Earthquakes and Volcanoes Explained

Understanding Earthquakes

Earthquakes occur when there is an instantaneous release of stored energy within the Earth. Soil displacements can cause large fissures on the ground, falling buildings, and other damage. The point inside the Earth where an earthquake originates is called the focus or hypocenter. The surface area directly above the focus is called the epicenter. Seismic waves are captured by highly sensitive instruments called seismographs and recorded on seismograms. Different scales have been used to measure the magnitude of earthquakes, but the most commonly used is the Richter scale. When an earthquake occurs at sea, it can generate a large tidal wave called a tsunami.

Earthquake Origins

• Tectonic earthquakes: Occur due to the movement of rock masses along faults or fractures and friction between tectonic plates. Often, after the main shock, there are aftershocks of varying intensity. These earthquakes can occur through different processes and at different depths. There is a difference between those that take place in a movement of blocks along a fault, which are often the most intense, and those that take place at subduction zones where an oceanic plate enters the mantle.
• Volcanic earthquakes: Occur due to soil movement and eruptions that are sometimes very explosive. They are far less frequent and less intense than tectonic earthquakes.

Global Earthquake Distribution

Tectonic earthquakes are distributed as follows:

• A high seismic belt surrounding the Pacific Ocean (the "Ring of Fire").
• A second belt of intense seismic activity across the Mediterranean Sea and into Asia.
• A third high seismic belt crosses the Atlantic Ocean, primarily along the Mid-Atlantic Ridge.

Volcanoes and Their Distribution

The distribution of volcanoes practically coincides with the foci of earthquakes. They are located in active areas of our planet, such as young ridges and transform faults. Volcanoes are arranged in the following areas:

• Constructive plate boundaries.
• Destructive plate boundaries (including subduction zones).
• Diffuse or deep zones.
• Hot spots.

How Volcanoes Form

Volcanoes are geological structures formed by magma that originates inside the Earth's crust and mantle and comes to the surface.

• In fissural volcanoes, magma rises through fractures in the crust. Basaltic lava ejected from the mantle is very hot and fluid, covering many square miles. These large formations are called basaltic plateaus.
• In central volcanoes, the magma flows through a central vent, called a crater.

Types of Volcanic Eruptions

Volcanic eruptions can be terrestrial or undersea.

• Terrestrial volcanic eruptions: These are more or less violent depending on the characteristics of the magma and the way in which gases are released. If the magma is fluid, activity is less explosive. If the magma is viscous, strong explosions occur.
• Undersea volcanic eruptions: Volcanic eruptions located below sea level are different from terrestrial ones.
  • When eruptions are superficial, they are often very violent, producing underwater explosions as lava comes in contact with seawater.
  • If eruptions occur more than 300 m deep, the lava that emerges quickly solidifies on contact with water to form pillow lava.