A Level Physical Geography - The Hjulstrom Curve

Summary

In this lesson on physical geography, students learn about the Holstrom curve, which illustrates the relationship between river velocity and particle size. The curve features three key zones: the transport zone, where particles are actively moved; the deposition zone, where particles become stationary; and the erosion zone, where high energy allows for particle removal. The lesson emphasizes how different particles require varying energy levels for erosion and transport, with special attention to the unique properties of clay. Interactive questions enhance understanding, and students are encouraged to explore further resources for a deeper grasp of river dynamics.

Takeaways

• 🌊 The Holstrom curve illustrates the relationship between river velocity and particle size in terms of erosion, transportation, and deposition.
• 📈 The graph consists of two axes: the x-axis represents particle size in millimeters, while the y-axis indicates average velocity.
• 🚧 The curve is divided into three zones: Transport Zone, Deposition Zone, and Erosion Zone, each representing different particle movement behaviors.
• 🏞️ The Transport Zone lies between the entrainment velocity and the full velocity, where particles are actively moved along the river.
• 🏖️ The Deposition Zone occurs when river velocity falls below the full velocity, leading to particles becoming stationary.
• 💨 The Erosion Zone is where the river has sufficient energy to pick up and erode particles, located above the entrainment velocity.
• 💡 Particle types include clay, silt, sand, gravel, pebbles, and boulders, each requiring different energy levels for erosion, transport, or deposition.
• 🧪 Smaller particles are generally easier to pick up due to lower energy requirements, except for clay, which tends to stick together.
• 🔄 As energy decreases downstream, particles reach full velocity and are deposited when there isn’t enough energy to continue transport.
• ❓ The lesson encourages interaction through questions, allowing students to pause and check their understanding before moving on.

Q & A

What is the Holstrom curve?

The Holstrom curve is a diagram that illustrates the relationship between the velocity of a river and the size of particles that can be eroded, transported, and deposited by the river.

How is the Holstrom curve structured?

The Holstrom curve is structured with a pair of axes: the x-axis represents particle size in millimeters, while the y-axis indicates average velocity.

What are the three main zones depicted in the Holstrom curve?

The three main zones are the transport zone, the deposition zone, and the erosion zone.

What characterizes the transport zone?

The transport zone is located between the entrainment velocity (blue curve) and the full velocity (yellow curve), where particles are moved downstream by the river.

What happens in the deposition zone?

In the deposition zone, particles become stationary because the river's velocity is below the full velocity, meaning there is not enough energy to transport them.

What is the erosion zone?

The erosion zone is situated above the entrainment velocity, where the river has enough energy to pick up and erode particles.

How do particle sizes affect their movement in a river?

Smaller particles generally require less energy to be picked up, making them easier to transport, while larger particles like pebbles and boulders require more energy to be eroded or transported.

Why are clay particles an exception in terms of erosion?

Clay particles are an exception because they have bonds that make them stick together, making them harder to erode despite being smaller than sand particles.

What is the significance of full velocity in river dynamics?

The full velocity is significant because it represents the consistent velocity needed for the deposition of particles; if the river's velocity drops below this level, particles will be deposited instead of transported.

What should students do if they have questions after the lesson?

Students are encouraged to check out www.Revislevel for more information and resources on physical geography or to clarify any doubts they may have.