Waves and Coastlines Chapter 13 Oceans, Winds, Waves, and Coastlines N. Lindsley-Griffin, 1999 Geology Today Barbara W. Murck Brian J. Skinner Sea arches, California

Ocean Waves Wave Properties Houghton Mifflin 1998; N. Lindsley-Griffin, 1999

N. Lindsley-Griffin, 1999 A single particle at the surface moves in a circular path as each wave passes. Motion decreases to nothing, at a depth equal to one-half the wavelength. Ocean Waves

Waves Near Shore As bottom shallows, waves are forced into smaller space. Their shape distorts as the front slows down. Waves “feel” bottom

N. Lindsley-Griffin, 1999 Breakers form as the wave oversteepens and topples Waves Near Shore

Waves Change Near Shore N. Lindsley-Griffin, 1999 Fig , p. 387

Erosion by Waves The part of a wave that “feels” bottom first, slows down. The part still in deeper water moves faster, and the entire wave line curves, forcing wave energy towards headlands. Houghton Mifflin 1998; N. Lindsley-Griffin, 1999

Erosion by Waves Headlands are eroded by waves refracted towards them. Less resistant rock (like shale) will erode faster. More resistant rock (like sandstone) will be left behind as sea stacks. N. Lindsley-Griffin, 1999

Erosion by Waves Sea stacks Oregon coast Sea cliffs, sea stacks northern California coast N. Lindsley-Griffin, 1999

Waves move away from the prevailing wind direction, approaching coastlines at an angle. N. Lindsley-Griffin, 1999

Transport of Sediments As waves approach shore at an angle, they generate a current parallel to shore called the longshore current. N. Lindsley-Griffin, 1999 Wind Longshore Current

Transport of Sediments Waves run up shore at an angle Water runs straight back along steepest slope Sediment particles are transported along shore in a zigzag path Net motion = beach drift N. Lindsley-Griffin, 1999

Longshore current and beach drift combine to transport large quantities of sediment parallel to the shore N. Lindsley-Griffin, 1999 Transport of Sediments Fig , p. 389

Sediment transport by longshore current N. Lindsley-Griffin, 1999

Groins - Sand is deposited by longshore current on the up-current side; eroded by wave action on the down- current side. Human Interference J. Wiley, J.R. Griffin,

N. Lindsley-Griffin, 1999 Erosive effect of wave action decreased by breakwater; beach builds out. Asymmetry of beach indicates longshore drift direction from bottom to top. Human Interference J. Wiley, J.R. Griffin, 1999

Water carried onshore must find a path back to sea Rip currents flow out to sea along narrow channels and broad sheets J. Wiley; N. Lindsley-Griffin, 1999 Transport of Sediments

Rip currents transport sediments out to deeper water, can create dangerous undertows. J. Wiley; N. Lindsley-Griffin, 1999

N. Lindsley-Griffin, 1999 Breaking waves apply force in a narrow plane Erosion is greatest in a knife-edge right at water level Effects: wave-cut benches undermined sea cliffs sea arches and caves sea lion perches Waves Near Shore Sea lions, La Paz, Mexico Wave-cut bench and sea cliffs, Oregon

Wave-cut notches and sea caves represent the early stage of undermining that eventually results in mass-wasting collapse of cliffs and sea stacks Waves Near Shore N. Lindsley-Griffin, 1999 Sea Cave, California Wave-cut notch, New Brunswick

J. Wiley; N. Lindsley-Griffin, 1999 Waves Near Shore

N. Lindsley-Griffin, 1999 Wavecut bench at water level, uplifted wavecut bench - north of San Francisco, California Coastal Landforms

N. Lindsley-Griffin, 1999 Two wave-cut benches, with headlands and beaches (Tongue Point, New Zealand) Coastal Landforms Fig , p. 390

N. Lindsley-Griffin, 1999 Tectonically uplifted wave-cut bench with fossil sea stacks (north of San Francisco, CA) Coastal Landforms Modern sea stack Fossil sea stack

Coastal Landforms Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999

N. Lindsley-Griffin, 1999 Sea arches form where waves cut through headlands. Eventually wave action and mass wasting will remove the top of the arch and leave sea stacks behind. Coastal Landforms

Longshore drift deposits sand in a south- pointing spit at the mouth of the Russian River, northern California Coastal Landforms

A tombolo is a spit or bar that connects an island or sea stack to the mainland. Big Sur coast, California Coastal Landforms

Tombolo seen from space Coastal Landforms J. Wiley, J.R. Griffin, 1999

A baymouth bar blocks the mouth of a bay. (Oregon coast) Coastal Landforms

Houghton Mifflin 1998 N. Lindsley-Griffin, 1999 Beach houses attacked by hurricane, North Carolina Human Interference