The Earth’s surface is composed of dynamic features shaped by immense forces acting both above and below the crust. Understanding the formation of these landforms provides insight into the history and ongoing processes that define our physical environment. These structures influence everything from climate and water availability to the distribution of human populations.
Defining Landforms and Their Scale
A landform is a naturally formed, recognizable feature on the solid surface of the Earth. Geomorphologists categorize these features by their elevation, slope, and underlying rock structure; their collective arrangement is known as topography. Landforms exist across a spectrum of sizes. Macro-scale landforms include immense features like continents and ocean basins, while secondary, or micro-scale, features are smaller components such as hills, valleys, and individual dunes.
Creation by Internal Geologic Forces
The largest landforms originate from endogenic processes, powered by thermal energy stored deep within the Earth’s interior. This heat drives the movement of lithospheric plates (plate tectonics), which builds up and elevates the crust. When tectonic plates collide, compressional forces cause rock layers to bend and fold, creating fold mountains such as the Himalayas. Tensional or compressional forces can also fracture the crust (faulting), resulting in the formation of block mountains and rift valleys. Volcanism, another endogenic process, occurs when molten rock rises through fissures to the surface, where it cools and solidifies to build volcanic mountains.
Modification by External Forces
Once landforms are created, they are subjected to exogenic processes, which reduce their elevation and redistribute material across the surface. These external forces are driven by solar energy and gravity, operating through a combination of weathering, erosion, and deposition. This wearing down of the relief is collectively known as denudation. Weathering is the initial process of breaking down rock into smaller fragments through physical, chemical, and biological means. Physical weathering fractures the rock, while chemical weathering alters its mineral composition. Erosion then transports these weathered materials away, with agents like running water, wind, and ice carrying the sediment. Finally, deposition occurs when the transporting agent loses energy, causing the sediments to settle and accumulate, often forming features like floodplains and deltas.
Primary Terrestrial Landform Types
The interaction between internal building forces and external modifying forces results in four primary types of terrestrial landforms: mountains, plateaus, plains, and valleys.
Mountains
Mountains are large landforms that rise significantly above the surrounding land, featuring steep slopes and sharp peaks. They are most commonly formed by the compression of tectonic plates or through volcanic accumulation.
Plateaus
Plateaus are elevated areas characterized by a relatively flat, table-like surface. They form through the uplift of horizontal rock layers or by extensive volcanic flows. Plateaus often feature steep edges that rise abruptly from the surrounding terrain, and their summits are flattened by long-term erosion.
Plains
Plains are vast stretches of land with minimal changes in elevation, generally having a low elevation relative to sea level. These expansive, flat areas are often formed by the deposition of sediment carried by rivers or glaciers, or they can be the exposed portion of a continental shelf. Their flat terrain and fertile soil make them important agricultural regions.
Valleys and Canyons
Valleys and Canyons are low-lying depressions situated between higher lands. Valleys are primarily created by the erosive action of rivers, forming a characteristic V-shape, or by glaciers, which carve a wider U-shape. Canyons are an extreme form, representing deep and narrow valleys where a river has cut through rock layers.