Formation of Mountain has been the subject of debate by many scholars. Mountains are landforms that exceed three hundred meters in height, relative to their surrounding land borders. The interactions of geochemical, geophysical, and structural forces, deep inside the Earth and those on the surface, millions of years ago, had resulted in the formation of the mountains. Strictly speaking, their existence was associated with the collision and drifting of continental plates, their subsequent thrusting, and uplift, after that.
Numerous research findings have shown that the majority of mountains were born at the constructive and destructive interfaces of oceanic and continental plates. Furthermore, structural thrusting and uplift processes made them outstanding. Also, other processes like rainfall, weathering, and erosion, helped to refine them into distinct edifices. A few of them are localized, while others manifested in associations, which are popularly referred to as mountain ranges.
Characterization of Mountain Formation, According to Type
Mountain typology arose from the circumstances that preceded their birth. For example, plate tectonics, volcanism, rifting, sedimentation, etcetera were the main drivers of different orogenic events. Even though the processes mentioned above are connected in a way, specific distinguishing attributes, helped geologists to categorize them in their respective classes.
Fold Mountains
Fold mountains are among the prevalent types of mountains, found in different parts of the world today. They occurred at destructive interfaces, where oceanic crusts and continental plates collided. Further, this event forced the more substantial oceanic crust to plunge beneath the less dense, sediments-bearing continental plate.
Consequently, thrusting took place, then followed by significant uplift to heights of several kilometers. Meanwhile, the subducted plate, in most cases, were buried deep into the hot mantle. Immediately this happened; it ignited the reaction of the over-heated mantle with the oceanic plate. This incident then culminated in the partial melting of rocks and other components of the mantle.
In the process of time, complete melting produced a hot liquid substance, called molten magma. Under the influence of subsurface pressure, this volatile fluid migrated in an upward direction seized the opportunity of the opening that was created at the subduction zone, from where it exited to the Earth’s surface. Lower surface temperature, allowed it to cool off into what is referred to as lava.
The overall effect of this process is that it emplaces magmatic bodies and plutonic rocks. It further boosted the size of the pre-existing structure. Compaction and homogeneity, then made the entire massive structure to become very solid. Earth’s surface processes like rainfall, wind, water and glacier erosions, helped to rework these massive rocky outcrops into high peaks.
Recall that the collision of both plates, as earlier described, was a destructive process. The effect of this collision resulted in severe structural deformation of some components of these plates. That is the more reason why this class of rock looks folded, with anticlinal and synclinal structural features. Himalayan mountains in Asia, the Alps in Europe, the Andes in South America, the Rockies in North America, and the Urals in Russia, are some examples of Fold Mountains.
Under Sea Mountain Ranges
When two plates drift apart, their interface is known as a constructive plate margin. This plane became an active orogenic zone because of the opening that was created by the separated plates. Eventually, that gap was filled with sediments and rock fragments that were dislodged from the lithosphere.
We must take note that underneath the Earth’s surface is a highly heated enclosure of molten magma. Therefore, the active gap referred to above, later induced, and paved the way for the volatile fluid to flow from the mantle towards the surface.
The decrease in temperature, as the magma journeyed its way upwards, made it to solidify and eventually extruded the overlying crust. This magmatic extrusion later produced an enormous bulge of mountainous outcrops—these mountain ranges spread over tens of kilometers of the seafloor. Typical examples of this mountain type are the Mid-Oceanic Ridge and the East Pacific Rise.
Volcanic Mountains
Volcanic mountains were formed when plates moved over active hot spots. Since the plates could only move over these candle-like spots for a distance of few inches per year, their impacts became severe on specific portions of the overriding plates in the course of seafloor spreading.
The prolonged heating by the hot spot, induced melting of the asthenosphere beneath the plate. With a long period of melting, volcanic eruption eventually took place, and the extruded magma then cooled off at the surface to produce volcanic mountains. This type of mountain is common in many active hot spot regions of the world. For instance, Mount Saint Helens in North America, Mount Pinatubo in the Philippines, Mount Kea and Mount Loa in Hawaii, are examples of this type of mountain.
