Why are trenches bordering chains of volcanoes and island arcs? What happens at trenches? How do oceanic ridges form?

Running Head: GEOGRAPHY
Geography
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1GEOGRAPHY
Question 2- Why are trenches bordering chains of volcanoes and island arcs? What
happens at trenches? How do oceanic ridges form?
The Volcanoes can be considered as the vibrant manifestation of the plate tectonics
processes. These are extremely common along with the divergent and convergent plate
boundaries. These are also found in the lithospheric plates which are away from the plate
boundaries. The ocean trenches are the long and narrow depressions on the seafloor. These
are the chasms which are at the deepest part of the ocean and the natural sports too. These
trenches are found in also each ocean basin. The deepest trenches ring the Pacific ocean that
is called the “Ring of Fire” consisting of the active volcanoes. The island arcs on the other
hand form on the opposite edge of a subducted slab. Taken for example, there is a
connecting subducting slab along with a trench. One example of the island arc is the Kurli
Island Aleutian Isands of Alaska.
There are many happenings in the deep-ocean trenches. The oceanic crust bends downward
in order to form a deep ocean trench. Afterwards the oceanic crust starts sinking back to the
mantle through a special process named as subduction. The meeting point of continental crust
Deep ocean trench Island arc

2GEOGRAPHY
and oceanic crust develop the trench. At the same time, the oceanic crust sinks in the
continent and gets into the mantle having bent towards it. The oceanic ridges are the long
submarine mountain chains which extend approximately 80,000 kilometres. These are the
most significant parts of the ocean basins. As a whole, the oceanic ridge system can be
considered as the most prominent characteristic on the surface of the earth. The oceanic
crusts are developed at the seafloor which spreads the centres at those oceanic ridge crests.
The earthquakes at the ridge crests signify that oceanic crust is in high tension at that point.
Question 4- Explain the origin of the magnetization pattern of the ocean floor.
There are various types of evidence which support the sea-floor spreading theory of
Hess. The evidences are the eruptions of the molten materials, the magnetic strips in the rock
of the ocean floor and the rocks themselves. As per the theory of Hess, the oceanic crusts
form along the submarine mountain zones which are also known as the mid-ocean ridge
system. It gradually spreads out laterally away from them. This played a pivotal role in the
growth of the plate tectonics that is a theory which revolutionized geologic thought in the 20th
century. At the time when the scientists became aware of the patterns in the rocks of the
ocean floor, more support was found for the sea-floor spreading. It is surprising to note that
the magnetic poles of the earth have reversed themselves several times in the history of the
earth. About 8,000,00 years ago the last reversal had happened. The scientists have
discovered that rocks which make up floor of the ocean lie in the patterns of magnetic strips.
These are the strips which hold a record of reversals in the magnetic field of the earth.