Chapter 12: Coasts

Classification (difficult task) tectonics active passive sea-level change may vary widely causes global (eustatic) from +6m to -125 m in the last 2 MY volume of water available (can be tied up in ice) capacity of ocean basins (can be reduced by faster sea- floor spreading) volume changes due to temp changes local tectonics isostacy

Primary Coasts characterisitics young usually shaped by terrestrial processes sea level change exposes new areas to erosion heavy deposition extends the land into the sea

Primary coasts cut by land erosion, then flooded by sea-level rise drowned river valleys fjords cut by wave erosion, then sea-level falls wave-cut terraces built out by land processes river deltas - fig p 294 moraines volcanic earth movement upward downward

Secondary Coasts old shaped by waves

Secondary Coasts: Wave Erosion methods abrasion hydraulic pressure dissolution effects sea cliffs sea caves sea stacks and arches wave-cut platform shore straightening caused by wave refraction waves focus on headlands

Secondary Coasts: Beaches deposits that accumulate in low energy areas sand is always being moved profile fig p 300 backshore - cliffs, dunes, seawall berm crest foreshore - intertidal zone off shore - longshore trough and bar rip currents on-shore and off-shore seasonal big waves - sand moves off-shore small waves - sand moves back on-shore effect of sea walls

Secondary Coasts: Transportation & Deposition longshore drift transportation wave motion pushes in at an angle gravity pulls straight out sand moves along the shore effects sand moves in the direction of the predominant waves barrier islands spits, baymouth bars, & tombolos effects of groins, piers, jetties, breakwaters

Secondary Coasts: Transportation & Deposition coastal cells sand moves entry point - cliffs, river, etc longshore drift exit point - submarine canyon human structures (dams, groins, jetties, piers, breakwaters) can block flow of sand

Other Types of Coasts reefs mangrove swamps estuaries

Estuaries types drowned river mouths fjords bar-built (barrier island lagoons) tectonic (grabens) characterisitics salt-wedge partially mixed well mixed fjord reverse value productive sheltered brackish nurseries for the ocean lagoons & wetlands