I. Introduction
1. Mountains: Towering Elevations on Earth’s Surface
Mountains are towering landforms that rise above their surroundings, capturing our imagination with their majestic presence. Let us explore some fundamental aspects of mountains.
1.1 Elevations on the Surface of the Earth
Mountains represent some of the most significant elevations on the Earth’s surface. These impressive formations manifest in two primary settings: on continents and within oceans. They exhibit unique characteristics in each of these environments, shaping our planet’s diverse landscapes.
1.2 Mountains: More than 1000 Meters
To qualify as mountains, these landforms typically surpass an elevation of 1000 meters (3280 feet) above sea level. This height criterion distinguishes them from other land features, such as hills, which we will discuss shortly.
2. Hills: Gentle Undulations in the Terrain
While mountains dominate the skyline with their grandeur, hills represent gentler undulations in the Earth’s terrain. Let us explore their defining attributes.
2.1 Hills: Less than 1000 Meters
Hills are landforms characterized by their lower elevation compared to mountains. Generally, hills rise to heights less than 1000 meters (3280 feet) above sea level. Although less imposing than mountains, they still contribute to the captivating beauty of the natural landscape.
3. Mountain Ridges: Long Systems of Elevated Land
Mountain ridges are extensive networks of elevated land formations, comprising mountains and high hills aligned in a linear fashion. Let’s delve into the distinctive qualities of mountain ridges.
3.1 Narrow and Striking
Mountain ridges are narrow formations that traverse the Earth’s surface. These elongated land systems exhibit a continuous line of interconnected mountains and high hills. Their prominent profiles create visually striking vistas that captivate observers.
4. Mountain Ranges: Long and Narrow Strips of Elevated Land
Mountain ranges are notable landforms characterized by long, narrow strips of elevated terrain. These geological features play a significant role in shaping the Earth’s physical geography.
4.1 Continuous Elongated Elevations
Mountain ranges are distinguished by their continuous elongated elevations, typically encompassing a combination of mountains and hills. These elevated land strips stretch across vast distances, creating iconic landscapes and offering valuable insights into the Earth’s geological history.
5. Mountain Chains: Parallel Mountain Systems of Different Periods
Mountain chains are parallel systems of long, narrow mountains that span different periods in the Earth’s history. They provide valuable clues about the geological evolution of our planet.
5.1 Parallel and Narrow
Mountain chains consist of a series of mountains aligned in parallel fashion. These long and narrow formations often exhibit similar geological characteristics and share a common origin. Examining mountain chains allows us to trace the geological transformations that occurred during different periods in Earth’s history.
6. Mountain Systems: Diverse Ranges of the Same Period
Mountain systems encompass a collection of different mountain ranges that originated during the same geological period. By exploring mountain systems, we gain a deeper understanding of the Earth’s dynamic geological processes.
6.1 Distinct Ranges of the Same Period
Mountain systems consist of various mountain ranges that share a common origin and formation period. These ranges may exhibit unique characteristics and geographical distributions. Studying mountain systems contributes to our knowledge of the Earth’s complex geological history.
7. Mountain Groups: Unsystematic Patterns of Different Mountain Systems
Mountain groups comprise unsystematic patterns of different mountain systems. These collections of diverse landforms offer valuable insights into the Earth’s geological diversity.
7.1 Heterogeneous Arrangements
Mountain groups are characterized by their unstructured and heterogeneous arrangements of different mountain systems. These unique formations often exhibit diverse geological features and contribute to the intricate tapestry of the Earth’s landscape.
8. Cordilleras: Complex Assemblages of Mountain Systems and Groups
Cordilleras are complex assemblages consisting of multiple mountain systems and groups. These extensive formations shape vast regions of the Earth’s surface, each with its distinct characteristics.
8.1 Ridges, Ranges, and Mountain Chains
Cordilleras encompass a wide array of landforms, including ridges, ranges, and mountain chains. These interconnected elements create expansive and awe-inspiring geological formations. The complex nature of cordilleras allows us to appreciate the dynamic geological processes that have shaped our planet.
II. Types of Mountains
Mountains can be classified based on their origin. The two primary categories are original or tectonic mountains and circum-erosional or relict mountains.
1. Original or Tectonic Mountains
Tectonic mountains are further classified into volcanic mountains, folded mountains, block/horst mountains, and dome mountains.
1.1 Volcanic Mountains
Volcanic mountains are formed due to the accumulation of volcanic materials. They result from volcanic activity and can take various forms, such as cinder cones, composite cones, acid lava cones, and basic lava cones.
