Water that flows across the land runs downhill. Along the way, it can pick up and carry sediment ranging from fine clay to coarse sand or gravel.
As the water runs downhill, it cuts into the soil, forming channels called gullies. When gullies reach a low-lying area, they merge together, forming a larger stream. Streams merge together to form larger streams or rivers. Most sediment carried downhill eventually ends up in a stream and is carried away.
The amount of sediment a stream can carry depends on the speed and size of the stream. The speed of the water in a stream depends on its slope. The steeper the slope, the faster the water moves. Fast-moving or large streams can carry more sediment than slow-moving or small streams. Abrasion occurs as sediment in a stream collides with rock in and along the stream.
Pieces of rock are chipped away and rough edges in rocks and sediments themselves become rounded. The bedrock beneath streams is also eroded by abrasion. Sediment flowing in the water can cut deeply into the bedrock.
In this investigation, students examine models of river erosion. Groups build different types of river beds by filling stream tables with sand.
Each group perches one end of their stream table on some blocks to create a slope. They then pour water into the river bed through a spout. They watch as the water enters the stream bed and begins to carry away sand from the stream edges and the bottom.
The sediment is deposited at the end of the stream where the water stops flowing. They see that as sediment is eroded, the shape of the stream changes. This investigation is generally considered safe to do with students. The sand should be dampened prior to the start of the investigation. Fine sand can be inhaled and is a major irritant.
If the sand has not been dampened, provide disposable masks to students. Ensure that students wash their hands thoroughly after handling the sand. Make sure that water is well away from any electrical outlets or equipment. Also, review the investigation for your specific setting, materials, students, and conventional safety precautions. Many students have stood on the bank of a stream or river and watched its water flowing.
Many will probably not have seen streams or rivers from a high altitude or elevation. Begin the investigation by showing students the Images for Setting the Scene. Ask them the following:. Have your students discuss these questions, first in pairs, then groups and then as a whole class.
Record their answers on a flipchart that you can refer to throughout the investigation. Have your students discuss the question in pairs, then in groups, and then as a whole class.
Record their answers on a flipchart. Tell your students that they will be investigating this question and at the end of their study they will be able to provide reliable answers. Most students will have observed the movement of water in a stream or river, but they may not be aware of the effect of moving stream or river water on the land. Some students may have noticed that water flowing over land will move sediments and debris during a big rain storm, but they do not realize that this same process is continually taking place in rivers and streams.
Students who live near major rives may have had some experiences with the erosion of sediment due to flooding. Some students who live near, or have visited, shorelines of an ocean or lake, may have observed erosional features, but not understood how they formed.
Here are some initial questions that your students can discuss, in pairs, in groups, and as a whole class:. The narrow valley is 30 miles 48 kilometers long and 1 to 6 miles 1. It occupies an area of about , acres , hectares. At its northern end lies the region's largest mountain, Mount St. The valley is bordered by two mountain ranges, the Vaca Mountains on the east and the Macayamas Mountains on the west.
Flowing through the middle of this valley is the mile-long kilometer-long Napa River. The valley began to form about four million years ago when heat forces beneath Earth's crust in this region forced land on either side of the present-day valley upward into mountains. Certain areas between the mountains were widened and lowered into troughs as a result.
Napa Valley is such an area. After the valley's formation, eruptions from several volcanoes surrounding the valley blanketed the land in volcanic cinders and ash that accumulated to layers thousands of feet thick. The Shenandoah Valley, which is about miles kilometers long, lies between the Blue Ridge Mountains on the east and the Allegheny Mountains on the west. Both mountain ranges are part of the Appalachian Mountain system, which formed over million years ago.
The powerful erosive forces of water, wind, and frost have greatly eroded the Appalachians since then. Water runoff has carved the mountains' distinctive alternating pattern of ridges and valleys. The Shenandoah River, which runs through the valley, is a tributary of the Potomac River. It was the first of the tributaries in the area to reach the soft limestone layer that is now the base of the Shenandoah Valley.
