All questions of Arid or Desert Landforms for UPSC CSE Exam

Properties of Limestone, Chalk, and Dolomite

Limestone, chalk, and dolomite are three different forms of calcium carbonate. Let's understand the properties of each form of calcium carbonate mentioned in the given statements.

1. Limestone:
- In its pure state, limestone is made up of calcite or calcium carbonate.
- It is a sedimentary rock that is formed over millions of years by the accumulation of shells, corals, and other marine debris.
- Limestone is used as a building material, as a raw material for cement production, and as a source of calcium for agriculture.
- When magnesium is also present in limestone, it is called dolomite.

2. Chalk:
- Chalk is a very pure form of limestone that is white and rather soft.
- It is composed of microscopic shells of plankton that lived in the sea millions of years ago.
- Chalk is used for writing, drawing, and as a filler in paint, plastics, and other materials.

3. Solubility of Limestone:
- Limestone is soluble in rainwater, which, with carbon dioxide from the air, forms a weak acid.
- This acid reacts with the calcium carbonate in limestone and dissolves it, forming calcium bicarbonate.
- Over time, this process can create sinkholes and other features in limestone landscapes.

Conclusion:
From the above properties of limestone, chalk, and dolomite, we can conclude that all three statements given in the question are correct. Therefore, the correct answer is option 'D' - All of the above.

Features of Limestone Caves

Limestone caves are formed when water flows through porous rocks and dissolves the limestone, creating caverns and passageways. These caves often have unique and beautiful features that are a result of this geological process. The three main features that adorn the limestone caves are:

1. Stalactites: These are mineral deposits that hang from the ceiling of the cave and are formed by the dripping of mineral-rich water. Over time, the water evaporates, leaving behind a deposit of minerals that grows downwards. Stalactites can take on many shapes and sizes and are often found in clusters.

2. Stalagmites: These are mineral deposits that rise from the floor of the cave and are formed by the same process as stalactites. As water drips onto the cave floor, it leaves behind mineral deposits that grow upwards. Stalagmites can take on many shapes and sizes and are often found in clusters.

3. Pillars: Pillars are formed when stalactites and stalagmites merge together over time. As a stalactite grows downwards and a stalagmite grows upwards, they eventually meet and merge, forming a column or pillar. These pillars can be massive and create stunning natural formations in the cave.

Therefore, the correct answer is option 'D' - All of them.

Landforms of Chalk: Characteristics and Features

Chalk is a soft, white, porous sedimentary rock composed of the mineral calcite. It is formed from the remains of microscopic planktonic algae and foraminifera that lived in the warm, shallow seas of the Cretaceous period. The landforms of chalk are rather different from those of other limestones due to their unique characteristics and features.

Statement 1: The landforms of chalk are rather different from those of other limestones.

- Chalk is a soft, porous rock that weathers easily and is susceptible to erosion by water, wind, and ice.
- Chalk is usually found in the form of a plateau or escarpment, with steep, white cliffs facing the sea and gentle slopes inland.
- Chalk forms distinctive landforms such as caves, arches, stacks, and blowholes due to its solubility in rainwater and the erosive power of the sea.

Statement 2: There is little or no surface drainage and valleys which once contained rivers are now dry.

- Chalk is a porous rock that allows rainwater to soak through quickly, rather than forming surface runoff.
- As a result, there is little or no surface drainage on chalk landscapes, and river valleys that once contained water are now dry.
- This has led to the formation of dry valleys or coombes, which are steep-sided, narrow valleys with a flat floor that may contain a small stream or pool.

Statement 3: These are often called coombes.

- Coombes are a characteristic feature of chalk landscapes, but they can also be found on other types of rock.
- The word "coombe" comes from the Old English word "cumb", which means "valley" or "hollow".
- Coombes are often used for grazing animals or for growing crops such as wheat or barley.

