GC Leong Test: Vulcanism and Earth Quakes - UPSC MCQ

Both statements are accurate descriptions of different types of volcanoes. Statement-I correctly defines active volcanoes as those that continuously eject volcanic material at frequent intervals. Statement-II accurately explains dormant volcanoes as those that have not erupted for a long time but have the potential to erupt in the future. However, Statement-I and Statement-II do not necessarily relate to each other, hence, both statements are correct, but Statement-II does not explain Statement-I, making Option B the correct answer.

An active volcano, as per the details provided, is characterized by frequently ejecting volcanic material. These volcanoes are in a state of continuous activity, regularly releasing ash, gas, and lava. For example, Mount Etna in Italy and Stromboli in Sicily are considered active volcanoes. The consistent ejection of volcanic material distinguishes them from dormant and extinct volcanoes.

The Circum-Pacific belt, also known as the "Ring of Fire," is a major volcanic belt that encircles the Pacific Ocean basin. It is home to approximately two-thirds of the world's active volcanoes. This belt is characterized by high volcanic and seismic activity, making it one of the most geologically active regions on Earth. Volcanoes in this belt are known for their explosive eruptions and are a significant part of the global tectonic activity.

Let's examine each of the statements:

1. Statement 1: "An active volcano is one that has not erupted in historic times and is unlikely to erupt again." This statement is incorrect. An active volcano is one that is erupting or shows signs of erupting in the near future. For example, Mount Etna in Italy and Stromboli in Sicily are active volcanoes, regularly ejecting volcanic material.

2. Statement 2: "A dormant volcano is one that has erupted recently and continues to erupt frequently." This statement is incorrect. A dormant volcano is one that has not erupted in a long time but has the potential to erupt in the future. It is essentially "sleeping" but not extinct. Barren Island in the Andaman Sea is an example of a dormant volcano.

3. Statement 3: "An extinct volcano is one that has not erupted in historic times, and the possibility of future eruptions is considered remote." This statement is correct. An extinct volcano has no recorded eruptions in historic times, and the likelihood of future eruptions is very low. However, as history has shown, some volcanoes thought to be extinct, like Mount Vesuvius, have erupted unexpectedly.

Based on the analysis, only Statement 3 is correct. Therefore, the correct answer is Option D : 3 only

1. Circum-Pacific Belt - Known as the Ring of Fire: This is correctly matched. The Circum-Pacific Belt is indeed known as the Ring of Fire and houses around two-thirds of the world's volcanoes.

2. Mid-Continental Belt - Includes volcanoes of the Mid-Atlantic Ridge: This is incorrectly matched. The Mid-Continental Belt does not include the Mid-Atlantic Ridge volcanoes. Instead, it includes various volcanoes of the Alpine mountain chain and the Mediterranean region, such as Stromboli, Vesuvius, and Etna.

3. Mid-Atlantic Belt - Contains volcanoes of the Alpine mountain chain: This is incorrectly matched. The Mid-Atlantic Belt includes volcanoes along the Mid-Atlantic Ridge, not the Alpine mountain chain.

4. Old Faithful - Located in Yellowstone National Park, USA: This is correctly matched. Old Faithful is one of the most famous geysers in Yellowstone National Park, Wyoming, USA.

Thus, only pairs 1 and 4 are correctly matched.

Laccoliths are igneous mounds with a dome-shaped upper surface and a level base, fed by a pipe-like conduit from below. These landforms are formed by the intrusion of magma that does not reach the surface but instead creates a distinctive shape within the Earth's crust. Laccoliths play a significant role in shaping the topography of volcanic regions and are important features in the study of geology and volcanic processes.

To determine the correct statements, let's analyze each one:

Statement 1: The Circum-Pacific belt, also known as the "Ring of Fire," does indeed contain about two-thirds of the world's volcanoes. This is a well-known fact about the distribution of volcanoes globally, making this statement correct.

Statement 2: This statement incorrectly describes geysers. Geysers are not characterized by a continuous and non-explosive flow; rather, they are known for their intermittent and turbulent discharge of water and steam, often triggered by geothermal activity. Therefore, this statement is incorrect.

Statement 3: Hot springs are indeed more common than geysers and often contain dissolved minerals, which can have medicinal properties. This accurately describes the nature of hot springs, making the statement correct.

Thus, only statements 1 and 3 are correct. Therefore, the correct answer is Option C: 1 and 3 Only.

Statement-I correctly describes that volcanic activity is indeed connected with crustal disturbances, often found in regions that have experienced intense folding or faulting. This relationship is significant in understanding the geological processes associated with volcanic eruptions. Statement-II accurately defines laccoliths as igneous mounds with specific structural characteristics, including a dome-shaped upper surface and a level base, supported by a conduit from below. Furthermore, the conduit feeding the laccolith from beneath is a crucial aspect of their formation. Therefore, both statements are factually correct, and Statement-II provides additional explanatory details that complement and enhance the understanding conveyed in Statement-I.

1. Sill - An intrusion of molten magma made horizontally along the bedding planes of sedimentary rocks. This is correctly matched as sills are indeed horizontal intrusions.

2. Dike - An igneous mound with a dome-shaped upper surface and a level base. This is incorrectly matched. Dikes are vertical intrusions that cut across existing rock layers, not dome-shaped mounds.

3. Laccolith - A lens-shaped mass of igneous rock occupying the crest of an anticline or the bottom of a syncline. This is incorrectly matched. Laccoliths are dome-shaped intrusions with a flat base, whereas phacoliths occupy the crest of an anticline or the bottom of a syncline.

4. Batholith - A large emplacement of igneous intrusive rock, mainly granite, that forms from cooled magma deep in the Earth’s crust. This is correctly matched as batholiths are indeed large, deep-seated intrusive bodies.

Additional Information:

Dikes are typically vertical or steeply inclined sheets of rock that form when magma intrudes into pre-existing rock formations.

Laccoliths have a characteristic dome shape because the pressure of the magma causes the overlying strata to bulge upwards.

Phacoliths are typically found in the crests of anticlines or troughs of synclines, not as laccoliths.

Thus, only pairs 1 and 4 are correctly matched, making Option B the correct answer.

Statement-I talks about the distribution of volcanoes in the world, mentioning the three volcanic belts and volcanoes outside these belts. This aligns with the information provided in the initial content.
Statement-II, on the other hand, discusses hot springs produced by geothermal heated groundwater, which does not directly relate to the content about volcanic belts. Therefore, Statement-II is incorrect in the context of the given information.