CHARACTERISTICS OF RIVERS AND OCEANS?

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Donald Hall
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1 WHAT ARE THE CHARACTERISTICS OF RIVERS AND OCEANS? We depend on rivers and oceans for our survival. When they are threatened, all life on Earth is in trouble. We need to figure out what is harming our rivers and oceans and how to prevent more damage. The first step is to try to understand the characteristics and patterns of rivers and oceans. PHYSICAL CHARACTERISTICS OF RIVERS As rivers flow, from beginning to end, they are changed by the land. Their own shapes and patterns change. As well, they shape the land and affect the habitats of living things. PARTS OF A RIVER A river has many different parts. Read through Figure 4.5 to understand what each part is. Figure 4.6 illustrates the different parts of a river. River Part watershed drainage basin source tributary channel floodplain meander riverbank river bed delta mouth What is it? the line of high ground that separates water flowing in one direction from another the area drained by a river system where a river or stream begins, for example, a spring or glacier high in the mountains a stream or river that flows into a larger one the depression where water flows; the path a river takes flat, low-lying area near a river or stream that may be regularly flooded loop or bend in a river the land on the sides of the river the bottom of a river a plain formed by a deposit of sediment where a river enters a lake or ocean, typically in a triangular shape the part of the river where it flows into a larger body of water FIGURE 4.5 This chart explains the different parts of a river. 108 UNIT 1: Physical Patterns in a Changing World NEL

source watershed watershed tributaries drainage basin channel lake watershed main river channel floodplain river bank mouth meander delta drainage basin FIGURE 4.6 The parts of a river.

The change depends on the type and slope of the land they are moving through. A river running down a steep slope near its source will be straight and flow quickly.

It may deposit the materials in other locations. Its own shape changes. It may form meanders or a braided pattern. Meanders form on slow-moving rivers over land with little slope.

The river deposits any material it is carrying on the inner river bank, where the water is moving more slowly. This makes the water here more shallow over time.

2 source watershed watershed tributaries drainage basin channel lake watershed main river channel floodplain river bank mouth meander delta drainage basin FIGURE 4.6 The parts of a river. The river bed (not pictured) is the bottom of a river. RIVER PATTERNS As rivers flow, they often change the land through which they flow. They do this by erosion and deposition. The change depends on the type and slope of the land they are moving through. A river running down a steep slope near its source will be straight and flow quickly. A river running down a gentler slope, closer to where it will enter a lake or the sea, may have curves and flow more slowly. A river may erode material from its banks. It may deposit the materials in other locations. Its own shape changes. It may form meanders or a braided pattern. Meanders form on slow-moving rivers over land with little slope. In these areas, rivers curve. As the water flows into a curve, it strikes the outer river bank. If the river bank is made of soft rock, it will erode. This makes the meander larger over time. The river deposits any material it is carrying on the inner river bank, where the water is moving more slowly. This makes the water here more shallow over time. It is difficult for a shallow river flowing over a flat area to carry a heavy load of sediment. It may drop the materials, which form small bars. The river becomes a maze of interconnected channels as it flows around them. This makes a braided pattern (Figure 4.7). NEL deposition the process by which weathered material is laid down or deposited by wind, water, and ice FIGURE 4.7 This braided river is Hopkins River near Lake Ohau in New Zealand. How would I explain to a classmate how a braided river is formed? CHAPTER 4: Patterns of Rivers and Oceans 109

