oceanography chapter 2

seamounts vs table ounts

sea mounts - round cone shaped. - occur along the crest of the mid ocean ridge. - sea floor spreading moves it off its hot spot eventually -wave erosion turns is into a table mount. table mounts -flat on top - started off as a sea mount but wave wave erosion and distance traveled from hot spot flatten the top. - table mount carries shallow water features such as coral reefs down to deeper water.

the study of earths magnetic field is called.....

paleomagnetism. -which studies magnetic particles in rocks to determine their north south direction, and their angles relative to earths surface.

subduction can create.....

deep ocean trenches

the degree to which a magnetite particle points into earth is called its....

magnetic dip -magnetic dip is directly related to latitude. -dip needles no NOT dip at all at the magnetic equator. - at the north pole a dip needle points straight into the surface. - south pole dip needle is also vertical but pointing out instead of in. - magnetic dip increases with increasing latitude.

How is a earth quake intensity measured?

seismic moment magnitude. - high magnitudes at slow spreading mid atlantic ridge.

Who proposed continental drift?

Alfred Wegener

mid ocean ridge

- a continuos underwater mountain range that winds through every ocean basin in the world. - it is entirely volcanic in origin - rises 2.5 kilometers above deep ocean floor. - new ocean floor is formed at the crest or axis of the mid ocean ridge called the " spreading center". once separated filled with volcanic material.

intraplate features

- are far away from any plate boundary. -plate tectonics theory doesn't explain these

hot spots

- areas of intense volcanic activity that remain in the same location over long periods of geological time, and are unrelated to plate boundaries. - hot spots are intraplate features. -hotspots cause the continuing volcanism in yellowstone park. - hot spots are caused by mantle plumes

ocean trenches

- as sea floor spreading occurs along the mid ocean ridge, ocean floor is being destroyed at deep ocean trenches. - deepest part of ocean floor, and resemble a narrow crease. - earthquakes are caused here due to a plate being bent down back into earths interior. This process is known as subduction.

mantle plumes

- columnar areas of hot molten rock that arise from deep within the mantle. -stay put while plate rotates and new hot spot is on.

Age of the ocean floor

- deep sea drilling initiated to test sea floor spreading - mission was to collect ocean floor rocks for radiometric age dating. - the age of the ocean floor beneath deep sea deposits, is based on the pattern of magnetic stripes. -Atlantic had simple and most symmetric pattern of age distribution. - pacific had least. oldest floor 180 million years old

What features occur at plate boundaries?

- divergent - convergent -transform

subduction zone

- earth quakes happen near trenches, caused by plates dipping down and plunging back into earths interior known as subduction, and the sloping area from the trench along the downward moving plate is called the subduction zone.

earthquakes

- most large earth quakes occur along trenches reflecting the energy released during subduction. - other earthquakes occur along mid ocean ridge reflecting energy released during sea floor spreading. -most earth quakes are created by plates interacting with each other at their margins.

heat flow

- the heat from earths interior is released to the surface as heat flow - heat moves to the surface with magma in a convective motion. - most heat is carried to regions of mid ocean ridge spreading centers. -heat flow is high at mid ocean ridges -heat flow low at subduction zones.

is the ocean crust younger than continental crust?

- yes because the process that renews the sea floor doesn't occur on land -because of continental rocks low density they do not get recycled through sea floor spreading.

objections to continental drift

-Scientists rejected his theory saying it defines physics. - tidal attractions too small to move continents.

nematath

-a chain of existing volcanos that is progressively older as one travels away from the hot spot.

Frederick Vine and Drummond Matthews

-analysis of igneous rock stripes around mid ocean ridge. - as new basalt sea floor is added at mid ocean ridges , it is magnetized and lays at the existing magnetic field since the magnetic field reverses after so many years. -this produces a pattern of normal and reversed magnetic polarity at the mid ocean ridge.

continental accretion

-continental material added to edges of continent through plate motion

Harry Hess

-habit of leaving his depth recorder on at all times. - recordings showed mountain ridges near center of oceanbasins -and deep narrow trenches at the edge of the ocean basins. -Hess published History of Ocean Basins which contained the idea of sea floor spreading, and convection cells as the driving mechanism. - his ideas were right.

plate tectonic theories

-lithosphere floats on the ductile asthenosphere - large scale geological features occur along along plate boundaries. - two major tectonic forces 1) slab pull 2) slab suction

what evidence supports plate tectonics?

