Rising Sea Levels Rising Sea Levels

Over millions of years, Earth’s sea levels have risen and fallen. This is natural. Why does this happen? And how does it affect Earth’s surface?

During cold climate periods, or ice ages, the sea level falls. Water evaporates from the oceans. That precipitation becomes ice in gigantic glaciers and huge ice fields. About 20,000 years ago, it was much colder than it is today. The sea level was about 400 feet (125 meters) higher than it is now. That’s as tall as ten school buses stacked on end! But, as the climate warmed, a lot of the ice melted back into the oceans and the sea levels rose.

Sea levels are highest during warm climate periods, or inter-glacials. We are in an inter-glacial now. This period started about 10,000 years ago.

Rising Sea Levels

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One place that is affected by rising sea levels are the Maldives, a group of small islands in the Indian Ocean. It is one of the smallest countries on Earth. It’s also the lowest. The highest point of land is only seven and a half feet above sea level. If the sea levels keep rising, the Maldives could disappear completely!

Ocean water is also warmer. And, warm water takes up more space than cold water. Each drop of water expands as it gets warmer.

So how does the sea level change the surface of Earth? The land in very cold places, like Greenland and Antarctica is different. Glaciers and fields of ice are melting. Plants and animals that need a cold climate can’t live there anymore.

In places near the ocean, land is getting flooded more and more. Beaches are becoming smaller because the sand is being taken out to sea. Salt water from the ocean moves into freshwater rivers and streams. The plants and animals there have to move to other places with fresh water.

Maldives

India


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Have you ever wondered how the surface of Earth gets many of its different shapes? It’s partly because of erosion.

Erosion is the process that breaks things down. During erosion, small pieces of rock or soil move from one place to another. So, you can think of erosion as a way that bigger things are broken down into smaller things.

The usual tool of erosion is water. Think about a rock that you pick up at the ocean or in a river. It is probably very smooth. That’s because, over time, water has worn off all the sharp pieces. Now think about the mud next to a river or stream. That’s an example of erosion. The water is brown because it has taken away many tiny bits


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Erosion

over again. The rocks break and the water takes them away. On a sandy beach, the waves take away the sand and put it somewhere else.

Wow! Did you ever think that the same water you drink could change Earth’s surface?

of soil. And the shape of the river or stream is changed, even if only a little. Water can even break large boulders. It doesn’t seem like water is strong enough to break down and carve out rock, does it? However, moving water is amazingly powerful.

One famous example of erosion by water is the Grand Canyon. For five million years, the rushing water of the Colorado River broke off small pieces of rock and carried them away toward the sea. Today, the Grand Canyon is one mile deep and, in some places, eighteen miles wide. And it’s all because of erosion!

Erosion also changes the shape of coastlines. Waves hit rocks over and


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DID YOUKNOW?

At the bottom of the Grand Canyon are rocks that are 1.8 billion years old.

Water is a powerful force. And in its solid form, ice, it can change the shape of mountains and valleys.

A glacier is a river of ice. As a glacier moves, it erodes the land. How does it do this? There are two ways.

The first way is called plucking. Plucking is when the glacier breaks off, or plucks, large pieces of the ground and carries them away. These large pieces leave big holes and long, deep grooves in the ground.

The second way is called abrasion. Abrasion is when the glacier takes away smaller pieces of rock. These smaller pieces act like sandpaper to Earth’s surface. They smooth down and polish larger rock surfaces.

Glaciers

DID YOUKNOW?

Ten percent of land area on Earth is covered with glacial ice.


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Many fjords have coral reefs at the bottom. These reefs are the home of many kinds of fish and plant life.

Skerries are found near fjords. A skerry is a small rocky island. Skerries are formed by glaciers, too.

Glaciers take away soil and rocks, but when they do that, they make islands, valleys, and even a place for fish to live!

Erosion by glaciers happens very slowly. How slowly? It can take a glacier hundreds or even thousands of years to change the surface of Earth.

One example of glacial erosion is in California’s Yosemite National Park. In Yosemite, glaciers have carved away the sides of mountains, making high rock walls and deep valleys.

