Classroom presentations to accompany Understanding Earth , 3rd edition

Classroom presentations to accompany

Understanding Earth, 3rd edition

prepared by

Peter Copeland and William Dupré

University of Houston

Chapter 17Chapter 17The Oceans

The OceansThe Oceans

Steve Terrill/Stock Market

Fig. 17.1

Sandy Beach, North Carolina Barrier Island

Peter Kresan

Boulder Beach, Massachusetts

Fig. 17.2Raymond Siever

Wave height depends on:

• Wind velocity

• Wind duration

• Distance over which wind blows

Wave-generated Orbital WavesWave-generated Orbital Waves

Fig. 17.3

Wave characteristics

• Length (L): distance between crests

• Height (H) : vertical distance between crest and trough

• Period (T): time for successive waves to pass a fixed point

Velocity (V) of waves

V = L/T

Waves in shallow water

• Wave height Increases

• Wave length decreases

• Velocity decreases

• Period doesn’t change

Surf zone

Zone between where the waves break to point furthest up the shore where the waves wash up

Changes in Waves as they Approach the Beach

Fig. 17.4

Wave refraction

• Bending of wave crests as they approach the beach at a non-normal angle

• Caused by the change in velocity of waves as a function of water depth

Fig. 17.6

Wave Refraction

Waves Bending as they Approach the Beach

Fig. 17.5John S. Shelton

Fig. 17.7

Refraction at

Headlands and Bays

Fig. 17.8

Longshore Drift

Sediment transport near shore, parallel to the beach

• Longshore drift: sediment carried by swash and backwash along the beach

• Longshore currents: currents parallel to the beach within the surf zone

Tides

Twice daily rise and fall of the sea caused

by the gravitational attraction between

• earth and moon (lunar tides)

• earth and sun (solar tides)

Lunar Tidal Bulges

Fig. 17.9

Interaction between lunar and solar tides during the lunar month

causes:• Neap tides: when two tidal components

are out-of-phase, hence lower than usual, and

• Spring tides: when two tidal components are in-phase, hence higher than usual.

Earth-Moon-Sun Alignment and Neap-spring Tides

Fig. 17.10

Spring tides Neap tides

Fig. 17.11

Exposed tidal flats

Mont-Saint-MichelFrance

Thierry Prat/Sygma

Terrace Exposed at Low Tide

Fig. 17.12James Valentine

Major parts of beaches

• Offshore: from where the waves begin to feel bottom to the surf zone

• Foreshore: includes the surf zone, tidal flats, and swash zone

• Backshore: from beyond the swash zone to the highest level of the beach

Major Parts of a Beach

Fig. 17.13

Sand budget

The inputs and outputs of sediment by

erosion and sedimentation.

Fig. 17.14

Sand Budget of a Beach

Preventing beach erosion

• Structural approaches (e.g., groins): typically cause increased erosion downcurrent of structure

• Non-structural approaches (e.g., beach nourishment, land use planning): expensive, but don’t cause erosion in new areas

Groin: Built to Prevent Updrift Erosion Causes

Downdrift Erosion

Deposition

Erosion

Phillip Plissin/Explorer

Beach Nourishment, New Jersey

U.S. Corps of Engineers, New York District

Factors determining rates of erosion or deposition

• Uplift

• Subsidence

• Rock type

• Sea-level changes

• Wave heights

• Tidal range

Fig. 17.15

Sea Stacks

Kevin Schafer

Fig. 17.16

Wave-cut TerraceExposed at Low Tide

John S. Shelton

Fig. 17.17

Southern Tip of Cape Cod

Steve Durwell/The Image Bank

Fig. 17.19

Past 160 Years of Shoreline Change, Southern Cape Cod

Partially Developed Barrier Island

Fig. 17.18

Gulf of Mexico

LagoonMainland Florida

Barrier Island

Richard A. Davis, Jr

Uplifted Coastal Terrace

Fig. 17.20John S. Shelton

Mapping the seafloor

• Satellite measurements

• Echo sounding profiles

• Side-scan sonar

• Manned and unmanned submersibles

From Gravity Anomaly to Seafloor Topography

D.T. Sandwell & W.H.F. Smith/Scripps Institute of Oceanography

Fig. 17.22

Congo Submarine Canyon

Echo sounding profile

Fig. 17.23

Loiki Seamount

Imaged Using

Side-scan Sonar

Ocean mapping Development center, University of Rhode Island

Fig. 17.21

The Benthic Explorer Unmanned Submersible

T. Kleindinst/Woods Hole Oceanographic Institute

Fig. 17.24

Topographic Profile of the North Atlantic Ocean

Atlantic bathymetric features

• Continental shelf

• Continental slope

• Continental rise

• Abyssal plains

• Seamounts

• Mid-ocean ridge

Pacific bathymetric features

• Continental shelf

• Continental slope

• Trench

• Abyssal plains

• Seamounts

• Mid-ocean rise

Fig. 17.25

Continental shelf

Continental slope

Continental rise

Praxton & Haxby, 1996

From the Continental Rise to the Mid-Atlantic Ridge

Fig. 17.26

Fig. 17.27

Topography of the North Atlantic Ocean

Detail from H.C. Berannrket, based on Heezen & Tharp

Topographic Profile of the Western Pacific Ocean

Fig. 17.28

Fig. 17.29

Atlantic Passive Margin Off New England

Turbidity Current

• Flow of muddy water down a slope

• Forms deposits known as turbidites

Turbidity Currents

Fig. 17.30

Fig. 17.31a

Fig. 17.31b

Sandfall at the

Head of a Submarine

Canyon

U.S. Navy

“Black smoker” from the East Pacific Rise

D.B. Foster/Woods Hole Oceanographic Institute

Fig. 17.32

Central Rift Valley of the Mid-Atlantic Ridge

Fig. 17.32Macdonald & Fox, 1990

Some of the Maldive

Islands in the Pacific

Fig. 17.33

Atoll

Fringing Reef

Guido Alberto Rosi/The Image Bank

Fig. 17.34

Evolution of a Coral Reef

Types of marine sediment

• Terrigenous material eroded from the continents

• Biochemically precipitated shells of marine organisms

• Abiotic chemical precipitates

Fig. 17.35

Oceanic Ooze

Scripps Institute of Oceanography,University of California, San Diego

Carbonate Compensation Depth

Fig. 17.36

Depth below which carbonate material dissolves in seawater