Part I- Introduction and key definitions

The phenomena of earthquake volcanic eruptions and tsunami are the three most important geological processes which on the one hand cause enormous human and economic disaster but on the other hand are very interesting from the scientific point of view. It provides us a very useful window to study how the planet earth and other planets of the solar system were formed, what goes on in the interior and surface of the planets. In this series of articles, we present an account of various important such disasters with an emphasis on their underline causes.

If we superimpose a map of active volcanoes in the world on a map of earthquakes during the past thirty years, we can see that their location match reasonably well. Most of the volcanism and seismic activity on Earth is localized on the boundaries between tectonic plates. However, these two phenomena are not directly related.

The best example of an obvious correlation between volcanism and seismically active zones is the “Ring of Fire” skirting the Pacific Ocean. All around the Pacific Ocean, we find subduction zones. In subduction zones, the dense and hydrated oceanic lithosphere sinks in the mantle. The water contained in the oceanic crust lowers the melting point of the surrounding rocks, which creates magma. This hotter and less dense magma moves toward the surface, where it generates the intense volcanism that gave its name to the “Ring of Fire”.

But in the case of the “Ring of Fire”, earthquakes and volcanoes are not directly related. Of course, earthquakes happen in these subduction zones, but they do not really cause eruptions.

Subduction zones are plate tectonic boundaries where two plates converge, and one plate is thrust beneath the other. This process results in geohazards, such as earthquakes and volcanoes

Below we give certain keywords and concepts that will help us understand the phenomena

1:-Richter scale

It is a scale to measure the magnitude of energy released by an earthquake. This scale was devised by Charles F. Richter in the year 1930. The number indicating magnitude or intensity ranges between 0 and 9 but the scale has no upper limit of number because it is a logarithmic scale

2:-Volcanic Explosivity Index (VEI)

It is a numeric scale that measures the relative explosivity of historic eruptions. The volume of products, eruption cloud height, and qualitative observations  are used to determine the explosivity value

3:-Mercalli scale

It is the scale of the measurement of the degree of the destructiveness of the intensity of the earthquake. This scale is generally known as the Mercalli intensity scale.

4:-Tectonic processes

Tectonics is the process that controls the structure and properties of the Earth’s crust and its evolution through time. These include the processes of mountain building

5:-Tectonic plates

Plate tectonics is a scientific theory describing the large-scale motion of the plates making up the Earth’s lithosphere since tectonic processes began on Earth between 3.3 and 3.5 billion years ago

6:-Subduction zone

A subduction zone is a region of the Earth’s crust where tectonic plates meet.

7:-Focus

It is the point of the origin of earthquake inside the earth

8:-Epicenter

The place on the ground surface which is perpendicular to the buried focus or hypocenter and recording the seismic waves for the first time is called the epicenter.

9:-Trench

A trench is a type of excavation or depression in the ground that is generally deeper than it is wide, and narrow compared with its length.

10:-Seafloor spreading

Seafloor spreading is a process that occurs at mid-ocean ridges, where a new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.

11:-Continental drift

Continental drift is the hypothesis that the Earth’s continents have moved over geologic time relative to each other, thus appearing to have “drifted” across the ocean bed.

12:-Faults

A fault is a fracture in the crustal rocks wherein the rocks are displaced along a plane called fault plane

 13:-Folds

Wave-like bends formed in the crustal rocks by tangential compressive forces resulting from horizontal movement caused by endogenic forces originating deep within the earth are called folds.

14:-Ridges

A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance.

15:-Magma

Magma is an extremely hot liquid and semi-liquid rock located under Earth’s surface. This magma can push through holes or cracks in the crust, causing a volcanic eruption

19:-Endogenic

The forces coming from deep within the earth caused by thermal variation are called endogenic forces which create relief features of various dimensions.

17:-Lithosphere

The lithosphere is the rocky outer part of the Earth. It is made up of the brittle crust and the top part of the upper mantle. The lithosphere is the coolest and most rigid part of the Earth.

18:-Geomorphic forces

The physical and chemical interactions between the Earth’s surface and the natural forces acting upon it to produce landforms.

19:-Mantle

A mantle is a layer inside a planetary body bounded below by a core and above by a crust. Mantles are made of rock or ice and are generally the largest and most massive layer of the planetary body.

20:-Velocity of tectonic plates

Tectonic plates move at rates that vary from less than 6 feet per 100 years to 66 feet per 100 years and these rates may have been faster in the ancient past. At an average rate of 33 feet per 100 years, a tectonic plate can move 62.5 miles in 1 million years.

In part 2 of this series, we will discuss the major earthquakes volcanic eruption and their underline causes