Understand Plate Tectonics & Continental Drift

Geological Mountain Building Forces Cause Earthquakes and Volcanoes

Feb 2, 2009

Plate tectonic theory grew from Wegener's continental drift hypothesis and is the unifying theory underlying modern geology and geophysics.

Tectonic processes cause movement or distortion of Earth's surface. Tectonic processes, including volcanoes, earthquakes, movement along fault lines, crust folding, and uplifting, have shaped Earth's surface and occur on other planets.

Continental Drift and the Origin of Plate Tectonics

Looking at a map, the west coasts of Europe and Africa fit into the east coast of the Americas. It looks as if they could once have been the same continent.

In 1912 Alfred Wegener suggested, on the basis of this similarity and the additional similarities of various geological and fossil patterns, that they had indeed once been one continent. Wegener's theory, called continental drift, suggested that these continents were indeed drifting apart very slowly. Wegener suggested the idea, but did not suggest a force that might cause this motion.

At the time, geologist considered Wegener a bit of a crackpot and held his continental drift hypothesis in poor regard. It just seemed too farfetched. However evidence accumulated to the point that by the 1960s Wegener's ideas no longer seemed so outlandish.

Undersea mapping revealed an underwater chain of volcanic mountains, the Mid-Atlantic Ridge, that matched the pattern of shorelines. Magnetic patterns matched on either side of the ridge, as if the ocean floor were spreading apart as the continents drifted away from each other. Plate tectonics explained these observations.

Theory of Plate Tectonics

According to plate tectonics, Earth's crust is divided into plates. The Mid-Atlantic Ridge marks the boundary between the American plates and the European-African plates.

Tectonic plates float on the mantle which is in a slowly flowing plastic like state. Hot spots deep in Earth's core cause very slow convection currents in the mantle. Because continental plates float on the mantel these convection currents move the plates very slowly.

Most tectonic activity occurs at the boundaries between tectonic plates. For example, the Pacific rim, called the ring of fire, forms the boundary of the Pacific plate and has more earthquake and volcanic activity than any other region on Earth.

The Mid-Atlantic Ridge is an example of plates drifting apart. Lava flows upward from the mantle, forms undersea volcanoes, and spreads outward. Continental plates can also collide. In these cases continents are squeezed upward to form mountains. The Himalayas are a good example.

Continental plates can collide with oceanic plates such as in the west coast of South America. The continental plate forms high mountains, the Andes in South America. The oceanic plate forms a subduction zone in which the plate material flows back into the mantle to complete the convection current.

Plate Tectonics Unifies Geology and Geophysics

Prior to the emergence of plate tectonics, geologists could describe individual geologic features. They could not however very well explain the causes of and the connections between different types of geologic features. Plate tectonic theory provided both a mechanism for Wegener's continental drift hypothesis and an underlying theory that explained Earth's geologic structure and evolution. This theory provided the type of unification to geology that evolutionary theory provided to biology.

Plate tectonic activity often results in natural disasters such as volcanoes, earthquakes, and tsunamis. As geophysicists and geologists increase their understanding of tectonic activity, they may eventually learn to predict when these disasters will occur. These predictions could save many lives.