Earthquakes and Volcanoes

Earthquakes and Volcanoes

Earthquakes

The sudden tremors or shaking of the Earth's crust are called an earthquake. When a part of the earth's surface moves backward and forward or up and down, the earth's surface 'quakes', and these are called 'earthquakes'.

• The Earth's crust is made up of different parts of various sizes.

• They are called plates.

• Most of the earthquakes in the world are caused by the movements of the plates (Tectonism).

'Seismology' is the special branch of Geology that deals with the study of earthquakes.

'Richter scale' and 'Mercalli scale' are the instruments to measure/record the magnitude and the intensity of an earthquake, respectively.

Seismic Waves

The place where the seismic waves originate beneath the Earth's surface is called the focus of the earthquake. The epicenter is that point on the ground surface which is closest to the focus.

Seismic waves are recorded on the seismograph. Seismic waves are mainly of three types:

1. Primary waves

2. Secondary waves

3. Surface or Long waves

NASA launched the first-ever INSIGHT (Interior Exploration using Seismic Investigation, Geodesy and Heat Transport) Mission (on 5 May 2018) to explore the deep interior of Mars. It was launched by United Launch Alliance (ULA) Atlas V rocket from Space Launch Complex 2 at Vandenberg Air Force Base in California.

The Earthquake Zones in India

The Indian plate is moving from south to north. That is why there are earthquakes in the Himalayan region.

Earthquakes occur in Assam, Arunachal Pradesh, Nagaland, Tripura, Manipur, Mizoram, Andaman and Nicobar Islands, Jammu and Kashmir, the northwestern region of Uttar Pradesh, the northern region of Bihar, etc.

During the last few years, there have been several earthquakes of varying intensities in Maharashtra and Gujarat.

Volcanic Activity

Magma or molten rock is formed beneath the ground surface due to various reasons.
This molten rock ruptures the ground and pours out. Sometimes, it cools down beneath the ground surface instead of pouring out.

All these activities are called volcanic activities. Volcanic activities have been taking place since time immemorial.

Types of Volcanoes

There are three types of Volcanoes:

1. Active Volcanoes

2. Dormant Volcanoes

3. Extinct Volcanoes

1. Active Volcanoes

• These volcanoes constantly eject volcanic lava, gases, ashes, and fragmental materials.

• It is estimated that there are more than 500 active volcanoes in the world.

• Etna and Stromboli are the most significant examples of this category.

• Stromboli is known as the Lighthouse of the Mediterranean.

Other volcanoes of this category are:

• Cotopaxi of Ecuador (the World's highest active volcano)

• Mt. Erebus of Antarctica (the only active volcano of the continent)

• The active volcano on Barren Island in the Andaman and Nicobar Islands, India

2. Dormant Volcanoes

These volcanoes become quiet after their eruptions for some time, and there is no indication of future eruptions, but suddenly they erupt very violently and cause enormous damage to human health and wealth.

Important examples of this category are:

• Vesuvius (Italy)

• Fujiyama (Japan)

• Krakatao (Indonesia)

• Dormant volcanoes in the Narcondam Island, now believed to be active after the Tsunami of December 2004, (Andaman & Nicobar)

3. Dead or Extinct Volcanoes

These are those volcanoes that have not erupted for thousands of years, and there is no indication of future eruption as well.

Main examples of this category are:

• Mt. Kenya and Mt. Kilimanjaro (Eastern part of Africa)

• Chimborazo (Ecuador)

• Popa (Myanmar)

• Damavand (Iran)

• Koh-i-Sultan (Pakistan)

• Aconcagua in the Andes Mountains

Volcanic Eruptions

The pouring out of magma or molten rock through the ground surface is called a volcanic eruption.

At the time of eruption, the magma, steam, fragments of rock, dust, and gaseous substances are ejected with great force from under the ground surface through a pipe-like passage.

• The opening of this pipe on the Earth's surface is known as the vent, which forms a crater.

• The lava, which is thrown into the sky during an eruption, falls to the ground in the form of solid fragments. Dark clouds gather in the sky, and it begins to rain heavily.

• The volcanic ash and dust mix with the rainwater, giving rise to hot mud flows.

Types of Volcanic Eruptions

Volcanic eruptions are classified into two types depending on the manner of ejection of the magma:

1. Central eruption

2. Fissure eruption

Central Eruption

This type of eruption gives rise to conical or dome-shaped hills. Some examples of volcanic mountains formed due to central eruption are:

• Mt. Kilimanjaro in Africa

• The Fujiyama in Japan

• The Vesuvius and Mount Etna in Italy

It is poured acidic lava.

Fissure Eruption

• These eruptions take place at a very slow speed. Since this lava is more fluid, it spreads over longer distances.

• The lava cools down on the ground over a period of time, increasing the thickness of the surface in that area.

• Basalt plateaus are formed due to these eruptions.

• Basalt plateaus are also found in Brazil in South America, Saudi Arabia in West Asia, and the Deccan Plateau in India.

• In Maharashtra, the fertile black regur soil has been formed from basalt rocks. It is also called black cotton soil.

The Opening of an Exploded Volcano is of Different Types

Some important types are:

Crater

• This is a funnel or cup-shaped opening at the top of the volcanic cone.

• It gets filled up with rainwater, then it forms a crater lake, e.g., Loner Lake in Buldhana district (Maharashtra).

• Sometimes, many small craters are formed in a single crater.

• This takes place when the explosion is of less intensity than that of the pre-existing crater; these are known as Nested craters, e.g., the three small craters of Mountain (Philippines).

Caldera

• This is a widened form of a crater, which is formed due to depression of the crater or expansion of the volcanic mouth or vent due to successive eruptions.

• Depending on their intensity and duration, volcanic eruptions can create calderas as much as 100 km (62 miles) wide.

• Mt. Aso of Japan is an example of a Caldera.

• The Toba Caldera on the Indonesian island of Sumatra is the newest resurgent caldera.

World Distribution of Volcanoes

The explanation of volcanic regions of the world, based on the Plate tectonic theory, is the most accepted one.

According to this theory:

• Destructive plate boundaries account for about 80% of the volcanic regions

• Constructive plate margins for about 15%

• The remaining ones are in the interior parts of the plates, which are not yet explained by the Plate tectonic theory

Major Volcanoes of the World

Final Thoughts

The study of earthquakes and volcanic activities provides deep insights into the dynamic nature of Earth’s crust. Earthquakes, caused by the sudden movement of tectonic plates, are measured using the Richter and Mercalli scales and studied under seismology, which helps us understand their origin and effects.

Volcanoes, on the other hand, have been shaping our landscapes for millions of years. Whether active, dormant, or extinct, they form unique landforms and fertile soils, like the Deccan Plateau's basaltic soil. The classification of volcanic eruptions into central and fissure types highlights the different ways magma reaches the surface.

Knowing the earthquake-prone zones and major volcanoes of the world is essential for disaster preparedness and environmental understanding. These natural phenomena show that Earth is not static but constantly evolving, creating both challenges and opportunities for human life.