What is Plate Tectonics? How Does It Affect Earthquakes and Volcanism?

What is Plate Tectonics? How Does It Affect Earthquakes and Volcanism?

Have you ever thought about how the surface of our planet has been shaped for millions of years? The answer lies in the concept of plate tectonics. Plate tectonics is a theory that suggests the lithosphere is made up of massive plates that interact with each other. The interacting plates form geomorphological structures such as mountains and ocean ridges. However, that’s not all. Plate tectonics also triggers deadly earthquakes and volcanic eruptions.

What is Plate Tectonics?

Plate tectonics is a scientific theory that describes the movement and behavior of the Earth’s lithosphere. It is based on the idea that the lithosphere is made up of several large and small plates that are in constant motion. These plates can move towards, away from, or slide past each other. Plate tectonics is responsible for creating mountains, earthquakes and volcanoes, as well as shaping the Earth’s landscape over millions of years.

The theory of plate tectonics has three main components. The first component is continental drift, which suggests that the continents were once a single landmass and have since moved apart. This idea was first proposed by Alfred Wegener in 1912. The second component is seafloor spreading, which explains how new oceanic crust is created at mid-ocean ridges and is pushed away from these ridges by the movement of the surrounding plates. This theory was developed in the 1960s by Harry Hess and Robert Dietz.1 The third component is plate boundaries, which are the regions where different plates meet.

Types of Plate Boundaries

There are three types of plate boundaries: divergent, convergent, and transform.2

Divergent plate boundaries are regions where plates are moving away from each other. This movement creates a gap or rift between the plates, which allows magma from the mantle to rise up and solidify into new crust. This process is called seafloor spreading. The East African Rift and the Iceland Plateau are two examples of divergent plate boundaries.

Convergent plate boundaries are regions where plates are moving towards each other. When two plates meet, one plate usually sinks beneath the other in a process called subduction. This creates a deep trench and can lead to volcanic eruptions and earthquakes. The Himalayas, where the Indian Plate is colliding with the Eurasian Plate, and the Japan Trench, where the Pacific Plate is subducting beneath the Eurasian Plate, are two examples of convergent plate boundaries.

Transform plate boundaries are regions where plates are sliding past each other horizontally. These boundaries are associated with large faults, which can produce earthquakes. The North Anatolian Fault in Turkey and the San Andreas Fault in the United States are two examples of transform plate boundaries, where tectonic plates slide past each other horizontally.

Causes of Plate Movement

The movement of tectonic plates is a geological process that has been shaping the surface of our planet. This movement is influenced by various forces that cause the plates to shift, collide, and separate.

Mantle convection: One of the main reasons for plate movement is mantle convection. The mantle is the hot, molten rock layer between the Earth’s crust and core. As it gets heated by the core, it rises towards the surface, carrying tectonic plates with it. As the plates move over the mantle, they are either pushed apart or brought together, depending on the direction of the convection currents.

Gravity: The Earth’s gravity causes tectonic plates to either converge or move away from each other. This movement results in the formation of either convergent or divergent boundaries. When plates converge, they can create mountain ranges or cause volcanic eruptions. When they diverge, it can cause the creation of rift valleys and oceanic ridges.

The Earth’s Rotation: The plates move around the planet due to the Earth’s rotation, causing the formation of new boundaries or the reconfiguration of existing ones.

External Forces: External forces such as asteroid impacts or glacier movements can also influence plate movement. The impact of asteroids can cause earthquakes and create new boundaries, while glacier weight can depress the Earth’s crust, resulting in changes in the distribution of tectonic plates.

Continental Drift

Back in 1912, a German scientist named Alfred Wegener proposed something radical. He noticed that the coastlines of South America and Africa fit together perfectly like puzzle pieces.3 This led him to suggest that the two continents were once connected. But, unfortunately, his theory was initially rejected by the scientific community. Why? Because they couldn’t explain how the continents could move.

Plate tectonics, tectonic plates
It is believed that during the Late Paleozoic era, there was only one supercontinent called Pangea.
Photo: Fama Clamosa (Wikimedia) ©️CC BY-SA 4.0

However, things changed when similar fossils were found on different continents. For example, the Mesosaurus, an ancient reptile, was discovered in both South America and Africa, indicating that the continents were once linked. Moreover, rocks of the same age and composition were found on opposite sides of the Atlantic Ocean. All of this supported the idea that they were once part of the same landmass.

