1. Wave Action:
* Erosion: Waves crashing against the shore erode the coastline, breaking down larger rocks into smaller pebbles. This process is stronger near the shoreline where waves have the most energy.
* Transportation: Waves carry these pebbles along the shore, sorting them by size. Larger pebbles are typically heavier and harder to move, so they tend to accumulate near the shoreline where the wave energy is highest.
2. Sediment Supply:
* Local Rock Formations: The type of rocks present in the surrounding area dictates the composition of the pebbles. Harder rocks like granite or quartz will form larger pebbles that resist weathering.
* River Input: Rivers can carry sediment from upstream, including large pebbles, to the shore. This process can significantly influence the size of pebbles near the shore.
3. Beach Slope:
* Steeper Beaches: Steeper beaches are more exposed to wave energy and have less time for waves to sort the sediment. This can result in a wider range of pebble sizes, including larger ones, near the shore.
* Gently Sloping Beaches: Gently sloping beaches are less exposed to wave energy. This allows waves to sort the sediment more effectively, often resulting in smaller pebbles near the shore.
4. Other Factors:
* Wind: Wind can also transport and deposit pebbles on the beach, further influencing their distribution.
* Tides: Tides can play a role in the movement and sorting of pebbles, especially in areas with significant tidal ranges.
In summary, the presence of large pebbles near the shore is a result of a complex interplay of wave action, sediment supply, beach slope, and other factors. The exact reasons for their accumulation will vary depending on the specific location and its unique geological and environmental conditions.
