Which drainage pattern is best formed in the area of alternate hard and soft rocks

Analyze the question The question asks which drainage pattern develops where the rocks alternate between hard (resistant) and soft (less resistant) bands, such as in folded mountain regions.

Explain the concept A drainage pattern is the arrangement of a river and its tributaries. It is controlled mainly by rock type and structure:

• Trellised: Looks like a garden trellis. Main rivers flow in parallel valleys cut along the soft rock bands. Short tributaries join them at right angles, running down the sides of the ridges. It forms in folded areas with alternating hard and soft rocks, e.g. the Appalachians.
• Dendritic: Branches like a tree. It forms on uniform rock, such as homogeneous clay or granite, with even resistance.
• Radial: Rivers flow outward from a central high point, such as a volcanic cone or dome.
• Annular: Rivers form a ring around a dome, following weaker rock bands in a circular layout. It is less common and is associated with eroded domes.

Step-by-step solution

1. The key phrase is "alternate hard and soft rocks", which means different resistance to erosion.
2. Rivers cut down more easily through the soft rock, so the main streams line up along those bands and run parallel.
3. Tributaries drain the hard-rock ridges and join the main streams at roughly right angles.
4. That parallel-plus-right-angle layout is the trellised pattern.
5. Dendritic needs uniform rock, radial needs a central peak, and annular needs a dome. None of these fits alternating bands as well.

Answer: A. Trellised

Tip: Think of a trellis as a fence grid, with straight parallel lines crossed at right angles, matching the alternating rock bands. Quick links to remember:

• Uniform rock → dendritic
• Volcano or dome → radial
• Alternating hard and soft rock → trellised