As it did, it carved out the Shenandoah Valley, dissolving the limestone and carrying the sediments north to the Potomac. Lying in the Sierra Nevada Mountains in central California is a 0. Measuring 7 miles 11 kilometers long and 1 mile 1. The Merced River runs through the valley. Geologists estimate that a few million years ago, it began to carve a valley where the present-day.
Yosemite Valley, seven miles long and one mile across, was formed during six key geologic stages that occurred over millions of years. Yosemite Valley lies. The Sierra Nevada Mountains were uplifted and tilted westward, causing the river to gradually, then rapidly, erode a deep, steep-walled canyon.
About 2 million years ago, North America's climate began to cool and glaciers began to form. During one of the major glacial periods, about , years ago, ice thickness in the area was up to 6, feet 1, meters. Massive, flowing glacial ice caused tremendous amounts of rock to be carved and transported to the area, creating massive rock formations that still exist.
The flow and retreat of glaciers through Yosemite Valley occurred many times until about 10, years ago, when the last major glacial period ended in North America.
What remained was a U-shaped valley that was actually deeper than the present-day Yosemite Valley. Rock debris from the glacier had dammed the valley creating ancient Lake Yosemite, which covered the valley floor.
Streams from hanging valleys above fell in towering waterfalls. The tallest of these is Yosemite Falls, which presently drops 2, feet meters to the valley floor. Ultimately, sediment filled in the lake until it formed the existing valley floor. Huber, N. Washington, D. Geological Survey, Geological Survey and the National Park Service. Valley Glaciers. Toggle navigation. Photo by: Peter Wey. Valley: Words to Know Alpine glacier: A relatively small glacier that forms in high elevations near the tops of mountains.
Base level: The level below which a stream cannot erode. Erosion: The gradual wearing away of Earth surfaces through the action of wind and water. Fjord: A deep glacial trough submerged with seawater. Floodplain: An area of nearly flat land bordering a stream that is naturally subject to periodic flooding.
Glacial trough: A U-shaped valley carved out of a V-shaped stream valley by the movement of a valley glacier. Glacier: A large body of ice that formed on land by the compaction and recrystallization of snow, survives year to year, and shows some sign of movement downhill due to gravity.
Hanging valley: A shallow glacial trough that leads into the side of a larger, main glacial trough. Levee natural : A low ridge or mound along a stream bank, formed by deposits left when floodwater slows down on leaving the channel. Mass wasting: The spontaneous movement of material down a slope in response to gravity. Meander: A bend or loop in a stream's course. Rift valley: The deep central crevice in a mid-ocean ridge; also, a valley or trough formed between two normal faults.
Stream: Any body of running water that moves downslope under the influence of gravity in a defined channel on Earth's surface. U-shaped valley: A valley created by glacial erosion that has a profile suggesting the form of the letter "U," characterized by steep sides that may curve inward at their base and a broad, nearly flat floor. Valley glacier: An alpine glacier flowing downward through a preexisting stream valley. V-shaped valley: A narrow valley created by the downcutting action of a stream that has a profile suggesting the form of the letter "V," characterized by steeply sloping sides.
Also read article about Valley from Wikipedia. User Contributions: 1. Ryann E. I enjoyed all this information about valleys. I also enjoyed the pics you put up too make your point and to understand what you are saying and meaning. The part i liked was the valley vocab. This is one of the most enjoyable reading i heard so far.
Keep up the great work! The R. I had a huge test coming up and this website totally helped Measure content performance.
Develop and improve products. List of Partners vendors. Share Flipboard Email. Amanda Briney. Geography Expert. Amanda Briney, M. Featured Video. Cite this Article Format. Briney, Amanda. An Overview of Valley Formation and Development. The Process and Definition of Geomorphology. Geologic Maps of the 50 United States. Appalachian Plateau Geology and Landmarks. Mechanical Weathering Through Physical Processes. An Overview of the Last Global Glaciation. Your Privacy Rights. To change or withdraw your consent choices for ThoughtCo.
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