Home >> Science & Nature >> Nature

Characteristics of a Transform Boundary

The Earth's crust, known as the lithosphere, is made of irregularly shaped segments, called plates. These plates are from 4 to 40 miles thick, and move on convection currents generated from the Earth's core. The movement of these plates over time has drastically changed the shapes of our continents, as well as created and destroyed oceans and built mountains. Where these plates meet are called boundaries. Transform boundaries, or transform faults, are a type of tectonic boundary.

Types of Boundaries
- There are three types of lithospheric, or tectonic, plate boundaries: Convergent, divergent and transform. These boundaries are where two or more tectonic plates meet and interact. When the pressure that builds between two plates is released intermittently, we experience earthquakes. Each type of boundary has certain characteristics which serve to define the boundary.
Convergent Boundaries
- In convergent, or destructive, boundaries, one plate is pushed underneath another in areas called subduction zones. As one plate dives under the other, the subducting plate heats up and liquefies, forming magma. This magma may rise to the surface as volcanoes. Around the edges of the Pacific Plate there are many volcanoes and this area is known as the Ring of Fire. In the ocean, these volcanoes can form island arcs, such as the Aleutian Islands. If two plates converge but one plate cannot subduct under the other, mountains are formed. The Himalayas were formed via this mechanism.
Divergent Boundaries
- Divergent boundaries are locations where two plates move away from one another, known as spreading centers. The Pacific Ridge is one such boundary. Here, magma from the mantle wells up toward the surface and cools, forming a new crust. As it continues to upwell, the new crust acts to push the old crust towards convergent boundaries, where the oldest crust is destroyed through subduction. Divergent boundaries thus are a major mechanism for the movement of tectonic plates.
Transform Boundaries
- Transform boundaries are where two plates slide past each other horizontally. No new crust is created or destroyed, so they are also known as conservative boundaries. Where the North American and Pacific plates slide past one another is the San Andreas fault. Here, the Pacific plate is moving northwest past the North American plate, which is moving southeast. This movement has been occurring for the past 10 million years. The San Francisco earthquakes of 1906 and 1989 resulted from this movement. However, the majority of transform faults occur in the deep ocean. At these faults, earthquakes result from the movement of the two plates past one another. Transform faults offset spreading ridges, producing zig-zag margins.

Nature