Earth’s Layers, Plate Tectonics, and Mountain Formation
What Are the Different Layers of the Planet?
The Earth is made up of three concentric zones: the crust, mantle, and core.
The crust is the thin outer layer forming the continents and the ocean floor. Oceanic crust is thinner and denser than continental crust. Some ocean floors are only 15-20 km thick. The crust is enriched in O, Si, Al, Ca, Na, and radioactive elements.
The mantle is the middle layer, rich in Mg, Fe, and silicates (combinations of mainly silica and oxygen), and the core is the dense inner layer composed of iron and nickel. The inner part of the core is liquid and extremely hot.
Meaning of Mountain
Mountains can be explained as landforms that rise well above the surrounding land for a limited area in the form of a peak. Mountains are steeper, larger, and taller than hills and are more than 600 meters in height.
Types of Plate Movement
Divergence, convergence, and lateral slipping.
At the boundaries of the plates, various deformations occur as the plates interact; they separate from one another (seafloor spreading), collide (forming mountain ranges), slip past one another (subduction zones in which plates undergo destruction and remelting), and slip laterally.
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.
Asthenosphere
The asthenosphere is the highly viscous, mechanically weak, ductilely-deforming region of the upper mantle of the Earth. It lies below the lithosphere, at depths between 100 and 200 km below the surface, but perhaps extending as deep as 700 km.
Plate Tectonics
Eurasian plate, Australian-Indian plate, Philippine plate, Pacific plate, Juan de Fuca plate, Nazca plate, Cocos plate.
Types of Convergence
- When a plate of continental crust converges with a plate of oceanic crust, the heavier oceanic crust will move under the continental crust, and this process is called subduction. This is the process through which mountains and volcanoes are formed when the subducted oceanic crust is melted and recycled to the surface (e.g., West coast of North and South America).
- When a plate of oceanic crust converges with another plate of oceanic crust, the older crust will subduct under the newer crust that is less dense, leading to volcanic ring islands (e.g., Japanese islands).
- When two plates of continental crusts come into contact with each other, neither of them will subduct beneath the other due to their densities. So this collision leads to the formation of big mountains with fragments of oceanic sediments in them, even in the highest peaks (e.g., Alps in Europe, Himalayas in Asia).
Types of Mountains
Mountains can be classified into five different basic types based on the cause that formed the mountain, type of rocks, shape, and placement of land.
- Fold Mountains: These are the most common types of mountains. These are formed when two continental tectonic plates collide and their edges crumble to form mountains. The crust is uplifted, forming folds on top of the other.
- Fault-Block Mountains: The fault-block mountains or block mountains are created when faults or cracks in the Earth’s crust force materials or blocks of rock upward or down.
- Dome Mountains: Also called Upwarped Mountains. These mountains are formed when large amounts of molten rock or magma push the Earth’s crust from underneath. The magma, in this case, never reaches the top surface of the Earth.
- Volcanic Mountains: Are created by volcanoes, as the name suggests. They are created when magma pushes its way from beneath the Earth to the crust, and when it reaches the surface, it erupts as lava, ash, rocks, and volcanic gases. These erupting materials build around the vent through which they erupted. These mountains are then shaped by further eruptions, lava flows, and collapses. Mount Fuji in Japan, Mount Rainier in the US, including Mauna Loa and Mauna Kea on the Big Island of Hawaii, are examples of volcanic mountains.