Plate tectonics explained—What are tectonic plates, and how does plate tectonics work?
- Maria Baias
- Apr 1
- 4 min read
Updated: Apr 1
Ever wonder what’s really happening beneath your feet? The ground you’re walking on is not as solid as you may think. It is actually broken into giant pieces that fit together like a giant jigsaw puzzle. These are the tectonic plates—giant masses of land that sometimes crash into one another, other times rip apart, and even slide along one another. Their movement shapes our planet, giving birth to mountains, triggering earthquakes, and even shapes the ocean floors. In this post, we’ll learn what are tectonic plates, the science behind the movement of tectonic plates, how plate tectonics is responsible for earthquakes, volcanoes, and mountains, and learn which are the major and minor tectonic plates on Earth.
What are tectonic plates?
In order to understand tectonic plates, we first need to understand the Earth's layered structure, so we can see exactly where the tectonic plates are located.
The Earth has several layers - the crust, the mantle, and the core.
When it comes to tectonic plates, we’re only interested in the crust and the mantle. Together, the crust and the uppermost section of the mantle form the lithosphere, which is divided into large rock slabs, called “plates”. These plates are in continuous movement and slide above the next layer of the mantle, called the asthenosphere. The scientific theory behind the movement of these large plates and how they interact with one another is called plate tectonics.
Tectonic Plate Boundaries
The movement of tectonic plates creates three types of boundaries between plates, depending on how they move relative to one another:
convergent boundaries
divergent boundaries
transform boundaries
Convergent boundaries
Convergent boundaries occur when two plates move closer together and collide. Convergent boundaries occur when a continental plate collides with another continental plate, when an oceanic plate collides with a continental plate, or when two oceanic plates collide.
Continental plates collision
When two continental plates collide, the collision causes the Earth's crust to crumple and deform, creating massive mountain ranges. One example is like the Himalayas, which started forming because of the collision between the Indian Plate and the Eurasian Plate, a process which began about 45 million years ago and continues today.
Over time, as converging tectonic plates keep pushing against each other, the mountains continue to grow, their growth eventually slowed or stopped because of gravity and erosion. While erosion does wear down the mountains, the growth rate of the mountain is often faster than the rate of erosion, allowing them to reign over long periods of time.
Oceanic and continental plates collision
When an oceanic plate and a continental plate converge, the oceanic plate, which is denser, is pushed beneath the lighter continental plate. This process is called subduction. As the oceanic plate sinks into the mantle, the layer beneath Earth’s crust, it melts and joins the magma, which can rise to the surface during volcanic eruptions. This process is responsible for creating many volcanic systems along subduction zones, such as those in the "Ring of Fire,” around the Pacific Ocean.
Have you ever seen an active volcano? Let me know in the comments if you have, and where it was.
Oceanic plates collision
When two oceanic plates converge, one plate is pushed beneath the other, forming a deep-sea trench. One example is the Mariana Trench, in the North Pacific Ocean, which is the deepest point in the Earth's ocean floor.
The convergence of oceanic plates can also lead to underwater volcanoes, which, over time, may grow into volcanic islands.
Divergent boundaries
Both on land and in the ocean, divergent boundaries occur when two plates move further apart from each other.
Continental diverging plates
On land, this process gives birth to massive rift valleys. One example is the Great Rift Valley in East Africa, where the divergence of tectonic plates is slowly splitting the region apart.
Oceanic diverging plates
At divergent boundaries in the ocean, magma from the mantle rises through these rifts and solidifies, creating new oceanic crust. This process forms underwater mountain ranges called mid-ocean ridges, where volcanic activity is common.
Transform boundaries
Transform boundaries occur when tectonic plates slide along one another. During this process, no new crust is created or destroyed as we’ve seen in the previous two boundaries. Instead, the friction along fault lines gives rise to earthquakes. One example is the San Andreas Fault in California, where the Pacific and North American plates slide along each other.
Tectonic plates on Earth
Depending on the size of tectonic plates, they are split into major, minor, and micro plates.
Major tectonic plates
There are 7 major tectonic plates. From the largest plate to the smallest plate, they are:
The Pacific Plate
The North American Plate
The Eurasian Plate
The African Plate
The Antarctic Plate
The Indo-Australian Plate (while it is made up of two separate plates—the Indian plate and the Australian plate—they are often referred to as one major plate)
The South American Plate
Minor tectonic plates
There are also several minor tectonic plates (5), including:
The Somali Plate
The Nazca Plate
The Philippine Sea Plate
The Arabian Plate
The Caribbean Plate
The Cocos Plate
The Scotia Plate
Micro tectonic plates
In addition to the major and minor plates, there are also many micro plates. One important micro plate worth mentioning is The Juan de Fuca Plate that is part of the Ring of Fire, its movements leading both to earthquakes and volcanic eruptions.
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