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Tectonic Plates
The Earth̵7;s surface is made up of great tectonic plates, which slowly drift into, over, and against one another. These plates form along mid-ocean ridges, where magma from under the earth̵7;s surface wells up and forms new crust. The plates̵7; crust is then pulled towards subduction zones, where one plate slips below another plate and returns to the magma. Tectonic plates grind against each other as they move in different directions, causing pressure to mount. This pressure is released through earthquakes, when sections of rocky crust break apart and move in different directions.
Earthquakes and Uplift
The basic types of faults are reverse, normal, and strike-slip. Reverse faults form when plates run into each other, and one plate slides up and over the other. This uplifts sections of the earth̵7;s crust, which can lead to mountain formation. Normal faults occur when plates expand away from one another. They cause sections of crust to fall away, creating valleys. Strike-slip faults occur when two plates grind against one another by moving in different directions. Geological uplift occurs when earthquakes thrust rock up out of the ground. Both strike-slip faults and thrust faults can cause geological uplift, but by their nature thrust faults are most capable of doing so.
Mountain Uplift
The process of geological uplift has been recorded due to earthquakes; for example, uplift of 15 meters has been recorded in Alaska within seconds of earthquakes. Given long periods of time, such earthquakes and uplift are responsible for the formation of mountains. The mountains of California developed over the course of 250 million years. First, the North American Plate struck and began to subduct the Pacific Plate, forming ranges like the Klamath Mountains. Then the Pacific Plate changed directions and began to slip north along the North American Plate, forming the San Andreas Fault and uplifting the Coast and Transverse mountain ranges.
Volcanic Mountains
Besides geological uplift, volcanic activity can also create mountains. Volcanic activity causes earthquakes, but volcanic mountains are not formed by earthquakes like typical mountains. Volcanoes occur when building pressure beneath the earth̵7;s crust forces molten rock, or magma, up through the crust. As the magma rises, it pushes up portions of rocky crust. These conical mountains form as volcanic lava and ash accumulate at the surface. An example of volcanic mountains is the Hawaiian islands, which are actually the mountain peaks formed by volcanoes that began along the ocean floor.