Class 11 Geography (Fundamental of Physical Geography) Chapter 3 Interior of the Earth

Key Concept: Seismic Waves

c) P-waves

[Solution Description] P-waves are the fastest type of seismic waves. They are primary waves that travel quickly through both solid and liquid layers of the Earth, making them the first to be detected by seismographs.

Key Concept: Basic Terms

c) Movement of tectonic plates

[Solution Description] Tectonic earthquakes are primarily caused by the sudden movement of large blocks of the Earth’s crust along faults, which is due to plate tectonics. The intense stress and pressure build-up at these fault lines eventually get released as seismic energy, causing an earthquake.

Key Concept: Basic Definitions

c) It is a vertical structure formed by solidified lava in cracks

[Solution Description] A dyke is a vertical structure formed when magma solidifies in cracks that cut across pre-existing layers.

Key Concept: Arrival Sequence

b) After P-waves

[Solution Description]

S-waves are known as secondary waves because they arrive after primary waves, also known as P-waves. The sequence of arrival is important in seismology for determining the location and structure of earthquakes.

Key Concept: Volcano Types

d) Composite Volcano

[Solution Description] Composite volcanoes are known for their highly viscous lava, which often leads to explosive eruptions due to the buildup of pressure. These eruptions can be quite violent and are a defining characteristic of composite volcanoes.

Key Concept: Process Understanding

c) Effective stress between soil particles

[Solution Description] Soil liquefaction during an earthquake happens when saturated soil substantially loses stiffness and strength, typically due to ground shaking. This occurs because water pressure within the pores of the soil increases significantly, leading to a decrease in effective stress between soil particles. As a result, the solid structure is compromised, causing the soil to behave like a liquid.

Key Concept: Mining Depths

d) 12 km

[Solution Description] The Kola Superdeep Borehole is one of the deepest boreholes in the world, reaching a depth of approximately 12 kilometers. This was part of a scientific drilling project aimed at studying the Earth’s crust.

Key Concept: Basic Terminology

b) To study oceanic crust

[Solution Description] The primary purpose of the Integrated Ocean Drilling Project (IODP) is to study the composition and structure of the Earth’s subsurface, particularly the oceanic crust, by drilling into the seabed.

Key Concept: Basic Definition

b) Waves that travel along the Earth’s surface

[Solution Description] Surface waves travel along the Earth’s surface and are generated by the interaction of body waves with surface rocks.

Key Concept: Intrusive Forms

c) Sill

[Solution Description] A sill is an intrusive igneous body that forms when magma intrudes parallel to existing strata, solidifying into a tabular sheet.

Key Concept: Basic Definition

d) Primary Waves

[Solution Description] P-Waves are also known as Primary Waves because they are the fastest type of seismic waves and arrive first during an earthquake.

Key Concept: Basic Identification

c) P-wave

[Solution Description] P-waves are classified as primary waves in earthquake terminology. They are body waves and are the first to arrive during seismic events.

Key Concept: Wave Types

c) P-waves

[Solution Description] P-waves are the only type of body waves that can travel through solids, liquids, and gases due to their longitudinal nature. S-waves, on the other hand, can only move through solid materials.

Key Concept: Formation Process

b) Dyke

[Solution Description] Dykes are wall-like structures that form when magma solidifies in vertical cracks within existing rock layers, thus resulting in a perpendicular orientation relative to the ground.

Key Concept: Geological Features

a) Exfoliated granite domes.

[Solution Description] Lacoliths are often associated with domal hills composed of granite rocks that may exhibit exfoliation due to weathering processes.

Key Concept: Formation Characteristics

b) Phacolith

[Solution Description]

The formation known for its wavy mass of intrusive rocks located at the base of synclines or at the top of anticlines, and connected to magma chambers, is called Phacolith.

Key Concept: Wave Types

a) P-waves

[Solution Description] P-waves, or primary waves, are compressional waves that can travel through both solids and liquids. S-waves, on the other hand, can only travel through solids.

Key Concept: Basic Concept

c) To explore deeper depths of the Earth’s crust

[Solution Description] The main goal of the Deep Ocean Drilling Project is to explore deeper depths of the Earth’s crust in order to gain insights into its composition and history.

Key Concept: Wave Types

b) S-waves

[Solution Description] S-waves, also known as secondary waves, can travel only through solid materials. Unlike P-waves, which can travel through solids, liquids, and gases, S-waves require a medium that has shear strength. Therefore, they cannot propagate through liquids or gases.

Key Concept: Scale Identification

d) Mercalli scale

[Solution Description] Earthquake intensity is measured using the Mercalli scale, which ranges from 1 to 12.

Key Concept: Volcanic Materials

b) Lava

[Solution Description] Lava is one of the most common materials released during a volcanic eruption as it flows from a volcano’s vent.

