What has its head at one end and its mouth at the other end ?
A river ! The place where a river begins is called its head. And the place where it comes to an end, where it flows into a lake or the sea, is called its mouth.
At the edge of the sea, a river's mouth is often a sort of dumping place. As a river moves through the land, it tears sand and soil into it. The river carries all this sand and soil with it on its journey to the sea.
If there are no strong tides or big waves at the river's mouth, the soil and sand sink down to the bottom. As this soil and sand pile up in the riverbed, a kind of island forms in the middle of the river's mouth. Then the river has two branches that flow into the sea.
Slowly, the island gets bigger. In time, islands form in each of the branches. These islands split the river into still more branches. And after a long, long time, there is a great plain at the river's mouth, with many branches of the river running through it. This plain, usually shaped somewhat like a triangle, is called a delta. It gets its name from a letter of the Greek alphabet called "delta", which is shaped like a triangle.
The deltas of such rivers as the Mississippi, the Nile, and the Amazon are hundreds of miles (kilometers) wide. These deltas have been growing for thousands of years. They will keep growing for many years to come.
A river ! The place where a river begins is called its head. And the place where it comes to an end, where it flows into a lake or the sea, is called its mouth.
At the edge of the sea, a river's mouth is often a sort of dumping place. As a river moves through the land, it tears sand and soil into it. The river carries all this sand and soil with it on its journey to the sea.
If there are no strong tides or big waves at the river's mouth, the soil and sand sink down to the bottom. As this soil and sand pile up in the riverbed, a kind of island forms in the middle of the river's mouth. Then the river has two branches that flow into the sea.
Slowly, the island gets bigger. In time, islands form in each of the branches. These islands split the river into still more branches. And after a long, long time, there is a great plain at the river's mouth, with many branches of the river running through it. This plain, usually shaped somewhat like a triangle, is called a delta. It gets its name from a letter of the Greek alphabet called "delta", which is shaped like a triangle.
The deltas of such rivers as the Mississippi, the Nile, and the Amazon are hundreds of miles (kilometers) wide. These deltas have been growing for thousands of years. They will keep growing for many years to come.
No comments:
Post a Comment