Which drainage pattern is best established in the areas of alternate hard and soft rocks

Analyze the question: The question asks which drainage pattern develops where hard and soft rocks alternate, such as in folded landscapes with parallel ridges and valleys.

Concept: Drainage patterns

• Trellis: Main streams run parallel to each other along the strike of soft rock belts. Short tributaries join them at right angles. It develops in folded or tilted areas with alternating resistant and less resistant rocks, such as the Appalachians.
• Centripetal: Streams flow inward to a central basin or depression, such as a crater or a desert basin.
• Radial: Streams flow outward from a central high point, such as a volcano or dome.
• Annular: Streams form a ring-like pattern around a dome. Here, rivers follow the weaker rock bands, so it is a variant that can also involve alternating rocks, but it is specific to eroded domes.

Solution:

1. Alternating hard and soft rocks means the rivers will erode the soft rock bands more easily and form valleys there.
2. The main rivers therefore run parallel along the soft rock outcrops.
3. The tributaries join them at right angles down the sides of the ridges. This gives the grid or "garden trellis" look.
4. This is the trellis pattern. Annular is limited to dome structures, so it is not the best general answer.

Answer: A. trellis

Exam tip: Link each pattern to its trigger:

• Trellis = Tilted or folded alternating rocks (parallel ridges and valleys)
• Radial = Rising dome or volcano (flows outward)
• Centripetal = Center basin (flows inward)
• Annular = Around a dome (ring)