3 READING AND ANALYZING TOPOGRAPHIC MAPS You read about topographic maps on pages 22 to 23 when you learned how to read elevations on maps. You can use the contour lines on a topographic map, such as on Figure 4.8, to draw cross-sections or profiles of landforms so you can see the shape of the land. We can read and analyze topographic maps by drawing cross-sections. Follow the steps below to draw a cross-section as shown in Figure 4.8. N Topographic Map, Bow River Valley, Alberta 1800m 1600m Bow Valley Parkway m 520 m 1400m 1800m 1600m 1400m 1800m 2000m forest picnic area trail road railroad FIGURE 4.8 This map of a section of the Bow River Valley in Alberta is part of a larger map. Not all the details shown on the larger map are included on this small section. DRAWING CROSS-SECTIONS USING TOPOGRAPHIC MAPS Place the edge of a piece of paper along the line A-B on Figure 4.9. Mark where each contour meets the paper. To each of the marks, add the elevations from each contour. STEP 1 A B Place your marked paper along the x axis. Label A where x and y meet. Label B at the appropriate point along the y axis. Add a title: Cross-Section along A-B. Draw another cross-section: a section of the Bow River Valley (Figure 4.8). Your A-B line should go from the top of the map to the bottom. It should run through the highway bridge across the river. Add labels to your cross-section to describe the valley s shape. STEP 2 STEP 3 STEP 4 STEP 5 STEP 6 STEP 7 1 cm 10 km (1: ) FIGURE 4.9 Contour lines On another paper, begin a graph. Draw an x axis and a y axis. Write numbers on the y axis that correspond to the numbers on the contour lines. Transfer the marks from your paper edge to the graph by adding dots at the correct elevation. Join the dots with a pencil line. Find a hilltop, a steep slope, and a gentle slope on the cross-section. Label each. Label the scales Vertical scale 1 cm = 25 m and Map scale 1 cm = 10 km. 110 UNIT 1: Physical Patterns in a Changing World NEL

They grow along two-thirds of coastlines of tropical areas of the world, including deltas and estuaries. RIVERS AFFECT THE LAND Rivers shape the land as they flow over it.

4 FIGURE 4.10 Houses built along a channel on the Mississippi River delta What risks would I face if I lived here? FIGURE 4.11 Mangrove forests, like this one in Thailand, are among the most biologically diverse forests. They grow along two-thirds of coastlines of tropical areas of the world, including deltas and estuaries. RIVERS AFFECT THE LAND Rivers shape the land as they flow over it. They may form valleys, floodplains, and deltas. When water flows through the mouth of a river into a large body of standing water, such as a lake or ocean, the river slows down. It deposits the sediment it is carrying near its mouth, generally forming a delta (Figure 4.10). The sediment can sometimes spread out into the sea, forming fingers through which the river flows. Delta land is very fertile. For example, the Ganges Delta in India and Bangladesh is one of the most fertile regions in the world. Deltas are very low land, and when rivers rise, the land floods. Some rivers have raised banks, or levees, which have formed naturally. Sometimes people build levees to protect their homes from flooding. An estuary is a partly enclosed body of water and a unique ecosystem. As the fresh water of the river mixes with the ocean s salt water, it stirs up sediment. This water creates excellent growing conditions for water plants, providing them with the minerals they need. Animals feed on the plants. The world s largest estuary is the Gulf of St. Lawrence. Many large cities are built on estuaries, including Jakarta, Indonesia, and Tokyo, Japan. I wonder why mangrove forests are so biologically diverse? How do they compare to rainforests? levee a raised bank on the edge of a river channel estuary a body of water along a coast where the river meets the sea and that contains a mix of fresh and salt water What might be one advantage of living beside a river? RIVERS AFFECT HABITATS Rivers are ecosystems. They provide a variety of habitats for plants and animals that may live in the water itself, on the riverbed, or on the riverbanks. There are also many types of habitats surrounding estuaries, depending on the local rocks and climate. These include mud flats, salt marshes, and mangrove forests (Figure 4.11). NEL CHAPTER 4: Patterns of Rivers and Oceans 111

