Waves
most formed by wind
size depends on wind velocity,duration, and on fetch (the distance that the wind blows over water)

In deep water, particles move in circular orbits
motion decreases with depth
wave base = 1/2 wave-length
 

Waves can approach shoreline at an angle, causing:

• wave refraction: waves bend to become more parallel to shoreline
• longshore current: water flows parallel to the coast

Wave erosion

• hydraulic action
• abrasion
• corrosion: chemical weathering

• Longshore drift: sand carried by longshore current
• Movement of sand by longshore drift forms spits and baymouth bars

Beach Sediment Budget
IN:

• from rivers (redistributed by longshore currents).
• offshore (sand, coral pieces, shells)
• local erosion

• -deposited on dunes
•  carried away by longshore drift and rip currents

Size of beach sediment depends on wave energy and sediment supply.

If sediment supply is low, erosional shoreline will form. Common feature: wave-cut platforms
Wave refraction focuses waves on headlands, forms arches and seastacks.

Emergent coast: rising relative to sea level.  Marine terraces form.

Submergent coast: sea level rising relative to coast. Drowned river mouths form estuaries.

Barrier Islands: sand islands separated from mainland by a lagoon

Origin:
Formed as spits ?
submerged beach ridges ?

Tides: oceans rise and fall in response to gravitational attraction to the Moon and Sun

Spring tide occurs when sun and moon line up
Neap tide occurs when sun is perpendicular to moon

On rocky coasts, tide pools form between high and low tide.
On sandy or muddy coasts, large tidal flats form