1. Crustal Plates
2. Continental Margins
3. Ocean Basins
4. Mid-Ocean Ridges
5. Trenches
6. Hot Spots

Earth's Structure

1. Core: iron rich, solid inside and molten outside
2. Mantle: semi-solid and plastic
3. Crust: thin, rigid and floating on the mantle

Asthenosphere

1. Place of magma (molten rock)
2. Mantle
3. Convection currents

Lithosphere

1. Place of rocks
2. Crust and Uppermost Mantle
3. 40-60 miles thick
4. Floats on the athenosphere

Types of Crust

1. Continental
   A. Mostly granite
   B. Relatively light
2. Oceanic
   A. Basalt
   B. Relatively heavy

Crustal Plates

1. Crust is broken into large pieces that float
2. 8 major and 12 minor plates
3. Continental Plates (mostly continental crust)
4. Oceanic Plates (mostly oceanic crust)
5. Mixed Plates (mix of continental and oceanic crust)

Plate Tectonics

1. Plates move in different directions
2. Plate movements cause earthquakes, volcanism, and mountain building
3. Plate movements are driven by convection currents in the mantle
4. Plate movements create oceanic ridges and trenches

Plate Boundaries

1. Plate boundaries mark the edges of plates
2. Plate boundaries are locations where two plates meet - marked by mountain chains, earthquakes, volcanoes, ridges, and trenches
3. Converging plate boundaries (where plates are colliding) - Subduction zone - marked by trenches and island arcs
4. Diverging plate boundaries (where plates are moving apart) - Spreading center - marked by ridges and rift valleys
5. Transform plate boundaries (where plates are sliding past each other) - Shearing zone - marked by transform faults

Continental Drift

1. Movements of continents
2. Caused by movements of the plates that continents are located on

Birth of an Ocean

1. A spreading center within a continent creates a rift that is flooded by seawater

The Sea Floor Adjacent to Land

1. The sea floor near a continent is made up of continental crust (granitic), and its topography mimics the adjacent land.
2. It is covered by sediments of continental originmade of eroded rock.
3. Coarse materials are closest to shore and fine-grained muds are offshore.

Continental Shelf

1. Continuation of continent under seawater
2. Slopes gently seaward
3. Water generally less 130 meters deep
4. Average 65 miles wide
5. Width varies: U.S. East coast up to 311 miles but U.S. West coast narrow
6. The abrupt transition between the continental shelf and the continental slope is called the shelf break

Continental Slope

1. Marks seaward extent of continent
2. Average slope is 4-5 degrees (slope varies in steepness)
3. 1,000-2,000 meters down to basin depths

Types of Margins

1. Active continental margins border on plate boundaries and are thereby geologically active
2. Passive continental margins are located away from plate boundaries and are geologically inactive

Continental Rise

1. A ridge of sediment parallel to the continental shelf and seaward of the continental slope
2. Formed by sediments transported downslope from land then moved parallel to the base of the slope to form the rise
3. Materials in the rise originate on the shelf and are transported to the rise by slumps, slides, and turbidity currents (sediment-loaded gravity currents)
4. Rises are found only along passive continental margins (ex. the east coast of the United States)

Submarine Canyons

1. Narrow V-shaped depressions in the shelf and slope
2. Can be several km wide and up to 1,200 m deep
3. Often associated with rivers (not always)
4. Transport sediments down the slope

The Floor of the Deep-Sea

1. A basin is a large area of ocean floor lying at a depth of more than 2,000 m.
2. Basins have distinct topographic features some without continental counterparts.
3. The sea floor of a basin is made up of oceanic crust (basaltic) often covered by sediments of oceanic origin.

Abyssal Plains

1. Broad, relatively flat areas of sea floor that extend from the continental rise on passive continental margins and thus found around the edges of most oceans
2. At depths of from 4,000 to over 5,000 m
3. Although generally flat and gently sloping abyssal plains are often hilly
4. Abyssal hills are volcanoes almost completely covered by sediments, found in lines parallel but at a distance from ridges and are found covering large areas of the Pacific and Atlantic seafloor.

Ridge Systems

1. Mountainous systems with many volcanoes that extend for thousands of miles
2. Formed by sea floor spreading (divergent movement of one crustal plate away from another)
3. Up to 2 miles high and 1,200 miles wide
4. Often in mid-ocean but some are near continents
5. Intersected by fracture zones

Rift Valleys

1. Spreading centers where new oceanic crust is produced
2. 12-30 miles wide and 1 mile deep
3. Located along the center of a ridge system
4. Contain hydrothermal vents (undersea gysers) that support life

Fracture Zones

1. Large cracks in the sea floor that may extend for thousands of miles
2. Fracture zones are associated with ridge systems running perpendicular to the ridge or with transform plate boundaries
3. May offset continental margins
4. Volcanoes and mountains are often associated with fracture zones

Trench Systems

1. Long, very deep depressions in the sea floor
2. Formed by subduction (movement of one crustal plate under another)
3. There are 31 trenches with bottoms lying from 4.5 to 6 miles below the ocean surface

Seaward Side of Trenches

1. The continental slope ends abruptly at a trench and a continental rise is absent
2. Sea floor seaward of a trench is irregular and hilly

Landward Side of Trenches

1. Trenches produce volcanoes on their landward sides
2. May form island arcs if there is no continent on the overiding side of the subduction zone (oceanic crust dives under oceanic crust)

Mantle Hot Spots

1. A stationary hot spot in the mantle
2. Plumes of hot magma force their way up through the crust overlying the hot spot
3. Create undersea volcanoes
4. When crustal plates drift over a long lasting hot spot a chain of volcanoes is created

Seamounts

1. Mountains that rise from the basin floor reaching heights of thousands of meters e.g., Mt. Mauna Kea 9,180 meters
2. They often occur in groups or chains.
3. They may be formed by the drifting of the crustal plate over a hot spot in the asthenosphere.
4. They may break the ocean surface to form islands
5. Seamounts occur in large numbers in the Pacific and Indian Oceans where they often form linear chains