1) Earths MAgnetic Field 2) Paleomagnetism 3) Apparent polar wondering 4)Magnetic polarity revearsals 5) Paleomagnetism and the ocean floor: -using a magnetometer to map the deep waters -strips measured on floor called magnetic anomalies

What were Alfred Wegeners evidence supporting the continental drift?

1) Fit of the continents: -Sir Edward Bullard used a computer program to fit the continents together by using depth below sea lever rather than using the shorelines. 2) Matching sequence of rocks and mountain chains: - matching sequence of rocks and mountain chains. -similar rock types, ages, and structure found on different continents. 3) Glacial age and other climatic evidence: -Wegener noticed history of glacial activity on now tropical areas. -Which meant A) there was a world wide ice age which is unlikely because of found coal deposits in other places. or B) tropical areas were once located close to the pole. -also the direction of glacial flow and rock scouring - plant and animal fossils indicate different climate than todays. 4) Distributions of organisms: -several fossil organisms found on different landmasses that could not have crossed the oceans. such as the Mesosaurus.

3 types of convergent plate boundaries

1) Oceanic Continental - denser oceanic plate is subducted releasing gases that melt overlying mantle. - the basalt magma mixes with the granite from the continental crust and producing intermediate lava between basalt and granite called andesite. - andesite eruptions are explosive. - continental arc 2) Oceanic- Oceanic convergence: - older oceanic plate subducted because of higher density creating deep ocean trenches. -buoyant molten material rises fueling active volcanos. -creating an island arc. -molten material is mostly basaltic 3) Continental-Continental convergence: - neither are subducted because of low density. - produces a tall uplifted mountain made from sedimentary rock

3 stages of development in coral reefs

1) fringing reefs -develop along the margins of a landmass as an island - suitable living for reef building corals. -associated with active volcanoes, that kill coral reefs when lava runs down the side so no thick coral reef. 2) barrier reef -follows the fringing reefs -separated from land mass by lagoon 3)atoll - reefs continue to grow after volcano is submerging further and further.

rock effected by earths magnetic field..

1) igneous rocks - all contain magnetite -pieces of magnetite in magma align themselves with earths magnetic field, and once magma cools scientists record the angle of earths magnetic field. -most successful igneous rock is basalt with high magnetite content, and make up the oceanic crust. 2) Sedimentary rocks: -also contains magnetite -only if in water, it can align itself with earths magnetic field, and after rocks are buried scientists can see where rock originated from

Convergent Boundary Traits:

1) two plates coming together- -destroying oceanic crust. 2) deep ocean trenches. Which marks the beginning of the subduction zone. 3) Volcanic arc: - an arc shaped row of highly active and explosive volcanos. - it parallels the trench and occurs above subduction zone 4) deep earth quakes - great forces involved - mineral structure changes

Transform Boundary features

1) two types of transform faults: A) oceanic transform fault - most common B) continental transform fault -cuts across continent . 2) transform faults always occur between two segments of a mid ocean ridge. 3) Transform faulting: - the movement of one plate past another -produces shallow, strong earthquakes in lithosphere -oceanic transform fault 4) San Andreas fault: -cuts through continental crust producing large earthquakes. - a continental transform fault.

Divergent boundaries traits

1)when two plates move apart, such as along the mid ocean ridge. -2)common features along mid ocean ridges are rift valleys. - a rift valley is a downdropped linear depression, showing the plates are being pulled apart not pushed. 3) sea floor spreading occurs - rifting occurs when further splitting of the land, and more spreading causes land to drop below sea level. 4) Oceanic Rise- Fast spreading, gentle slope, east pacific 5) Oceanic Ridges: -slow spreading, steep slopes, mid atlantic ridge 6) the faster the sea floor spreads the less energy is released in each earth quake.

paleography

the study of historical changes of continental shapes and positions.