Book 24, Question 114
Why are there huge piles of sand and gravel in some places?
Long ago, in the Ice Age, glaciers carried sand, gravel, and boulders over great distances. When the ice melted, it dropped them in piles and ridges. Meltwater rivers also washed and sorted the sand and gravel. Today, many of these deposits are dug out for roads and buildings.
More fun facts
- Sand and gravel are dug up in every state in the United States.
- Sand and gravel make up about 42 percent of all the rock material, called aggregate, produced in the country.
- Most of it was laid down either by glacier meltwater or by rivers and streams.
- Glacier meltwater deposits are found in northern areas and high mountains, and they often make excellent building material.
- In dry areas like the Great Basin of the western U.S., much sand and gravel sits in fan shaped deposits called alluvial fans, which need lots of processing.
- River gravel usually gets less coarse the farther it is carried from the rock it came from.
- More than 90 percent of aggregate travels by truck, and hauling it 30 to 50 miles can double its cost, so pits are built close to where it is used.
Sources: U.S. Geological Survey
Questions kids ask
What is the other main kind of aggregate?
Crushed stone, such as limestone dug from quarries.