Final answer:
A slowly flowing river carrying sediment and reaching the ocean will form a delta, a triangular-shaped landform made of sand and mud. This occurs as the river's current slows down, depositing the sediment it carried at the mouth, with the shape and extent influenced by the local marine conditions.
Step-by-step explanation:
When a river carrying a sediment load flows into the ocean and slows down, it will typically form a delta. This landform arises due to the deposition of sediments as the river's current diminishes upon reaching a larger body of water. Deltas are typically low-elevation areas composed of sand and mud and can be often recognized by their triangular shape.
The process starts with a river gradually widening and slowing down as it flows away from its source, often due to decreasing slope and the joining of tributaries. During this phase, sedimentation increases, which includes various particle sizes based on the distance from the shore—sand being closest, then silt, and clay being deposited further away. In the marine environment, such sediment assemblages form distinct layers that gradually transition from one to another.
Over time, the continuous accumulation of these sediments at the mouth of the river builds up, leading to the creation of a delta. This process is enhanced in regions where ocean currents and wave action are minimal, allowing for more accumulation. The resulting deltas are rich ecosystems and are vital for human activity, often hosting ports, farmlands, and settlements.