Ocean Floor Flashcards
Pangea
the theory that there was just one land mass
Theory of Plate tectonics
theory that suggests that the outer crust of the Earth, known as the lithosphere, consists of a number of separate plates which ‘float’ on the underlying layer (the mantle)
Convergent boundaries
where two plates are moving toward each other
Divergent boundaries
where two plates are moving away from each other and new crust is forming from magma that rises to the Earth’s surface between the two plates
Transform boundaries
where plates slide sideways past each other
Evidence supporting the theory of plate tectonics includes:
- fits between continents (for example the east coast of South America and the west coast of Africa);
- paleontology showing the distribution of fossil species;
-magnetic stripes in the ocean floor.
The pattern of magnetic stripes provides clear evidence of ocean floor spreading
Lithosphere
the rigid outer part of the earth, consisting of the crust and upper mantle
Subduction
(where one plate is forced under another)
the sideways and downward movement of the edge of a plate of the earth’s crust into the mantle beneath another plate
Ocean trenches are…
long and narrow and are the deepest part of the ocean floor
Mid-ocean ridges are…
underwater mountain ranges, formed by upward movement and cooling of the underlying magma, which cools and solidifies as it emerges
Mountain range formation occurs at…
divergent tectonic plate boundary and is responsible for seafloor spreading
Abyssal plains
relatively flat areas of the ocean floor, situated between ocean ridges and continental rises
Mantle convection (process of abyssal plain being formed)
the upwards movement of molten material from the oceanic crust, which solidifies and forms new ocean crust.
How is a volcano formed
where there is an opening in the Earth’s crust, allowing hot gases and molten rock to escape from below the surface
Volcanoes can be formed…
where tectonic plates are moving towards each other (convergent)
Earthquakes occur when…
there is a sudden release of energy in the Earth’s crust, creating shock waves
What happens when two plates slip past eachother?
they may lock. Continued plate movement results in strain building up until the plates suddenly move again, release stored energy and creating an earthquake
Tsunami
a very large wave produced by the sudden movement of a very large volume of water
Process of tsunami development
In deep, oceanic water, a tsunami wave travels quickly. As the wave approaches shallow, coastal water, it slows down but forms large, waves
Hydrothermal vents occur…
in the deep ocean, typically along mid-ocean ridges where two tectonic plates are diverging
How are hydrothermal vents formed?
- Sea water which seeps into cracks in the ocean floor and water from the upwelling magma, is released from the hot magma
- A hydrothermal vent forms where the hot water passes up through the ocean floor and, as it cools, the dissolved minerals start to precipitate out.
Minerals in a hydrothermal vent include…
the sulphide of iron, copper and zinc.
Hrydrothermal vents can be super heated when…
There is high pressure
Isostasy
the buoyant properties of layers of rocks which floats on other layers, according to their density and thickness
Continental shelf
a gently sloping region surrounding the continents, over which the sea is relatively shallow covered with sediment, derived from erosion of the continents
The depth of water over the continental shelf depends upon two main factors:
- isostatic changes in land height
- changes in sea level
The principle of isostasy shows that…
the Earth’s crust is generally higher where it is thicker and less dense; lower where it is thinner and more dense
Littoral zone can also be called…
the intertidal zone
Littoral zone
the area of a coast between the high water mark and the lowest part of the shore which is permanently submerged
Littoral zone is the part of the sea shore that…
the land meets the sea
The nature of the shore depends on two main factors:
- The geology of the adjacent land (shape of the shore and substrate that makes the shore)
- The exposure to erosion by the sea (wave action and erosion and organisms that live there)
Some types of rock, such as granite, are…
resistant to weathering and break down less easily than softer rocks, such as sandstone
What does repeated pounding effect of the sea do to the rocky shores?
grades the rocks according to size with the largest boulders being left at the top of the shore
Rocky shores often show…
clear zonation of different species, which many appear in distinct bands along the shore
Resistance to desiccation
time spent out of water and in changing temperature before death
Environmental factors that influence communities on a rocky shore
- desiccation
- temperature
- wave action
- light intensity
- aspect
- slope
- the nature of the substrate
Zonation
a separation of organisms in a habitat into definite zones or bands according to biological and physical factors, common in rocky shore habitats
High-tide zone
- Area that only has water during high tides
- Organisms must survive long periods of time with no water and fluctuating temperatures.
- Organisms have strategies to avoid predators.
- Organisms include: chitons, crabs, isopods and barnacles
Middle-tide zone
- Area exposed to air once or twice a day during low tide.
- Organisms need strategies to cope with desiccation.
- Organisms include: limpets, periwinkles and mussels
Low-tide zone
- Usually covered with water except during the lowest tides
- Organisms have few strategies for avoiding desiccation
- Organisms include: seaweed algae, sea stars, sea urchins, sea anemones and oysters
Mangroves form..
woodland or a shrubland habitat, in coastal or estuarine conditions where sedimentation of silts occurs
The extensive root system…
help to trap particles suspended in the water and reduce water flow - which increases the deposition of sediments
The root systems and accumulated sediments..
provide habitats for a wide variety of other organisms, including algae, oysters, crabs, barnacles and other crustaceans, sponges and fish
The root system of mangroves also…
dissipates wave energy and thus helps to protect coastal areas from erosion
Primary physical factors that mangroves have to contend with for survival:
- High salt content in water (salinity)
- Low oxygen content in the substrate (anoxic soil)
Red mangrove roots are nearly…
impermeable to salt because of a very efficient filtration method
Black mangroves expel…
salt through pores on the underside of their leaves
Perches the mangrove above the high tide
Prop roots
Prop roots can absorb…
oxygen through their bark
Pneumatophores
Specially adapted root structures which obtain oxygen directly from the air (Black mangroves)
Sandy shores are formed by
erosion of sandstone and deposition of sediments by waves
Sandy shores are unstable because
the fine mineral particles are easily moved by winds and tides
Infauna
animals living within the sediment of the ocean floor, river or lake beds
Types of infaunas
ghost crabs
bivalve molluscs annelid worms (such as ragworms and lugworms)
Where is least exposed to erosion?
Muddy shores as the silt particles include very fine mineral sediments and organic remains
Estuaries
a semi-enclosed coastal body of water, which has a connection with the sea and within which sea water is diluted with fresh water derived from land drainage
Many estuaries have a…
muddy substrate as the relatively slow flow of water allows fine suspended particles to settle
Deltas are formed when…
a river carrying suspended sediments reaches a large body of water, such as a lake or an ocean
As the river increases in width…
the flow rate of water decrease (slows down) and, as a result, the suspended sediments settle
