Final answer:
A delta is a landform created at the mouth of a river as it slows down and deposits sediment, often forming a triangular shape. Deltas occur where rivers meet larger bodies of water and the sediment carried by the river settles.
Step-by-step explanation:
The feature formed when a river deposits its sediment near its mouth is known as a delta. This often triangular-shaped section of land is created as the waters of the river slow down and split into multiple channels, leading to the accumulation of sand and silt that has been transported downriver. Deltas are frequently found where a river empties into a larger body of water such as an ocean or a large lake, and the slowdown in water flow allows the carried sediment to settle. The Yukon River in Alaska is one such example where a delta has formed.
Rivers with high silt content that discharge into oceans with minimal currents and wave action are adept at building deltas. Conversely, rivers with low silt content or in areas where ocean currents or wave action are strong often form estuarine areas, where fresh water mixes with salt water. Along the river's journey, the widening of the channel and a decrease in the gradient cause a reduction in current speed, resulting in more sediment being deposited as the river approaches its mouth.