1. Unit 7: Ocean Geology
Floor Structure, Plate Tectonics, Layers of the Earth, Plates/Boundaries, Earthquakes/Tsunamis/Ring of Fire

2. Ocean Floor Structure

3. Continental Shelves Zones adjacent to a continent or around an island
Extending from where water begins to where there is a definite steep decline to the depths of the ocean floor.
The water covering the continental shelves forms shallow seas (50 – 100 meters deep)

4. Continental Slope
Both the slope and shelve are still considered part of the continent, even though they are below the sea surface.
Extends from the continental shelf at an average depth of about 135 meters, to the ocean floor depth

5. Ridges Long, narrow, Continuous mountain chains on the ocean floor
Largest features in ocean basins.
Most prominent feature on the Earth’s surface.
The largest is the East Pacific Rise
The other example of a large ridge is the Mid-Atlantic Ridge

6. Seamounts
Isolated/ extinct underwater volcanic mountains on the sea floor
Cone shaped/ often flat topped
They haven’t reached the surface, yet
They rise abruptly from the abyssal plain to the heights of at least 3300 feet above the ocean floor
Example: Indian Ocean contains the most, and also found in Hawaii

7. Guyots (pron…guy yo) A seamount with a flat top
Created by Wave action eroded the top when above sea level
It is a dead volcano

8. Trenches
Long, narrow, and deep depressions of the sea floor, steep Tides that form at the subduction zones, where oceanic crust folds under continental crust
As ocean plates move toward continents, they are drawn under forming the deep trenches
There are 26 in the world: 3 in Atlantic ocean, 1 in Indian ocean, 22 in the Pacific ocean.
They are also the tectonic areas

9. TRENCHES

10. Island Arcs
Volcanic island chains that form on the opposite edge of a subducted plate
Example: Japanese Islands, & Aleusian Islands (Alaska)

11. Canyons Deep furrows that cut across the continental shelf and slope
Usually v-shaped
Usually associated with major rivers

12. Abyssal Plains: most common in Atlantic, in Pacific deep trenches around the continents trap most of the sediment before it reaches the open ocean
Nearly level areas on the sea floor
Covers almost a 1/3 of Earth’s surface.
Lie between the edges of continents and underwater mountain ranges
Consist of beds of volcanic rock topped with layers of sediments thousands of feet deep
At this depth, the water is near freezing, and pressure is hundreds of times greater than the surface, and there is absolutely no light, but the species living here have adapted to the harsh conditions and eat a “snow” of dead organic matter that falls from the upper ocean layers, they have slower metabolisms, so they don’t eat often

13. BASINS
Deep depressions of the sea floor of more or less circular or oval form.

14. HYDROTHERMAL VENTS
Fractures in the Earth’s surface where geothermally-heated water pulses through
Found where hot magma is close to the surface crust
Examples: hot springs and geysers on land, on ocean floor they are called submarine hydrothermal vents or black smokers.
Discovered in 1977 around the Galapagos Islands
The water never boils due to the extreme pressure
Precipitation of minerals (sulfides) gives it it’s shape and color
Organisms found here rely on the minerals and chemicals dissolved in the fluids of the vents.
Too deep for sunlight to penetrate, so they rely on chemosynthesis using heat, methane, and sulfur compounds to convert into energy.

15. HYDROTHERMAL VENTS

16. COLD SEEPS
Vent that is not superheated, but hydrogen sulfide, methane, and hydrocarbon rich fluid still seep out into the surrounding water.
Creates rock formations and reefs over time when mixed with seawater.
Organisms living here are reliant on bacteria that produce energy from the chemical compounds in the water in this area.

17. Importance of Ocean Floor Features
Ridges separate deep ocean waters into distinct basins
Seamounts, guyots, and underwater mountains interrupt ocean currents and produce turbulence, which mixes the water vertically

18. The Changing Ocean
The face of the Earth is always changing and throughout geologic history oceans have been created and destroyed.
The ocean floor is moving at a rate of about ½ to 6 inches a year due to plate tectonics
Roughly 200 million years ago the Earth's surface was very different from the familiar pattern of land we know today.
All of the land masses were grouped together into one vast supercontinent called Pangaea.
The rest of the globe was covered by a single great ocean known as Panthalassa

19. The Changing Ocean
Slowly, over millions of years, the great land mass split apart.
The pieces began to move over the Earth's surface driven by slowly churning currents in the molten rocks beneath the Earth's hard outer layers.
The gigantic plates on the Earth's crust move like a conveyor belt.
As new areas of ocean floor form at mid-ocean ridges, old areas are dragged down, or subducted, into the Earth's mantle, which explains why the older rocks cannot be found.