Key Concept: Scale Range

c) 1-12

[Solution Description] The Mercalli intensity scale ranges from 1 to 12, where 1 indicates that an earthquake is not felt and 12 indicates total destruction.

Key Concept: Definition Recall

c) Focus (Hypocentre)

[Solution Description] The point within the Earth where an earthquake starts is known as the focus or hypocentre.

Key Concept: Comparative Analysis

d) They have cooler and more viscous lava

[Solution Description] Composite volcanoes typically have steeper slopes and are more explosive compared to shield volcanoes. This is due to the cooler and more viscous lava that forms composite volcanoes, leading to pressure build-up and explosive eruptions.

Key Concept: Comparison with Lacoliths

c) Batholiths cover larger areas without a level base

[Solution Description] Batholiths are significantly larger than lacoliths and do not have a level base, unlike lacoliths which are smaller intrusions with a flat base.

Key Concept: Effect Comparison

a) Ground Shaking

[Solution Description] Ground shaking typically causes the most damage to buildings and infrastructure as it directly impacts their structural integrity.

Key Concept: P-Waves Characteristics

d) Solid, liquid, and gas

[Solution Description] P-waves, or primary waves, can travel through solids, liquids, and gases, making them the fastest traveling seismic waves.

Key Concept: Basic Definition

b) Magnitude of earthquakes

[Solution Description] The Richter Scale is designed to measure the magnitude of earthquakes, which relates to the energy released by the earthquake event.

Key Concept: Indirect Sources

d) Magnetic field observations

[Solution Description]

Indirect sources provide insights into the Earth’s interior without direct observation. These include phenomena such as gravitation, magnetic fields, and seismic activity that offer clues about subsurface conditions.

Key Concept: Magma Source

c) Asthenosphere

[Solution Description] Magma primarily originates from the asthenosphere, which is the upper portion of the mantle. The heat and pressure conditions in this region allow rocks to partially melt, forming magma. This process occurs due to the temperature and pressure environment in the asthenosphere.

Key Concept: Basic Definition

d) Reservoir induced earthquakes

[Solution Description]

The term used for earthquakes that occur due to the loading and/or influx of water in a reservoir created by a dam is “reservoir induced earthquakes.”

Key Concept: Lava Flow Characteristics

c) The flows are extensive, covering vast areas with low-viscosity lava.

[Solution Description] Lava flows in flood basalt provinces are typically extensive and can spread over hundreds of kilometers due to their low viscosity. This allows the lava to travel great distances before solidifying, resulting in broad, layered landscapes.

Key Concept: Length of Ridges

c) 70,000 km

[Solution Description] The world’s mid-ocean ridge system is over 70,000 km long, making it the longest mountain range on Earth. It spans across multiple oceans and plays a crucial role in seafloor spreading and the creation of new oceanic crust.

Key Concept: Earthquake Effects

b) Ground Shaking

[Solution Description] Immediate effects of an earthquake can include phenomena like ground shaking, landslides, soil liquefaction, and tsunamis. Ground shaking is one of the primary immediate effects.

Key Concept: Types of Volcanoes

a) Shield Volcano

[Solution Description]

A shield volcano is characterized by broad, gentle slopes formed by the eruption of low-viscosity basaltic lava that can flow long distances. This creates a wide, gently sloped structure.

Key Concept: Magma vs. Lava

b) Magma is found beneath the Earth’s surface; Lava erupts onto the Earth’s surface

[Solution Description] Magma is molten rock beneath the Earth’s surface, while lava is molten rock on the Earth’s surface. The key difference lies in their location relative to the Earth’s crust.

Key Concept: Direct vs. Indirect Sources

c) Magnetic field studies

[Solution Description]

Indirect sources provide data through interpretations rather than physical samples. Gravity anomalies, caused by variations in mass distribution, contribute to understanding the structure beneath the Earth’s surface without direct access.

Key Concept: Impact of Water

b) It increases the explosivity of the eruption.

[Solution Description] When water enters a shield volcano’s vent during an eruption, it can increase explosivity due to rapid steam generation. This steam buildup can cause more violent eruptions.

Key Concept: Shadow Zones

b) Due to their inability to propagate through liquid

[Solution Description] S-waves cannot travel through liquids, so when they encounter the Earth’s liquid outer core, they are blocked, creating a shadow zone on the opposite side of the planet where these waves are not detected.

Key Concept: Cause Identification

c) Collapse of underground mines

[Solution Description] The primary cause of collapse earthquakes is the collapse of underground mines, often associated with intense mining activities.

Key Concept: Wave Types

d) P-waves

[Solution Description]

P-waves are the primary waves which are known as compressional waves and have the ability to travel through solids, liquids, and gases due to their longitudinal nature. They are the fastest type of seismic waves.

Key Concept: Location Identification

b) Western Maharashtra

[Solution Description] According to the syllabus, dykes are commonly found in the western Maharashtra area.