Conclusion

All three statements are correct. The unique characteristics of chalk, such as its solubility, porosity, and susceptibility to erosion, have led to the formation of distinctive landforms and features, including dry valleys or coombes. These features are characteristic of chalk landscapes and have important ecological and agricultural significance.

Cockpit Country - Jamaica

- Cockpit Country is correctly matched with Jamaica.
- The Cockpit Country is a rugged and densely forested area located in the interior of the island of Jamaica.
- It is known for its unique topography, characterized by steep limestone hills and deep valleys, giving it a "cockpit-like" appearance.
- This region is of great ecological significance and is home to a diverse range of plant and animal species, some of which are endemic to Jamaica.
- The Cockpit Country also serves as an important watershed, providing water to numerous rivers and streams that flow through the region.
- It is recognized as a globally significant biodiversity hotspot and is protected as a national park and forest reserve.

Kentucky - United States

- Kentucky is correctly matched with the United States.
- Kentucky is a state located in the southeastern region of the United States.
- It is known for its rolling hills, horse farms, bourbon distilleries, and the iconic Kentucky Derby horse race.
- The state is also famous for its bluegrass music and is often referred to as the "Bluegrass State."
- Kentucky is bordered by seven states and is known for its diverse geography, which includes the Appalachian Mountains in the east and the Mississippi River in the west.
- The state has a rich history, particularly in relation to the Civil War and the Underground Railroad.
- Kentucky is also home to Mammoth Cave National Park, which is the longest known cave system in the world.

Pennines - France

- The Pennines are not correctly matched with France.
- The Pennines are a range of hills and mountains in Northern England, not in France.
- They extend from the Midlands in central England to the Scottish Borders.
- The Pennines are often referred to as the "backbone of England" due to their central location and prominent geological features.
- This region is known for its rugged beauty, with deep valleys, steep slopes, and high moorland plateaus.
- The Pennines are popular for outdoor activities such as hiking, cycling, and rock climbing.
- They also have a rich cultural heritage, with historic towns and villages scattered throughout the region.

In conclusion, the correct matches are:

1. Cockpit Country - Jamaica
2. Kentucky - United States

Therefore, the correct answer is option 'A' - 1 and 2 only.

Batu Caves, Kuala Lumpur, Mammoth Caves, Kentucky and Carlsbad Cave, New Mexico, in U.S.A. and Postojna Caves, Yugoslavia.

Statement 1: Limestone vegetation in tropical regions is luxuriant because of the heavy rainfall all year-round.

Explanation:
- Limestone is a type of sedimentary rock primarily composed of calcium carbonate. It is often found in tropical regions where there is abundant rainfall and warm temperatures.
- The heavy rainfall in tropical regions provides the necessary moisture for the growth of vegetation on limestone.
- The warm temperatures in these regions also contribute to the luxuriant growth of vegetation as they provide an optimal environment for plant growth.
- The high amount of rainfall ensures that there is a constant supply of water for plants, which is essential for their survival and growth.
- Additionally, the rainfall helps in the leaching of nutrients from the limestone, making them available for plant uptake.
- The combination of abundant rainfall, warm temperatures, and nutrient availability makes limestone vegetation in tropical regions lush and dense.

Statement 2: Settlements are scattered, and the population is often sparse.

Explanation:
- In many tropical regions, settlements are often scattered and the population is sparse.
- This is primarily due to the geographical features and the characteristics of the tropical environment.
- Tropical regions often have dense forests, rugged terrains, and a lack of infrastructure, which makes it difficult for large-scale settlements to flourish.
- The dense forests and rugged terrains create barriers to transportation and communication, making it challenging to establish and maintain settlements.
- The lack of infrastructure, such as roads, electricity, and water supply, further hinders the development of large settlements in tropical regions.
- Moreover, the tropical climate with its high temperatures and high humidity can be challenging for human habitation, leading to a preference for more scattered settlements.
- The sparse population in tropical regions is also influenced by factors such as limited economic opportunities, lack of basic amenities, and the presence of diseases endemic to the area.
- However, it is worth noting that there are exceptions to this general trend, and some tropical regions may have densely populated settlements, particularly in areas with better infrastructure and economic opportunities.

