Coastal geomorphology: a natural beach is typically built with which type of locally available material, considering the sorting action of waves and the resulting stable profile?

Introduction / Context:
Beaches form where waves and currents sort sediments by size and density. The resulting profile reflects a balance between wave energy and the mobility of grains: very fine particles are often winnowed offshore, while coarser, heavier particles remain to build a more stable beach face.

Given Data / Assumptions:

• Wave climate at the site is sufficient to mobilize a range of sediment sizes.
• Beach material is locally sourced (fluvial, cliff erosion, or offshore supply).
• Sorting by wave action favors deposition of grains that can be mobilized but also remain stable under typical conditions.

Concept / Approach:
Under persistent wave action, the finest fractions are often carried to deeper, calmer water (forming offshore bars or suspended plumes), while the coarsest material that waves can still move tends to accumulate on the foreshore and upper beach. Thus, beaches are commonly described as being built of the largest material that the prevailing waves can transport and rework.

Step-by-Step Solution:
Recognize sorting: waves preferentially remove silt and very fine sand offshore.Understand stability: coarser sand, gravel, or shingle resists backwash more effectively, remaining on the beach.Conclude that the characteristic beach material corresponds to the largest size that the local waves can still move and deposit.

Verification / Alternative check:
Field observations show storm-dominated coasts with shingle/gravel beaches, while lower-energy coasts hold medium sands—both reflect “largest movable local material.”

Why Other Options Are Wrong:

• “Large” (option B) is vague; the key is the largest size the waves can still mobilize.
• “Fine/finest” (options C and D) are typically transported offshore unless the energy is very low.

Common Pitfalls:

• Assuming finer material always builds bigger beaches; often it is removed by backwash.

Final Answer:
with largest material locally available to the waves