Key Concept: Core Characteristics

c) 5,100 km

[Solution Description] The transition from liquid to solid occurs at the boundary between the outer and inner core of Earth. Since the outer core is liquid and the inner core is solid, this transition occurs at a depth corresponding to the boundary between these two regions. This transition takes place at approximately 5,100 km.

Key Concept: Comparison with P-Waves

d) The S-wave shadow zone is larger than the P-wave shadow zone.

[Solution Description]

The shadow zone of S-waves is larger than that of P-waves. This is because S-waves cannot travel through the Earth’s liquid outer core, while P-waves can travel through both solid and liquid layers, leading to a narrower shadow band for P-waves.

Key Concept: Basic Definition

a) Movement of tectonic plates

[Solution Description] Earthquakes are primarily caused by the sudden release of energy in the Earth’s crust due to movement along faults.

Key Concept: Basic Definition

b) Epicentre

[Solution Description]

The point on the Earth’s surface directly above the focus, or hypocentre, where an earthquake originates, is known as the epicentre. This is a basic definition related to earthquakes.

Key Concept: Wave Propagation

a) P-waves

[Solution Description]

The speed of seismic waves is determined by their type and the medium through which they travel. P-waves, or primary waves, are longitudinal waves that compress and expand the material through which they move. These waves can travel through both solid and liquid, making them the fastest type of seismic wave. S-waves, on the other hand, are slower because they only travel through solids. Surface waves are even slower as they travel along the Earth’s surface.

Key Concept: Simple Cause and Effect

c) To understand mass distribution in Earth’s crust

[Solution Description] Geological studies use gravity anomalies because they provide information about the mass distribution in Earth’s crust, which is essential for understanding subsurface structures.

Key Concept: Volcano Type Identification

a) Shield Volcano

[Solution Description] The type of volcano that is typically associated with low-explosivity and fluid basalt lava is the Shield Volcano. This type of volcano forms from very fluid lava flows that result in broad, gentle slopes.

Key Concept: Direct Sources

c) Volcanic eruptions

[Solution Description] Direct sources provide firsthand evidence about the interior of the Earth. Surface rocks, mining activities, deep drilling projects, and volcanic eruptions are considered direct sources because they offer physical samples or observations from beneath the surface.

Key Concept: Direct Sources

d) Volcanic eruptions

[Solution Description] Mining and volcanic eruptions are considered direct sources of information about the earth’s interior because they provide physical samples or observable data directly from beneath the earth’s surface.

Key Concept: Wave Arrival

a) Only P-waves

[Solution Description] Beyond 145° from the epicenter, seismographs typically record only P-waves. This occurs because S-waves do not travel through the Earth’s liquid outer core, while P-waves are capable of passing through this layer but are partially blocked in the shadow zone.

Key Concept: Structural Analysis

c) Large collapsed depression

[Solution Description] Calderas are characterized by their large collapsed depressions formed due to the emptying of the magma chamber and subsequent collapse of the surface area above it.

Key Concept: Wave Types

b) S-wave

[Solution Description] S-waves, or secondary waves, do not travel through liquids. This characteristic leads to the formation of a shadow zone for these waves beyond 105° from the earthquake’s epicenter.

Key Concept: Richter Scale

c) 0-10

[Solution Description] The Richter scale is used to measure the magnitude of earthquakes. It assigns a single number to quantify the amount of seismic energy released by an earthquake. The scale ranges from 0 to 10, where each whole number increase represents a tenfold increase in amplitude of the waves.

Key Concept: Lava Viscosity

d) Creates explosive eruptions

[Solution Description] Composite volcanoes are characterized by eruptions of cooler and more viscous lavas compared to basalt. The higher viscosity results in obstruction of lava flow, which accumulates pressure under the crust until it is released explosively. Therefore, the eruptions tend to be explosive.

Key Concept: Lithosphere Components

c) Crust and uppermost mantle

[Solution Description] The lithosphere is composed of the earth’s crust and the uppermost part of the mantle. This includes both the oceanic and continental crust along with a portion of the underlying mantle.

Key Concept: Seismic Waves and Layers, Advanced Seismic Analysis

c) By analyzing wave speed and direction changes

[Solution Description] The study of seismic waves involves observing how these waves change speed and direction as they travel through different materials. When seismic waves encounter the boundary between the Earth’s mantle and core, their speed changes significantly. Primary waves (P-waves) slow down as they enter the outer core, leading to a shadow zone where no waves are detected. This indicates that the outer core is liquid because P-waves can travel through liquids but at reduced speeds. Secondary waves (S-waves), which cannot travel through liquids, are completely absent beyond this shadow zone, further confirming the liquid nature of the outer core. Thus, seismic wave behavior helps determine that the inner core is solid, while the outer core is liquid.