Block Mountains
The force and impact of rifting that was occasioned by regional drifting of continental plates, caused the thinning of parts of the Earth’s crust. In areas where this impact was intense, faults and brittle deformation were generated.
Next, there was a movement of adjacent blocks along their common fault plane, and the block that seemed higher at any point of the fault plane suddenly moved downwards and later caused the subsidence of the graben.
The up-thrown block is referred to as a horst, while the downthrown block is called a graben. Most times, fault-controlled block mountains have a steep front side and a sloping backside. The most popular type of Block Mountain is the East African rift system, the Sierra Nevada Mountains in North America, and Harz Mountain in Germany.
Plateau Mountains
In simple terms, the plateau is referred to as a tableland because of its flat topographic relief. Plateaus can be formed from one or more of the previously stated mountain-building processes. Uplifts from the collision of tectonic plates and pilled-up lava deposits on the surface of the Earth may cause a part of the land to be significantly elevated. They become shaped and distinct from their surrounding land area due to the impacts of rivers, flooding, and glacier activities. Mountains mostly cover an area of several kilometers. Tibetan, Mongolian, Deosal, Colorado, and so on are some examples of plateau Mountains.
Mountain Formation and Earth’s Transition
Since the past 4.5 billion years, the Earth has witnessed numerous changes. Areas that were hitherto rivers in the past are today land areas because of mountain building processes. Also, elevated land areas are now being submerged due to this changing cycle. Indeed, the dynamic Earth is in a constant state of give-and-take. What is seen today on the Earth is a reflection of what happened in the past. It means that the Earth is in a constant state of subtraction and addition, this was necessary for it to maintain a stable equilibrium.
The interior of the Earth contains hot boiling fluid, called molten magma. The volatile state of the Earth’s subsurface has contributed to the instability of the Earth. Therefore, to relieve the Earth of its heat and pressure, the volcanic eruption had to occur in different parts of the globe, and water, in turn, found its way to occupy the spaces created by the extruded fluid.
This is with the intention to cool the Earth. Undigested remains (Xenoliths) of pre-existing parent rocks embedded in younger lithospheric materials, suggested that geological events must have reduced several massive structures to intangible pieces millions of years ago.
Besides, there are also relics of rocks that have been reduced from prominent outcrops to rubbles, and this means that the parent rock is already extinct. No doubt, the present is key to the past. The existence of craters geologically infers that they are extinct volcanoes that are presently inactive because of prevailing surface processes.
Though, slowly, plate tectonics is powered by convection currents, which today has witnessed the relocation of continents, thousands of kilometers away from their previous locations. For example, the South America plate was part of Africa over 500 million years ago. Plate tectonics have made some continents to shrink, while others have experienced crustal thickening.
Weathering, erosion, glacial movement, earthquakes, and other geological processes have reduced many mountains to flat surfaces. It is enough to prove that older mountains that existed at the early stages of the Earth are today, no more.
Worthy of note, is the fact that marine regression and transgression exercises, produced vast piles of sediments in some oceans, and as climatic conditions in some parts of the world grew harsh, most seas then shrunk in their sizes. Over time, these accumulated sediments became uplifted far above their original heights. While new mountains are still slowly being formed today in different parts of the word, surface processes are gradually reducing existing mountains to smaller sizes.
Conclusion
Mountain building processes have been the subject of debate by many scholars. However, more influential pieces of evidence have shown that the interaction of overlying plate components and the hot mantle, as well as near-surface structural openings at subduction zones, were the primary conditions preceding mountain formation. Generally speaking, the process is structurally controlled. Migration of the hot molten magma to the surface can be described as a secondary process, and the surface refining effects of weathering, erosion, rainfall, etcetera are tertiary processes.
The Earth is struggling to achieve some sort of balance, which is challenging to attain. Therefore, it has been constrained to a process of profit and loss. At certain times, it has to relinquish its materials, and at other times, it must grant access to supply from its interior.
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Featured Image: Formation of Mountains
M.Sc Geology, Nigeria
