Mountains are large landforms that rise steeply above the surrounding land. While their huge size and rugged peaks make them seem permanent, they are constantly being built and shaped by powerful forces working deep inside our planet. Understanding how mountains are formed requires looking beneath our feet to the slow, steady movement of the Earth’s outer layer.
Earth’s Moving Plates
The Earth’s tough outer layer, called the lithosphere, is not one solid piece but is broken into massive sections known as tectonic plates. The continents and ocean floors sit on top of these plates, which are constantly moving due to heat currents deep within the planet’s mantle. This slow motion is incredibly gradual—about as fast as your fingernails grow—but it exerts enormous force. The way two plates interact when they meet determines the type of mountain that will be formed.
Squeezing and Piling Mountains
The most common way mountains are built is through a slow-motion crash between two continental plates. When these plates push directly into each other, neither is easily pushed down, forcing the land to move upward. Over millions of years, the immense force of this collision causes the Earth’s rock layers to crumple, buckle, and pile high into what are called fold mountains. This process pushes ancient layers of rock far above where they started. Mountain ranges like the Himalayas and the Andes were created this way, and they continue to grow taller as the plates keep pushing.
Fire and Magma Mountains
Not all mountains are formed by compression; some are built from the inside out. These are volcanic mountains, which often form near where one plate slides beneath another. Intense heat deep beneath the surface melts rock into magma. Since magma is lighter than the surrounding solid rock, it pushes its way up through cracks in the Earth’s crust. When magma bursts onto the surface, it becomes lava, which cools quickly and hardens. Every eruption adds a new layer of cooled lava and ash, building up the classic cone shape over thousands of years.
Shaping the Mountains
Once a mountain is built, the forces of nature begin to sculpt it. Wind, water, and ice constantly break down the rock through a process called weathering. This broken-down material is then carried away by erosion, which slowly wears the mountain away. Younger mountain ranges, like the Himalayas, still have sharp, jagged peaks because erosion has not had enough time to smooth them down. Older mountains, such as the Appalachian Mountains, have been exposed to millions of years of rain and wind, rounding their peaks into gentler, lower slopes.