So, how did the continents move? The mechanism behind continental drift is plate tectonics. The Earth’s crust is made up of several large plates that are constantly in motion. When these plates collide, they create mountain ranges and volcanic activity. Conversely, when plates move apart, they can create rift valleys and oceanic ridges.

The movement of continents has had a significant impact on the Earth’s climate and ecosystems. As the continents have shifted, they have altered the pattern of ocean currents, influencing global climate patterns. The movement has also enabled the evolution of distinct ecosystems in different parts of the world by allowing species to evolve in isolation.

What Are the Earth’s Plates?

Our planet’s surface is divided into seven massive puzzle-like pieces called tectonic plates. Each plate is named after the continent or ocean that it mostly lies beneath.

Tectonic plates, plate tectonics
Tectonic Plates
Photo: United States Geological Survey

The Pacific Plate is the largest of all the plates. It covers about one-third of the Earth’s surface. It’s surrounded by the Pacific Ring of Fire, which is an area where there’s a lot of volcanic activity and earthquakes. This plate is also responsible for the formation of the Hawaiian Islands.

The North American Plate is mostly under North America, including the US, Canada, and some parts of Mexico. It stretches into the Atlantic Ocean and covers Greenland. The San Andreas Fault in California marks the boundary between the North American and Pacific Plates.

The Eurasian Plate covers most of Eurasia, including the United Kingdom, Continental Europe, Russia, and China. It also extends into the Arctic and Atlantic Oceans. The collision between the Indian Plate and the Eurasian Plate formed the Himalayan mountain range.

The African Plate is beneath Africa, Madagascar, and parts of the Atlantic Ocean. The South American Plate and the African Plate moves away from each other at the Mid-Atlantic Ridge. The Mid-Atlantic Ridge is what created the Atlantic Ocean.

The Antarctic Plate is mostly beneath Antarctica and the surrounding ocean floor. It interacts with the Pacific Plate at the Pacific-Antarctic Ridge, which is where the two plates are moving away from each other.

The Indo-Australian Plate, which covers the Indian subcontinent, Australia, and parts of Southeast Asia, was formed when the Indian and Australian plates fused together during the Eocene period. It is bounded by the Mid-Indian Ridge, where the plate is moving away from the African Plate.

Finally, the South American Plate is mostly beneath South America, including parts of the Atlantic and Pacific Oceans. The Andes Mountains were formed by the collision of the South American Plate with the Nazca Plate along a convergent boundary.

Tectonic Events: Earthquakes and Volcanic Eruptions

The interaction between tectonic plates is a crucial factor that influences earthquakes, which happen when the Earth’s crust experiences sudden and rapid movements.

As tectonic plates move, stress builds up within the Earth’s crust, and this can lead to the creation of faults. These faults are breaks in the Earth’s crust where rocks on either side of the break move relative to each other. When the stress within the Earth’s crust becomes too great, the rocks along a fault can suddenly shift, releasing energy in the form of seismic waves. It is this sudden release of energy that causes earthquakes.

The type of earthquake that occurs is dependent on the type of plate boundary where the earthquake takes place. At divergent boundaries, earthquakes are generally less severe because the plates’ movement is slow and gradual. Conversely, at convergent boundaries, earthquakes can be extremely powerful because the plates are moving towards each other, causing a much greater buildup of stress. The subduction of one plate beneath another at convergent boundaries can also cause volcanic eruptions, which are another type of geological hazard.

The movement of tectonic plates also has a significant impact on volcanism. Volcanic activity is frequently linked to plate boundaries, particularly convergent boundaries where one plate is subducted beneath another. Transform boundaries and divergent boundaries can also cause volcanic activity, although such events are less commonly associated with them.

  1. History of Ocean Basins“, Harry HESS, Petrologic Studies, A. E. J. Engel, Harold L. James, B. F. Leonard, Geological Society of America, 1962^
  2. “The Little Book of Planet Earth”, Rolf MEISSNER, Copernicus, 2002nd edition, ISBN: 978-0387952581^
  3. “The History of Continental Drift – Alfred Wegener”, archived from bbm.me.uk^