Fig. 11-11, p. 253
There are many different kinds of beaches which are generally characterized by the dominance of waves, tides, rivers and currents, and in particular differ by the amount of energy, which results in either Erosion or Deposition
High energy Erosion Fig. 11-4, p. 249
Low energy Deposition
Types of Coastlines
Sydney Harbor Australia A drowned river system Fig. 11-CO, p. 244
A fjord, Alaska Fig. 11-8, p. 251
Glacially eroded beach in Maine
An actively growing coastline, Hawaii Fig. 11-9, p. 251
A collapsed caldera Hawaii Fig. 11-10, p. 252
A mangrove swamp Fig. 11-24, p. 261
A Birdfoot Delta Fig. 11-22a, p. 260
Ganges- Brahmaputra Delta Fig. 11-22b, p. 260
Great Barrier Reef Australia Fig. 11-23, p. 261
Coral reef coastline in Florida
Transitional: Reef & Lagoon
In 1990, 50% of the U.S. population lived within 75 km of a coast. By 2010, 75% of the U.S. population will live within 75 km of a coast.
What about changes in sea level? glacial/interglacial timescale Increase of ~120 meters
Fig. 11-2b, p. 247
Florida coast during the last glacial maximum Fig. 11-3a, p. 248
Florida coast after global warming Fig. 11-3b, p. 248
Tectonic uplift Marine Terraces
Marine Terraces California Fig. 11-29, p. 265
Waves Fig. 9-CO, p. 198
Motion of water in a wave is circular Motion of energy of he wave is forward Fig. 9-1, p. 200
Fig. 9-2, p. 201
Waves are defined by their wavelength (L) Waves have are produced by a disturbing force and dissipated by a restoring force Table 9-1, p. 202
Waves may also be classified by defined by their frequency (f) Fig. 9-4, p. 202
Bigger waves move faster and tend to group together (dispersion) You will see the big waves from a storm first Fig. 9-8, p. 206
Biggest waves seen in the West Wind Drift Waves as tall as 36 ft are common Fig. 9-10, p. 207
Coastal Erosion Fig. 11-4, p. 249
Coastal Erosion Erosion is caused by the abrasive action of moving sand & gravel Tectonics, rock type & land surface processes contribute to shaping a coast Hydraulic pressure of breaking waves is a large contributor to mechanical erosion
Coastal Erosion Sea caves, arches, and stacks develop as refracted waves attack the coast Refracted waves focus energy on headland sides Zones of bedrock weakness allow preferential erosion Caves form, evolve into arches and stacks
Coastal Erosion Sea cliffs & wave-cut platforms Sea cliffs are produced by undercutting Cliff retreats over time as cliff face collapses Waves erode & remove debris Wave-cut platforms develop Flat surface commonly visible at low tide Widening platform protects cliff Beaches may develop on wide platforms
Fig. 11-5a, p. 250
Fig. 11-5b, p. 250
Fig. 11-5c, p. 250
Fig. 11-5d, p. 250
Wave Refraction Waves are bent as a portion slows Waves drag on the bottom & slow Shoreline is uneven, some deeper areas Wave is bent, becomes parallel to shore Wave energy is: concentrated on headlands dissipated in bays
Selective erosion of the headlands tends to straighten a coast
Highest point of the beach where waves reach at high tide Fig. 11-12, p. 253
Backshore Windblown dunes, some vegetation Fig. 11-12, p. 253
Foreshore Active zone of the beach Fig. 11-12, p. 253
Longshore troughs and bars Below low tide; Formed by waves, backwash and longshore currents Fig. 11-12, p. 253
Beaches are temporary and can change with the seasons Summertime beach Fig. 11-13a, p. 254
Wintertime beach Fig. 11-13b, p. 254
Calm conditions in the Spring and Summer build up sand on the beach Spring Summer Wintertime storms remove sand from the beach and deposit offshore Winter Fig. 11-13c, p. 254
Coastal Deposition Shoreline systems receive sediment from a variety of sources
Coastal Deposition Shoreline systems receive sediment from a variety of sources Much is land derived, river transported
Coastal Deposition Shoreline systems receive sediment from a variety of sources Much is land derived, river transported Moved by longshore drift
Coastal Deposition Shoreline systems receive sediment from a variety of sources Much is land derived, river transported Moved by longshore drift Deposited in low energy areas
Coastal Deposition Shoreline systems receive sediment from a variety of sources Much is land derived, river transported Moved by longshore drift Deposited in low energy areas Shell and coral debris is common in tropical regions
Coastal Deposition Beaches Shore built of unconsolidated sediments, usually sand sized particles Shape & size of beach dependent on wave energy Beach slope is often a function of particle size, coarser = steeper beach face
Longshore Drift One of the most important shoreline processes Occurs when waves hit the shore at angles other than 90 o Breakers push material up the beach at an angle Backwash pulls material down perpendicular to shore
Geometry of longshore drift
Longshore Drift Repetition of this process moves material parallel to beach face Beach drift & longshore currents are generated creating longshore drift Large volumes of sand may move Rip currents may develop if large volumes of water accumulate onshore
Geometry of longshore drift
Fig. 11-20, p. 258
Fig. 11-14, p. 255
Fig. 11-15a, p. 256
Fig. 11-15b, p. 256
Fig. 11-33, p. 268
Fig. 4-11, p. 86
Coastal Deposition Spits Form by longshore drift of sediment Extend across mouth of bays & estuaries Tombolos Outward built beach connecting to an island Island refracts waves away from beach
Longshore drift creates spits
Spits can create more beach
Coastal Deposition Barrier islands Offshore islands parallel to shoreline Common on gently sloping coasts Separated from mainland by a lagoon Islands may migrate by Longshore drift parallel to coast Toward/away from the coast by sea level change
Barrier Islands and Bay Mouth Bars Fig. 11-16, p. 257
Barrier islands Bay Mouth Bars Fig. 11-17, p. 257
Transitional: Barrier Islands
Barrier islands
Barrier Islands Cape Hatteras Fig. 11-18, p. 258
Cape Hatteras and the Chesapeake Bay Fig. 11-7, p. 251
Barrier Islands change rapidly Fig. 11-19, p. 258
Barrier Islands
Barrier Islands
Barrier Islands Ocean City, MD Fig. 11-21c, p. 259
Fig. 11-21, p. 259
Fig. 11-31, p. 267
Fig. 11-32, p. 268
Estuaries Fig. 11-25, p. 262
Fig. 9-24, p. 218
Fig. 9-25, p. 219
Fig. 9-26, p. 220
Fig. 9-27, p. 221
Fig. 9-29b, p. 222
Fig. 9-29c, p. 222
IG4e_18_23 The Effect of the Wind on Land
IG4e_18_25
IG4e_18_26a
IG4e_18_22
Aeolian River Crossbedding in rivers and deserts (aeolian)
Cross Beds Zion National Park, UT