- Which of the following statements best describes the primary cause of most intraplate earthquakes?
(a) Movement along pre-existing fault lines reactivated by distant tectonic stresses.
(b) The direct pressure exerted by rising magma plumes beneath the lithosphere.
(c) Density variations within the Earth’s mantle causing localized convective upwelling.
(d) The isostatic rebound of the crust following the melting of large ice sheets.
Answer: (a)
Explanation: While other factors can contribute, intraplate earthquakes are primarily attributed to the reactivation of ancient faults within continental plates due to stresses transmitted from plate boundaries. - The Wadati-Benioff zone is a seismic zone associated with:
(a) Mid-oceanic ridges and divergent plate boundaries.
(b) Transform faults and strike-slip motion.
(c) Subduction zones and inclined zones of deep earthquakes.
(d) Hotspot volcanism and mantle plumes.
Answer: (c)
Explanation: The Wadati-Benioff zone marks the inclined plane where an oceanic plate descends beneath another plate at a subduction zone, generating earthquakes at increasing depths. - Which type of volcanic eruption is characterized by the effusive outpouring of highly fluid basaltic lava, forming broad, gently sloping shield volcanoes?
(a) Plinian
(b) Pelean
(c) Hawaiian
(d) Vulcanian
Answer: (c)
Explanation: Hawaiian eruptions are known for their low-viscosity basaltic lava flows, creating shield volcanoes with gentle slopes. - The distribution of volcanoes and earthquakes is closely related to:
(a) Variations in atmospheric pressure and wind patterns.
(b) The boundaries of tectonic plates.
(c) The Earth’s magnetic field and its fluctuations.
(d) The distribution of major river systems and sedimentary basins.
Answer: (b)
Explanation: The vast majority of earthquakes and volcanoes occur along the edges of Earth’s tectonic plates, where they interact through divergence, convergence, or transform motion. - Which of the following seismic waves arrives at a seismograph station first and is compressional in nature?
(a) Love waves
(b) Rayleigh waves
(c) Secondary waves (S-waves)
(d) Primary waves (P-waves)
Answer: (d)
Explanation: P-waves are the fastest seismic waves and travel through both solid and liquid materials by compressing and expanding the rock in the direction of wave propagation. - The Volcanic Explosivity Index (VEI) is a scale used to measure the explosiveness of volcanic eruptions. Which of the following factors is NOT directly used in determining the VEI?
(a) The volume of tephra ejected.
(b) The height of the eruption column.
(c) The duration of the eruptive phase.
(d) The chemical composition of the erupted lava.
Answer: (d)
Explanation: While the chemical composition influences the viscosity and thus the explosiveness, the VEI is primarily based on the volume of ejected material, eruption column height, and eruption duration. - Which of the following is a significant secondary effect often associated with major earthquakes in coastal regions?
(a) The formation of large calderas.
(b) The generation of tsunamis.
(c) Increased rates of chemical weathering.
(d) Significant alterations in global wind patterns.
Answer: (b)
Explanation: Undersea earthquakes, particularly those occurring at subduction zones with vertical displacement of the seafloor, can generate devastating tsunamis. - The circum-Pacific belt, also known as the “Ring of Fire,” is characterized by a high concentration of:
(a) Fold mountains and rift valleys.
(b) Active volcanoes and earthquakes.
(c) Large sedimentary basins and oil reserves.
(d) Ancient shield volcanoes and stable continental crust.
Answer: (b)
Explanation: The Ring of Fire is a major area around the Pacific Ocean where numerous volcanic eruptions and earthquakes occur due to intense tectonic activity at convergent plate boundaries. - Which type of volcano is formed from alternating layers of lava flows and pyroclastic material (ash, cinders, bombs)?
(a) Shield volcano
(b) Cinder cone volcano
(c) Composite volcano (Stratovolcano)
(d) Lava dome
Answer: (c)
Explanation: Composite volcanoes, or stratovolcanoes, are characterized by their steep slopes and are built up by successive eruptions of both lava and pyroclastic debris. - The Mercalli intensity scale is used to measure the:
(a) Energy released at the focus of an earthquake.
(b) Magnitude of an earthquake based on seismograph readings.
(c) Effects of an earthquake at a specific location based on observed damage.
(d) Frequency of seismic waves generated by an earthquake.
Answer: (c)
Explanation: The Mercalli scale is a subjective scale that measures the intensity of an earthquake based on its observed effects on people, buildings, and the environment. - The phenomenon of liquefaction, often associated with strong earthquakes, primarily occurs in:
(a) Solid bedrock formations.
(b) Dry, compacted sandy soils.
(c) Water-saturated, unconsolidated sediments.
(d) Areas with high levels of groundwater but cohesive clay soils.
Answer: (c)
Explanation: Liquefaction happens when loose, water-saturated sediments temporarily lose their strength and behave like a liquid due to the shaking from an earthquake. - A large, basin-shaped depression formed by the collapse of a volcano after a major eruption empties the magma chamber is known as a:
(a) Crater
(b) Vent
(c) Caldera
(d) Fumarole
Answer: (c)
Explanation: Calderas are significant volcanic depressions formed by the collapse of the ground surface following the evacuation of a large volume of magma. - Which of the following volcanic hazards consists of a fast-moving current of hot gas and volcanic matter that flows down the flank of a volcano during an explosive eruption?
(a) Lava flow
(b) Lahar
(c) Pyroclastic flow
(d) Volcanic ash fall
Answer: (c)
Explanation: Pyroclastic flows are extremely dangerous, high-speed mixtures of hot gas and volcanic debris that can cause immense destruction. - The concept of seismic gaps is important in earthquake forecasting because it suggests:
(a) Areas along a fault that have experienced frequent small earthquakes are more likely to have a large earthquake soon.
(b) Segments of active faults that have not experienced a significant earthquake for a long time may be prone to future large earthquakes.
(c) The energy released by small earthquakes can prevent the occurrence of larger earthquakes in the same region.
(d) The timing of earthquakes is entirely random and cannot be predicted based on past seismic activity.
Answer: (b)
Explanation: Seismic gaps are segments of active faults that are “locked” and accumulating stress because they haven’t ruptured in a long time, making them potential sites for future large earthquakes. - The formation of the Deccan Traps in India is associated with:
(a) Subduction of the Indian plate beneath the Eurasian plate.
(b) Rifting of the Indian subcontinent from Gondwana.
(c) Hotspot volcanism as the Indian plate moved over the Reunion hotspot.
(d) Collision of the Indian plate with the Tibetan plateau.
Answer: (c)
Explanation: The massive Deccan Traps are a large igneous province believed to have formed due to extensive basaltic lava flows resulting from the Indian plate passing over the Reunion hotspot. - Which of the following statements accurately distinguishes between the focus and the epicenter of an earthquake?
