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Passive plate margins
No active tectonic boundaries
Continental Shelf
- avg 50 miles wide and 425 ft deep
- gradient of 1/10 of one degree (10 ft/mile)
- shelves represent 7.5 % of the oceans area.
- usually contain important mineral and petroleum deposits &
- evidence of sea level change
- drilling & dredging has produced remains of animals abundant
the last ice age when sea levels were much lower.
- usually consists of sediment washed off continent by
- leads into deeper water, steeper gradient
- avg 370 ft/ mile
- marks the true edge to a continent
- slope merges into a more gradual incline
- gradient of 20-40 ft/mile
- rise may extend for a hundred miles or more into the
deeper ocean
- consists of sediment moved downslope from the shelf to
the deep ocean
- sediment delivered here by turbidity currents moving
down the slope, which follow submarine
Active Margin
Active tectonic boundary
Show us the location of subduction zones
Pillow Basalts
Entire ocean recycles
every 6-8 million yrs!
Hydrothermal Sea Vents
Bacteria oxidize H2S (ingest it) chemically. Independent of the sun. Chemical photosynthesis.
Tube worms eat bacteria, clams, fish eat tube worms, etc.
Unique ecological system on our planet -- doesn’t need the sun’s heat.
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Warm ocean
Volcanic Island
Subsidence plus erosion; barrier reef
continually builds and remains in the
same place.
Barrier Reefs
Island eventually erodes away leaving behind
the reef, now called an Atoll.
Wave Movement
Longshore Current
Beach Storm Response
Summer: No storms. Steep beach.
Winter: Storms interact with dunes, move
sand offshore onto bars. Flat beach, wavecut dunes.
Bars march back up to shore and dock onto beach
over period of days or months, forming steep beach.
Barrier Islands
Tidal Channel
Baymouth Bar
Groin Field
Seawall Erosion
Seawall Erosion
Sea Level Rise
Western Headward Erosion
Wavecut Cliff
Sea Arch
Sea Stack
Wavecut Beach