Earthquakes and Volcanoes

Earthquakes and Volcanoes

Earthquakes

• The sudden tremors or shaking of the earth's crust is 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 the 'earthquake'.
• 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' the special branch of Geology, It deals with the study of earthquake.
• '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 and 3. Surface or Long waves.

NASA launched 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 times immemorial.

There are three types of Volcanoes:

1. Active Volcanoes 2. Dormant Volcanoes 3. Extinct Volcanoes.

1. Active Volcanoes:

These volcanoes constantly eject volcanic lavas, gases, ashes and fragmental materials. It is estimated that there are more than 500 active volcanoes in the world. Etna and Strombol are the most significant examples of this category. Stromboli is known as the Light house of the Mediterranean. Other volcanoes of this category are - Cotopaxi of Ecuador (World's highest active volcano), Mt. Erebus of Antarctica (the only active volcano of the continent) and the active volcano in the Barren Island of the Andaman and Nicobar Islands, India.

2. Dormant Volcanoes:

These volcanoes become quiet after their eruptions for some time and there is no indication for 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) and Dormant volcanoes in the Narcondam Island, now believed to be active after Tsunami of December 2004, (Andaman & Nicobar).

3. Dead or Extinct Volcanoes:

These are those volcanoes which have not erupted since 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) and Koh-i-Sultan (Pakistan) and Aconcagua in Andes mountains.

Volcanic Eruptions

• The pouring out of the magma or molten rock through 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 mixes 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 domeshaped hills. Some examples of volcanic mountains formed due to central eruption are Mt. Kilimanjaro in Africa, the Fujiyama in Japan and the Vesuvius and Mount Etna in Italy.
• It is basically 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 and Saudi Arabia in West Asia and Deccan plateau in India.
• In Maharashtra, the fertile black regur soil has beer formed from basalt rocks. It is also called black cotton soil.

The opening of exploded volcano is of different types Some important types are—

Crater this is funnel or cup-shaped opening at the top of the volcanic cone. It gets filled up with rain water 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 take place when the exposition was of less intensity than that of pre-existing crater, these are known as Nested craters, e.g. the three small craters of Mountain (Philippines).

Caldera this is widened form of crater which is formed due to depression of the crater or expansion of 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 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, rased 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% of the volcanic regions and remaining are in the interior parts of the plates which are not yet explained by the Plate tectonic theory.

Major Volcanoes of the World