(a) The focus is the point on the Earth’s surface directly above the epicenter, where the intensity of shaking is usually highest.
(b) The epicenter is the point within the Earth where the earthquake rupture starts, and the focus is the geographic point on the surface directly above it.
(c) The focus and the epicenter are synonymous terms referring to the location on the Earth’s surface where earthquake damage is most severe.
(d) The focus is the area of maximum ground shaking, while the epicenter is the point where the seismic waves originate.
Answer: (b)
Explanation: The focus (or hypocenter) is the point of origin of an earthquake within the Earth, where the fault rupture begins. The epicenter is the point on the Earth’s surface directly above the focus. - The presence of pillow lavas is a strong indicator of:
(a) Explosive volcanic eruptions in sub-aerial environments.
(b) Effusive volcanic eruptions occurring underwater.
(c) Volcanic activity associated with highly viscous, silica-rich magma.
(d) Ancient volcanic vents that have been exposed by erosion.
Answer: (b)
Explanation: Pillow lavas are bulbous, pillow-shaped formations that result when basaltic lava erupts underwater and cools rapidly. - Which of the following factors primarily determines the viscosity of magma?
(a) The temperature of the magma.
(b) The pressure exerted on the magma.
(c) The silica content of the magma.
(d) The volume of dissolved gases in the magma.
Answer: (c)
Explanation: The silica content is the most significant factor influencing magma viscosity. Higher silica content leads to more complex silicate structures, increasing the magma’s resistance to flow. - The concept of isostatic adjustment is most relevant to understanding:
(a) The formation of deep-sea trenches at subduction zones.
(b) The long-term vertical movements of the Earth’s crust in response to changes in mass distribution.
(c) The rapid uplift associated with volcanic eruptions.
(d) The horizontal displacement of land along transform faults.
Answer: (b)
Explanation: Isostatic adjustment refers to the Earth’s crust’s tendency to achieve gravitational equilibrium. When weight is added or removed (e.g., through ice sheet formation or melting, erosion, or deposition), the crust will sink or rise to compensate. - Which type of seismic wave is responsible for most of the damage during an earthquake due to its large amplitude and slow propagation speed along the Earth’s surface?
(a) P-waves
(b) S-waves
(c) Love waves
(d) Body waves
Answer: (c)
Explanation: Love waves are a type of surface wave that moves the ground from side to side in a horizontal plane perpendicular to the direction of propagation. Their large amplitude and surface travel make them particularly destructive. - A volcanic landform characterized by a broad, flat area built up by successive flows of highly fluid basaltic lava is a:
(a) Volcanic dome
(b) Cinder cone
(c) Lava plateau
(d) Stratovolcano
Answer: (c)
Explanation: Lava plateaus are extensive, relatively flat areas formed by the accumulation of numerous fluid basaltic lava flows spreading over vast distances. - Which of the following is NOT a common precursor phenomenon used in earthquake prediction?
(a) Changes in animal behavior.
(b) Anomalous tilting or bulging of the ground.
(c) Variations in the radon gas concentration in groundwater.
(d) Significant alterations in the Earth’s magnetic field polarity.
Answer: (d)
Explanation: While changes in the Earth’s magnetic field strength can occur, significant alterations in its polarity are not considered a reliable precursor to earthquakes. The other options have been observed in some instances before earthquakes. - The process by which water-saturated volcanic ash and debris flow rapidly down the slopes of a volcano, often triggered by heavy rainfall or the melting of snow and ice during an eruption, is known as a:
(a) Pyroclastic surge
(b) Lahar
(c) Block and ash flow
(d) Debris avalanche
Answer: (b)
Explanation: Lahars are dangerous mudflows or debris flows composed of volcanic material, water, and often vegetation, capable of traveling long distances and causing significant destruction. - Which of the following plate tectonic settings is least likely to be associated with significant volcanic activity?
(a) Divergent plate boundaries at mid-oceanic ridges.
(b) Convergent plate boundaries with subduction zones.
(c) Transform plate boundaries with strike-slip motion.
(d) Intraplate settings associated with mantle plumes.
Answer: (c)
Explanation: Transform plate boundaries, where plates slide past each other horizontally, generally do not involve the melting of the mantle necessary for significant magma generation and volcanism. - The Moment Magnitude scale is preferred over the Richter scale for measuring large earthquakes because it:
(a) Is based on the observed intensity of shaking rather than instrument readings.
(b) Directly relates to the physical size of the fault rupture and the energy released.
(c) Can accurately measure the magnitude of earthquakes regardless of their depth.
(d) Uses a logarithmic scale that saturates at lower magnitudes, unlike the Richter scale.
Answer: (b)
Explanation: The Moment Magnitude scale provides a more accurate measure of the total energy released by an earthquake, especially for large events, as it is based on the seismic moment, which is related to the fault area, slip distance, and rock rigidity. - The East African Rift Valley is a classic example of a:
(a) Convergent plate boundary forming a mountain range.
(b) Divergent plate boundary leading to continental rifting and volcanism.
(c) Transform plate boundary with significant strike-slip faulting.
(d) Intraplate volcanic region associated with a long-lived mantle plume.
Answer: (b)
Explanation: The East African Rift Valley is a zone where the African plate is splitting apart, resulting in the formation of rift valleys, faulting, and volcanic activity. - Which of the following volcanic gases, when released in large quantities, can have significant short-term cooling effects on the Earth’s atmosphere?
(a) Carbon dioxide (CO2)
(b) Water vapor (H2O)
(c) Sulfur dioxide (SO2)
(d) Helium (He)
Answer: (c)
Explanation: Sulfur dioxide (SO2) emitted during volcanic eruptions can react in the atmosphere to form sulfate aerosols, which reflect sunlight back into space, leading to a temporary cooling effect. - Paleoseismological studies, which involve the investigation of prehistoric earthquakes, primarily rely on the analysis of:
(a) Historical records and eyewitness accounts.
(b) Instrumental seismograph data from past centuries.
(c) Geological evidence of past fault ruptures, such as offset layers and liquefaction features.
(d) Changes in the Earth’s magnetic field recorded in ancient rocks.
Answer: (c)
Explanation: Paleoseismology uses geological techniques to identify and characterize past earthquakes, providing crucial information for understanding long-term seismic hazard in a region. - The phenomenon of volcanic tremor, often monitored by seismographs near active volcanoes, is primarily caused by:
(a) The sudden fracturing of rocks due to tectonic stresses.
(b) The movement of magma and volcanic fluids beneath the Earth’s surface.
(c) The impact of pyroclastic flows on the volcano’s flanks.
(d) Atmospheric pressure changes affecting the volcanic edifice.
