Quiz #3 Due Wednesday before Midnight Exam #1: 7PM, 2/15 (Tuesday) Here

Class #9 OCEAN BASINS AND SEA FLOOR_ What’s down there? Understanding the ocean basins in light of Plate Tectonics

The shape of the ocean bottom Plate Tectonics Theory provides a way to understand: Why we have ocean basins The origins of many undersea features

The "hypsographic" curve Gives percent of Earth surface at each elevation Observations: Sharp, narrow transition between continents and ocean Reflects fundamental differences in the crust (oceanic versus continental crust)

What percentage of Earth surface is higher than xxx meters elevation? Mean elevation of continents = +840 m Mean depth of oceans = -3,700 m

Provinces of the sea floor: Major Provinces Continental margins Ocean basin floor Mid-ocean ridges Trenches

Provinces of the sea floor: Major Provinces Continental margins Continental Shelf Shelf Break Continental Slope Continental Rise Submarine canyons

Continental Shelf is an underwater extension of the continent. Continental Margin ends near where continental crust (incl. sediments) ends

General Diagram of a Continental Margin Note: Vertical dimension is expanded!!!!

(Here’s the same figure, no vertical exaggeration)

Provinces of the sea floor: Major Provinces 1. Continental Margins- Last time 2. Ocean basin floor Ave. depth = 4,000m - 6,000 m Many areas flat (mantled by sediments) Volcanic features -Islands, often in chains (e.g., Hawaii) -Underwater hills, seamounts, "guyots"

Sea Floor Features

Seismic (= sound wave) Profiling: Reveals layers of sediment and rock

Provinces of the sea floor: Major Provinces 1. Continental Margins- Last time 2. Ocean basin floor 3. Mid-ocean ridges and rises Curvilinear feature circling the earth Higher than surrounding areas Divergent plate boundary Young, hot oceanic lithosphere

Mid-Ocean Ridges: Details Composed of basalt from undersea volcanoes Rift valley at the plate boundary- earthquakes Heat flow high Magmas carry additional heat into upper crust Some magmas erupt to form lavas Water circulation driven by this heat Hydrothermal vents

http://www.youtube.com/watch?v=rFHtVRKoaUM&feature=related

Fracture Zones

Provinces of the sea floor: Smaller Provinces (small area, still important) Trenches 6,000m - 11,000 m deep -- deepest regions Occur at margins of oceans, especially Pacific East Pacific -- edge of continental margin West Pacific -- associated with volcanic island chains

Trenches Where are they? Almost all found around the Pacific Why are they deep? Bending of plate Downward pull of dense, sinking lithosphere Continental margins greatly altered by trenches

Trenches

Shallow <100km Deep