5 CHARACTERISTICS OF OCEANS The ocean s water is always on the move. As it moves, the water forms patterns. As well, the massive amounts of moving water affects the land, the climate, and the ocean and coastal ecosystems. NATURAL CHANGES TO OCEANS There is evidence that ocean temperatures and global ocean currents change naturally over time. For example, the Gulf Stream current has stopped flowing across the Atlantic Ocean several times over the past million years. As well, as you learned in Chapter 1, the ocean floors change. As Earth s plates shift, they slowly cause sections of the sea floor to spread. The Atlantic Ocean is getting wider. The Pacific plate is sliding under plates along its western edge. As a result, the Pacific Ocean is getting smaller. GEOGRAPHY AT WORK MARINE GEOLOGIST Christina Symons (Figure 4.12) graduated from university with a degree in geology. Geology is the study of Earth, including its history and its structure. Then, while she was working on a master s degree, she got involved in a research study mapping the ocean floor near New Zealand. Everything up until then had been land-based, she recalls. Then I just fell in love with the ocean. The experience inspired Symons to switch the focus of her studies. She went on to earn a master s degree in underwater geology and then completed a PhD in geology. Marine geologists study the ocean floor and the natural processes that take place there. FIGURE 4.12 Dr. Christina Symons, sitting in the pilot s sphere of the Mermaid Sapphire submarine This means learning about everything from volcanic eruptions to plate tectonics. They sometimes look for natural resources, such as gas, oil, and minerals. They also map, and help predict, damage to the ocean floor caused by natural disasters. Symons is continuing as part of the team mapping the ocean floor along the rim of the Pacific Ocean Basin. In 2012, she was a member of the team supporting filmmaker James Cameron s solo dive to the deepest known point in the ocean. GPS, or the Global Positioning System, is an important mapping tool for Symons. It is a navigational system. Satellites orbiting around Earth send signals to GPS receivers. People use the receivers to locate their exact position. It s one thing to collect high-resolution images of the sea floor, says Symons, but you must know where you are on the Earth to make a useful map. What excites Symons about her work? As she says, The best part is we are mapping the sea floor that no one has ever seen, and for the most part, no one has ever mapped. So we are learning something about a brand-new place. MAKING CONNECTIONS 1. How does a career in marine geology connect with geography? 2. In what ways might mapping the ocean floor be different from mapping land that is above sea level? 112 UNIT 1: Physical Patterns in a Changing World NEL

6 OCEAN PATTERNS: GLOBAL CURRENTS Ocean currents are flows of seawater that move in one direction. Some currents are deep over 400 m below the surface and some are at the surface of the ocean. Deep currents are flows of cold water. Surface currents are warmed by the Sun and pushed by winds. As the warm surface water is moved away, cooler water is drawn up from below. This circulation creates a global pattern of ocean currents (Figure 4.13). The currents flow in roughly circular patterns known as gyres. In the northern hemisphere, they move in a clockwise direction. In the southern hemisphere, they move in a counterclockwise direction. Warm currents begin in the tropics. They bring warm water toward the cooler regions. Cold currents begin in the polar regions. They bring cool water toward the tropics. In this way, ocean currents help move energy around the globe. gyre a large, circular oceanic surface current Arctic Circle Global Ocean Currents ARCTIC OCEAN EUROPE Tropic of Cancer NORTH AMERICA ATLANTIC OCEAN ASIA PACIFIC OCEAN AFRICA Equator Tropic of Capricorn PACIFIC OCEAN SOUTH AMERICA INDIAN OCEAN AUSTRALIA N Antarctic Circle km ANTARCTICA cold current warm current The Gulf Stream, which moves warm water from the tropics into the North Atlantic, is one of the strongest ocean currents. It starts in Florida and follows the east coast of the United States and Newfoundland, where it crosses into the Atlantic Ocean. It is a large, powerful ocean current. The Gulf Stream influences the climate of both the east coast of North America and the west coast of Europe. It can also make cyclones and hurricanes stronger and more damaging. FIGURE 4.13 This map shows the warm and cold ocean currents of the world. NEL CHAPTER 4: Patterns of Rivers and Oceans 113

~ El Nino a mass of warm water that travels from the western to eastern Pacific ~ La Nina cooling of surface water near South America Why might meteorologists study ocean currents to make predictions

