In world physical geography, which of the following famous river valleys is a classic example of a rift valley formed by crustal tension and subsidence?

Introduction / Context:
A rift valley is a deep, elongated trough formed when a block of the Earth's crust subsides between two faults due to tensional forces. Such valleys are important evidence of tectonic activity and are studied in physical geography and geology. Some rift valleys are associated with rivers that occupy the low lying trough. This question asks you to identify which among the listed river valleys is a classic textbook example of a rift valley.

Given Data / Assumptions:

• We are comparing well known river valleys: Amazon, Thames, Rhine, and Mississippi.
• The task is to identify which valley is structurally a rift valley.
• We assume standard definitions of rift valleys formed by crustal extension and faulting.
• Only one option fits the classic description used in school geography books.

Concept / Approach:
The Rhine valley, particularly the Rhine Graben, is famous in physical geography as a rift valley located between the Vosges and Black Forest mountains in Europe. It was formed by crustal extension, where a block of land subsided between two roughly parallel faults, creating a long, narrow depression later partly filled by the River Rhine. The Amazon valley, Thames valley, and Mississippi valley are primarily erosional or structural river valleys but are not classic rift valleys formed by tensional faulting in the way the Rhine valley is. Therefore, by matching the definition of a rift valley with these examples, the Rhine valley stands out as the correct answer.

Step-by-Step Solution:
Step 1: Recall that a rift valley is formed when a block of the Earth's crust drops down between two faults due to tensional forces. Step 2: Identify the Rhine valley (Rhine Graben) in Europe as a well known rift valley example. Step 3: Remember that geography textbooks often show diagrams of the Rhine rift valley between the Vosges and Black Forest ranges. Step 4: Recognise that the Amazon, Thames, and Mississippi valleys are large river valleys but not labelled as rift valleys formed by subsidence between faults. Step 5: Conclude that the Rhine valley is the correct answer to this question.

Verification / Alternative check:
Physical geography references and maps of European tectonic structures highlight the Rhine Graben as a rift valley. They describe its formation through crustal stretching and faulting, with the Rhine River occupying part of the depressed block. In contrast, descriptions of the Amazon basin focus on its vast drainage area and sedimentation, while the Thames and Mississippi valleys are treated mainly as fluvial features without rift valley origins. This difference in geological explanation confirms the Rhine valley as the classic rift valley among the options.

Why Other Options Are Wrong:
The Amazon valley is a huge river basin in South America, mostly formed by fluvial processes and tectonic subsidence on a continental scale, but it is not classically described as a long narrow rift valley between two fault blocks, so option A is incorrect. The Thames valley in England is a river valley shaped largely by erosion and deposition, not by rift formation, so option B is wrong. The Mississippi valley is a broad alluvial valley influenced by river processes and sedimentation rather than a distinct rift valley structure, making option D incorrect. Only the Rhine valley fits the textbook definition of a rift valley.

Common Pitfalls:
A common mistake is to assume that any large or famous river valley must be a rift valley, which is not true. Another pitfall is not recalling the geological origin and simply guessing based on familiarity with names like Amazon or Mississippi. To avoid this, remember specific examples: the Rhine valley in Europe and the East African Rift valleys are classic rift valley cases, clearly distinguished from ordinary erosional river valleys in geography texts.

Final Answer:
The famous river valley that is a classic example of a rift valley is the Rhine valley.