Volcano/Earthquake (Important for APSC)

Earthquakes and volcanoes are both fascinating natural phenomena that involve significant geological activity resulting in dramatic changes to the Earth’s surface. These events occur suddenly and are characterized by the generation of substantial deformations within a relatively short period of time.

Earthquakes, often referred to as seismic events, occur when there is a sudden release of energy in the Earth’s crust. This release of energy results in the generation of seismic waves, which propagate through the Earth’s rocks and cause the ground to shake. These seismic waves can vary in intensity, from minor tremors that go unnoticed to catastrophic quakes that can cause widespread destruction. Earthquakes can be triggered by various geological processes, such as tectonic plate movements, volcanic activity, or even human activities like mining and drilling.

On the other hand, volcanoes are geological features that form when there is a rupture or crack in the Earth’s crust that allows magma, volcanic ash, and gases to escape to the surface. The formation of volcanoes is often associated with the movement of molten magma from the Earth’s mantle to the surface. This molten magma, which contains dissolved gases, rises through fractures or weaknesses in the Earth’s crust beneath the volcano. When the pressure builds up sufficiently, it can lead to an explosive eruption, releasing the magma, ash, and gases into the atmosphere.

Volcanic eruptions can vary in size and intensity, ranging from relatively gentle effusive eruptions, where lava flows steadily from the volcano, to highly explosive eruptions that eject large amounts of ash and pyroclastic materials into the air. Volcanic eruptions can have significant environmental and societal impacts, including the creation of new landforms, changes in climate, and even disruptions to air travel due to ash clouds.

Earthquakes and volcanoes are two remarkable natural processes that showcase the dynamic nature of our planet. While earthquakes result from the sudden release of energy within the Earth’s crust, causing ground shaking, volcanoes are geological features formed by the escape of magma, ash, and gases from beneath the Earth’s surface. Both phenomena are critical to the understanding of Earth’s geology and have far-reaching implications for the environment and human society.

Definition of Earthquake 

The term “earthquake” encompasses the sudden movement along a fault line, which includes the ensuing ground shaking and the release of seismic energy triggered by fault slippage, volcanic or magmatic events, or other abrupt shifts in stress within the Earth’s crust.

Definition of volcano

A volcano is a fracture or opening in the crust of a celestial body, such as Earth, through which molten lava, volcanic ash, and gases are released from a subterranean magma chamber. On our planet, volcanoes are primarily located in regions where tectonic plates either move apart or come together, with a significant portion of them existing beneath the ocean’s surface.

Types of Earthquake

• Tectonics Earthquake
• Volcanic  Earthquake
• Explosion  Earthquake
• Collapse  Earthquake

Tectonics Earthquake

The Earth’s crust is composed of fragmented land masses known as tectonic plates, capable of slow and gradual movement. These plates exhibit various forms of motion:

1. Converging Motion: Plates move toward each other.

2. Diverging Motion: Plates move away from each other.

3. Transform Motion: Plates slide horizontally past each other.

4. Colliding Motion: Plates collide with significant force.

Tectonic earthquakes, a result of plates sliding over each other, are the most common type of earthquake. These earthquakes can range in magnitude from small to large and are responsible for much of the world’s destruction. High-magnitude tectonic earthquakes can cause widespread devastation, potentially toppling entire cities in seconds.

Volcanic  Earthquake

Comparatively, volcanic earthquakes are less common than tectonic earthquakes and typically occur in proximity to volcanic eruptions.

Volcanic earthquakes can be categorized into two main types:

1. Volcano-Tectonic Earthquakes:These seismic events often occur following a volcanic eruption. During an eruption, magma is expelled from beneath the Earth’s crust, creating voids that need to be filled. As surrounding rocks rush to occupy this space, it leads to significant earthquakes.

2. Long-Period Volcanic Earthquakes: These earthquakes typically manifest after a volcanic eruption, usually in the days leading up to a major explosion. Before such an eruption, there are rapid changes in temperature within the magma beneath the Earth’s crust. These temperature fluctuations trigger seismic waves, resulting in an earthquake.

In some instances during volcanic activity, the escape route for magma becomes obstructed, causing a buildup of pressure. When this pressure becomes intolerable, it can release explosively, generating a powerful earthquake in the process. These volcanic earthquakes, though less common than tectonic ones, are a critical aspect of understanding volcanic processes and their associated seismic events.

Explosion  Earthquake

These earthquakes result from nuclear detonations and are referred to as man-made or induced earthquakes. They represent a profound consequence of contemporary nuclear warfare. In the 1930s, when the United States conducted nuclear tests, numerous small towns and villages bore the devastating brunt of these alarming actions.

