Question

You and a friend set up an umbrella and chairs at a beach. Your friend then goes into the surf zone to play Frishee with another person. Several minutes later, your friend looks back toward the beach and is surprised to see that she is no longer near where the umbrella and chairs were set up. Although she is still in the surf zone, she is 30 yards away from where she started. How would you explain to your friend why she moved along the shore?

Short answer

Your friend moved due to longshore drift, caused by waves hitting the shore at an angle.

Step-by-step solution

Introduce the concept of longshore drift

Explain that the phenomenon of moving along the shore is known as 'longshore drift.' This is a process that occurs when waves approach the coastline at an angle, rather than directly.

Discuss the action of waves

Describe how waves carry sand and other materials along the coastline due to their angle of approach. This causes objects and even people in the water to slowly drift parallel to the shore.

Apply the concept to the situation

Your friend moved along the shore because the waves were likely coming in at an angle, pushing her down the beach. This consistent action over several minutes caused the movement while she was focused on playing.

Key concepts

Wave Action

Wave action refers to the way waves move and interact with the shore. When wind blows across the surface of the water, it creates waves. These waves travel, carrying energy towards the coast. The angle at which waves approach the shore is crucial because it determines the direction of energy movement.
When waves hit the shore at an angle, their energy doesn't just move directly in and out. Instead, it pushes water and anything floating in it, like your friend, diagonally along the beach.

• Waves have a swash—when they surge up onto the beach.
• Then they have a backwash—when water flows back into the sea.

This zigzag effect causes the gradual movement of your friend parallel to the shore.

Coastal Processes

Coastal processes are the dynamic actions that shape and change the coastline. These include erosion, transportation, and deposition. Waves, tides, and currents all play a significant role in these processes.

The key factors in coastal processes are:

• Wave action, which can erode coastlines, move sand, and transport sediments.
• Currents, which can be driven by tides or wind, shaping the coastline over time.
• Wind, which can also carry sand and create dunes.

These processes often work together to reshape the coastal landscape. In the case of your friend, the waves transported her along the shore through the process of erosion and sediment transport. This movement is part of natural coastal dynamics that occur daily.

Sediment Transport

Sediment transport is the movement of sand, pebbles, and other small particles along the coast. When waves approach diagonally, they pick up sediment and carry it along the shore with each wave action.
This process is part of longshore drift, where sediments are constantly being shifted parallel to the coast. Over time, this can significantly alter beaches as sediments are continuously deposited and eroded.
The main factors influencing sediment transport include:

• The direction and strength of wave action.
• Wind strength, which affects wave generation.
• Current strength and direction.

In the case of your friend on the beach, the waves moved her position just as they moved sand and other particles, demonstrating the natural and ongoing process of sediment transport.