20. What is Continental Drift?
Proposed by Alfred Wegener in 1915
States that the continents were once connected as a larger land mass, before the were pulled apart.
This theory was not accepted until we discovered seafloor spreading years later.

21. Continental Drift – Pangea Breaking Apart
Northern part split to form North Atlantic Ocean 200 mya
South Atlantic and Indian oceans begin to form 150 mya
Continents continue to drift apart. Atlantic Ocean gets wider each year

22. CHANGING OCEAN & EARTH cont..
By about 35 million years ago the pattern of land and sea was very much like it is today.
But the continents are still moving and as the Atlantic and Indian oceans continue to get wider by a few inches every year, the Pacific is slowly shrinking.
At the northeast corner of Africa we can see the start of a new ocean.
For the last 25 million years, the Red Sea has been widening.
If it continues at the same rate, in 200 million years it will be as wide as the Atlantic is today.

23. LAYERS OF THE EARTH The Earth is composed of four different layers.
Many geologists believe that as the Earth cooled the heavier, denser materials sank to the center and the lighter materials rose to the top.
Because of this, the crust is made of the lightest materials (rock- basalts and granites) and the core consists of heavy metals (nickel and iron).
The crust is the layer that you live on, and it is the most widely studied and understood.
The mantle is much hotter and has the ability to flow.
The Outer and Inner Cores are hotter still with pressures so great that you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth!!!!!!

24. Layers of the Earth Crust Upper Mantle Lower Mantle Inner core
Outer core
Crust
Upper Mantle
Lower Mantle

25. CRUST The Earth's Crust is like the skin of an apple.
It is very thin compared to the other three layers.
The crust is only about 3-5 miles (8 kilometers) thick under the oceans (oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust).
The temperatures of the crust vary from air temperature on top to about 1600 degrees Fahrenheit (870 degrees Celcius) in the deepest parts of the crust.
You can bake a loaf of bread in your oven at 350o F, at 1600o F rocks begin to melt.
The crust of the Earth is broken into many pieces called plates.
The plates "float" on the soft, plastic mantle which is located below the crust.
These plates usually move along smoothly but sometimes they stick and build up pressure.
The pressure builds and the rock bends until it snaps. When this occurs an Earthquake is the result!
The seven continents and ocean plates basically float across the mantle which is composed of much hotter and denser material.

26. 2 TYPES OF CRUST Oceanic crust Continental crust 3-5 miles thick
Made of lighter basalt rock or lava rock
More dense, so they sink
Crust is newer, because it is constantly moving and sinking under continents
Continental crust
Thicker than oceanic crust
Made of heavier rock like granate
Less dense, so they ride on top of oceanic crust
Older than

27. The Mantle Layer of the earth directly below the crust
Made of very hot, dense, liquid rock
The liquid mantle moves very slowly because of convection currents (hot liquid moves in a circular, up and down pattern)
The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere.
The layer below the rigid lithosphere is a zone of asphalt-like consistency called the Asthenosphere.
The asthenosphere is the part of the mantle that flows and moves the plates of the Earth.

28. Convection Currents
Many geologists believe that the mantle "flows" because of convection currents.
Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling, sinking again and then heating, rising and repeating the cycle over and over.
The next time you heat anything like soup or pudding in a pan you can watch the convection currents move in the liquid.
Plates of the earth’s crust float on the liquid mantle, and move with the action of the convection currents
The crust gets a free ride with these currents. A conveyor belt in a factory moves boxes like the convection currents in the mantle moves the plates of the Earth.
Because of this the plates "float" on it like oil floats on water.
The mantle is made of much denser, thicker material.

29. And Their Effects on the Earth
Plate Tectonics
And Their Effects on the Earth

30. Theory of Plate Tectonics
States that plates make up the outer layer of the Earth and have slowly moved long distances throughout the history.
This theory explains how the continents once fit together in a single continent called Pangaea.
The movement of continents explains how animals became separated onto different continents, and it explains how mountains, volcanoes, and ocean trenches were formed, and why earthquakes occur.
The underlying theory behind plate tectonics is that the force of gravity is stronger on a heavy, cooled ocean floor than it is on a hotter and lighter floor.

31. TECTONIC PLATE THEORY
came about in the 1960s to explain seafloor spreading and continental drift.
Around 1915 a scientist named Alfred Wegener published the first edition of "The Origin of Continents and Oceans" in which he proposed that the shapes of the east coast of South America and the west coast of Africa indicate that may have been attached at some point in history.
Developed the Theory of Continental Drift - he explain the presence of identical rocks on opposite sides of the Atlantic Ocean, and tropical plant fossils in the Arctic Circle were due to the fact that the continents must have shifted over time.
In 1962, American geologist Harry Hess suggested that, instead of continents moving through the ocean crust, an entire ocean basin and its connected continent actually moved together as a plate.
Once the Theory of Plate Tectonics was accepted, a multitude of questions were explained and a scientific revolution occurred in geophysics and geology.