7 ~ El Nino a mass of warm water that travels from the western to eastern Pacific ~ La Nina cooling of surface water near South America Why might meteorologists study ocean currents to make predictions about the weather? OCEAN PATTERNS: EL NIÑO AND LA NIÑA On page 113, you saw a map of the pattern formed by the ocean s warm and cold currents. El Niño is another example of a pattern formed by an ocean. Every two to seven years, a change in the regular currents in the Pacific Ocean occurs. Warmer water is pushed from the western Pacific across to the eastern Pacific near South America. This is called El Niño. These conditions bring warmer, wetter conditions to South America and warmer and drier weather to much of North America. El Niño conditions can last for up to two years. La Niña is a cooling of the surface water near South America. Every three to five years, it creates weather conditions that are the reverse of El Niño conditions. These conditions affect global climate patterns and local weather. They can result in more storms, higher precipitation, and more extreme seasonal temperatures. For example in 1982 to 1983, there were severe storms in the southern United States and droughts in Australia. In 1997 to 1998, there were severe droughts in the Western Pacific and record-breaking high temperatures globally. Figure 4.14 shows a 2011 flood in Thailand caused by monsoon rains. Experts blamed La Niña for the heavy rains that year. OCEANS CHANGE THE LAND When waves and currents reach the shoreline, they can erode rocks and cliffs, over time. They can create features such as sea stacks (Figure 4.15). They can wear down stones and shells of sea life into grains of sand. They can also transport sediment and deposit it to form long narrow bands of sand called sand spits. OCEANS AFFECT THE CLIMATE As you read in Chapter 2, the oceans are part of the climate system. Currents on the surface of the ocean and the winds move the heat from the equator to other, colder parts of the world. This affects the climates from region to region. OCEANS AFFECT HABITATS One reason oceans are so important is because they offer many different habitats for plants and animals. Coastlines are where land meets ocean. The mixing of both land and water elements provides homes to many plant and animal species. As well, the shallow areas of the ocean close FIGURE 4.14 In 2011, officials at the National Disaster Warning Foundation blamed a prolonged La Niña cycle for unusually heavy monsoon rains that caused flooding in central and northern parts of Thailand. I wonder what a diagram of El Nino ~ and La Nina ~ would look like? 114 UNIT 1: Physical Patterns in a Changing World NEL

FIGURE 4.15 These cliffs and sea stacks, called the Twelve Apostles, are on the south coast of Australia. I wonder what kind of stone these sea stacks are?

8 FIGURE 4.15 These cliffs and sea stacks, called the Twelve Apostles, are on the south coast of Australia. I wonder what kind of stone these sea stacks are? to land the continental shelves right down to the deepest parts of the ocean contain life. Differences in the amount of light, temperature, and chemical makeup of the water create a variety of habitats as the depths increase. For example, water moves from deep in the ocean up to the surface. The deeper, colder layers of the ocean contain nutrients and carbon dioxide (CO2). As they rise, they bring the nutrients and CO2 to the warmer surface layers. This allows different types of algae to grow in the sun. In turn, many forms of life feed on these plants. In this way, oceans affect the living conditions of many marine plants and animals. continental shelf the shallow gently sloping submerged zone of a continent next to an ocean algae a simple plant ranging from one-celled forms to seaweed and giant kelp marine relating to the sea CHECK-IN 1. COMMUNICATE Create a model showing different parts of a river. Include different drainage patterns in your model. 2. INTERRELATIONSHIPS Make sketches to identify two river features that can create challenges for people. Label your sketches to show how these features can present problems. NEL 3. INTERPRET AND ANALYZE What are some key ways in which the ocean is similar to, and different than, the land? CHAPTER 4: Patterns of Rivers and Oceans 115

Chapter 1 Section 2. Land, Water, and Climate

Chapter 1 Section 2. Land, Water, and Climate Chapter 1 Section 2 Land, Water, and Climate Vocabulary 1. Landforms- natural features of the Earth s land surface 2. Elevation- height above sea level 3. Relief- changes in height 4. Core- most inner