Collapse  Earthquake

These earthquakes are typically of smaller magnitude and frequently happen in close proximity to underground mining operations. They are occasionally termed “mine bursts.” Collapse earthquakes are induced by the pressure buildup within rock formations.

This type of earthquake results in the caving-in of the mine roof, subsequently triggering additional seismic activity. Collapse earthquakes are notably common in small communities situated near underground mines.

Types of volcano 

• Cinder cones
• Composite volcanoes
• Shield volcanoes
• Lava volcanoes

Cinder cones

Cinder cones, geological features found in volcanic landscapes, exhibit distinct characteristics. They often take on a circular or oval shape and are formed as a result of volcanic eruptions originating from a single vent. What distinguishes them is the type of material ejected during these eruptions.

These cones are primarily composed of small fragments of lava, known as scoria, and pyroclastics. These materials are the result of explosive volcanic activity, where gas-rich magma is violently expelled from the vent. As the magma reaches the surface, it shatters into tiny fragments due to the rapid release of pressure. These fragments are then propelled into the air.

Composite volcanoes

Composite volcanoes, also known as stratovolcanoes, are characterized by their steep slopes and distinctive composition. These volcanoes are built up over time through the accumulation of numerous layers of volcanic materials, typically including high-viscosity lava, ash, and rocky debris. They manifest as towering, conical mountains formed by the alternating deposition of lava flows and other ejecta. These distinct layers, or strata, are responsible for the name “stratovolcano.”

Shield volcanoes

Shield volcanoes, characterized by their distinctive bowl or shield-like shape, possess gentle, elongated slopes primarily constructed by the flow of basaltic lava. These formations result from the eruption of low-viscosity lava, which can travel considerable distances from the volcanic vent.

Unlike explosive volcanic eruptions, shield volcanoes typically do not undergo catastrophic detonations. This tendency can be attributed to the magma’s low viscosity, which is often associated with lower silica content. Consequently, shield volcanoes are more frequently encountered in oceanic environments than on continental landmasses. Notable examples of shield volcanoes include the Hawaiian volcanic chain, marked by a series of shield cones, and their prevalence in Iceland’s volcanic terrain.

Lava volcanoes

Lava domes take shape when the lava being erupted is too viscous to flow freely, resulting in the accumulation of steep-sided mounds near the volcanic vent. These formations are a product of gradual eruptions involving highly viscous lava.

Occasionally, lava domes form within the confines of a prior volcanic crater. While they share similarities with composite volcanoes in their potential for explosive eruptions, the key distinction lies in the limited spread of their lava from the originating vent. Instead of flowing extensively, the lava typically piles up in close proximity to the vent, shaping these distinctive, steep-sided mounds.

Types of Volcanic Eruptions

The classification of volcanic eruptions hinges on a variety of factors, including magma chemistry, temperature, viscosity, volume, the presence of groundwater, and gas content. Here is an overview of the different types of volcanic eruptions:

1. Hydrothermal Eruption:These eruptions primarily involve the ejection of ash rather than magma. They are driven by the intense heat originating from hydrothermal systems.

2. Phreatic Eruption:Occurring when magma’s heat interacts with water, these eruptions typically do not involve magma but produce ash as a result.

3. Phreatomagmatic Eruption:This type of eruption unfolds when newly formed magma interacts with water, leading to explosive volcanic activity.

4. Strombolian and Hawaiian Eruption: Hawaiian eruptions are characterized by fire fountains, while Strombolian eruptions involve explosive episodes caused by the expulsion of lava fragments.

5. Vulcanian Eruption:These eruptions are of short duration but can reach heights of up to 20 kilometers, featuring explosive activity.

6. Subplinian and Plinian Eruptions:Subplinian eruptions extend up to approximately 20 kilometers in altitude, while Plinian eruptions can reach even greater heights, ranging from 20 to 35 kilometers.

The diverse spectrum of volcanic eruptions underscores the complex interplay of geological and environmental factors, each giving rise to distinctive volcanic phenomena.

The distribution of earthquakes

Distribution of earthquakes is not random; instead, they tend to occur in specific patterns across the Earth’s surface. These seismic events primarily concentrate within three major zones:

1. Circum-Pacific Seismic Belt (Ring of Fire):This is the world’s most prominent earthquake belt and encircles the Pacific Ocean. Approximately 81 percent of the largest earthquakes on Earth occur within this belt. It derives its nickname, the “Ring of Fire,” from the fact that it aligns with the boundaries of tectonic plates. These boundaries often involve the subduction of oceanic crust beneath another plate, leading to earthquakes caused by plate slip and rupture.