Answer: (b)
Explanation: Volcanic tremor is a continuous, low-frequency seismic signal generated by the movement of magma, gases, and hydrothermal fluids within the volcanic plumbing system. It is an important indicator of potential eruptive activity. - Which of the following engineering strategies is most effective in mitigating earthquake damage to buildings in seismically active zones?
(a) Constructing rigid, unyielding structures to withstand ground shaking.
(b) Designing buildings with flexible connections and energy-absorbing mechanisms.
(c) Building lightweight structures with a high center of gravity.
(d) Anchoring buildings directly to the underlying bedrock without any insulation.
Answer: (b)
Explanation: Earthquake-resistant design focuses on allowing buildings to sway and dissipate energy during seismic shaking through flexible connections, damping mechanisms, and other engineering techniques, rather than resisting the forces rigidly. - Which of the following statements best describes the relationship between deep-focus earthquakes and plate tectonics?
(a) They are primarily associated with divergent plate boundaries where tensional forces dominate.
(b) They occur exclusively along transform faults where plates slide past each other horizontally.
(c) They are characteristic of subduction zones where a descending plate experiences high pressure and temperature.
(d) They are commonly found in intraplate settings, far from active plate margins, due to mantle plumes.
Answer: (c)
Explanation: Deep-focus earthquakes (those originating at depths greater than 300 km) are almost exclusively found in subduction zones. As the subducting plate descends into the mantle, it undergoes mineral transformations under high pressure and temperature, which can trigger seismic events. - A small, steep-sided volcano built from the accumulation of ejected volcanic debris, typically basaltic in composition, is known as a:
(a) Shield volcano
(b) Composite volcano
(c) Cinder cone
(d) Lava dome
Answer: (c)
Explanation: Cinder cones are formed from the relatively explosive eruption of low-viscosity magma, which fragments into pyroclastic material (cinders, ash, and bombs) that accumulates around the vent. - The phenomenon of “seismic shadow zones” provides evidence for:
(a) The existence of tectonic plates and their movement.
(b) The liquid outer core of the Earth that refracts and absorbs S-waves.
(c) The presence of compositional layering within the Earth’s crust.
(d) The heterogeneous nature of the Earth’s mantle and the presence of plumes.
Answer: (b)
Explanation: P-waves and S-waves behave differently when they encounter the Earth’s core. S-waves cannot travel through the liquid outer core, creating an S-wave shadow zone. P-waves are refracted at the mantle-core boundary, resulting in a P-wave shadow zone as well. - Which of the following factors is LEAST likely to influence the explosiveness of a volcanic eruption?
(a) The viscosity of the magma.
(b) The amount of dissolved gases in the magma.
(c) The rate at which magma rises to the surface.
(d) The density of the surrounding atmospheric air.
Answer: (d)
Explanation: The density of the atmosphere has a negligible impact on the internal processes driving volcanic explosivity, which are primarily controlled by magma properties like viscosity and gas content, as well as the rate of magma ascent. - The process of isostatic rebound is still significantly affecting which of the following regions due to the melting of large ice sheets since the last glacial maximum?
(a) The Andes Mountains
(b) The Himalayas
(c) Scandinavia and parts of North America
(d) The East African Rift Valley
Answer: (c)
Explanation: During the last glacial period, massive ice sheets depressed the Earth’s crust in regions like Scandinavia and North America. With the melting of these ice sheets, the land is slowly rising back to its equilibrium position, a process known as isostatic rebound. - Which type of fault is characterized by tensional forces that cause the hanging wall to move down relative to the footwall?
(a) Reverse fault
(b) Thrust fault
(c) Normal fault
(d) Strike-slip fault
Answer: (c)
Explanation: Normal faults occur in areas where the crust is being pulled apart (extension). This causes the hanging wall block to slide downward along the fault plane relative to the footwall block. - The formation of large igneous provinces (LIPs), such as the Siberian Traps or the Columbia River Basalts, is often attributed to:
(a) Subduction processes at convergent plate boundaries.
(b) The impact of large meteorites on the Earth’s surface.
(c) The activity of mantle plumes rising from deep within the Earth.
(d) Extensive crustal folding and faulting during orogenic events.
Answer: (c)
Explanation: Large igneous provinces are characterized by voluminous outpourings of basaltic lava over relatively short geological timescales and are widely believed to be the surface expression of hot, buoyant mantle plumes rising from the core-mantle boundary. - Which of the following is a significant environmental impact often associated with large explosive volcanic eruptions?
(a) A long-term increase in global average temperatures due to greenhouse gas emissions.
(b) The depletion of the ozone layer due to the release of chlorofluorocarbons.
(c) Short-term global cooling due to the injection of sulfate aerosols into the stratosphere.
(d) A significant increase in global sea levels due to the melting of volcanic ice caps.
Answer: (c)
Explanation: Large explosive eruptions release significant amounts of sulfur dioxide (SO2), which can convert to sulfate aerosols in the stratosphere. These aerosols reflect incoming solar radiation, leading to a temporary cooling of the Earth’s surface. - The Modified Mercalli Intensity (MMI) scale differs from the Richter scale primarily in that the MMI scale:
(a) Measures the energy released at the earthquake’s focus using seismograph data.
(b) Quantifies the magnitude of the earthquake based on the amplitude of seismic waves.
(c) Assesses the earthquake’s effects on people, buildings, and the environment at a specific location.
(d) Is a logarithmic scale while the Richter scale is a linear scale.
Answer: (c)
Explanation: The MMI scale is an intensity scale that subjectively evaluates the shaking and damage caused by an earthquake at a particular location based on observations. The Richter scale, on the other hand, is a magnitude scale that objectively measures the earthquake’s size based on seismograph recordings. - Which of the following geological features is most commonly associated with convergent plate boundaries where oceanic crust subducts beneath continental crust?
(a) Mid-oceanic ridges with rift valleys.
(b) Volcanic island arcs and deep-sea trenches.
(c) Broad shield volcanoes and lava plateaus.
(d) Large strike-slip faults and transform zones.
Answer: (b)
Explanation: When oceanic crust subducts beneath continental crust, the descending plate melts, generating magma that rises to form volcanic mountain ranges on the continental plate. The subduction process also creates deep-sea trenches at the plate boundary. - The Himalayan mountain range is primarily a result of:
(a) Volcanic activity along a divergent plate boundary.
(b) The collision between two continental plates.
(c) Subduction of an oceanic plate beneath a continental plate.
(d) Hotspot volcanism in an intraplate setting.
