Slab pull

The Earth has big moving parts. Some parts are cold and heavy. These parts sink into the hot ground.

As they sink, they pull the rest down. This is a very strong pull. It is the main way the Earth moves.

Other forces help move the parts too. One force is called ridge push. This force is much weaker.

Some parts move even without sinking. This happens in many places. The ground stays busy moving.

The Earth has big moving parts called tectonic plates. Most of these plates move because of a force called slab pull. This happens at oceanic trenches. These are deep spots in the ocean floor.

Some plates are cold and heavy. They sink into the mantle. The mantle is the layer below the crust. As the plate sinks, it pulls the rest of the plate with it. This is a very strong force. In 1975, two men named Forsyth and Uyeda studied this. They found slab pull is the strongest force. It helps drive most plate motion.

Other forces also help move the plates. One force is called ridge push. It comes from rifts in the Earth. But ridge push is much weaker. It only provides 5 to 10 percent of the force. Some plates move without sinking at all. The North American Plate is one example. The African and Eurasian plates also move this way.

The Earth is made of moving parts called tectonic plates. One important way these plates move is through slab pull. This happens when a plate gets cold and heavy. It begins to sink into the mantle below. This sinking creates a downward force. This force pulls the rest of the plate along with it. It is a very important part of how our planet works.

How does this process work step by step? First, a tectonic plate cools down. As it cools, it becomes more dense. Dense means it is heavier for its size. This heavy plate sinks into the mantle at oceanic trenches. The sinking part is called a subducting plate. As it goes down, it pulls the rest of the plate behind it. This pull is the main driver of plate motion.

Scientists have studied these forces for a long time. In 1975, Forsyth and Uyeda used a special method. They used the inverse theory method to study the plates. They found that slab pull is the strongest force. It is much stronger than ridge push. Ridge push only provides 5 to 10 percent of the force. This discovery helped us understand plate tectonics better.

There are many different facts about these forces. Scientists use math to find the slab pull force. They look at gravity, which is 9.81 m/s2. They also look at the density difference. This difference is about 80 kg/m3. The slab length is measured above the 670 km boundary. They even look at the age of the slab. This age is measured in Ma, which means millions of years.

We can see how this affects different places on Earth. The Pacific Ring of Fire has many sinking slabs. These slabs help cool the Earth and its core-mantle boundary. Some areas have strong earthquakes from this movement. The Aleutian and Chile areas are good examples. Other plates move in different ways. The North American, African, and Eurasian plates do not sink. Instead, they move because of ridge push.

Slab pull is a major geophysical mechanism. It is a force that drives the movement of tectonic plates. This process occurs when a tectonic plate cools down over time. As the plate cools, it becomes more dense. This density causes the plate to sink into the mantle. This sinking creates a downward force along the rest of the plate. This force is a primary driver of plate tectonics on Earth.

The mechanism of slab pull works through a specific sequence of events. First, an oceanic plate moves away from a ridge and cools. This cooling makes the plate denser than the material beneath it. The dense part of the plate then begins to sink at oceanic trenches. This sinking part is known as a subducting plate. As the slab sinks, its weight pulls the rest of the plate behind it. This action is often paired with slab suction. Together, these forces account for almost all the force driving plate motion.

Scientists have identified different ways this force manifests. It can appear in two extreme forms. One form is aseismic back-arc extension. We see this in the Izu–Bonin–Mariana Arc. In this case, the movement does not cause many earthquakes. The other form involves strong earthquakes and back-arc thrusting. Examples of this include the Aleutian and Chile tectonics. These variations show how different plates respond to these massive forces.

Researchers have used math to define the slab pull force. Scientists look at several specific variables to calculate it. They use gravitational acceleration, which is 9.81 m/s2. They also measure the mean density difference between the slab and the asthenosphere. This difference is approximately 80 kg/m3. The calculation also requires the slab length. This length is only measured above the 670 km boundary. Finally, they include the age of the slab in Ma, or millions of years.

Our understanding of these forces changed due to important studies. In 1975, researchers Forsyth and Uyeda conducted a study. They used the inverse theory method to analyze plate motion. Their work showed that slab pull is the strongest driving force. Before this, some models suggested plates rode on convection cells. These models acted like conveyor belts. However, most modern scientists believe this is not the case. They found that the asthenosphere does not cause motion through basal friction.

The significance of slab pull is clear when comparing it to other forces. Ridge push is another force caused by rifts. However, ridge push contributes only 5 to 10% of the total force. Slab pull and slab suction are much more powerful. We can see the impact of these forces in the Pacific Ring of Fire. The subducting slabs there help cool the Earth and its core-mantle boundary. This process helps regulate the temperature of our planet's deep interior.

Different plates interact with these systems in unique ways. Some plates do not have subducting slabs at all. The North American Plate is not currently being subducted. The African, Eurasian, and Antarctic Plates are also not subducting. These plates move due to ridge push instead. In contrast, the African Plate experiences upwelling mantle plumes. These plumes come from the core-mantle boundary. This process produces rifting in the African and Ethiopian rift valleys.

The history of the Farallon Plate provides a complex example of these changes. It showed an evolution in slab width and movement. It once had a huge slab width. This caused the Nevada, Sevier, and Laramide orogenies. Later, it experienced the Mid-Tertiary ignimbrite flare-up. Eventually, it was left as the Juan de Fuca and Cocos plates. This area also shows the Basin and Range Province. This province is under extension due to slab break off and mantle return flow.