2. Alpide Earthquake Belt (Mid-Continental Belt): Extending from regions like Java and Sumatra through the Himalayas, the Mediterranean, and into the Atlantic, this belt accounts for about 17 percent of the world’s major earthquakes. It has witnessed some of the most destructive seismic events in history.

3. Mid-Atlantic Ridge:The third significant belt follows the submerged mid-Atlantic Ridge. This ridge marks the separation of two tectonic plates, creating a divergent plate boundary. Most of the mid-Atlantic Ridge is submerged underwater and far from human development.

Measurement of Earthquakes

Earthquakes release energy in the form of seismic waves, which propagate through the Earth. Scientists employ instruments called seismometers to measure these waves. Seismometers detect seismic waves beneath them and record them as a series of zig-zags. By analyzing this data, scientists can determine the earthquake’s location, time, and intensity, as well as gain insights into the properties of the rocks through which the seismic waves traveled.

Earthquake events are typically measured using either the Richter scale or the Mercalli intensity scale. The Richter scale quantifies the earthquake’s magnitude, representing the energy released. It employs a numerical scale from 0 to 10. On the other hand, the Mercalli intensity scale assesses the visible damage caused by the earthquake, using a range from 1 to 12.

Seismic Waves (Earthquake Waves)

Seismic waves are the energy waves generated by earthquakes or explosions. These waves travel through the Earth and are recorded by seismographs. Earthquake waves fall into two main categories: body waves and surface waves. Body waves are generated at the earthquake’s focus and propagate through the Earth’s interior. There are two types of body waves: P-waves (primary waves), which are the fastest, and S-waves (secondary waves), which can only travel through solid materials.

Body waves interacting with surface rocks give rise to surface waves. These waves move along the Earth’s surface and are the last to be recorded on seismographs. Surface waves can be more destructive, leading to the displacement and collapse of rocks.

Effects of Earthquakes

Earthquakes can have significant and immediate impacts, including:

1. Ground shaking

2. Differential ground settlement

3. Land and mudslides

4. Fires

5. Ground lurching

6. Avalanches

7. Ground displacement

8. Flooding from dam and levee failures

9. Structural collapse

10. Tsunamis (in coastal areas)

Earthquakes in India:

India is highly susceptible to earthquakes due to the presence of young, tectonically active fold mountains like the Himalayas. The country is divided into four seismic zones (II, III, IV, and V) based on scientific assessments of seismic activity, historical earthquake occurrences, and the tectonic characteristics of the region. These zones provide valuable insights into earthquake vulnerability and preparedness in different parts of India.

Causes of volcanism

Here are the key points about the causes of volcanism:

1. Heat Generation: Radioactive substances within the Earth undergo chemical reactions, producing significant amounts of heat deep within the planet.

2. Residual Heat: Heat left over from the Earth’s formation remains trapped at its core, contributing to the temperature difference between the inner and outer layers.

3. Temperature Contrast: This temperature difference drives convection currents in the Earth’s mantle, facilitating the movement of molten magma and gases.

4. Plate Boundaries: Convection currents give rise to convergent and divergent plate boundaries in the Earth’s crust.

5. Magma Movement: These plate boundaries provide pathways for molten magma and gases to rise toward the Earth’s surface.

6. Convergent Boundaries: At convergent plate boundaries, denser tectonic plates subduct beneath less dense ones, creating high-pressure conditions that lead to volcanic eruptions.

7. Seismic Activity: Earthquakes and other seismic events can expose fault zones in the Earth’s crust, allowing magma to flow to the surface, resulting in fissure-type volcanoes.

volcanism is driven by the heat generated by radioactive substances, residual heat, convection currents in the mantle, and plate boundary interactions, with seismic activity occasionally playing a role in volcanic eruptions.

Volcanic landscape

• Volcanic landscapes consist primarily of solidified lava and fragmented volcanic materials, contrasting with landscapes shaped by erosion.
• Constructional features in volcanic landscapes can be categorized into two types:

•  Cones, domes, and related forms.
• Plateaus and plains formed by lava and volcanic debris.

• Some volcanic complexes combine extruded lava domes and volcanic plateaus.
•  Negative features in volcanic landscapes include explosively blown-out rifts and hollows, with the largest known as calderas.
• Lakes are common in volcanic landscapes, occupying both explosion-made depressions and valleys obstructed by solidified lava or altered by volcanic subsidence.