Test: Geomorphology - 1 - 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.

1. Basic lavas are the hottest lavas and are highly fluid:

   • This statement is correct. Basic (mafic) lavas are hotter than acid (felsic) lavas and generally have a lower viscosity, making them more fluid and capable of flowing more easily.

2. When Basic lava flows from a volcano, it is very explosive:

   • This statement is incorrect. Basic lavas are typically less explosive compared to acid lavas. They tend to flow more smoothly and form broad shield volcanoes rather than explosive eruptions.

3. Acid lavas are highly viscous and cause less explosive volcanoes:

   • This statement is incorrect. Acid (felsic) lavas have higher viscosity due to their higher silica content, which makes them thicker and more resistant to flow. This viscosity tends to result in more explosive eruptions as gases are trapped and build up pressure.

4. Acid lava is also called as felsic lava:

   • This statement is correct. Acid lava is another term for felsic lava, which refers to lava that is rich in silica and aluminum minerals.

• 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.

Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’. When underground water comes in contact with the hot spot, steam is generated. Sometimes hot water from that region finds outlets at the surface. Such outlets are known as hot springs. 

• 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.

All the mentioned effects are immediate hazardous consequences of earthquakes:

1. Ground Shaking: The primary effect of earthquakes is the violent shaking of the ground, which can cause buildings and infrastructure to collapse.

2. Soil Liquefaction: During strong earthquakes, saturated soils can lose their strength and behave like a liquid, causing the ground to collapse or buildings to sink.

3. Fires: Earthquakes can rupture gas lines, break electrical circuits, or cause fires from other infrastructure damage.

4. Avalanches: Earthquakes can trigger landslides or avalanches in mountainous areas.

5. Tsunami: Underwater earthquakes can displace large volumes of water, generating tsunamis that can cause massive destruction along coastlines.

Thus, all of the listed effects are correct.

• 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.

Both statements 1 and 2 are correct.
1. The point where the energy is released during an earthquake is indeed called the focus. This is the exact location within the Earth's crust where the seismic waves originate.

2. The point on the surface, directly above the focus, is called the epicenter. This is typically the location where the earthquake is felt the strongest and where the most damage occurs.

• Tectonic earthquakes - sliding of plates along a fault plane.

• Volcanic earthquakes - Collapse of roofs of underground mines.

Explosions of chemicals like nuclear weapons, reservoir-induced earthquakes in areas where large reservoirs (e.g. Latur reservoir caused minor earthquake) are located.

• 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.

• 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.

Both Assertion and Reason are true, and Reason is the correct explanation for
Assertion.

Assertion (A): Passive continental margins do not exhibit significant seismic or volcanic activity.
This statement is true.

Definition: Passive continental margins are transition zones between continental crust and oceanic crust that are not associated with plate boundaries.

Characteristics: Due to their location away from active plate boundaries, these margins experience little to no tectonic activity.

Reason (R): They are located away from tectonic plate boundaries. This statement is true.

• Plate Tectonics Insight: Tectonic plate boundaries are sites where most of Earth's seismic and volcanic activities occur due to interactions between plates.
• Geographical Evidence: Passive continental margins, such as the eastern coasts of North and South America, are located far from active divergent, convergent, or transform boundaries.

Evaluation of the Relationship Between A and R:

• Both the assertion and the reason are accurate and interlinked.
• The reason provides a direct explanation for the assertion. The lack of tectonic plate boundaries at passive continental margins is the principal reason for the absence of significant seismic or volcanic activities at these locations.