Why Do Rivers Curve?

Summary

The video explores the contrasting behavior of mountain streams and meandering rivers on the plains. While mountain streams are confined by steep valleys, rivers in open plains have the freedom to shift their courses, forming meanders over time. Through examples like muskrats burrowing into riverbanks, the script shows how small disturbances can lead to dramatic changes in a river’s path. It explains how these bends continue to evolve until they form oxbow lakes, and highlights the regular patterns of river meandering observed globally. The video also touches on the terminology for these lakes in various cultures.

Takeaways

• 😀 Mountain streams are confined by steep valleys, while rivers in the plains have more freedom to shift their courses.
• 😀 Rivers on the plains meander and constantly change course due to softer soils, unlike the more rigid paths of mountain streams.
• 😀 A disturbance, like a muskrat burrowing into a riverbank, can set off a chain of events that alters the course of a river.
• 😀 Erosion caused by water rushing into weak riverbanks deepens the hollow and diverts more water, further shaping the river's path.
• 😀 Slower-moving water on one side of a river causes sediment to accumulate, eventually forming new land on the inside bank.
• 😀 Fast-moving water on the outside bank pushes the flow across the river, carving new curves and widening the stream.
• 😀 Meandering rivers follow a regular pattern, where the length of a meander is typically six times the width of the river's channel.
• 😀 Smaller meandering streams exhibit the same patterns as larger rivers, but on a miniature scale.
• 😀 Rivers continue to grow curvier until they loop back on themselves, forming an oxbow lake or similar features.
• 😀 Oxbow lakes, also called billabongs or lago en herradura, are formed when a river's curve becomes disconnected from its main flow.

Q & A

How do mountain streams and rivers on the plains differ in their behavior?

Mountain streams are confined by steep, rocky valleys, which restrict their course and make them run straight. In contrast, rivers on the plains have more freedom to shift their banks and change course, due to the softer soil, leading to meandering paths.

Why do rivers on the plains tend to meander rather than run straight?

Rivers on the plains meander because the softer soil allows them to erode their banks, forming curves. The flow of water constantly reshapes the land, making it difficult for the river to maintain a straight path.

How can the presence of a muskrat affect the river's course?

A muskrat burrowing a den in the riverbank can weaken the bank, causing it to crumble and erode. As water rushes into the hollow and continues to erode the bank, the river's course is altered, leading to further meandering.

What happens to the flow of water as the riverbank erodes?

As the riverbank erodes, water is diverted into the hollow, accelerating the erosion. This creates a feedback loop where the flow becomes stronger and deeper, further deepening the hollow, while the opposite bank experiences slower, weaker flow and deposition of sediment.

What is the relationship between water speed and sediment transport in a river?

Fast-moving water can carry small particles of sediment, while slow-moving water cannot. As the flow slows on one side of the river, it drops the sediment, creating shallower areas and promoting further changes to the river's course.

How does the meandering process contribute to the creation of new land?

As water erodes the outer bank of a river bend, it causes deposition on the inner bank, forming new land. This process continually reshapes the river’s course and creates land where the river once flowed.

Why do wider streams take longer to form bends?

Wider streams have more distance to cover before the current reaches the opposite bank, allowing for greater time for the erosion and deposition processes to create bends.

What is the typical relationship between the length of a meander and the width of the stream?

Measurements show that the length of one meander is typically about six times the width of the stream. This consistent pattern occurs in meandering rivers around the world.

What happens when meanders grow too large?

As meanders grow larger, the river can eventually cut through the bend, creating a more direct path. The old curve becomes an isolated water body, forming a crescent-shaped lake known as an oxbow lake.

What are some other names for an oxbow lake?

Oxbow lakes are known by different names depending on the region, such as billabongs, lago en herradura, or bras mort, but they all refer to the crescent-shaped remnants left behind when a river abandons a meander.