1.2 Folded Mountains
Folded mountains are true mountains and are the youngest mountains on Earth. They are formed by the folding of sedimentary rocks under strong compressive forces. These mountains extend for greater lengths but have smaller widths. They are typically found along the margins of continents facing oceans. Folded mountains are unique to Earth and hold the key to understanding the differentiation of the Earth’s crust. They are always part of a mountain range system. Examples of folded mountains include young folds, mature folds, and old folds.
Phases of Fold Mountain Orogeny
Fold mountain orogeny encompasses different periods in Earth’s history, resulting in various mountain systems:
- Archean Mountain: Eastern Ghats
- Caledonian Orogeny: Kjollen Mountains
- Harcynian Mountain: Appalachian Mountains, Urals, Great Dividing Range
- Alpine-Tertiary Mountain System: Andes, Rockies, Atlas, Carpathian Mountains, Alps, Himalayas
- Trans-Eurasian Mountain System: Pyrenees, Jura, Alps, Apennine (Italy), Carpathians, Caucasus, Georgia, Azerbaijan Mountain Range, Armenia
Types of Folds
The type of fold depends on the strength and direction of compressive forces:
- Symmetrical fold
- Asymmetrical fold
- Isoclinal fold
- Overturned fold
- Recumbent fold
- Nappe (see figure: Nappe)
- (Figure: Types of Folds)
1.3 Block/Horst Mountains
Block or horst mountains are formed by a combination of tensile, compressive, and tearing forces. According to the faulting theory, faulting in the ground surface leads to the formation of block mountains. This process involves the rise of the middle block between two mountains and the downward movement of side blocks, eventually resulting in a rift valley formation. Examples of block mountains include young block mountains around Albert, Warner, Klamath Lakes, and the Wasatch Range in the Utah province. Other examples include the Vosges and Black Forest Mountains, Salt Range of Pakistan, and Sierra Nevada Mountains in California.
1.4 Dome Mountains
Dome mountains originate from magmatic intrusion and the upwarping of crustal surfaces. They are characterized by their dome-shaped appearance and can be further classified into different types, including normal domes, lava domes, batholith domes, and laccolithic domes.
2. Circum-Erosional or Relict Mountains
Circum-erosional or relict mountains are remnants of past mountain erosion and denudation processes. These mountains have undergone significant weathering and erosion over time. Examples of relict mountains include the Vindhyach
al Ranges, Aravalli Mountains (a combination of fold and residual mountains), Satpura Range, Western Ghats, and Eastern Ghats (also a combination of fold and residual mountains).
Escarpments
Escarpments are steep vertical faces or cliffs that resemble mountain-like elevations. They can occur at the edge of a plateau, as part of a block mountain, or due to differential erosion. Escarpments are often the result of exposed intrusive landforms. Examples of escarpments include the Maikal Hills, Rajmahal Hills, Andalusian Mountains, Iberian Meseta, and Fouta Djallon.
III. Theories of Mountain Building: Unveiling the Forces Behind Earth’s Majestic Landforms
1. Geosynclinal Orogen Theory of Kober: Explaining the Formation of Mountains
The Geosynclinal Orogen Theory proposed by Kober aims to provide a comprehensive understanding of mountain building. Let’s delve into the key aspects of this theory.
1.1 Objectives: Origin and Development of Mountains
The Geosynclinal Orogen Theory seeks to explain the origin and development of mountains based on the concept of geosynclines. It elaborates on various aspects of mountain building, including their formation, geological history, evolution, and development.
1.2 The Base of the Theory: Process of Mountain Building
According to Kober, the process of mountain building, also known as orogenesis, occurs in geosynclines. Geosynclines are trough-like structures surrounded by rigid masses known as kratogens. The force of contraction, resulting from the cooling of the Earth, generates horizontal movements of these rigid masses, linking them with the geosynclines.
1.3 Mechanism of the Theory: Stages of Mountain Formation
The Geosynclinal Orogen Theory consists of three stages: lithogenesis, orogenesis, and gliptogenesis.
- Lithogenesis: This stage involves the creation of geosynclines due to the force of contraction caused by the cooling of the Earth.
- Orogenesis: In this phase, mountain building occurs through compressive forces generated by the movement of forelands. The contraction of geosynclinal sediments leads to the formation of mountain ranges. Parallel ranges are formed on either side of the geosyncline, while the middle portion unfolds to create a median range.
- Gliptogenesis: This stage represents the gradual rise of mountains and subsequent denudation processes, such as fluvial erosion, leading to the gradual lowering of the mountain’s height.