Answer: (b)
Explanation: The Himalayas are the result of the ongoing collision between the Indian and Eurasian continental plates, a process that has been folding and thrusting the crust upwards for millions of years. - A volcanic eruption characterized by episodic, moderate explosions that eject incandescent bombs and lapilli a few hundred meters into the air is termed:
(a) Plinian
(b) Vulcanian
(c) Strombolian
(d) Pelean
Answer: (c)
Explanation: Strombolian eruptions are named after the Stromboli volcano in Italy and are known for their relatively mild, repetitive explosions of gas-rich magma that eject incandescent volcanic bombs and lapilli. - The presence of serpentinite rocks in a geological setting often indicates:
(a) High-pressure metamorphism associated with continental collision.
(b) The interaction of water with ultramafic rocks, typically found in oceanic crust and upper mantle.
(c) Extensive hydrothermal activity associated with felsic volcanism.
(d) The presence of ancient evaporite deposits in a sedimentary basin.
Answer: (b)
Explanation: Serpentinization is a metamorphic process that occurs when water interacts with ultramafic rocks like peridotite, commonly found in the oceanic crust and upper mantle, forming serpentine minerals. This process is often associated with subduction zones and mid-ocean ridges. - Which of the following geodetic techniques is most effective for measuring subtle changes in the Earth’s surface elevation over large areas, which can be indicative of magma accumulation or tectonic strain?
(a) Traditional leveling surveys.
(b) Tiltmeters installed on volcanic slopes.
(c) Interferometric Synthetic Aperture Radar (InSAR).
(d) Strainmeters deployed across fault zones.
Answer: (c)
Explanation: InSAR uses satellite radar imagery to detect millimeter-scale changes in ground deformation over broad areas, making it a powerful tool for monitoring volcanic activity and tectonic strain buildup. - The recurrence interval of a large earthquake on a specific fault segment refers to:
(a) The duration of the earthquake shaking at a particular location.
(b) The average time period between successive large earthquakes on that fault segment.
(c) The depth of the earthquake’s focus below the Earth’s surface.
(d) The magnitude of the smallest earthquake that can trigger a larger event on the same fault.
Answer: (b)
Explanation: The recurrence interval is a statistical estimate of how often earthquakes of a certain magnitude are likely to occur on a given fault segment, based on historical seismicity and paleoseismic data. - Which of the following scenarios is most likely to generate a significant tsunami?
(a) A shallow-focus, large-magnitude strike-slip earthquake occurring on land.
(b) A deep-focus, moderate-magnitude earthquake occurring beneath the abyssal plain.
(c) A shallow-focus, large-magnitude thrust earthquake causing vertical displacement of the seafloor.
(d) A moderate-magnitude volcanic eruption producing a large volume of ashfall.
Answer: (c)
Explanation: Tsunamis are typically generated by large-magnitude, shallow-focus earthquakes that cause significant vertical displacement of the seafloor, particularly those occurring at subduction zones where thrust faulting is common. - The process of decompression melting, which plays a significant role in magma generation, occurs primarily at:
(a) Subduction zones due to the release of volatiles from the descending plate.
(b) Mid-oceanic ridges and continental rift valleys where the lithosphere thins and pressure decreases.
(c) Hotspots where mantle plumes transfer heat to the overlying lithosphere.
(d) Areas of intense crustal compression during mountain building events.
Answer: (b)
Explanation: Decompression melting happens when the pressure on hot mantle rock is reduced, allowing it to melt without a change in temperature. This is common at divergent plate boundaries like mid-oceanic ridges and rift valleys where the lithosphere is pulled apart and thins. - Which of the following statements accurately describes the relationship between the depth of an earthquake’s focus and the extent of its felt area?
(a) Deeper earthquakes generally have a smaller felt area compared to shallow earthquakes of the same magnitude.
(b) Deeper earthquakes generally have a larger felt area because seismic waves travel through a greater volume of the Earth.
(c) The depth of the focus has no significant impact on the extent of the felt area; magnitude is the primary factor.
(d) The relationship between focal depth and felt area varies depending on the local geological conditions.
Answer: (b)
Explanation: While magnitude is a primary determinant of the felt area, deeper earthquakes tend to have a broader felt area because the seismic waves radiate outwards from a greater depth, affecting a larger portion of the Earth’s surface, although the intensity of shaking directly above the epicenter might be less than that of a shallow earthquake of the same magnitude. - A volcanic dome is a steep-sided, bulbous landform formed by the eruption of:
(a) Highly fluid basaltic lava that flows over long distances.
(b) Viscous, silica-rich lava that piles up around the vent.
(c) Large volumes of pyroclastic material ejected during explosive eruptions.
(d) Alternating layers of lava and ash in stratovolcanoes.
Answer: (b)
Explanation: Volcanic domes are formed by the slow extrusion of highly viscous, silica-rich lava that cannot flow easily and therefore accumulates around the volcanic vent, creating a steep-sided dome shape. - The concept of “aseismic creep” refers to:
(a) The slow, continuous movement along a fault without generating significant earthquakes.
(b) The rapid, stick-slip motion along a fault that causes large seismic events.
(c) The gradual cooling and solidification of magma within a volcanic conduit.
(d) The slow deformation of rocks in the Earth’s mantle due to convection.
Answer: (a)
Explanation: Aseismic creep is a type of fault movement where the two sides of a fault slide past each other slowly and continuously, without producing the abrupt release of energy that causes earthquakes. - Which of the following regions is characterized by significant intraplate volcanism, believed to be associated with a mantle plume?
(a) The Andes Mountains
(b) The Aleutian Islands
(c) The Hawaiian Islands
(d) The Mid-Atlantic Ridge
Answer: (c)
Explanation: The Hawaiian Islands are a classic example of volcanism associated with a hot mantle plume. As the Pacific plate moves over this stationary plume, a chain of volcanic islands has formed. - The phenomenon of “resonance” during an earthquake can lead to increased damage to buildings, particularly those:
(a) Built on solid bedrock.
(b) With a natural frequency of vibration similar to that of the seismic waves.
(c) That are very tall and flexible.
(d) Constructed with lightweight materials.
Answer: (b)
Explanation: Resonance occurs when the frequency of the earthquake’s seismic waves matches the natural frequency of vibration of a building. This can amplify the shaking and lead to more severe damage or even collapse. - Which of the following volcanic hazards is most likely to have long-lasting impacts on global climate?
(a) Localized lava flows destroying infrastructure.
(b) Pyroclastic flows affecting areas close to the volcano.
(c) The injection of sulfur-rich gases into the stratosphere during a major explosive eruption.
(d) Lahars inundating valleys and causing localized flooding.
Answer: (c)
Explanation: Sulfur dioxide (SO2) injected into the stratosphere can form sulfate aerosols that persist for months to years, reflecting sunlight and causing a measurable cooling effect on global climate. - The Benioff zone is characterized by a systematic variation in the depth of earthquakes, with deeper earthquakes occurring:
(a) Closer to the volcanic arc associated with the subduction zone.
