The Copper River delta in Alaska is a beautiful example of what a river delta can look like.
One of the many important aspects of understanding rivers is the delta, a build up of sediment carried down by the force of moving water. Within the general concept of the river delta, sub-types also exist.
General Formation
A river delta is a triangle shaped buildup of sand and soil that ended up in the river and was carried along to a more stagnant body of water. Sediment-filled water hits more slowly moving water and the sediment settles to the ground, spreading out in a fan-like fashion. This builds up until eventually a land mass is formed.
Layers of Buildup
The sedimentary structure of a river delta includes three formations: the bottomset beds, the foreset beds and the topset beds. The horizontal bottomset beds (settled silt) form first, then angular foreset beds form (larger sediment-like sand carried along the main channel) and finally the horizontal topset beds (sediment with gravel and sometimes boulders) form last.
Alluvial Fan Versus Delta
Though similar in appearance, alluvial fans and deltas are different. A delta's composition includes fine-grained sediment, has a shallow slope and flows into another body of water. An alluvial fan, on the other hand, has a sharp slope with coarse sediment and can flow into either a landmass or into a body of water. When it does flow into water it is called an alluvial fan delta.
Considerations
Deltas can be destroyed by human interference. If a river is diverted or completely dammed, the delta can erode.
Tags: body water, bottomset beds, carried along, flow into, foreset beds
