Diagram A a cross section showing the speed or velocity of water through a meander. Diagram B a labelled cross section to show the key features of the meander. Note that on the shallower inside of the bend sediment can accumulate to form a slip off slope, whereas on the deeper outside of the bend where the current is faster and erosion operates, a river cliff forms.
In the diagrams below, erosion of the outside of the meander means that the neck of land becomes narrower and narrower over time. On the inside of the bend the slow flow encourages the deposition of beaches. After a long time the neck of land gets totally cut through by erosion processes such as hydraulic action and abrasion watch an animation of this. This cuts off the meander bend which is totally isolated by deposition leaving an Ox bow lake , which is a crescent shaped lake that will eventually fill with reeds and sediment over time.
Rivers flood on a regular basis. The area over which they flood is known as the floodplain and this often coincides with regions where meanders form.
When rivers flood in the middle valley the cover an area of land known as the flood plain. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.
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This water is the lifeline of ecosystems around the world. Erosion is the process where rocks are broken down by natural forces such as wind or water. There are two main types of erosion: chemical and physical. In physical erosion, the rock breaks down but its chemical composition remains the same, such as during a landslide or bioerosion, when plants take root and crack rocks. Explore the process of erosion with this collection of resources.
Floods are events where water overflows onto land that is typically dry. This can occur when there is a large amount of rain, rapid snow or ice melt, a blast of water onto a coastline during a storm, or the failure of manmade infrastructures, such as dams or levees.
Floods are among the most expensive and frequent natural disasters in the United States, and as the impacts of climate change are more acutely felt, floods are expected to worsen. In addition to property damage, floods, on average, kill more people than tornadoes, hurricanes, or lightning strikes in the United States each year.
Learn more about floods with these resources. The environmental hazards you face depend on where you live. For example, if you live in northern California you are more likely to be impacted by a wildfire, landslide, or earthquake than if you live in Charleston, South Carolina, but less likely to be hit by a hurricane.
This is because the physical conditions in each place are different. The active San Andreas fault runs through California and causes regular earthquakes, while the warm waters transported by the Gulf Stream can intensify a storm heading for South Carolina.
These environmental hazards shape human activity regionally. Learn more about environmental hazards with this curated resource collection. Mesopotamia is thought to be one of the places where early civilization developed. It is a historic region of West Asia within the Tigris-Euphrates river system.
In fact, the word Mesopotamia means "between rivers" in Greek. Home to the ancient civilizations of Sumer, Assyria, and Babylonia these peoples are credited with influencing mathematics and astronomy. Use these classroom resources to help your students develop a better understanding of the cradle of civilization.
A terrestrial ecosystem is a land-based community of organisms and the interactions of biotic and abiotic components in a given area. Examples of terrestrial ecosystems include the tundra, taigas, temperate deciduous forests, tropical rainforests, grasslands, and deserts. The type of terrestrial ecosystem found in a particular place is dependent on the temperature range, the average amount of precipitation received, the soil type, and amount of light it receives.
Use these resources to spark student curiosity in terrestrial ecosystems and discover how different abiotic and biotic factors determine the plants and animals found in a particular place. A flood happens when water overflows or soaks land that is normally dry. Floods can be destructive to humans and the natural environment, but they also help to drive biodiversity and are essential to the functioning of many ecosystems.
When rivers flood, sediment gets deposited on the floodplain. This sediment is called overbank deposits. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.
Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. A floodplain or floodplain is a generally flat area of land next to a river or stream.
It stretches from the bank s of the river to the outer edges of the valley. A floodplain consists of two parts. The first is the main channel of the river itself, called the floodway. Floodways can sometimes be seasonal , meaning the channel is dry for part of the year.
Beyond the floodway is the flood fringe. The flood fringe extends from the outer banks of the floodway to the bluff line s of a river valley. Bluff lines, also called valley walls, mark the area where the valley floor begins to rise into bluffs. The flood fringe of the seasonal Todd River extends the floodplain to square kilometers square miles. Some floodplains are extraordinarily wide. The Barotse floodplain of the Zambezi River, for example, is a vast wetland stretching thousands of kilometers through Angola, Zambia, and Botswana.
The Barotse floodplain includes the sandy Kalahari basin , which is waterlogged during the rainy season and an extension of the nearby Kalahari Desert during the dry season. Some rivers have very narrow floodplains. In fact, some rivers, or parts of rivers, seem to have no floodplain at all. These rivers usually have a steep stream gradient —a very deep, fast-moving channel.
Ngonye Falls, Zambia, marks a remote stretch of the Zambezi River where the floodplain is extremely narrow. As the Zambezi leaves the wide floodplain of the sandy Kalahari, it enters a narrow basalt channel as fast-moving whitewater rapids.
There are two major processes involved in the natural development of floodplains: erosion and aggradation. The erosion of a floodplain describes the process in which earth is worn away by the movement of a floodway. A floodplain is an area of land which is covered in water when a river bursts its banks. Floodplains form due to both erosion and deposition. Erosion removes any interlocking spurs , creating a wide, flat area on either side of the river. During a flood, material being carried by the river is deposited as the river loses its speed and energy to transport material.
Over time, the height of the floodplain increases as material is deposited on either side of the river. Floodplains are often agricultural land, as the area is very fertile because it's made up of alluvium deposited silt from a river flood.
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