Another example of glacial erosion are the fjords in Norway. A fjord is a long, narrow inlet of water that starts inland and goes out to sea. The glaciers cut out valleys with high, steep sides. A fjord can be thousands of meters deep. The water of a fjord is very calm, so it is a good harbor for boats.


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Earth’s surface is always changing. One way that it changes is by frost wedging. Frost wedging happens in many places in the world where the temperature rises above or falls below the point of freezing (32 degrees Fahrenheit). So how does frost wedging happen?

Rocks have cracks that start on the surface but don’t go all the way through the rock. These cracks are called joints. When it rains, water falls

into the cracks in the rocks. The water can stay in the joints for a long time. Then, when the temperature goes below freezing, the water becomes ice.


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Frost Wedging

rock breaks apart and the pieces tumble down.

You can see where frost wedging has happened around you. Just look for places with lots of sharp, broken up rocks, like at the bottom of a hillside. Or, large rocks that have big splits down the middle of them.

Believe it or not, water can change its volume, or how much space it fills. When water goes from liquid to solid, it expands, or gets bigger. So, when the water in the joint freezes and becomes ice, it gets bigger. This ice pushes against the sides of the joint, just like if you were standing in the middle of the joint and pushing the sides apart with your arms. The joint becomes wider.

Then, when the temperature rises and the ice melts, it rains again. Now, the joint is a little wider and more water can get into it. When the temperature drops again, the water freezes, expands, and pushes the joint open a little more. This process happens again and again until the


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DID YOUKNOW?

It can take a year for a rock to crack from frost wedging.

Water is a powerful force of nature. When there is too much water too fast, it’s called a flood. A flood can change Earth’s surface.

Flooding can happen anywhere with rivers, a coastline, or streams. One example of flooding is when there are days of heavy, steady rain. The water level in the river rises and goes over its banks. Another way a flood can happen is when snow melts very quickly and the water runs into the rivers. Then the river overflows. One more example of flooding is when wind from a storm in the ocean pushes large amounts of water onto land.

One kind of flooding happens quickly and without much notice. It’s called a flash flood. A flash flood happens when there is a lot of rain


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1Connecting Passage

then pile up at a narrow point or turn in the river. This ice jam stops the natural flow of the river and the river overflows its banks.

Any kind of flood can destroy farms and make them unusable. But floods can also be helpful. A flood can bring a large amount of water and sediments to fields. These sediments give the land nutrients so crops can grow.

in a short period of time. A river floods with no warning to the people who live around it. In a narrow canyon or valley, floodwater can flow very quickly. It can be extremely destructive. It can wash away houses and trees, farms and buildings. A flash flood on a mountain can erode the soil and wash it down the slopes.

Flash floods can also happen because of an ice jam. In cold weather, the waters of a river can turn to ice. If the weather warms up suddenly, the ice can break into big chunks. These big chunks can move down the river and

DID YOUKNOW?

Flooding along the banks of the Nile River in Egypt is an example of good flooding. In ancient times, farmers knew that the higher the flood waters, the better their crops would be.


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Student ReSponSe Sheet IndIvIdual ReadIng

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Key Question

How does water change Earth’s surface?

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1. Read the Key Question. Then read the passage. Look for information in the article that helps you answer the Key Question. Circle or underline these details.

2. Now look back at the article. Write the details you circled or underlined on the Main Idea and Details Ladder below.

3. Think about the Key Question. Write your answer to the Key Question using the details you found in the article you read.

My First Answer

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Student ReSponSe Sheet Team dIscussIon

Main Idea:

Key Question


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Meet with your team. Talk about each article your team read.

1. Tell the team what you learned in the article you read. Show the Main Idea and Details Ladder you made.

2. Look at the ladders your team made. Compare the details in each of your stories by looking at the information in your Main Idea and Details Ladders. Answer these questions together.

•How is the main idea in each article similar?

•Inwhatwaysdoeswateroftenchangeasurface?

Next, write the details that answer the Key Question on the Main Idea and Details Ladder below. Write only the details that are in every article your team read.

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Rising Sea Levels Rising Sea Levels

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