Understanding Earthquakes and Volcanoes
Earthquakes and volcanoes are significant natural phenomena occurring within the Earth. Below is a detailed overview of these phenomena:
Earthquakes
In English, earthquakes refer to sudden vibrations in the Earth’s crust caused by the release of stored energy. These events typically occur along geological faults — zones where rock masses move relative to one another. It is noteworthy that substantial information about earthquakes was limited prior to the invention of seismology.
Volcanoes
Known as volcanoes in English, these are openings in the Earth’s crust through which hot magma, gases, steam, and dust escape. Eruptions may transpire in a controlled manner within a localized area or occur chaotically over broader regions. The term originates from the Roman word “Vulcan,” meaning the god of fire. Volcanoes are generally found in geological fault zones or at the boundaries of tectonic plates.
Causes of Earthquakes
Earthquakes can arise from various causes, but it is evident that they are prevalent along geological faults such as the well-known Pacific fault, which influences numerous densely populated coastal regions including cities in New Zealand, Papua New Guinea, Japan, and the western coasts of the Americas. Another notable example is the Alpid fault, which stretches from the Mediterranean Sea eastward to the East Indies. Here are the primary causes of earthquakes occurring in various parts of the world:
Natural Forces
This refers to the release of vast amounts of energy stored within the rocks of the Earth’s crust due to natural forces such as the movement of rocks and large bodies, gravitational forces, and chemical reactions. Collectively, these factors contribute to what are known as tectonic earthquakes.
One of the most famous examples of this type of earthquake is the San Andreas Fault earthquake of 1906, which slipped over a distance of 430 km. Geologist Harry Fielding Reid explained this phenomenon through the elastic rebound theory, suggesting that it occurs when the potential energy in the rocks reaches a threshold that exceeds their strength, resulting in fractures and the release of massive energy extending several kilometers along weakened zones.
Volcanic Activity
A major contributor to seismic activity is volcanic activity, which is caused by the movement of adjacent rocks to the volcano that releases significant energy, either in the form of heat from the magma moving in underground reservoirs or as abundant gases.
Earthquakes resulting from such activities are termed volcanic earthquakes. A prominent example can be found in the earthquakes occurring around the volcanoes along the Pacific Ring of Fire, where these volcanoes are situated hundreds of kilometers away from the centers of most well-known shallow earthquakes.
Industrial Causes
This category encompasses human activities responsible for causing specific types of earthquakes, such as the injection of fluids into deep wells, large underground nuclear explosions, mining operations, and the filling of large reservoirs that release latent energy and relieve pressure on the surrounding rocks, consequently triggering earthquakes.
These phenomena are known as induced earthquakes. Notably, filling large reservoirs is one of the most significant culprits, with over 20 documented instances of increased local seismicity following the filling of dams, including the Hoover Dam in the United States, the High Dam in Aswan, Egypt, and the Kariba Dam located on the border between Zimbabwe and Zambia.
The most widely accepted explanation for these occurrences is that the rocks near the dams were already under stress due to regional tectonic forces, rendering them primed for slipping. When water is introduced into these reservoirs, it alters the pressure dynamics, resulting in earthquakes, although it is reassuring to note that these events are generally not dangerous.
Causes of Volcanoes
Volcanoes occur when heated materials within the Earth erupt to the surface. These materials are referred to as lava when they are on the surface and magma when they remain underground. This can include volcanic rock, ash, gases, steam, and more. In other words, volcanic eruptions are driven by rising magma from the Earth’s interior, which can happen for three key reasons:
Tectonic Plate Movement
The Earth’s crust is composed of tectonic plates that move slowly and drift apart, creating gaps that allow magma to rise from below to fill these voids. This process can also occur underwater, resulting in the formation of underwater volcanoes.
Converging Tectonic Plates
Conversely, the movement of tectonic plates towards one another can cause the crust to buckle and descend into the Earth. The resultant heat and pressure lead to the melting of crustal material, generating the primary magma that forms volcanoes.
Hot Spot Activity
Hot spots are areas within the Earth that display elevated temperatures, which heat the magma, reducing its density. When its density decreases, the magma rises, leading to the formation of volcanoes.