(b) Farther away from the volcanic arc, towards the trench.
(c) Along the transform faults that offset the subduction zone.
(d) At random depths regardless of the distance from the trench or volcanic arc.
Answer: (b)
Explanation: In a subduction zone, the descending oceanic plate bends and sinks into the mantle. Earthquakes occur along this inclined zone (the Benioff zone), with deeper earthquakes occurring farther inland from the trench, beneath the overriding plate and the associated volcanic arc. - Which of the following is a crucial factor in determining the potential for a volcanic eruption to produce hazardous pyroclastic flows?
(a) The temperature of the erupted lava.
(b) The color of the volcanic ash emitted.
(c) The viscosity of the magma and the presence of dissolved gases.
(d) The height of the volcanic edifice above sea level.
Answer: (c)
Explanation: Pyroclastic flows are hot, fast-moving currents of gas and volcanic debris. They are more likely to occur with viscous, silica-rich magma that traps significant amounts of dissolved gases. When the pressure is released during an eruption, these gases can cause explosive fragmentation of the magma, leading to the formation of pyroclastic flows. - The addition of water to mantle rocks at subduction zones lowers their melting point, facilitating the generation of magma. This process is known as:
(a) Fractional crystallization
(b) Assimilation
(c) Flux melting
(d) Magmatic differentiation
Answer: (c)
Explanation: Flux melting occurs when the addition of volatiles, such as water released from a subducting oceanic plate, lowers the melting temperature of the overlying mantle wedge, leading to the formation of magma. - Rayleigh waves are a type of seismic surface wave that cause the ground to move in a(n):
(a) Side-to-side horizontal motion.
(b) Back-and-forth compressional motion.
(c) Elliptical motion in the vertical plane, similar to waves on water.
(d) Up-and-down vertical motion.
Answer: (c)
Explanation: Rayleigh waves travel along the Earth’s surface and produce a retrograde elliptical motion of particles in the vertical plane, meaning the particles move both vertically and horizontally in a circular or elliptical path, with the sense of rotation being opposite to the direction of wave propagation near the surface. - Monitoring changes in the concentration of volcanic gases, such as sulfur dioxide (SO2) and carbon dioxide (CO2), can provide valuable insights into:
(a) The magnitude of past volcanic eruptions.
(b) The depth of the volcano’s magma chamber.
(c) The ascent of magma towards the surface and the potential for an eruption.
(d) The rate of erosion of the volcanic edifice.
Answer: (c)
Explanation: Changes in the composition and flux of volcanic gases can indicate that magma is rising towards the surface, degassing as it ascends due to decreasing pressure. This is a key indicator of potential eruptive activity. - The collapse of a volcanic edifice or a portion of it can generate a rapid, destructive flow of rock debris and volcanic material known as a:
(a) Lahar
(b) Pyroclastic flow
(c) Debris avalanche
(d) Lava flow
Answer: (c)
Explanation: Debris avalanches are sudden, rapid flows of unsorted rock debris, often triggered by volcanic instability, earthquakes, or heavy rainfall. They can travel long distances and cause significant devastation. - Induced seismicity, or earthquakes caused by human activities, can be associated with:
(a) Large-scale afforestation projects.
(b) The construction of wind farms in seismically stable regions.
(c) The impoundment of large reservoirs, which increases stress on underlying faults.
(d) The implementation of strict building codes in earthquake-prone areas.
Answer: (c)
Explanation: The weight of water in large reservoirs can increase the pore pressure in the underlying rocks and lubricate existing faults, potentially triggering earthquakes. This is a well-documented cause of induced seismicity. - Which of the following statements accurately describes the relationship between mid-oceanic ridges and earthquakes?
(a) Mid-oceanic ridges are characterized by large-magnitude, deep-focus earthquakes due to intense compressional forces.
(b) Earthquakes along mid-oceanic ridges are typically shallow-focus and of low to moderate magnitude, associated with tensional stresses and faulting.
(c) Seismic activity is absent along mid-oceanic ridges as the plates are moving apart smoothly without significant friction.
(d) The largest earthquakes on Earth tend to occur along mid-oceanic ridges due to the immense scale of the divergent plate boundaries.
Answer: (b)
Explanation: Mid-oceanic ridges are divergent plate boundaries where new oceanic crust is formed. The tensional forces cause normal faulting and strike-slip faulting, resulting in shallow-focus earthquakes that are generally of low to moderate magnitude. - A maar is a volcanic crater formed by:
(a) The collapse of the summit of a shield volcano.
(b) A violent explosion caused by the interaction of magma with groundwater.
(c) The accumulation of ash and cinder around a volcanic vent.
(d) The slow extrusion of viscous lava forming a dome.
Answer: (b)
Explanation: Maars are broad, low-relief volcanic craters formed by phreatomagmatic eruptions, which occur when rising magma interacts explosively with shallow groundwater, creating a steam-driven explosion that excavates a crater. - The S-P interval, which is the time difference between the arrival of S-waves and P-waves at a seismograph station, can be used to determine:
(a) The magnitude of the earthquake.
(b) The intensity of shaking at the seismograph location.
(c) The distance from the seismograph station to the earthquake’s epicenter.
(d) The depth of the earthquake’s focus.
Answer: (c)
Explanation: P-waves travel faster than S-waves. The greater the distance between the seismograph and the earthquake’s epicenter, the larger the time difference (S-P interval) between their arrival times. This difference can be used to calculate the distance to the epicenter. - Which of the following volcanic features is formed by the accumulation of fluid basaltic lava flows erupting from fissures?
(a) Composite volcano
(b) Cinder cone
(c) Shield volcano
(d) Lava dome
Answer: (c)
Explanation: Shield volcanoes, like those in Hawaii, are characterized by their broad, gently sloping shape, formed by the eruption of highly fluid basaltic lava that flows easily over large distances from fissures and a central vent. - The concept of a “seismic gap” is based on the idea that:
(a) Earthquakes occur randomly in space and time and there are no predictable patterns.
(b) Stress tends to accumulate along portions of active faults that have not ruptured recently.
(c) Small earthquakes frequently release enough energy to prevent larger earthquakes from occurring.
(d) The occurrence of volcanic eruptions can reliably predict the timing and location of nearby earthquakes.
Answer: (b)
Explanation: A seismic gap is a segment of an active fault that has not experienced a major earthquake for a long time, despite surrounding segments having ruptured. This suggests that stress is building up in the gap and it may be prone to a future large earthquake. - Which of the following regions is well-known for its transform plate boundary and associated strike-slip earthquakes?
