Test: Natural Hazards & Disasters - UPSC MCQ

• The world's distribution of earthquakes coincides very closely with that of volcanoes. Regions of great seismicity such as a circum-Pacific ring of fire arc also regions of major volcanic eruptions. Many processes in and around volcanoes can generate earthquakes. Most of the time, these processes are faulting and fracturing that does not lead to an eruption.

• Also, earthquake activity beneath a volcano almost always increases before an eruption because magma and volcanic gas must first force their way up through shallow underground fractures and passageways. When magma and volcanic gases or fluids move, they will either cause rocks to break or cracks to vibrate. So, both statements are incorrect.

• Composite volcanoes are characterised by eruptions of cooler and more viscous lavas than basalt. These volcanoes often result in explosive eruptions.

• Along with lava, large quantities of pyroclastic material and ashes find their way to the ground. This material accumulates in the vicinity of the vent openings leading to the formation of layers, and this makes the mounts appear as composite volcanoes.

• Batholiths: Large dome-like structures are developed when a large body of magmatic material is cooled in the deeper depth of the crust. They cover large areas. Sometimes, these granitic bodies assume depth that may be several kilometres. A cooled portion of the magma chambers is known as batholiths.

• Laccoliths: Large dome-shaped intrusive bodies with a level base that are connected by a pipe-like channel arising from below arc known as laccoliths. It is similar to the surface volcanic domes of the composite volcano that are located at deeper depths. The domal hills of granite rocks are spotted in the plateau of Karnataka. Though now exfoliated, most of these are examples of laccoliths or batholiths.

• When the water of the spring is at temperatures substantially higher than the air temperature of the surrounding area, it is called as hot spring or thermal spring.

• In most hot springs, groundwater heated by shallow intrusions of magma (molten rock) in volcanic areas is discharged. But some thermal springs are not connected to volcanic activity. In such cases, convective circulation plays a role, by heating the water.

• Mount Aso, a volcano in southern Japan, has erupted. It is the first such eruption in 22 years, causing flight cancellations and prompting warnings to stay away from its crater.

• This eruption has spewed out lava debris and smoke, shooting plumes of ash a kilometre into the sky.

• Galapagos Islands are formed due to hotspot activity. The Galapagos Islands are located off the west coast of South America straddling the equator. It belongs to Ecuador.

• The Galapagos are located at the confluence of several currents including the cold Humboldt Current travelling north from South America and the Panama Current travelling south from Central America making the islands cooler than you would think and providing the perfect environment for the unique mix of wildlife that inhabits the islands.

• Galapagos were instrumental in developing Darwin’s Theory of Evolution.

• Atlantic coasts have very few volcanoes and that too dormant ones.

• The Pacific Ocean has many volcanoes due to its activeness in volcanic eruptions called the Ring of Fire.

• The Ring of Fire stretches from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan, and into New Zealand. Sri Lanka lies outside the ring.

• The southern portion is more complex, with several smaller tectonic plates in collision with the Pacific plate from the Mariana Islands, the Philippines, Bougainville, Tonga etc.

Earthquake is a natural hazard. The following are the immediate hazardous effects of earthquake

Immediate Hazardous Effects of Earthquake

Earthquakes can cause devastating damage to infrastructure, significantly impact human life, and lead to catastrophic environmental consequences. The immediate hazardous effects of an earthquake include:

- Ground Shaking
- The most direct and immediate effect of an earthquake is ground shaking. This is caused by the passage of seismic waves through the ground, and it can lead to the collapse of buildings and other structures, landslides, and ground rupture.

- Soil Liquefaction
- Soil liquefaction occurs when the strength and stiffness of a soil are reduced by earthquake shaking or other rapid loading. Liquefaction can cause buildings to tilt, sink, or collapse due to the loss of support.

- Fires
- Earthquakes can lead to fires due to gas line breaks, electrical shorts, or the spilling of flammable materials. These fires can be especially destructive and difficult to control, especially if the earthquake has damaged water supply systems.

- Avalanches
- In mountainous regions, earthquakes can trigger avalanches and landslides, burying communities and blocking roads and rescue routes. The displacement of large amounts of snow or debris can cause additional damage and loss of life.

- Tsunami
- Undersea earthquakes can displace a large volume of water, generating tsunamis. These high-energy waves can travel across ocean basins and cause extensive damage to coastal communities, including flooding, destruction of property, and loss of life.

Conclusion

Each of these effects can significantly exacerbate the immediate impact of an earthquake, leading to a complex disaster scenario that requires a multifaceted response effort. Understanding these hazards is crucial for preparedness, response, and recovery efforts in earthquake-prone regions.

• Most earthquakes occur at the boundaries where the plates meet. The locations of earthquakes and the kinds of ruptures they produce help scientists define the plate boundaries.

• There are three types of plate boundaries: spreading zones, transform faults and subduction zones. Transform Plate Boundaries are locations where two plates slide past one another. The fracture zone that forms a transform plate boundary is known as a transform fault. Most transform faults are found in the ocean basin and connect offsets in the mid-ocean ridges.

• Plate margins witness several plate collisions, sliding, transformation etc that result in volcanism or earthquakes.

• Most of them are found in the Ring of Fire Some earthquakes also occur within the plates but not as frequently as on the plate margins.

• The point where the energy is released is called the focus.

• The point on the surface, nearest to the focus, is called the epicentre.

The correct answer is:

      (D).   1 and 3 only

Earthquakes are most prone to occur in areas where there are active volcanoes and tectonic fault planes. While large reservoirs can induce seismic activity in some cases, they are not a primary factor in earthquake occurrence.

• The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave, and, consequently, the first to ‘arrive’ at a seismic station. The P wave can move through solid rock and fluids, like water or the liquid layers of the Earth.

• The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium.

• The two types of earthquakes are body waves and surface waves. Waves that are generated from the release of energy at the focus travel through the body by moving in all directions. Hence, it is named body waves.

• Interaction between body waves and the rock’s surface generates a new set of waves. This is called surface waves. These waves move along the surface. Because these waves travel through materials that have different densities, the velocity changes.

• The density of the material is directly proportional to the velocity, that is, if the material is denser, the velocity is higher. There is a change in direction of the waves when they get reflected or refracted by materials with different densities.

• The boundaries where the plates meet experience most earthquakes. Locations of earthquakes and the kinds of ruptures they produce serve as a great source of information to scientists to define the plate boundaries. The three types of plate boundaries are spreading zones, transform faults and subduction zones. At spreading zones, molten rock rises, which pushes two plates apart and adds new material at their corners.

• Divergent boundaries are those at which crustal plates move away from each other, such as at mid-oceanic ridges.

• The formation of a new ocean crust that is pushed away from both sides of the ridge fault creates a tension setting that results in the formation of the graben. Earthquakes arc located along the normal faults that form the sides of the rift or beneath the floor of the rift.

• Transform faults are found where plates slide past one another. Shallow-focus earthquakes occur along transform boundaries where two plates move past each other.

• Earthquakes are located along the normal faults that form the sides of the rift or beneath the floor of the rift.

• However, transform faults are found where plates slide past one another. Shallow-focus earthquakes occur along transform boundaries where two plates move past each other.

• There are two types of body waves generated during an earthquake. They are called P- and S-waves.

• An important fact about S-waves is that they can travel only through solid materials. This characteristic of the S-waves is quite important as it has helped scientists to understand the structure of the interior of the Earth.