River formations Flashcards
Flashcards for the formation of river formations (12 cards)
Describe each step of Hydraulic action
As water flows in a river, it exerts pressure on the riverbed and banks. This is the basic force behind hydraulic action. When the water rushes against the sides of the river channel or into cracks and crevices in the rock, it compresses air within these spaces. This compression can be quite powerful. The compressed air can cause the rock to crack and eventually break apart. Over time, as water continuously flows and pushes into these cracks, bits of the rock or soil are dislodged and removed. This process can erode the riverbanks and deepen the riverbed. The movement of water is not always smooth. Turbulence increases the efficiency of hydraulic action, as swirling water can strike against the river banks and bed from different angles, attacking the weaknesses in the rock or soil. The material that has been broken off is then picked up and carried away by the river, a process known as transportation. This further contributes to the shaping of the river channel.
State the summarized version of Hydraulic Action
Hydraulic Action is when the sheer force of the water enters
cracks in the rock and forces pieces of rock to break off.
Describe each step of attrition
As a river transports sediment, the particles collide with each other. These collisions can cause bits of the particles to break off, especially if the material is brittle or already fractured. Over time, this process not only reduces the size of the particles but also rounds them off, making river pebbles characteristically smooth and rounded. Attrition results in the gradual reduction of the size and angularity of sediment as it is transported downstream.
State the summarized version of Attrition
Attrition is a process where rocks and sediment particles carried by river water knock against each other. This causes them to break apart into smaller, more rounded pieces.
Describe each step of corrasion/abrasion
The river uses the sediment and rocks it carries as tools for erosion. When these particles hit the bed and the sides of the river channel, they scrape away the material. This process is especially effective in rivers carrying a large amount of sediment and at high velocities, where the force of the particles against the channel can be quite powerful. As rocks and sediment are transported, they become smaller and more rounded due to attrition, affecting the efficiency and nature of abrasion downstream.
State the summarized version of corrasion/abrasion
Abrasion, also known as corrasion, is the process by which the river’s load (the sediment it carries) grinds against the riverbed and banks, wearing them away much like sandpaper.
Describe each step of Solution/chemical erosion
Water, especially when slightly acidic, can dissolve certain types of minerals and rocks. Rainwater absorbs carbon dioxide from the atmosphere and the soil, forming a weak carbonic acid that is very effective at dissolving calcium carbonate in limestone. As the river water flows, it chemically interacts with the rocks, dissolving soluble materials into the water. Unlike attrition and abrasion, where material is physically carried away, in solution, the material is dissolved in the water and carried away in solution form. This process can significantly alter the landscape, especially in areas rich in limestone, leading to features like karst landscapes.
Describe the formation of a levee
Formation: Levees are raised embankments found alongside rivers. They are formed through deposition.
Process: During times of flooding, rivers overflow their banks and slow down, depositing sediment along their banks.
Build up: Over time, repeated flooding events deposit layers of sediment, building up the levees and creating a raised embankment along the river channel.
Describe the formation of a waterfall
Formation: Waterfalls are formed when a river flows over a sudden change in elevation, such as a steep cliff or rock ledge.
Process: The force of the water erodes the underlying rock, often undercutting it and creating an overhang.
Collapse: As the overhang collapses due to erosion, a vertical drop is formed, resulting in the formation of a waterfall.
Describe the formation of a ox bow lake
Formation: Oxbow lakes are formed when a meander is cut off from the main river channel.
Process: Over time, the neck of the meander narrows as erosion continues on the outer bank and deposition occurs on the inner bank.
Cutoff: Eventually, during a flood event, the river cuts through the narrow neck, creating a new, straighter channel.
Isolation: The abandoned meander becomes isolated from the main channel, forming an oxbow lake.
Describe the formation of a meander
Formation: Meanders are winding bends in a river channel formed through erosion and deposition.
Process: As a river flows, it erodes the outer bank of a bend through hydraulic action and abrasion, creating a cutbank.
Deposition: Simultaneously, deposition occurs along the inner bank of the bend, forming a point bar.
Migration: Over time, the continuous erosion and deposition processes cause the meander to migrate downstream, creating a winding pattern in the river channel.
Describe the formation of a V-shaped valley and U-shaped valley
Formation: V-shaped valleys are typically formed by the erosive force of rivers, while U-shaped valleys are formed by glaciers.
V-shaped Valley: Rivers erode downwards into the landscape over time, forming narrow valleys with steep sides that resemble the letter “V”.
U-shaped Valley: Glaciers carve out valleys by plucking and abrasion, resulting in wider valleys with a flat bottom and steep sides that resemble the letter “U”.