(a) The Andes Mountains
(b) The San Andreas Fault system in California
(c) The Mid-Atlantic Ridge in Iceland
(d) The East African Rift Valley
Answer: (b)
Explanation: The San Andreas Fault system in California is a classic example of a transform plate boundary where the Pacific and North American plates are sliding past each other horizontally, resulting in frequent strike-slip earthquakes. - Volcanic ash poses a significant hazard to aviation primarily because it can:
(a) Cause rapid cooling of aircraft engines due to its high moisture content.
(b) Obscure visibility and interfere with aircraft navigation systems.
(c) Melt and solidify within jet engines, leading to engine failure.
(d) Significantly increase the weight of the aircraft, affecting its aerodynamics.
Answer: (c)
Explanation: Volcanic ash is composed of tiny, abrasive particles that can be ingested into jet engines. The high temperatures within the engine can cause the ash to melt and then solidify on critical components, leading to engine damage or failure. - The study of paleoseismology helps scientists to:
(a) Predict the exact time and magnitude of future earthquakes.
(b) Understand the long-term earthquake history of a region and estimate recurrence intervals.
(c) Measure the instantaneous ground deformation during an ongoing earthquake.
(d) Determine the chemical composition of rocks deep within the Earth’s mantle.
Answer: (b)
Explanation: Paleoseismology involves studying geological evidence of past earthquakes, such as fault scarps, offset layers, and liquefaction features, to reconstruct the history of seismic activity in a region over long timescales and estimate the average time between large earthquakes (recurrence interval). - Which of the following is NOT a common method used for monitoring volcanic activity?
(a) Measuring changes in ground deformation using GPS and tiltmeters.
(b) Analyzing the chemical composition and emission rates of volcanic gases.
(c) Tracking changes in the Earth’s magnetic field around the volcano.
(d) Monitoring seismic activity, including volcanic tremors and earthquakes.
Answer: (c)
Explanation: While changes in the Earth’s magnetic field can occur due to various geological processes, it is not a primary or widely used method for the routine monitoring of volcanic activity. The other options are established techniques for detecting signs of unrest and potential eruptions. - The formation of a volcanic island arc is most commonly associated with:
(a) Hotspot volcanism over a stationary mantle plume beneath an oceanic plate.
(b) Rifting of a continental plate leading to linear chains of volcanoes.
(c) The subduction of an oceanic plate beneath another oceanic plate at a convergent boundary.
(d) Volcanism along a transform fault where magma rises through fractures in the crust.
Answer: (c)
Explanation: Volcanic island arcs are curved chains of volcanic islands that form above subduction zones where one oceanic plate descends beneath another. The melting of the subducting plate generates magma that rises to the surface and erupts to form the arc. - The ascent of magma towards the Earth’s surface is primarily driven by:
(a) The Earth’s rotation and Coriolis force.
(b) The density contrast between the less dense magma and the surrounding denser rocks (buoyancy).
(c) The pressure exerted by overlying tectonic plates.
(d) The gravitational pull of the Moon and Sun.
Answer: (b)
Explanation: Magma, being less dense than the surrounding solid rock, experiences an upward buoyant force that drives its ascent towards the surface. The pressure from overlying rocks also plays a role, but buoyancy is the primary driving mechanism. - Volcanic bombs are pyroclastic fragments that:
(a) Are fine-grained particles less than 2 mm in diameter.
(b) Are angular blocks of solidified lava ejected during an eruption.
(c) Were molten or semi-molten when ejected and acquired aerodynamic shapes during flight.
(d) Are porous, lightweight rocks formed from solidified volcanic foam.
Answer: (c)
Explanation: Volcanic bombs are large (>64 mm) pyroclastic projectiles that were molten or partially molten when ejected from a volcano and solidified during their flight, often acquiring streamlined or spindle shapes due to aerodynamic forces. - In the context of earthquakes, stress refers to the force per unit area acting on a rock, while strain refers to:
(a) The energy released during the rupture of the rock.
(b) The resulting deformation or change in shape and volume of the rock.
(c) The speed at which seismic waves propagate through the rock.
(d) The frequency content of the seismic waves generated.
Answer: (b)
Explanation: Stress is the force applied to a rock, and strain is the deformation that results from that stress. Earthquakes occur when the stress exceeds the strength of the rock, causing it to fracture and release the accumulated strain energy. - Remote sensing techniques, such as thermal infrared imaging, can be valuable in monitoring volcanoes by detecting:
(a) Changes in the chemical composition of erupted gases.
(b) Subtle changes in the volcano’s shape and elevation.
(c) Increased heat output associated with rising magma.
(d) The presence of magnetic anomalies around the volcanic edifice.
Answer: (c)
Explanation: Thermal infrared imagery can detect changes in the surface temperature of a volcano, which can indicate the presence of hot magma rising towards the surface or increased fumarolic activity, both potential precursors to an eruption. - A significant impact of large earthquakes in coastal areas can be a change in groundwater levels due to:
(a) The melting of ice caps and glaciers caused by seismic shaking.
(b) The compression and dilation of aquifers and changes in pore pressure within the ground.
(c) The generation of tsunamis that inundate coastal freshwater sources with saltwater.
(d) Increased rates of chemical weathering of rocks, releasing dissolved minerals into the groundwater.
Answer: (b)
Explanation: The shaking and deformation of the ground during an earthquake can compress or expand aquifers, leading to temporary or permanent changes in groundwater levels and flow patterns. Changes in pore pressure within the subsurface can also affect groundwater. - Columnar jointing, a distinctive pattern of fractures in volcanic rocks, typically forms in:
(a) Pyroclastic flows due to rapid cooling from the surface.
(b) Viscous lava domes as they slowly solidify under pressure.
(c) Basaltic lava flows and sills as they cool and contract.
(d) Volcanic ash deposits that have been compacted and cemented.
Answer: (c)
Explanation: Columnar jointing is a geological structure characterized by sets of intersecting closely spaced fractures, referred to as joints, that divide the rock into long, polygonal columns. It typically occurs in basaltic lava flows and shallow intrusive igneous rocks (sills and dikes) that cool relatively slowly from the surface downwards, causing contraction and fracturing. - Seismic moment ((M_0)), a measure of the size of an earthquake, is directly proportional to:
(a) The peak amplitude of the seismic waves recorded by a seismograph.
(b) The intensity of shaking experienced at a particular location.
(c) The area of the fault rupture, the average displacement on the fault, and the shear modulus of the rocks.
(d) The duration of the earthquake shaking.
Answer: (c)
Explanation: The seismic moment ((M_0)) is a fundamental measure of the size of an earthquake that is related to the physical properties of the fault rupture, given by the formula (M_0 = \mu A d), where (\mu) is the shear modulus of the rocks, (A) is the area of the fault that ruptured, and (d) is the average displacement (slip) on the fault. - Over geological timescales, large and prolonged episodes of volcanic eruptions can potentially lead to:
(a) A significant increase in the rate of continental drift.
