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What Is a Rift Zone?

Phil Riddel
Phil Riddel

Depending on whether the context is plate tectonics or volcanology, the term "rift zone" can mean two different but related things; in general terms, it can be regarded as an area where rock in the Earth’s crust has been stretched, resulting in fissures and fractures through which magma can rise, as lava, to the surface. Lava can vary in composition according to its origin, and different types of lava have different physical characteristics. Rift zones form in areas where the magma below the surface is basaltic in nature — this type of lava is relatively runny and has a low gas content. This means that eruptions are not explosive: instead, the lava tends to flow relatively quietly out of fractures in the crust. Basaltic, or mafic, lava comes from deep in the mantle and is associated with spreading centers, or areas where continental plates are moving apart.

Rift zones can form at these spreading centers, where the crust is stretched by convection within the mantle. There are a number of rift zones of this type in the form of mid-oceanic ridges, such as the North Atlantic Ridge, where the North American and Eurasian plates are moving apart. Here, the oceanic crust is fracturing, and ridges are formed by the solidification of magma rising to the surface. The gradual spreading apart of the oceanic crust in these areas limits the extent to which ridges can build up, but in some particularly active areas, sometimes called “hot spots,” the new rock that is being formed relatively rapidly can reach the surface, resulting in volcanic islands such as Iceland and the Hawaiian islands.

Rift zones are fractures in the Earth where magma rises to the surface as lava.
Rift zones are fractures in the Earth where magma rises to the surface as lava.

Tectonic rift zones can also appear on land where a new split is forming, creating plates that move apart. A good example is the Great Rift Valley in East Africa. The land sinks along the line of the split, forming a widening valley between two volcanic ridges. Eventually, when the land sinks below sea level, ocean water will flow in, forming a new ocean.

The Hawaiian Islands were formed at hot spots of underwater rift zones where newly formed rock reached the surface.
The Hawaiian Islands were formed at hot spots of underwater rift zones where newly formed rock reached the surface.

Over time, repeated outpourings of basaltic lava that occur at hot spots can form a type of large volcano known as a shield volcano. These have long, gentle slopes formed from many layers of solidified basaltic lava, and localized rift zones can form on their slopes, due to stretching of the rock due to gravity. Large fractures can form at points of weakness in the rock, allowing lava to flow to the surface and resulting in lateral eruptions, as opposed to eruptions from the main vent. As with ocean floor eruptions, these are non-explosive in nature. Mauna Loa on Hawaii provides a textbook example of this kind of rift zone.

Repeated outpourings of lava may create shield volcanos.
Repeated outpourings of lava may create shield volcanos.

There are a number of distinctive geological features that are associated with rift zones on shield volcanoes. Dikes are wall-like structures formed by lava that has risen into fractures in the rock and solidified. Often, the solidified lava is harder than the surrounding rock, which erodes more quickly, leaving the dike exposed. Fissure eruptions may eject blobs of molten lava, known as “spatter,” a few meters into the air. These can accumulate around eruption sites, forming spatter cones and more linear structures called ramparts.

A rift zone can occur when two of earth's tectonic plates are moving away from each other.
A rift zone can occur when two of earth's tectonic plates are moving away from each other.

Rift zones are not confined to the Earth. On Mars, the enormous canyon known as Valles Marineris is a huge rift zone that, at 2,000 miles (3,000 kilometers) long and up to 12,500 feet (3,800 meters) deep, dwarfs any similar features on our planet. It is thought to have formed over a period from 3.5 billion to 2 billion years ago and seems to have resulted from the stresses associated with major volcanic activity nearby.

Frequently Asked Questions

What exactly is a rift zone?

Iceland is a volcanic rift zone.
Iceland is a volcanic rift zone.

A rift zone is a region where the Earth's crust and lithosphere are being pulled apart due to tectonic forces. This process creates a series of fractures or faults, leading to the formation of a linear valley or a depression. Rift zones are often associated with volcanic activity, as the thinning crust allows magma to rise more easily to the surface.

Where can rift zones be found?

Rift zones are typically found at divergent plate boundaries where tectonic plates are moving away from each other. One of the most famous examples is the East African Rift, which stretches over 3,000 kilometers from the Red Sea down to Mozambique. Other notable rift zones include the Mid-Atlantic Ridge and the Rio Grande Rift in North America.

What geological features are associated with rift zones?

Rift zones are characterized by distinctive geological features such as long, deep valleys, fault lines, escarpments, and volcanic activity. The stretching and thinning of the Earth's crust in these areas can lead to the formation of basins and the development of new oceanic crust, as seen in the case of the Red Sea, which is gradually widening due to the activity of the East African Rift.

How do rift zones affect local ecosystems?

Rift zones can have a profound impact on local ecosystems. The geological activity can create unique habitats, such as hot springs and geothermal areas, which support specialized life forms. Additionally, the formation of new landforms can lead to the isolation of species and the development of high levels of endemism, contributing to biodiversity in these regions.

Can rift zones lead to the creation of new oceans?

Yes, rift zones can lead to the creation of new oceans. As tectonic plates continue to diverge, the rift can deepen and widen, eventually forming a new ocean basin. This process is evident in the Red Sea, which is an embryonic ocean forming as the Arabian Plate moves away from the African Plate. Over millions of years, this could evolve into a fully-fledged ocean.

Are rift zones prone to natural disasters?

Rift zones are indeed prone to natural disasters such as earthquakes and volcanic eruptions. The movement of tectonic plates and the accumulation of stress along faults can lead to seismic activity. Volcanic eruptions are also common due to the presence of magma close to the Earth's surface. These events can be hazardous to nearby populations and infrastructure.

Discussion Comments

Authordor

A subduction zone is when one tectonic plates "rides over" another plate forcing the second plate back down into the mantle. The Pacific plate is currently being subducted by the North American plate. Its most visible sign is the San Andreas fault and earthquakes of a high frequency and destructive power.

Ravellu

If a rift zone is a tearing or separation of tectonic plates, what is a subduction zone?

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    • Rift zones are fractures in the Earth where magma rises to the surface as lava.
      By: Vibe Images
      Rift zones are fractures in the Earth where magma rises to the surface as lava.
    • The Hawaiian Islands were formed at hot spots of underwater rift zones where newly formed rock reached the surface.
      By: guynamedjames
      The Hawaiian Islands were formed at hot spots of underwater rift zones where newly formed rock reached the surface.
    • Repeated outpourings of lava may create shield volcanos.
      By: klikk
      Repeated outpourings of lava may create shield volcanos.
    • A rift zone can occur when two of earth's tectonic plates are moving away from each other.
      A rift zone can occur when two of earth's tectonic plates are moving away from each other.
    • Iceland is a volcanic rift zone.
      Iceland is a volcanic rift zone.