Genre Comprehension Skill Text Features Science Content Nonfiction Compare and Contrast Captions Diagrams Rocks and Soil Labels Glossary Scott Foresman Science 3.7 ì<(sk$m)=bdicij< +^-Ä-U-Ä-U ISBN 0-328-13828-2
Vocabulary decay igneous rock loam metamorphic rock mineral nutrient rock sedimentary rock soil Extended Vocabulary delta drought famine fertilize floodplain irrigate oasis by Kristin Cashore Picture Credits Every effort has been made to secure permission and provide appropriate credit for photographic material. The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions. Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd). 1 Mike Surowiak/Getty Images; 6 Airphoto; 9 (T) Robert Harding World Imagery/Alamy Images, (B) John Hepver/The British Museum/DK Images; 11 NASA/Photo Researchers, Inc.; 12 (B) Trygve Bolstad/Panos Pictures; 13 Ian Berry/ Magnum Photos; 14 (BL) Martin Harvey/NHPA Limited. Unless otherwise acknowledged, all photographs are the copyright of Dorling Kindersley, a division of Pearson. ISBN: 0-328-13828-2 Copyright Pearson Education, Inc. All Rights Reserved. Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permission(s), write to Permissions Department, Scott Foresman, 1900 East Lake Avenue, Glenview, Illinois 60025. 3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05
What You Already Know A rock is a solid, nonliving material made of minerals. There are three kinds of rock. Igneous rock forms from molten minerals and gases. Sedimentary rock forms from sediments. Metamorphic rock is rock that has been changed because of heat, pressure, or both. Minerals form from nonliving matter. You can identify a mineral by its color, streak, and other properties. Most things that we use contain minerals. Air, water, and rock particles make up three of soil s four ingredients. Sands, silts, and clays account for soil s rock particles. These rock particles contain minerals that are rich in nutrients. The fourth ingredient in soil is humus. Humus is made up of dead and decaying plants and animals. Crops grow best in soil that has a lot of water and nutrients. One of the best soils for crops is called loam. Most land gets its water from rain. However, some places get their water through flooding. People usually think of floods as being harmful events that hurt the land and its living things. But some floods bring water and needed nutrients to dry land. In this book you will learn about these kinds of floods. flooded rice field metamorphic rock 2 3
Facts on Floods Floods are caused by overflowing bodies of water, including rivers, lakes, and streams. They are also caused by groundwater rising up to the surface and overflowing the land. When the soil becomes saturated, meaning when it can t hold any more water, its water table, or the top layer of groundwater, floods the land. A flood can be one of the most harmful forces in nature. It can harm people and crops, ruin homes, and spread diseases. However, there are some places where floods bring important benefits. People depend on some annual floods to bring water and minerals to the land. Farmers often grow rice near flooding rivers. Rice grows well in this flooded paddy field. Historically, rivers like the Nile in Egypt have flooded regularly. The Nile s waters irrigate the land. Irrigation makes the soils of the Nile floodplain some of the most fertile in the world. Quick quiz: What did the ancient civilizations of Egypt, Mesopotamia, China, and India all have in common? Answer: They all developed along huge rivers. The irrigation provided by their rivers annual floods supported farming, trade, and many other activities. Flooding rivers carry silt. This silt is rich in nutrients. It fertilizes the land and creates productive farmlands when flood waters deposit it there. If it weren t for these fertile floods, drought and famine might happen in many places. river in flood floodplain The Thames (TEMZ) Flood Barrier was built to prevent flooding in London. The floodplain is the low area covered by a river during a flood. 4 5
Deltas So how does a flooding river work? As it moves downhill over rocks and land, it collects soil particles rich in nutrients. When the river reaches flatter ground, it slows down. Most rivers flow into a lake, sea, or ocean. When a river reaches the lake, sea, or ocean, it drops its particle load. Over a long period of time, this material forms an area of land at the mouth of the river, called a delta. Deltas are made fertile by the nutrients they receive from floods. There are fertile deltas all over the world. For people who live near these deltas, the river can be both a friend and an enemy. If the river does not flood enough, people may suffer drought and famine. If it floods too much, then property is damaged and people are hurt. So everyone hopes the river floods just enough! When rivers flood, they do more than irrigate floodplains and spread minerals. They also change the shape of the land. Some land gets eroded, or washed away. Other land gets this washed away material, which builds up. And the river itself sometimes changes its course. To prevent such changes, many countries have dammed their major rivers. Later you will read about the damming of the Nile and its results. Rivers move quickly on steep land. When they reach level land, they slow down and spread out. Floodplain The Mississippi Delta covers an enormous amount of land in the southeastern United States. Delta 6 7
