River geomorphology: Statement I says that incised meanders are formed in the mature stage of a river, while Statement II says that incised meanders are characterised by rejuvenation and upliftment of the land. What is the correct relationship between these two statements?

Introduction / Context:
This question assesses understanding of fluvial landforms, specifically incised meanders. It uses an assertion and reason format with two statements about when incised meanders form and what they indicate. The learner must evaluate the truth of each statement and determine whether one explains the other. Knowledge of river stages, rejuvenation, and vertical erosion is needed to answer correctly.

Given Data / Assumptions:

• Statement I: Incised meanders are formed in the mature stage of a river.
• Statement II: Incised meanders are characterised by rejuvenation and upliftment of land.
• We assume the standard three stage model of river development: youthful, mature, and old stages.

Concept / Approach:
Meanders are sinuous bends in a river, commonly associated with the mature stage when lateral erosion and deposition dominate. Incised meanders, however, are meanders that have been cut deeply into the landscape due to renewed vertical erosion. This renewed erosion usually occurs when the river is rejuvenated, either because of uplift of the land or a drop in base level (such as sea level fall). The key is to distinguish ordinary meanders of the mature stage from incised meanders that reflect rejuvenation rather than simple maturity.

Step-by-Step Solution:
Step 1: Consider Statement I. It claims incised meanders are formed in the mature stage. While meanders commonly occur in the mature stage, incised meanders specifically are associated with renewed downcutting, not simply the normal mature stage conditions. Step 2: Because incised meanders form when a previously established meandering river gains renewed energy to erode vertically, they are more correctly linked to rejuvenation rather than the ordinary mature stage. Therefore, Statement I is false as stated. Step 3: Evaluate Statement II. Rejuvenation occurs when there is uplift of the land or a fall in base level, increasing the river gradient and enhancing vertical erosion. Step 4: This increased vertical erosion cuts deeply into the existing meander pattern, producing incised meanders that often appear as steep walled meandering valleys. Step 5: Therefore, Statement II is true, since incised meanders are indeed characteristic of rejuvenation and upliftment of land.

Verification / Alternative check:
Textbooks on geomorphology often provide diagrams of meanders in different stages. Ordinary meanders with wide floodplains are associated with the mature stage. When rejuvenation occurs, the river entrenches itself into its previous floodplain, yielding incised or entrenched meanders. Some sources use specific examples like the Colorado River or other rejuvenated rivers to illustrate such features. These references confirm that incised meanders are tied to rejuvenation rather than solely to the mature stage described in Statement I.

Why Other Options Are Wrong:

• Both true and Statement II explains Statement I: This would require Statement I to be correct, which it is not, because it misplaces incised meanders strictly in the mature stage without mentioning rejuvenation.
• Both true but Statement II not explanation: Again, this assumes Statement I is true, which is incorrect.
• Statement I true, Statement II false: This reverses the actual situation. Statement II accurately describes the rejuvenation context of incised meanders.

Common Pitfalls:
The main pitfall is confusing ordinary meanders with incised meanders. Students often remember that meanders belong to the mature stage and then apply that fact incorrectly to incised meanders. Another error is to ignore the role of rejuvenation and land uplift, assuming that any deeply cut valley is simply youthful. Remember that incised meanders require a preexisting meandering pattern plus renewed downcutting, which is directly linked to rejuvenation processes.

Final Answer:
Statement I is false but Statement II is true, so the correct option is Statement I is false but Statement II is true.