(b) Major shifts in the Earth’s magnetic poles.
(c) Alterations in global climate patterns due to changes in atmospheric composition.
(d) A decrease in the frequency of large asteroid impacts.
Answer: (c)
Explanation: While individual large eruptions can cause short-term cooling, prolonged periods of intense volcanism can release significant amounts of greenhouse gases like CO2, potentially leading to long-term warming trends and other alterations in global climate patterns over geological timescales. - Earthquake-resistant design of buildings often incorporates the principle of base isolation, which involves:
(a) Constructing buildings with extremely rigid frames to withstand ground shaking without any movement.
(b) Separating the building’s foundation from the ground using flexible bearings or pads to reduce the transmission of seismic forces.
(c) Using very lightweight materials in construction to minimize the inertial forces during an earthquake.
(d) Anchoring the building directly to the bedrock with deep, rigid pilings to prevent any swaying.
Answer: (b)
Explanation: Base isolation is a technique used to protect buildings from earthquake damage by decoupling the structure from the ground.1 Flexible bearings or isolators are placed between the foundation and the superstructure, allowing the ground to move beneath the building while the building itself experiences significantly reduced shaking. - The devastating tsunami that occurred in the Indian Ocean in 2004 was primarily generated by:
(a) A large volcanic eruption in the Sunda Strait causing a massive underwater landslide.
(b) A giant meteorite impact in the deep ocean triggering a massive displacement of water.
(c) A very large magnitude, shallow-focus earthquake along the subduction zone off the coast of Sumatra, Indonesia.
(d) A series of underwater nuclear tests that caused a significant disturbance of the seafloor.
Answer: (c)
Explanation: The 2004 Indian Ocean tsunami was triggered by a massive (magnitude 9.1-9.3) shallow-focus earthquake along the Sunda megathrust, where the Indian plate subducts beneath the Burma plate. The earthquake caused a significant uplift of the seafloor, displacing an enormous volume of water and generating the devastating tsunami. - The term “lahar” is derived from:
(a) Ancient Greek, meaning “molten rock flow.”
(b) Icelandic, referring to a glacial outburst flood associated with volcanic activity.
(c) Indonesian, describing a volcanic mudflow or debris flow.
(d) Hawaiian, denoting a slow-moving, pasty lava flow.
Answer: (c)
Explanation: The term “lahar” originates from Indonesia and specifically refers to a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. These flows are often triggered by heavy rainfall or the melting of snow and ice during or after a volcanic eruption. - Which of the following is a primary reason why some volcanic eruptions are highly explosive while others are effusive?
(a) The overall size and height of the volcano.
(b) The age of the volcano and the duration of its dormancy period.
(c) The composition and viscosity of the magma, particularly its silica and gas content.
(d) The proximity of the volcano to major tectonic plate boundaries.
Answer: (c)
Explanation: The explosiveness of a volcanic eruption is largely determined by the viscosity of the magma and the amount of dissolved gases it contains. High-viscosity, silica-rich magma traps gases, leading to a buildup of pressure and explosive eruptions. Low-viscosity, basaltic magma allows gases to escape more easily, resulting in effusive lava flows. - The Mohorovičić discontinuity (Moho) marks the boundary between:
(a) The Earth’s inner and outer core.
(b) The Earth’s crust and the upper mantle.
(c) The Earth’s upper and lower mantle.
(d) The Earth’s mantle and the outer core.
Answer: (b)
Explanation: The Moho is the boundary between the Earth’s crust (both oceanic and continental) and the underlying mantle. It is characterized by a significant increase in seismic wave velocities as they pass from the crust to the denser mantle rocks. - Which of the following tools or techniques is most commonly used to measure the precise deformation of a volcano’s surface, which can indicate magma movement beneath?
(a) Seismometer networks
(b) Gas chromatography
(c) Global Positioning System (GPS) receivers
(d) Thermal infrared cameras
Answer: (c)
Explanation: GPS receivers deployed on the flanks of a volcano can precisely measure changes in the volcano’s shape and elevation over time. Swelling or tilting of the ground can indicate the accumulation of magma beneath the surface, a potential precursor to an eruption. - The concept of isostasy helps to explain why:
(a) Oceanic crust is denser and thinner than continental crust.
(b) Mountain ranges have deep roots extending into the mantle.
(c) Earthquakes primarily occur along plate boundaries.
(d) The Earth’s outer core is liquid while the inner core is solid.
Answer: (b)
Explanation: Isostasy is the state of gravitational equilibrium between the Earth’s lithosphere and asthenosphere. Less dense crust “floats” on the denser mantle. Mountain ranges, being less dense and having a large mass, displace a greater volume of the asthenosphere, resulting in deep crustal roots that provide buoyancy and support their height. - The process of spallation, which can contribute to rock fracturing during an earthquake, is primarily caused by:
(a) The chemical weathering of minerals along pre-existing fault lines.
(b) The intense compressional forces acting perpendicular to the direction of wave propagation.
(c) The reflection of seismic waves at the Earth’s surface, generating tensile stresses.
(d) The frictional heating along the fault plane during rapid slip.
Answer: (c)
Explanation: Spallation occurs when seismic waves, particularly compressional waves, reach the Earth’s surface and are reflected back into the ground as tensile waves. If these tensile stresses exceed the tensile strength of the near-surface rocks, they can cause fracturing and the detachment of rock fragments. - A Plinian volcanic eruption is characterized by:
(a) The effusive outpouring of basaltic lava flows forming shield volcanoes.
(b) Mild, episodic explosions ejecting incandescent bombs and lapilli.
(c) Extremely violent explosions that produce sustained eruption columns of ash and gas reaching high into the stratosphere.
(d) The formation of low-profile cinder cones from the accumulation of pyroclastic debris.
Answer: (c)
Explanation: Plinian eruptions, named after Pliny the Younger’s description of the eruption of Mount Vesuvius in 79 AD, are the most explosive type of volcanic eruption. They involve the ejection of vast quantities of ash, pumice, and volcanic gases, forming high, sustained eruption columns that can have significant atmospheric and climatic impacts. - The asthenosphere, a layer in the Earth’s upper mantle that plays a crucial role in plate tectonics, is characterized by:
(a) Being completely rigid and incapable of flow.
(b) Having a high degree of partial melting, allowing it to behave plastically over long timescales.
(c) Being the primary source of the Earth’s magnetic field.
(d) Having seismic wave velocities significantly higher than the overlying lithosphere.
Answer: (b)
Explanation: The asthenosphere is a weaker, more ductile layer in the upper mantle beneath the lithosphere. It is characterized by a small percentage of partially molten rock, which allows it to flow slowly over geological timescales in response to stress, facilitating the movement of the overlying tectonic plates. - Which of the following methods is most effective for determining the precise three-dimensional structure of the Earth’s interior, including the location of subducting slabs and mantle plumes?
