Geology 200

Study Guide

Unit 11:
Waves, Beaches, and Coasts

Overview

Shorelines are interfaces where the hydrosphere meets the lithosphere. At ocean shorelines, constantly mobile ocean waters interact with the coastline. Surface currents generated by the wind, tidal movements from gravitational pull, and ocean circulation driven by density differences all contribute to the dynamic environment. Varying topography, geological makeup, and climate result in environments that differ from place to place.

This unit begins by introducing coastal processes, followed by a brief discussion on waves and energy transfer from wind to the shoreline via water waves. To give an insight into the mechanisms involved, the unit explores near-shore circulation. Next, we will examine beach environments and discuss the movement of sediment along the shore. Following an exploration of coastal classification (based on how they form), the unit concludes with a discussion about the links between the biosphere and the coasts.

Objectives

After completing this unit, you should be able to

  1. outline the basic properties of waves, including wave height, wave trough, wave crest, and wavelength.
  2. explain how water waves transfer energy from wind to the coastal environment.
  3. describe processes that occur in the surf zone.
  4. describe the processes associated with nearshore circulation, including wave refraction, longshore currents, and rip currents.
  5. outline processes that occur in the beach environment, and describe the basic structure of a beach including the beach face, sand bars, and berms.
  6. explain how sediment is transported by longshore drift, and describe how spits, baymouth bars, and tombolos form.
  7. describe how human activities can interfere with longshore sediment transport.
  8. describe features that characterize erosional coasts, and explain how the erosion of headlands results in sea cliffs and coastal straightening.
  9. explain how erosion on coasts forms sea caves, wave-cut platforms, stacks, and arches.
  10. outline the characteristics of depositional coasts (including barrier islands); the characteristics of drowned coasts (including estuaries and fjords); and the characteristics of uplifted coasts.
  11. outline the interactions that can occur between the biosphere and the physical coastal environment.
  12. explain how climate change could influence processes within the coastal environment.

Section 1: Introduction to Coastal Processes and Water Waves

After introducing coastal processes, Section 1 outlines how water waves transmit energy from winds onto the coastline. In addition to basic wave properties, you will learn how waves generated offshore can travel to the coast where they break as they approach the shoreline. Energy dissipated in the process plays a critical role in shaping coastal landforms.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • Introduction to Chapter 14: Waves, Beaches, and Coasts, including "Shoreline Dynamics" (pp. 340-341).
  • “How Do Waves Form” (pp. 341-343).

Study Questions

  1. What is wave height? What factors influence the height and speed of water waves?
  2. What is the wavelength of a water wave?
  3. Explain how breakers develop and how they form surf.

PDF icon Answer Key

Section 2: Near-Shore Circulation and Beaches

In Section 2 we examine water circulation close to the shoreline. Wave refraction is an important process that occurs when waves approaching the coast bend as they approach the shoreline. Longshore currents arise from water that moves parallel to the coast, while rip currents flow seaward, perpendicular to the coastline. All of these modes of water movement are key factors in determining the distribution of energy along the shore. Hence, they play an important role in the nature of erosion, the extent of erosion, sediment transport, and deposition along the coast.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “What Happens When Waves Reach the Shore” (pp. 343-345).
  • “How Do Beaches Develop” (pp. 345-346).

Study Questions

  1. What causes water wave refraction along a coast?
  2. What is a longshore current?
  3. What are rip currents?
  4. What part of the coast forms the beach? Which part of the beach is the berm?

PDF icon Answer Key

Section 3: Longshore Drift of Sediment

Longshore drift refers to the movement of sediment parallel to the shoreline on the beach face and in the surf zone. The typical rate of sand movement in this manner ranges from 5-10 m per day, but movement distances exceeding hundreds of metres have been recorded in places. Over extended periods of time, large volumes of sediments can be transported in this manner. Such sediment transport can interfere with many economic activities along the coast, and physical structures can be constructed to control sand movement. Although such constructions serve a useful purpose, they are costly and can have deleterious effects on the coastal environment.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “Why Does Sand Move along a Shoreline” (pp. 346-349).

Study Questions

  1. What causes longshore drift of sediment along a coast?
  2. What is the difference between a spit and a baymouth bar?
  3. How does longshore drift form tombolos?
  4. Explain how the construction of groins and jetties can cause erosion further along the shoreline.
  5. How does sand transported by a river to the sea end up along the beach?

PDF icon Answer Key

Section 4: Coastal Types

Coasts evolve from a range of different geological processes. In this section we learn about features that distinguish some of the most common coastal types and the processes by which such landscapes emerge. The section will cover erosional coasts, depositional coasts, drowned coasts, and uplifted coasts.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “Why are There Different Types of Coasts” (up to “The Biosphere and Coasts”) (pp. 349-358).

Study Questions

  1. Why does coastal straightening occur on an erosional coast?
  2. What are sea caves, and how do they form?
  3. How do barrier islands form?
  4. What causes coasts to drown?

PDF icon Answer Key

Section 5: The Biosphere and Coasts

The first part of Section 5 looks at how a coastal environment can be modified by the biosphere. It briefly examines the effects of algal reefs and mangrove vegetation. The second part of the section examines the effects of sea level rise on the coastal environment. After briefly discussing how global warming may lead to sea level rise, we will examine factors that characterize coasts that are vulnerable to negative impacts of sea rise. After discussing the combination of factors (including sea level rise and ground subsidence) that contributed to the destruction caused by Hurricane Katrina in New Orleans (2005), the section concludes by outlining the dangers posed by an increase in extreme weather events as a result of global warming and the potential effects of such events on the coastal environment.

Reading Assignment

Plummer, C. C., Carlson, D. H., & Hammersley, L. Physical Geology (15th ed.).

  • “The Biosphere and Coasts” (pp. 358-359).
  • “Coasts in Peril – The Effects of Rising Sea Level” (pp. 354-355).

Study Questions

  1. How do reefs protect a shoreline?
  2. How can mangroves benefit other marine organisms in the coastal zone?
  3. Briefly outline of the range of factors that led to the breach of levees in New Orleans in 2005, which resulted in the catastrophic flood.

PDF icon Answer Key

Unit 11 Self Test

You have now finished Unit 11, so please complete and submit the associated laboratory exercise and assignment. Instructions can be found in the Assignment Drop Boxes section of the course homepage.

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