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Chapter 18: Problem 6

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe the motion of water molecules in a wave. How does wave refraction cause longshore currents? (E)

Short Answer

Expert verified
In a wave, water molecules move in an elliptical path, with larger circles of motion at the surface and smaller circles at greater depths. Wave refraction is the bending of a wave as it enters shallow water or encounters an object, causing a change in direction. Longshore currents are the movement of water parallel to the shoreline, occurring when waves approach the shore at an angle due to wave refraction. The energy transfer from the refracted waves to the coastal waters creates longshore currents that transport water, sand, and sediment along the coastline.

Step by step solution

01

Define the Motion of Water Molecules in a Wave

In a wave, the motion of water particles (or molecules) is generally elliptical, meaning they move in an elongated circular path. The water molecules at the surface exhibit larger circles of motion (with more significant amplitude), while those at greater depths experience smaller circles (with lesser amplitude). As the water depth increases, the elliptical paths of water molecules become smaller until negligible motion is observed.
02

Introduce Wave Refraction

Wave refraction is the bending or change in the direction of a wave as it moves into shallow water or encounters an object. When a wave enters a shallow region like a shoreline, the part of the wave in shallower water experiences a reduction in velocity, whereas the part in deeper water maintains speed. This change in velocity causes the wave to bend towards the slower part, altering its direction gradually.
03

Describe Longshore Currents

Longshore currents are the movement of water parallel to the shoreline, which is caused by waves approaching the shore at an angle rather than directly head-on. As the waves refract and collide with the shore, the energy transfer results in water being pushed along the beach in the direction of wave travel. These currents contribute to the transport of sand and sediment along coastlines, leading to various coastal features and erosion patterns.
04

Explain the Relationship Between Wave Refraction and Longshore Currents

Wave refraction is responsible for creating longshore currents. When waves approach the shoreline at an angle, the part of the wave in shallower water (closer to the shore) experiences wave refraction as it slows down. Meanwhile, the deeper part of the wave maintains its speed. This difference in velocity causes the wave to bend, directing more energy along the shoreline at an angle. The transfer of energy from the waves to the coastal waters creates the longshore currents that move parallel to the shore, transporting water, sand, and sediment along the coastline.

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Most popular questions from this chapter

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. How much of the Earth's surface do oceans cover? (F)

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe how waves affect a rocky coast and how such coasts evolve. (F)

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. What factors control the direction of surface currents in the ocean? What is the Coriolis effect, and how does it affect oceanic circulation? Explain thermohaline circulation. (C)

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe the components of a beach profile. Identify the backshore zone, foreshore zone, and wave base in the profile. (F)

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. . In what ways do people try to modify or "stabilize" coasts? How do the actions of people threaten coastal areas? (G)
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