Karst topography: Statement I says that by far the most common topographic landform in a Karst terrain is the sinkhole, and Statement II says that topographically a sinkhole is a depression that can vary in depth from less than a metre to a few hundred metres. How are these two statements related?

Introduction / Context:
This question examines understanding of Karst topography, which develops in regions of soluble rocks such as limestone. The focus is on sinkholes, which are characteristic features of Karst landscapes. The learner needs to interpret two given statements about sinkholes and decide whether both are correct and whether the second statement properly explains the first. This is a conceptual geography and geomorphology question involving logical reasoning about related statements.

Given Data / Assumptions:

• Statement I: By far the most common topographic form in a Karst terrain is the sinkhole.
• Statement II: Topographically, a sinkhole is a depression that varies in depth from less than a metre to a few hundred metres.
• A Karst terrain is an area where dissolution of soluble rocks creates distinctive surface and subsurface features.

Concept / Approach:
Karst landscapes are characterised by features such as sinkholes, dolines, caves, and disappearing streams. Among these, sinkholes (also called dolines) are widespread and numerous. They appear as shallow or deep depressions in the ground formed by dissolution or collapse of underlying rock. To answer the question, we need to check the factual correctness of each statement and then determine whether Statement II explains why sinkholes are the most common landform in Karst terrain as expressed in Statement I.

Step-by-Step Solution:
Step 1: Evaluate Statement I. Standard physical geography texts describe sinkholes as the most common and diagnostic surface form in Karst regions. Therefore, Statement I is true. Step 2: Evaluate Statement II. A sinkhole is defined as a rounded depression of various depths, which can be less than a metre deep or extend hundreds of metres, depending on geological conditions and the degree of collapse or dissolution. Therefore, Statement II is also true. Step 3: Consider whether Statement II explains Statement I. The description in Statement II shows that sinkholes are common surface depressions of varying size and depth in Karst regions, which fits with the idea that these features dominate the topography. Step 4: Because sinkholes form extensively wherever soluble rock is present and water can percolate, they naturally become the most abundant topographic form in Karst landscapes, so the detailed description in Statement II supports and clarifies the claim in Statement I. Step 5: Therefore, both statements are true, and Statement II is the correct explanation of Statement I.

Verification / Alternative check:
A further check can be made by recalling that Karst regions are often mapped by counting sinkholes, as they are numerous and easy to identify on aerial photographs and topographic maps. Such regions may have hundreds or thousands of sinkholes. The depth variation, from shallow depressions to deep pits, is indeed a well documented aspect of sinkhole morphology. This consistency with textbook descriptions confirms that the statements are factually correct and that the detailed definition in Statement II helps explain the general statement in Statement I.

Why Other Options Are Wrong:

• Both true but Statement II is not the correct explanation: This is incorrect because the morphology and depth range described in Statement II directly relate to why sinkholes dominate Karst topography.
• Statement I true, Statement II false: Statement II is factually correct, so this pairing is wrong.
• Statement I false, Statement II true: Statement I is not false; sinkholes are indeed recognised as the most common Karst surface landform.

Common Pitfalls:
Learners may confuse Karst features such as caves, underground streams, and sinkholes, sometimes thinking that caves are the most common form because they are dramatic. However, caves are often hidden below ground, while sinkholes cover large surface areas and are more numerous. Another mistake is to focus only on the depth description in Statement II and overlook how it supports the idea that sinkholes are widespread and varied, which is precisely what underlies Statement I. Remember that in assertion reason type questions, you must check both truth and the explanatory relationship.

Final Answer:
Both statements are individually true, and Statement II is the correct explanation of Statement I.