The Nile The Nile River is the longest river in the world. It has always been the center of life for Egyptians. The capital of Egypt, Cairo, is on the Nile. So is Khartoum, the capital of Sudan. Farther to the south, a branch of the Nile begins at Addis Ababa, the capital of Ethiopia. Although the Nile flows for hundreds of miles in Egypt, it gets its water from countries such as Ethiopia. It rains a lot in Ethiopia during the summer. For thousands of years the Nile carried the water from Ethiopia s rains all the way to Egypt. In the past this caused flooding. These fertile fields were watered by the flooding of the Nile. The Nile brings life to the dry lands on either side of it. When the Nile flooded, it made the narrow strip of land on either side of the river very fertile. The flooding river provided the water and nutrients needed to grow crops. Sometimes the river rose too much or not enough. In the worst years it didn t rise at all, leading to terrible drought and famine. The corn, rice, wheat, and other crops grown along the Nile needed a lot of people to tend to them, so families started having more children. This made the famine years even worse, because there were so many more mouths to feed. The Egyptian government decided to take steps to try to solve the problems created by drought and famine. They built the Aswan High Dam. ancient Egyptian carving of a farmer plowing a field 8 9
The Aswan High Dam, built in 1970, has stopped the Nile s annual floods and controlled the water supply. During rainy years it stores water. During times of drought it releases water. The dam also generates electricity for all of Egypt. The Aswan High Dam keeps people and houses safe from floods. It also helps prevent drought and famine. However, the dam has also had some very bad effects. By stopping the floods it has prevented the silt suspended in the EGYPT Nile Aswan High Dam Lake Nasser SUDAN The Nile River and the Aswan High Dam water from reaching the land. This has forced Egyptian farmers to use man-made fertilizers. As time passes, their land grows more dry and unhealthy without the traditional silt deposits. These temple ruins needed to be moved to higher ground after the Aswan High Dam was built. This is a satellite image of the Aswan High Dam. The dam holds back a huge reservoir of water. Aswan High Dam Because the dam held back the flow of the Nile, some of the lands behind the dam were permanently flooded. Thousands of people who lived on these lands had to leave their homes. Some ancient Egyptian relics were lost under the water. The Egyptians tamed their wild river, but their land would never be the same. 10 11
Bangladesh Ganges Brahmaputra BANGLADESH Meghna Bangladesh s flooding regions Bangladesh is a small country near India. The deltas of three big rivers, the Ganges, the Brahmaputra, and the Meghna, form much of Bangladesh s land. These rivers start all the way up in the Himalayas. They end at the Indian Ocean. Bangladesh floods if there is a lot of snow melting in the Himalayas. It also floods if there is heavy rain upstream in India and elsewhere. The yearly rainstorms, called monsoons, also flood Bangladesh. The floods bring rich silt deposits, which make Bangladesh one of the most fertile places in the world. Farmers in Bangladesh are used to flooding. Many of them build their houses on stilts. That way when the floods come, the people don t have to leave! However, some years the flooding causes terrible devastation. It harms people and animals, washes away houses, and destroys crops. The farmers who live near Bangladesh s rivers must always be alert. Many Bangladeshi people have adopted ways to live above the floods. Bangladesh s flat land and many rivers flood easily. 12 13
Okavango Delta The Okavango River originates in Angola and flows through Namibia and Botswana, in southern Africa. This river is unique. It does not end at a lake, sea, or ocean. Instead, it ends at a wetland in the middle of the Kalahari Desert. This wetland is called the Okavango Delta, and it is one of the largest inland deltas in the world. The Okavango Delta is an oasis of life in the harsh desert. It floods every summer. This flooding irrigates and fertilizes the delta so that a variety of plants and animals can grow and live there. ANGOLA Whenever a river floods, it can cause destruction. But sometimes people depend upon floods to fertilize and irrigate their lands. Sometimes flooding even helps plants and animals. Rivers are not predictable. Sometimes they re supposed to rise, but fail to. Other times they do rise, but when they re not expected to! In the best years, rivers rise just the right amount, at just the right time. This is when the people and the land are happy to have a fertile flood! These elephants would not have enough to eat if it weren t for the flooding of the Okavango. Okavango NAMIBIA Okavango Delta BOTSWANA Okavango Delta The annual floods of the Okavango bring life to the Kalahari Desert. 14 15
Glossary delta drought famine an area of land that usually forms near the mouth of a river a severe shortage of water, caused by lack of rain or lack of expected flooding a food shortage that causes severe hunger and starvation What did you learn? 1. What makes a fertile flood so good for the farmers and the community? 2. What are some of the natural events that will cause the rivers to flood in Bangladesh? 3. What makes the Okavango River different from the other rivers you read about in this book? fertilize floodplain irrigate oasis to supply the minerals and nutrients that plants need to grow the area on either side of a river that is covered with water during a flood to transport water to plants to help them grow a fertile spot in the middle of the desert, caused by the presence of water 4. In this book you read about the flooding of the Nile River and the building of the Aswan High Dam. Write to explain how the Aswan High Dam has changed the behavior of the Nile River. Give examples of both good and bad effects of the Aswan High Dam. 5. Compare and Contrast What are the similarities between irrigating and fertilizing? What are the differences? 16