Chapter 12: Coasts

Classification (difficult task)tectonics

activepassive

sea-level changemay vary widelycauses

global (eustatic) from +6m to -125 m in the last 2 MYvolume 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

characterisiticsyoungusually shaped by terrestrial processes

sea level change exposes new areas to erosionheavy deposition extends the land into the sea

Primary coastscut by land erosion, then flooded by sea-level

risedrowned river valleysfjords

cut by wave erosion, then sea-level fallswave-cut terraces

built out by land processesriver deltas - fig p 294

morainesvolcanicearth movement

upwarddownward

Secondary Coasts

oldshaped by waves

Secondary Coasts:Wave Erosion

methodsabrasionhydraulic pressuredissolution

effectssea cliffssea cavessea stacks and archeswave-cut platformshore straightening

caused by wave refractionwaves 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 drifttransportation

wave motion pushes in at an anglegravity pulls straight outsand moves along the shore

effectssand moves in the direction of the predominant wavesbarrier islandsspits, baymouth bars, & tomboloseffects of groins, piers, jetties, breakwaters

Secondary Coasts:Transportation & Depositioncoastal cells

sand movesentry point - cliffs, river, etclongshore driftexit point - submarine canyonhuman structures (dams, groins, jetties, piers,

breakwaters) can block flow of sand

Other Types of Coasts

reefsmangrove swampsestuaries

Estuaries

typesdrowned river mouthsfjordsbar-built (barrier

island lagoons)tectonic (grabens)

characterisiticssalt-wedgepartially mixedwell mixedfjordreverse

valueproductiveshelteredbrackishnurseries for the

oceanlagoons & wetlands