A landform is a natural feature on the Earth’s surface. These features vary significantly in scale, ranging from immense continental plains and towering mountain ranges to smaller elements like river valleys and isolated sand dunes. The study of these physical features and the processes that create and modify them is known as geomorphology. Landforms are dynamic structures, constantly being shaped and reshaped by forces originating both deep within the Earth and upon its surface over geologic time.
How Landforms Are Categorized
Landforms are grouped primarily based on the dominant forces responsible for their creation, a system known as genetic classification. This method separates features based on whether they were formed by forces originating inside the Earth (endogenic) or those acting externally (exogenic).
Endogenic forces, driven by the Earth’s internal heat, include plate tectonics, faulting, and volcanism, which generally build up the crust. Exogenic forces, powered by solar energy and gravity, involve weathering, erosion, and deposition. These external forces work to wear down and redistribute crustal material.
The interplay between these forces determines the Earth’s topography. Internal forces create large-scale initial relief, while external forces modify and smooth this relief over millions of years. Landforms are thus products of uplift and destruction, a continuous cycle of creation and modification.
Landforms Shaped by Internal Earth Processes
Internal processes (endogenic forces) are responsible for the largest landforms on the planet, often involving tectonic plate movement. One common result is the formation of Fold Mountains, which arise from intense compression when two continental plates collide. This pressure causes rock layers to buckle and fold, pushing the crust upward into high peaks like the Himalayas.
Fault-block Mountains form where tensional or compressional forces fracture the Earth’s crust. Vertical movement along these faults leads to some blocks being uplifted (horst) and others dropping down (graben), creating mountains with steep, linear fronts separated by rift valleys. Tectonic Plateaus are similarly formed by large-scale uplift, resulting in broad, elevated, and relatively flat-topped areas of crust.
Volcanic activity also shapes the landscape, producing features based on the magma’s properties. Shield Volcanoes, like Mauna Loa, are built by eruptions of highly fluid, low-viscosity basaltic lava that spreads out widely over great distances. This process results in a broad, dome-shaped structure with gentle slopes.
In contrast, Composite Cones (stratovolcanoes) are steep-sided, conical mountains formed by alternating layers of highly viscous, silica-rich lava and fragmental materials such as ash and cinders. The sticky nature of this lava prevents it from flowing far, building up the symmetrical cone shape and leading to more explosive eruptions due to trapped gases.
Landforms Created by Surface Forces (Erosion and Deposition)
External processes (weathering, erosion, and deposition) constantly wear down and modify landforms created by internal energy. Water is a powerful agent of erosion, carving out V-shaped Valleys as rivers rapidly cut downward through the landscape. The eroded material is transported and deposited downstream, forming Alluvial Plains or floodplains, which are flat, fertile stretches built up by layers of river sediment.
Glaciers are a significant erosional force, creating U-shaped Valleys by scouring the sides and bottom of pre-existing river valleys with ice and rock debris. When these glaciers melt, they deposit poorly sorted material called moraine, which can form ridges and hills at the edges of the ice. Along coastlines, wave action constantly shapes the land through both erosion and deposition.
Erosive wave energy carves out steep Cliffs and sea arches from resistant rock. Depositional processes lead to the formation of Beaches, where sand and gravel are accumulated along the shore. Wind action (aeolian processes) is effective in arid regions, shaping sand into Sand Dunes. These dunes form as wind transports and deposits sand particles when its energy decreases, allowing them to migrate and change shape over time.