A geological feature is any naturally occurring landform or structure found on the Earth’s surface or beneath it. These features are the physical expression of geological processes that have acted over immense spans of time. Their scale is vast, ranging from microscopic mineral grains to continental mountain chains. These features are not static but result from continuous, dynamic interactions between forces originating both within and outside the planet.
Defining the Landscape The Nature of Geological Features
Geological features are classified by their size and the forces responsible for their creation. Major landforms, such as mountains, plateaus, and plains, define the broadest outlines of the Earth’s topography. These large structures often dictate climate, drainage patterns, and human habitation. Smaller features, such as canyons, valleys, and individual fault lines, are categorized as minor landforms, providing localized detail for geologists studying specific processes.
The formation of these features is traced back to two primary, opposing categories of forces. Internal forces (endogenic processes) originate from the Earth’s interior heat and are responsible for building up the landscape. External forces (exogenic processes) are driven by solar energy and gravity, working to break down and reshape surface structures. This constant interplay between construction and destruction creates the diverse face of the planet.
Features Shaped by Internal Forces
The Earth’s internal heat drives tectonic plate movement and volcanism, which are the main constructive forces creating the largest geological features. These endogenic processes involve forces capable of deforming solid rock and creating significant vertical relief. The movement of lithospheric plates generates mountains, trenches, and rift valleys through three main types of stress: compression, tension, and shearing.
Compressional forces occur when plates move toward each other, causing the crust to buckle and thicken. This results in the formation of folded mountains, such as the Himalayas, where sedimentary layers are squeezed upward into massive anticlines and synclines. Convergent boundaries involving oceanic and continental crust also create deep ocean trenches where the denser plate is forced downward (subduction).
Tensional forces pull the crust apart, most notably at divergent plate boundaries. This stretching causes brittle rock to fracture, forming faults where blocks of crust slip past each other. A classic result of this tension is the rift valley, such as the East African Rift, where a central block of land subsides between two parallel faults. Shearing forces, where plates slide horizontally past one another, define features like the San Andreas Fault in California.
Volcanism represents another endogenic process, where molten rock (magma) rises through the crust to the surface. The shape of a volcano is directly related to the viscosity of the erupted magma. Shield volcanoes, like Mauna Loa in Hawaii, are built from highly fluid, low-viscosity basaltic lava that flows easily and spreads widely, creating a broad, gently sloping dome.
In contrast, stratovolcanoes (composite cones) are formed from thicker, more viscous magma that traps gas, leading to explosive eruptions. The sticky lava and ejected ash (tephra) pile up around the vent, forming the iconic, steep-sided cone shape. The alternating layers of lava flows and pyroclastic material give these volcanoes their name, as seen in examples like Mount Fuji.
Features Shaped by External Forces
External forces constantly modify and dismantle the structures built by internal forces through weathering, erosion, and deposition. These processes are powered primarily by solar energy, which drives the water cycle, and by gravity. Weathering physically or chemically breaks down rock, creating the raw material that erosion then transports.
Running water, or fluvial action, is a dominant agent of erosion. Rivers cut deep, narrow V-shaped valleys and canyons, such as the Grand Canyon, by continually removing material from the channel bed and sides. As rivers traverse flatter ground, they develop wide, looping curves called meanders, which constantly shift their position across the flood plain.
Glacial ice creates distinct features through its erosive power. As glaciers move, they scour the landscape, transforming V-shaped river valleys into broad, steep-sided U-shaped valleys. Where these glacial valleys meet the sea, they form deep inlets known as fjords. The movement of ice also produces bowl-shaped depressions on mountainsides called cirques.
The final stage of external processes is deposition, where transported sediment settles in new locations, building up new landforms. When a river carrying a heavy sediment load meets a large body of water, its velocity drops abruptly, causing the material to be deposited in a fan shape. This process creates a river delta, where the main channel branches into numerous distributaries. In arid regions, wind acts as an erosional and depositional agent, transporting sand grains that accumulate into large, mobile structures called sand dunes.