30 Jan 2024 : Daily Answer Writing
Q1) To what extent does the theory of plate tectonics explain the major geological features of the Earth’s surface? Discuss with suitable examples.
ANSWER
- Plate tectonics is a geological theory according to which earth’s lithosphere is broken into distinct plates floating on asthenosphere, upper part of the mantle.
- Tectonic plates are massive, rigid lithospheric slabs generally composed of both continental and oceanic crust.
- Volcanic activity, earthquakes, mountain-building and oceanic trench formation occur along these plate boundaries.
The plate tectonics theory is based on two major scientific concepts:
- Concept of continental drift: Continents are not static and they move over the earth surface.
- Concept of sea floor spreading: new crust is created by magma upwelling along the oceanic ridge, while the older crust is pushed on either side due to volcanic eruption and sinks back down in the mantle at ocean trenches.
Plate tectonic theory has a seminal role in explaining the formation of major geological features:
- Submarine features:
- a) Mid-oceanic ridges: Mid oceanic ridges occur along divergent plate boundaries. Here, new ocean floor is created as the tectonic plates diverge.
E.g., Mid-Atlantic ridges.
b) Trenches: Trenches are often the result of subduction of tectonic plates.
E.g., Kermadec trench, Marina trench etc.
c) Seamount and Guyots: Seamounts and guyots are result of underwater volcanic (tectonic) activity.
E.g., Axial seamount.
- Mountains:
a) Fold mountains: Fold mountains are formed when two or more tectonic plates push against each other (convergence).
E.g., Himalayas, Andes, Alps etc.
b) Block mountains: When the Earth’s crust cracks, faulting occurs, resulting in the formation of block mountains.
E.g., Vindhyas, Vosges mountains etc.
c) Volcanic mountains: Volcanic mountains, in general, are very closely found in the regions that have been intensely folded, faulted, subducted etc.
E.g., Mt. Fuji, Mt. Merapi etc.
- Rift valleys: Rift valleys are result of tectonic activity where the submergence of land masses occur between block mountains.
E.g., East African rift valley, Narmada rift valley etc.
- Plateaus:
a) Tectonic plateaux: Formed by earth movements that cause uplift.
E.g., Deccan plateau in India.
b) Volcanic plateaux: Molten lava may issue from the Earth’s crust and solidify to form lava plateaux.
E.g., Columbia snake plateau.
- Island arcs: Island arcs are formed along the convergent tectonic plate boundaries, principally originating on oceanic crusts.
E.g., Ryukyu Islands, Kuril Islands, Marina islands etc.
However, several geographical features of the Earth are explained outside of the plate tectonic theory:
- Landforms formed by running water.
E.g., flood plains, ox-bow lakes, deltas etc.
- Landforms formed by the activity of glaciation.
E.g., outwash plains, pyramidal peaks etc.
- Formation of the desert landforms occur independent of the volcanic activities. E.g., dunes, barchans etc.
- The Karst topography is formed by the dissolution of the soluble rocks such as limestones, dolomite, and gypsum.
E.g., Karst topography in Central America, Caribbean, Italy etc.
- Coastal landforms formed by the actions of waves, tides, currents etc.
E.g., cliffs, beaches etc.
Although many of the geological features can be well explained by the theory, plate tectonics is but a part of the larger framework of geological studies to understand various important geological features of the planet.
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