32. Tectonic plates
are huge fragments of Earth’s lithosphere, consisting of the crust fused with the upper mantle.
the lithosphere is made of plates of crust (both oceanic and continental).
They move over the hot, fluid part of the mantle.
Plate motion builds mountain ranges, but most of the effects of moving plates can be seen best on the ocean floor, where most of the plate boundaries are formed.
Plates have boundaries (edges) that come into contact with neighboring plates, causing earthquakes and/or volcanic activity

34. How did tectonic plates form?
Over time, smaller plates combined to form larger plates. The thinnest parts of the larger plates split to form the “edges” we see today.

36. How crust is formed
The oldest rocks on the ocean floor are about 180 million years old, whereas the oldest rocks on the continents are dated from 3.8 billion years ago.
This is because the ocean floor is constantly created and destroyed rather quickly.
New ocean floor is created in the mid-ocean ridges from hot magma rising in the mantle, coming out of the ridges, and then spreading away from the ridges.
As it cools, it forms new oceanic crust.
As the ocean floor plates move towards the continents, it is recycled into the mantle, as it is drawn downward in subduction zones.
Trenches form at these areas where the oceanic crust is subducted into the mantle at the continental crust.
Thus, subduction zones occur where oceanic crust meets continental crust.
The continental crust is less dense, so the oceanic crust sinks (subduction) back into the mantle.
This is a continual process, and explains why oceanic crust is so much newer and younger than continental crust.

37. How does new crust form?
Hot magma from the mantle spews out of specific areas of the earth
The magma cools, turning to either continental or oceanic crust (depending on where it is)

38. Three Types of Tectonic Plate Boundaries
Divergent
Convergent
Transform

40. 1. DIVERGENT BOUNDRIES: “pulled apart”, “rifting”
pulled apart” - the crust is extended, thinned, and fractured by the rising of hot mantle material (new crust is being formed as magma comes out of rifts or volcanoes).
Parallel ridges emerge as new ocean floor spreads out on either side of an ocean ridge.

42. Divergent Boundaries Iceland is full of volcanic activity
It straddles the Mid-Atlantic Ridge, where new crust is being made and spreading out.
Iceland is splitting along the spreading center between the North American and Eurasian Plates, as North America moves westward relative to Eurasia.

43. Consequences Ex. Krafla Volcano in northeastern Iceland.
Existing ground cracks have widened and new ones appear every few months.
From 1975 to 1984, numerous episodes of rifting (surface cracking) and volcanic eruptions took place along the Krafla fissure zone.
Before erupting, the ground would gradually rise 1-2 m before abruptly dropping,
Between 1975 and 1984, the displacements caused by rifting totaled about 7 m.

44. Continued
Aerial view of the area around Thingvellir, Iceland, showing a fissure zone (in shadow) that is an on-land exposure of the Mid-Atlantic Ridge.
Right of the fissure, the North American Plate is pulling westward away from the Eurasian Plate (left of fissure).

45. East Africa
East Africa may be the site of the Earth's next major ocean.
Plate interactions in the region provide scientists an opportunity to study first hand how the Atlantic may have begun to form about 200 million years ago.
Geologists believe that, if spreading continues, the three plates that meet at the edge of the present-day African continent will separate completely, allowing the Indian Ocean to flood the area and making the easternmost corner of Africa (the Horn of Africa) a large island.

46. (Photograph by Jacques Durieux, Groupe Volcans Actifs.)
Helicopter view (in February 1994) of the active lava lake within the summit crater of 'Erta 'Ale (Ethiopia), one of the active volcanoes in the East African Rift Zone.
Red color within the crater shows where molten lava is breaking through the lava lake's solidified, black crust.
(Photograph by Jacques Durieux, Groupe Volcans Actifs.)
Two helmeted, red-suited volcanologists -- observing the activity from the crater rim -- provide scale.

47. 2. Convergent Boundaries “plates colliding together”
Two plates meet and push on one another, until the pressure gives way, causing volcanoes to erupt
Responsible for forming mountains, and producing volcanic activity
Biggest contributor towards earthquakes
Subduction zones occur at convergent boundaries

48. What are Subduction zones?
When the density of the oceanic and continental crusts became very different, the oceanic crust sank where it met the continental crust, creating subduction zones.
Areas where oceanic plates collide with continental plates
The oceanic crust is pulled under the continental plate, where it melts in the hot magma.

