Rift

The ground can pull apart.

This pull makes a long crack. It can make a deep valley.

Water may fill the valley. This can make a big lake. Some rifts even have hot rocks from volcanoes.

These cracks can hold oil and gas. People find these things deep in the ground.

It is amazing to think the Earth can stretch like this.

A rift is a long zone where the Earth's outer layer is pulled apart.

This pulling can make a deep, long valley. We often call this a rift valley. Some valleys fill with water to make rift lakes.

As the ground stretches, it can break into parts. These parts are called segments. The breaks between these segments are called accommodation zones.

In some rifts, the ground on the sides rises up. These high sides are called rift shoulders. They are usually about 70 km wide.

Sometimes, heat from deep inside the Earth moves up. This can cause volcanic rocks to form.

Some rifts grow so much that they break apart completely. This creates new ocean floors. Rifts are also very useful to people. They can hold large amounts of oil and gas deep underground. In fact, 30 percent of the world's giant oil fields are found in rifts.

A rift is a long, straight zone where the Earth's outer layer is being pulled apart.

This pulling happens because of tectonic forces. As the ground stretches, it creates a deep depression. Scientists often call this a graben or a half-graben. If the rift stays above the sea, it forms a rift valley. Sometimes, these valleys fill with water to create large rift lakes.

These features are important because they show how our planet changes shape.

There are many steps in how a rift works. First, the upper part of the lithosphere—the Earth's outer layer—starts to stretch. This creates small, separate cracks called normal faults. These faults lead to isolated basins. As the rift grows more mature, these small faults link together. They form much larger, continuous faults along the rift axis. This process causes the ground to sink further. At the same time, the sides of the rift, called shoulders, can rise up.

History shows that rifting can happen in many different ways. Some rifts are passive, meaning they are driven by forces far away. Others are active and controlled by movement in the mantle deep below. Some rifts even go through many different phases over a long time. For example, the North Sea rift had several phases. This lasted from the Permian period until the Early Cretaceous. That is a very long time of over 100 million years.

Real numbers help us understand these huge structures. Rift shoulders are typically about 70 km wide. In some areas, the segments of a rift are very long. The Baikal Rift has segments longer than 80 km. In warmer areas, segments might be less than 30 km. Rifts are also very important for finding energy. About 30 percent of the world's giant oil and gas fields are in rifts. In 1999, experts estimated rifts held 200 billion barrels of oil.

You can think of a rift like a piece of dough being pulled. As you pull the sides, the middle gets thinner and stretches. If you pull hard enough, the dough might eventually snap. This is similar to how a rift can lead to a total breakup. When this happens, a new ocean floor is created. This is what we see at mid-ocean ridges.

Rifts connect the deep Earth to the world we see on the surface.

A rift is a linear zone where the Earth's lithosphere is being pulled apart. The lithosphere is the solid outer layer of our planet. This process is a key part of extensional tectonics, which describes how the Earth's crust stretches. Rifts create long depressions in the ground. Scientists often call these central downfaulted areas a graben. If the rift is a half-graben, it is controlled by a single main fault. When these rifts remain above sea level, they form rift valleys. These valleys can fill with water to create large rift lakes.

The way a rift forms follows a specific sequence of stages. At the beginning, the upper lithosphere starts to extend. This happens on a series of small, unconnected normal faults. These faults create isolated basins. This is often called passive rifting because it is caused by horizontal stresses. During this early stage, there is usually no magmatic activity. As the rift reaches a mature stage, these individual fault segments grow. They eventually link together to form much larger bounding faults. This concentration of extension causes the ground to sink more continuously along the rift axis.

As rifting reaches its climax, the crust thins significantly. This causes the Earth's surface to subside, or sink. At the same time, the Moho, which is the boundary between the crust and the mantle, rises. The mantle lithosphere also thins. This allows the asthenosphere, a hot layer of the mantle, to rise closer to the surface. This brings intense heat into the thinning lithosphere. The high heat can cause dehydration melting. This process can create metamorphic rocks like granulites or granites. This specific type of mountain-building in an extensional setting is called rifting orogeny.

Rifts are not always one long, continuous line. Instead, they usually consist of separate segments. The length of these segments depends on the thickness of the lithosphere. In cold, thick areas like the Baikal Rift, segments can be longer than 80 km. In warmer, thinner areas, segments may be less than 30 km. Where these segments meet, they form accommodation zones. These zones handle the differences in how the faults move. They can be simple relay ramps or very complex structures.

Some rifting processes eventually lead to a total continental breakup. This transition often happens at a triple junction. A triple junction is a place where three rifts meet over a hotspot. In many cases, two of these rifts evolve into seafloor spreading. This creates new oceanic crust at a divergent boundary. The third rift may fail to continue. These failed rifts are known as aulacogens. Successful rifting can create magma-rich margins with many volcanic features. Other margins are magma-starved and rely on large-scale faulting.

Rifts can also show a history of multiple phases over millions of years. The North Sea rift is a great example of this. It showed evidence of several separate rifting phases. This process lasted from the Permian period through the Earliest Cretaceous. That is a total period of over 100 million years. After rifting stops, a process called post-rift subsidence occurs. The mantle beneath the rift cools down. This causes a broad area of the ground to sink. Scientists use models like the McKenzie model or the flexural cantilever model to study this sinking.

These geological structures are very important for the global economy. The sedimentary rocks found in continental rifts hold many minerals and energy sources. For example, SedEx mineral deposits form when hydrothermal fluids are expelled at the seabed. Rifts are also major sites for oil and gas. About 30 percent of the world's giant oil and gas fields are found in rifts. In 1999, it was estimated that rifts held 200 billion barrels of recoverable oil. The Viking Graben and the Gulf of Suez Rift are notable examples of these energy-rich areas.