feel (sandy, silty, or clayey), detect the presence of organic debris, and infer whether it is an incipient or mature soil, considering its weathering and the profile visible on the embankment (thickness and horizons).
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Reasoned proposal: Write a one-page report linking how the recorded climate, slope, and soil properties interact in shaping the landscape. Design two measures based on native revegetation to prevent soil loss.
Evaluation criteria:
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Accuracy in obtaining data from the National Weather Service and in describing the relief.
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Well-founded analysis of the sample and the stages of soil formation.
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Scientific coherence in linking weathering with fluvial or pluvial landform processes.
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Feasibility and relevance of the proposed corrective measures.