The Seafloor Flashcards
(27 cards)
Percentage of earth’s surface area covered by water
71% and ~95% of inhabitable volume
Four major ocean basins
Pacific, Atlantic, Indian and Arctic
Earth core
~ 3400 km thick
Solid inner core and liquid outer core
Iron rich
Oceanic crust
Mostly Basalt
Denser than continental crust
Relatively young less than 200 million years old (because it’s denser it’s on the conveyor belt to be formed and destroyed )
Continental crust
Mostly granite
Less dense than oceanic crust
Up to 3.8 billion years old
How many tectonic plates are there
12 major tectonic plates
Divergent boundaries
Occurs when two tectonic plates move away from each other
As plates move apart new crust is formed usually around mid ocean ridges
Convergent boundaries
Two plates move towards each other,
Continent-Continent Collison
Two continental plates move towards each other, both plates are less dense so the plates collide and push upwards forming large mountain ranges (European Alps and Himalayas)
Continent-Oceanic crust collison
Oceanic crust subducts (more denser) under the continental crust
Results in the forming of volcanism, deep trenches and subduction zone creates mountains ranges (South America Andes)
Ocean-Ocean plate collision
Two oceanic plates collide, one runs over the other which causes it to sink onto the mantle forming a subduction zone
The subduction plate is bent downward to form a very deep depression in the ocean called trench
Transform Boundaries
Two plates slide past each other, may occur either on land or underwater
Such moments is rarely smooth and may cause tsunamis or earthquakes (San Andreas fault)
Mid-Ocean Ridges
A continuous chain of submarine volcanic mountains that encircle the globe like seams on a baseball
Rifts
Formed between plates at divergent boundaries (spreading centers)
Allows magma to side through rift, pushes up surrounding oceanic crust and cools to form new crust
Crust age: near ridges
Young rock and little sediment accumulation
Crust age: further from ridges
Older rocks and thick sediment layers from time accumulated
Where does crust recycling happen
Occurs at subduction zones
Lithogenous sediments
Derived from the break-down of continental rocks (weathering)
Large particles sink faster and give indication of distance from source
Fine particles may be transported long distances (Saharan dust to pacific ocean abyss)
Biogenous sediments
Derived from skeletons and shells of marine organisms
Two main forms: calcium carbonate and silica
Continental margins
Areas where continental and oceanic crust meet
Active margins
- More relative to each other (convergent, divergent and transform faults)
- Characterized by steep, rocky shorelines, narrow continental shelves and steep continental slopes (~6’), trench with no rise
Passive margins
Relatively inactive geologically
Characterized by flat, wide coastal plains, wide continental shelves and gradually sloping continental slopes (~2’)
Continental shelf
- shallowest part of the continental margin
- Covers ~8% of seafloor
- 0-200 m depth
- biological the richest area of the ocean
-composed of continental crust
Continental slope
-Closest thing to an exact edge of the continent
- covers ~11% of the seafloor
- 200-3000 m depth
- average gradient ~4’