Conclusion:
- Both statements are correct.
- Statement 1 explains the luxuriant growth of vegetation in tropical regions with limestone due to heavy rainfall and favorable temperatures.
- Statement 2 highlights the scattered nature of settlements and sparse population in tropical regions due to geographical features, lack of infrastructure, and challenging climatic conditions.

Swallow holes, also known as sinkholes, are geological formations that occur due to the dissolution of soluble rocks such as limestone or dolomite. These formations are commonly found in areas with karst topography, which is characterized by underground drainage systems and distinctive surface features.

Statement 1: Swallow holes are small depressions carved out by solution where rainwater sinks into the limestone at a point of weakness.

This statement is correct. Swallow holes are formed when rainwater infiltrates the ground and dissolves the underlying limestone or other soluble rock. Over time, this dissolution creates small depressions or cavities in the ground. These depressions act as entry points for the surface water to enter the underground drainage system. The water seeps through the rocks, enlarging the cavities and creating underground channels.

Statement 2: Swallow holes are also known as sinkholes.

This statement is also correct. "Swallow hole" and "sinkhole" are two terms used interchangeably to describe the same geological feature. Both terms refer to the depressions or cavities created by the dissolution of soluble rocks. The name "sinkhole" comes from the fact that these formations often appear as sudden depressions or holes in the ground, giving the impression that the surface is sinking.

Therefore, both statements 1 and 2 are correct.

In conclusion, swallow holes or sinkholes are small depressions carved out by solution where rainwater sinks into the limestone at a point of weakness. They are geological features formed due to the dissolution of soluble rocks and are commonly found in areas with karst topography. The terms "swallow hole" and "sinkhole" are used interchangeably to refer to these formations.

Explanation:
The correct answer is option 'C' which means that both statements are correct.

Statement 1:
Limestones are well jointed and it is through these joints and cracks that rainwater finds its way into the underlying rock.

Explanation of Statement 1:
Limestone is a sedimentary rock that is composed primarily of calcium carbonate. It is formed from the remains of marine organisms such as coral and shells that accumulate over time. Limestones are known to have a high degree of jointing, which means they have natural cracks and fissures.

Rainwater is slightly acidic due to the presence of dissolved carbon dioxide from the atmosphere. When rainwater comes into contact with limestone, it reacts with the calcium carbonate present in the rock. This reaction is known as carbonation, and it leads to the dissolution of the limestone.

The joints and cracks in limestone provide pathways for the rainwater to enter the underlying rock. Over time, as more and more rainwater seeps into these joints, it further dissolves the limestone and widens the cracks. This process is known as solution weathering. As a result, the joints become larger and interconnected, allowing even more rainwater to penetrate the rock.

Statement 2:
Progressive widening by solution enlarges these cracks into trenches and a most intriguing feature called limestone pavement is developed.

Explanation of Statement 2:
As mentioned earlier, the rainwater that enters the joints and cracks of limestone gradually dissolves the rock, resulting in the widening of these cracks. Over a long period of time, this continuous dissolution and widening process can lead to the formation of trenches.

Limestone pavement is a unique and intriguing landform that is developed as a result of the solution weathering of limestone. It is characterized by a flat and exposed surface with distinctive patterns of interconnected cracks and fissures. These cracks are known as grikes, and the flat blocks of limestone between the cracks are called clints.

The development of limestone pavement is a gradual process that involves the dissolution of limestone through rainwater infiltration, the widening of cracks into trenches, and the formation of grikes and clints. The resulting landform is visually striking and often supports unique ecosystems due to its distinctive hydrological and ecological conditions.

In conclusion, both statements are correct. Limestones are indeed well jointed, and rainwater does find its way into the underlying rock through these joints and cracks. The progressive widening of these cracks by solution weathering leads to the formation of trenches and the development of limestone pavement.