(a) Analyzing the mineral composition of volcanic rocks.
(b) Measuring the heat flow from the Earth’s surface.
(c) Studying the travel times and paths of seismic waves from earthquakes.
(d) Examining the variations in the Earth’s gravitational field.
Answer: (c)
Explanation: Seismic tomography is a technique that uses the travel times of seismic waves generated by earthquakes to create three-dimensional images of the Earth’s interior. Variations in seismic wave velocities can reveal structures like high-velocity subducting slabs and low-velocity mantle plumes. - The phenomenon of liquefaction during an earthquake can have severe consequences for infrastructure built on:
(a) Solid granite bedrock.
(b) Well-drained, compacted gravel deposits.
(c) Water-saturated, unconsolidated silts and sands.
(d) Stiff, over-consolidated clay soils.
Answer: (c)
Explanation: Liquefaction occurs when loose, water-saturated sediments like silts and sands temporarily lose their shear strength and behave like a liquid due to the shaking from an earthquake. This can cause buildings and other structures to sink, tilt, or collapse. - A caldera lake, such as Crater Lake in Oregon, typically forms:
(a) In a volcanic crater created by a small, localized explosion.
(b) When a lava flow blocks a pre-existing river valley.
(c) In the depression left after a large volcanic eruption causes the volcano’s summit to collapse.
(d) Due to the melting of glaciers on the summit of a dormant volcano.
Answer: (c)
Explanation: Caldera lakes form when rainwater and snowmelt accumulate in the large, basin-shaped depression (caldera) that is created after a major volcanic eruption empties the magma chamber, causing the volcano’s summit to collapse. - Which of the following gases, commonly emitted during volcanic eruptions, can react with water vapor in the atmosphere to form acid rain?
(a) Nitrogen (N2)
(b) Oxygen (O2)
(c) Sulfur dioxide (SO2)
(d) Helium (He)
Answer: (c)
Explanation: Sulfur dioxide (SO2) is a significant volcanic gas that, when released into the atmosphere, can react with water vapor to form sulfuric acid ((H_2SO_4)), a major component of acid rain. Acid rain can have detrimental effects on vegetation, aquatic ecosystems, and infrastructure. - The Wadati-Benioff zone is crucial evidence for the theory of:
(a) Continental drift.
(b) Seafloor spreading.
(c) Plate tectonics and subduction.
(d) Mantle convection.
Answer: (c)
Explanation: The inclined zone of deep earthquakes known as the Wadati-Benioff zone directly traces the descent of an oceanic plate into the mantle at a subduction zone. This provides strong evidence for the process of subduction, a key component of the theory of plate tectonics. - Which of the following volcanic landforms is typically associated with highly explosive eruptions of viscous, gas-rich magma?
(a) Shield volcano
(b) Lava plateau
(c) Composite volcano (Stratovolcano)
(d) Cinder cone
Answer: (c)
Explanation: Composite volcanoes, or stratovolcanoes, are formed by alternating layers of lava flows and pyroclastic material. Their steep slopes and explosive eruptions are characteristic of viscous, silica-rich magma with a high gas content. - The Mercalli Intensity scale is based on:
(a) Instrumental measurements of ground acceleration.
(b) The energy released at the earthquake’s focus.
(c) Subjective observations of the earthquake’s effects on people and structures.
(d) The frequency content of the recorded seismic waves.
Answer: (c)
Explanation: The Mercalli Intensity scale is a qualitative measure of the effects of an earthquake at a specific location, based on observations of how people felt the shaking and the damage caused to buildings and the environment. It is a subjective scale that varies from place to place for a single earthquake. - The concept of a “hotspot” in geology refers to:
(a) A region of unusually high geothermal gradient associated with shallow magma chambers at plate boundaries.
(b) A fixed area in the mantle where a plume of hot, buoyant material rises and causes volcanic activity at the surface.
(c) A zone of intense seismic activity along a major fault line due to friction and stress buildup.
(d) A region of hydrothermal vents on the ocean floor associated with mid-oceanic ridges.
Answer: (b)
Explanation: A hotspot is a localized area of high heat flow in the Earth’s mantle, often thought to be caused by a mantle plume – a rising column of hot, solid material. As tectonic plates move over these stationary hotspots, they can create chains of volcanoes, like the Hawaiian Islands. - Which of the following types of seismic waves typically causes the greatest amount of damage to buildings during an earthquake?
(a) Primary waves (P-waves) due to their high frequency.
(b) Secondary waves (S-waves) due to their ability to travel through liquids.
(c) Love waves (L-waves) due to their large amplitude and horizontal shearing motion.
(d) Rayleigh waves (R-waves) due to their high propagation speed.
Answer: (c)
Explanation: Love waves are a type of surface wave that travels along the Earth’s surface with a horizontal side-to-side motion perpendicular to the direction of propagation. Their large amplitude and the horizontal shearing forces they exert make them particularly destructive to building foundations. - The process of caldera formation is often associated with:
(a) The slow, continuous effusion of basaltic lava.
(b) A very large, explosive volcanic eruption that empties the magma chamber.
(c) The gradual uplift and erosion of a volcanic cone over millions of years.
(d) The intrusion of a large magma body beneath the Earth’s surface without any eruption.
Answer: (b)
Explanation: Calderas are large volcanic depressions that form when a massive explosive eruption empties the magma chamber beneath a volcano. The unsupported summit then collapses into the void, creating a wide, basin-shaped depression. - Which of the following factors is LEAST important in determining the magnitude of a tsunami generated by an earthquake?
(a) The magnitude of the earthquake.
(b) The depth of the earthquake’s focus.
(c) The amount of vertical displacement of the seafloor.
(d) The distance of the earthquake’s epicenter from the coastline.
Answer: (d)
Explanation: While the distance from the epicenter to the coastline affects the arrival time and potential impact of a tsunami, the magnitude of the tsunami itself is primarily determined by the magnitude and depth of the earthquake and, most importantly, the amount of vertical displacement of the seafloor that occurs during the earthquake. - The study of volcanology and seismology is crucial for:
(a) Predicting long-term climate change patterns.
(b) Understanding the formation of sedimentary basins and fossil fuels.
(c) Assessing and mitigating the hazards posed by earthquakes and volcanic eruptions to human populations and infrastructure.
(d) Exploring the potential for extraterrestrial life on other planets.
Answer: (c)
Explanation: Volcanology and seismology are essential scientific disciplines for understanding the processes that lead to earthquakes and volcanic eruptions. This knowledge is critical for assessing the risks associated with these natural hazards, developing monitoring and early warning systems, and implementing mitigation strategies to protect lives and property.