49. Trenches and Subduction
Trenches are the deepest parts of the ocean floor and are created by subduction.
If we could pull a plug and drain the Pacific Ocean, we would see a number of long narrow, curving trenches thousands of kilometers long and 8 to 10 km deep cutting into the ocean floor.

50. Two Oceanic Plates Converging
When two oceanic plates collide, one is usually subducted under the other, and in the process a trench is formed.
The Marianas Trench (paralleling the Mariana Islands), for example, marks where the fast-moving Pacific Plate converges against the slower moving Philippine Plate.
The Challenger Deep, at the southern end of the Marianas Trench, plunges deeper into the Earth's interior (nearly 11,000 m) than Mount Everest, the world's tallest mountain, rises above sea level (about 8,854 m).

51. Convergent plates can occur:
Between an oceanic and a continental plate
2. Between two oceanic plates or
3. Between two continental plates

52. Oceanic and Continental Crust Convergence
Off the coast of South America along the Peru-Chile trench, the oceanic Nazca Plate is pushing into and moving under the continental part of the South American Plate.
In turn, the South American Plate is being lifted up, creating the Andes mountains
Earthquakes are often followed by uplift of the land by as much as a few meters.

53. 3. TRANSFORM BOUNDRIES
Transform – “trans = across” - occurs when plates move past each other.
Ex. San Andres Fault in California

55. What is the difference between an earthquake and a tsunami?
Earthquakes can occur with any type of plate boundary, but they are more frequent at convergent boundaries, such as subduction zones.
This is because stress builds up at faults in the crust until it overcomes the strength of the rock, causing the fault to slip. When this happens, a huge amount of energy can be released in a short time.
A tsunami may be triggered if an earthquake causes the uplift or subsidence (sinking) of part of the sea floor. The water above suddenly rises or sinks, then flows to regain equilibrium. Surface waves radiate out at mph, and can quickly cross an entire ocean.

56. Tsunamis A series of ocean waves that sends surges of water onto land
Caused by large, undersea earthquakes at tectonic plate boundaries
When the plate rises or falls suddenly, it displaces the water above it, forming rolling waves that will become the tsunami

57. EARTHQUAKE http://www.youtube.com/watch?v=TzlodnjPAuc TSUNAMI
EARTHQUAKES, TSUNAMIS, VOLCANOES (45MIN)

58. Hotspots

59. What is a plate tectonic hotspot?
A hotspot is an area of volcanoes that form far from the edges of tectonic plates.
They usually form volcanic island chains in the middle of the plate, itself.
Hotspots are believed to form on the surface directly above extremely hot plumes of magma that are stationary, and lie deep within the mantle, possibly where the mantle meets the core.
As the plate moves on, the volcano on the surface is separated from its source of magma beneath, and becomes a “dead” volcano.
Dead volcanoes erode away with time, eventually sinking below the surface of the water, forming reefs or other underwater structures.
Hotspots are not limited to forming in the ocean…Yellowstone National Park is a hotspot that occurs in the continent itself.

60. Hotspots
An area of volcanoes that form in the middle of a tectonic plate
As the plate moves, the volcanoes on the surface move with it and are eventually cut off from its magma source

61. RING OF FIRE
The "Ring of Fire" is an arc stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America.
The Ring of Fire is composed over 75% of the world's active and dormant volcanoes.
This huge ring of volcanic and seismic (earthquake) activity was noticed and described before the invention of the Plate Tectonics Theory.
We now know that the Ring of Fire is located at the borders of the Pacific Plate and other major tectonic plates.

62. Ring of Fire

63. Plates are like giant rafts of the earth's surface which often slide next to, collide with, and are forced underneath other plates.
Around the Ring of Fire, the Pacific Plate is colliding with and sliding underneath other plates.
This process is known as subduction and the volcanic and seismic active area nearby is known as a subduction zone.
There is a tremendous amount of energy created by these plates and they easily melt rock into magma, which rises to the surface as lava, forming volcanoes.
Volcanoes are temporary features on the earth's surface and there are currently about 1500 active volcanoes in the world. About ten percent of these are located in the United States.

64. Formation of Volcanoes
When subduction occurs over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until the volcano rises above sea level to form an island volcano.
Such volcanoes are typically strung out in chains called island arcs. Volcanic island arcs, which closely parallel the trenches, are generally curved.

65. According to the hotspot theory, the volcanoes of the Hawaiian chain should get progressively older and become more eroded the farther they travel beyond the hotspot.
Kauai
5.5 million years old
Hawaii
.7 million years old