1.4 Evaluation of the Theory: Strengths and Limitations
While the Geosynclinal Orogen Theory offers valuable insights into mountain building, some aspects of the theory have faced scrutiny. The force of contraction alone may not be sufficient to explain the formation of gigantic mountains like the Himalayas. Additionally, the theory’s explanation of the north-south extension of mountains, such as the Rockies and Andes, remains inadequate. Nevertheless, the theory successfully explains the formation of folded mountains and provides a framework for understanding the structure of various mountain systems.
2. Thermal Contraction Theory of Jeffrey: Exploring the Influence of Cooling Earth
The Thermal Contraction Theory, proposed by Jeffrey, focuses on the origin and evolution of major relief features on Earth’s surface. Let’s delve into the key aspects of this theory.
2.1 Objectives: Origin and Distribution Patterns
The Thermal Contraction Theory aims to explain the origin and distribution patterns of major relief features, including continents, ocean basins, mountains, island arcs, and festoons.
2.2 Forces Responsible: Cooling of the Earth and Decreased Rotation Speed
According to Jeffrey, the forces responsible for these relief features are the cooling of the Earth and the subsequent decrease in the Earth’s rotation speed.
2.3 Mechanism of the Theory: Based on Thermal Contraction
The Thermal Contraction Theory is based on the concept of thermal contraction. As the Earth cools, it undergoes contraction, leading to the formation of various relief features.
2.4 Evaluation of the Theory: Challenges and Interpretations
While the Thermal Contraction Theory provides a plausible mechanism for the formation of relief features, it has faced criticism for erroneous concepts, such as the impact of decreased rotation speed of the Earth. The theory struggles to explain the uneven distribution of continents and oceans in the present-day Earth. However, it does offer insights into the even contraction from all sides of the Earth and provides a basis for understanding the arrangement of certain mountain ranges, like the Rockies and Andes.
3. Sliding Continent Theory of Daly: Unveiling the Downward Movement of Continents
The Sliding Continent Theory, proposed by Daly, focuses on the downward sliding movement of continental masses driven by gravitational forces. Let’s explore the key aspects of this theory.
3.1 Keynote: Downward Sliding Movement of Continental Masses
Daly’s Sliding Continent Theory posits that continents slide downward due to gravitational forces, contributing to mountain building and the formation of various relief features.
3.2 Objectives: Origin, Evolution, and Causes of Mountain Building
The theory aims to explain the origin, evolution, and causes of mountain building through the downward sliding movement of continental masses.
3.3 Forces Responsible: Gravitational Forces
The primary force driving the sliding continent process is gravity. Continental masses experience downward movement, which leads to the creation of mountains and other relief features.
3.4 Evaluation of the Theory: Limitations and Interpretations
Although the Sliding Continent Theory introduced the concept of downward sliding continental masses, its present-day interpretations have been challenged by newer scientific advancements. The theory does not align with current understandings of mountain building processes. However, Daly’s theory laid the groundwork for future research on the movement of continents and its role in shaping the Earth’s topography.
4. Plate Tectonic Theory: Revolutionizing our Understanding of Mountain Building
The Plate Tectonic Theory has revolutionized the field of geology and provides a comprehensive framework for understanding mountain building. Let’s delve into the key aspects of this influential theory.
4.1 Objectives: Explaining Relief Features and Tectonic Events
The Plate Tectonic Theory seeks to explain various relief features, including mountain building, as well as tectonic events such as faulting, folding, continental drift, vulcanicity, and seismic events.
4.2 Forces Responsible: Orogenetic Force and Thermal Convective Currents
The theory identifies two primary forces responsible for mountain building: orogenetic force, generated by the collision of plate boundaries, and thermal convective currents, which drive the movement of mountains.
4.3 Base of the Theory: Convergent Plate Boundaries
Plate tectonics occur at convergent plate boundaries, where two plates collide. These boundaries can be classified as constructive/divergent/accreting, destructive/consuming/convergent, or conservative/shear.
4.4 Mechanism of the Theory: Convergence and Collision of Plates
The Plate Tectonic Theory explains mountain building through the convergence and collision of plates at destructive plate boundaries. Three situations of plate motion are discussed: convergence of two oceanic plates, convergence of continental and oceanic plates, and convergence of two continental plates.
4.5 Evaluation of the Theory: Strengths and Cyclic Pattern of Mountain Building
The Plate Tectonic Theory has made significant strides in explaining the origin, evolution, and distribution of relief features. It accounts for the cyclic pattern of mountain building and identifies major periods of mountain formation throughout Earth’s history. Additionally, the theory offers insights into the breakup of the supercontinent Pangea and the subsequent evolution of continents and ocean basins.
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