Dale Wagner, age 171 of Monroe, Iowa, for his question

Why does the Mississippi have a delta?

The great Mississippi River begins as a little stream flowing from Lake Itasca in northwestern Minnesota. It is a clear, rippling river, growing bigger with each stream that joins it until it joins with the mighty Missouri. The Missouri is a torrent of red muddy water, full of silt it has gathered as it carved. its way through soft soil and farmlands. A little later, the swishing Ohio empties in a muddy torrent often greater than the combined Mississippi‑Missouri river.

Altogether some 250 tributaries and their branches add their streams to the Mississippi. Most of them pour in a heavy quota of mud. and silt. As the great river nears the sea, it is estimated that its dark waters carry more than a million tons of soil every day. This amounts to about 400 million tons of dirt in a year.

The great river aims to dump this debris in the sea. But hete it meets resistance. Two factors co:),Eire to make the river dump its debris to form a vast delta. First, the river has been flowing fast to reach the sea. The speed of its flow has kept the silt stirred up and suspended in the water. Compared with the speed of the river, the Gulf of Mexico is a relatively calm, still body of water. The flowing river meets a wall of resistance. Its waters are forced. to slow down suddenly. :gin this slower moving water,, the silt and debris tend to settle to the bottom.

Another factor is the various salts in the sea water of the Gulf of Mexico. The salts react on the fine floating silts and cause them to coagulate, or get into larger particles. These particles tend to sink, rather than stay suspended in the water.

So, when at least it reaches the sea, the great Mississippi is forced to give up the silt and soil it has stolen away from the land. In one year it dumps enough silt dumps enough silt to cover the state of Rhode Island with three inches of good topsoil.

The mud dumping area forms a rough triangle, some 12,000 square miles in area. We call it a delta be‑cause the Greek letter Delta was also shaped like a triangle. The Nile, the Amazon, the Colorado, and most of the world's great rivers form deltas of this sort and for the same reason.

Having dumped its piles of mud, the river now has another problem. It has to find a way through the mud to the sea. Usually it divides into a number of smaller channels. The Mississippi divides into four main channels and countless small streams in order to flow through its delta to the sea.

It is sad to think of all the silt and soil stripped from the land by a great river system. But actually the rich soil is merely transplanted. A delta grows, forming rich new land. Ages ago, the mouth of the Mississippi was near Cairo, Illinois, now 600 miles from the Gulf. All that rich plain was built by delta mud.