Mountains form through a variety of complex and varied geological processes primarily driven by the movement of tectonic plates. The three main mechanisms through which mountains are created are tectonic activity, volcanic activity and erosion.
Tectonic activity
Tectonic activity refers to the movement and interaction of Earth’s tectonic plates. These massive slabs of the Earth’s lithosphere fit together like a jigsaw puzzle and are constantly moving, although very slowly, which can cause earthquakes, volcanic activity, mountain building, and ocean trench formation.
Convergent Plate Boundaries occur when two tectonic plates collide, where one plate may be forced beneath the other in a process called subduction, leading to earthquakes, volcanic activity and to the formation of mountain ranges (e.g., the Himalayas spreading over India, Nepal, Buthan, Tibet and Pakistan, and the Cordillera Range spreading over both South and North America).
Divergent Plate Boundaries occur when plates moving away from each other, which can create new crust and form ridges (e.g. the Mid-Atlantic Ridge, with the North American and Eurasian plates spreading apart).
Transform Plate Boundaries are when plates slide past one another horizontally which can create stress and strain, leading to earthquakes. This causes fault lines and uplift, contributing to mountain formation (e.g. the San Andreas Fault in California). In this instance, no new crust is formed or destroyed: plates are just reshuffled.
Thus fold and block mountains can be created.
Fold Mountains arise when two tectonic plates collide at a convergent boundary. The immense pressure causes the Earth’s crust to buckle and fold, pushing rock upwards. (e.g. the Himalayas, a prime example, formed by the collision of the Indian and Eurasian plates over 25 million years ago).
Block Mountains, also known as fault-block mountains, occur when tectonic forces cause the crust to fracture. One block of rock may be pushed upwards while adjacent blocks sink, forming steep, rugged terrain (e.g. the Sierra Nevada range in California). Another example of Block Mountains is the Drakensberg range in South Africa, where the predominant rugged features of the range are due to block faulting and erosion.
Volcanic activity
Volcanic Mountains are formed when magma and volcanic debris from beneath the Earth’s crust erupt to the surface from a vent located at the volcano’s apex. Over time, repeated eruptions can build up significant height. There are two types: Stratovolcanoes, which grow mainly by repeated eruptions and avalanches of hot fragmental material with occasional flows, which tend to have layered internal structure, high silica content and slopes of about 30 degrees (e.g. Mount Fuji in Japan); and shield volcanoes formed by the eruption of very fluid lava with low silica content which can travel far, resulting in the slow accumulation of layers. They have gentle slopes and occur in the oceans forming volcanic islands (e.g. Mauna Kea in Hawaii).
Erosion
Erosional or residual mountains are carved out by water, ice or wind through time, without any tectonic activity or volcanic eruptions being involved. Erosion can sculpt existing landforms into mountains. Rivers and glaciers can carve deep valleys, leaving behind elevated regions known as erosional mountains. This process can take millions of years, steadily shaping the landscape (e.g. the spectacular Mount Roraima at the junction of Venezuela, Guyana and Brazil).
The formation of mountains is a complex mix of geological processes, which include tectonic activity, volcanic eruptions, and erosion. Whatever formation process each mountain went through, each range tells a unique story of the Earth’s dynamic history. The majestic formations that are mountains bear witness to the ongoing powerful forces at work that not only shape the landscape but also influence climate, biodiversity, and human activity. Understanding how mountains form enhances our understanding of the natural world and highlights the ongoing processes that continue to sculpt our planet.
