7 th Grade Lesson What is weathering and how does it change Earth s surface? Answer the question using the sentence frame. You have 4 minutes. Weathering is. This changes the Earth s surface because. 1
Objectives CONTENT OBJECTIVE(S) SWBAT: Analyze the effects of physical and chemical weathering on Earth s surface, including each kind of weathering. Relate the processes of erosion and deposition by water to the landforms that result from these processes. Describe erosion and deposition by wind, ice, and gravity as well as identify the landforms that result from these processes. LANGUAGE OBJECTIVE(S) Define weathering, physical weathering, chemical weathering, biological weathering, abrasion, oxidation, acid precipitation, erosion, and deposition. Answer checking for understanding questions aloud using the sentence frames provided on the slides. Next Generation Science Standards 2
Vocabulary: Weathering: the break down of rock material by physical and chemical processes. Physical weathering: the process by which rock is broken down into smaller pieces. Chemical weathering: the break down of rocks by chemical reactions. Biological weathering: is the weakening of rock by plants, animals and microbes. Abrasion: the breaking down and wearing away of rock material by the mechanical action of other rock. Vocabulary: Oxidation: the process by which other chemicals combine with oxygen. Acid precipitation: rain, snow, or sleet that contains high concentration of acids. Erosion: the process by which wind, water, ice, or gravity moves soil and sediment from one place to another. Deposition: the process in which material is laid down. 3
Weathering There are different types of weathering physical, biological, mechanical, and chemical. Physical, Chemical, or Biological? How do you know this? 4
Physical, Chemical, or Biological? How do you know this? Physical, Chemical, or Biological? How do you know this? 5
What causes physical weathering? Rocks can get smaller and smaller without a change in the composition of the rock. What causes physical weathering? Temperature change Gravity Pressure change Causes of physical weathering Wind Plant and animal actions Water 6
What causes physical weathering? TEMPERATURE CHANGE: Rise in temperature can cause a rock to expand. Decrease in temperature can cause a rock to contract. Repeated changes in temperature can cause the rock to crumble. Ice wedging or frost wedging can cause the rock to physically break a part. PRESSURE CHANGE: Rocks formed under pressure deep within Earth can become exposed. Exfoliation is the process by which the outer layers rock slowly peel away due to pressure change. What causes physical weathering? TEMPERATURE CHANGE PRESSURE CHANGE 7
What causes physical weathering? PLANT AND ANIMAL ACTION: Many animals dig holes into the ground, allowing rocks to be exposed. Roots can grow inside small cracks in rocks. The bigger the roots the more pressure it puts on rock. WIND, WATER, AND GRAVITY Wind, water, and gravity can cause abrasion. In water, rocks can become smooth and round. Wind can carry small particles and blast away at surfaces and wear them away. Gravity can cause large rocks and break more rocks below (landslide). What causes physical weathering? PLANT AND ANIMAL ACTION: WIND, WATER, AND GRAVITY 8
Checking for understanding: What are factors that causes physical weathering? One thing that causes physical weathering is. How can plants cause physical weathering? Plants can cause physical weathering by. How can animals cause physical weathering? Animals can cause physical weathering by. How can gravity cause physical weathering? Gravity can cause physical weathering by. How can water cause physical weathering? Water can cause physical weathering by. How can pressure cause physical weathering? Pressure can cause physical weathering by. How can temperature cause weathering? Temperature can cause weathering by. What causes chemical weathering? Things that cause chemical weathering include oxygen in the air and acids. 9
What causes chemical weathering? REACTIONS WITH OXYGEN Oxygen reacts with compounds that make up rocks and causes a chemical change. Sometimes rock changes color. Rocks can contain iron and when combined with oxygen it turns it into rust (oxidation). REACTIONS WITH ACID PRECIPITATION Acids break down most minerals faster than water. Acid precipitation causes rocks to break down and change composition. What causes chemical weathering? REACTIONS WITH OXYGEN REACTIONS WITH ACID PRECIPITATION 10
What causes chemical weathering? REACTIONS WITH ACIDS IN GROUND WATER Ground water can contain acids and cause rocks to dissolve. Small cracks can form caves over time under Earth s surface. Stalagmites and stalactites are common features in cave systems that shows chemicals are deposited by dripping water from underground. REACTIONS WITH ACIDS IN LIVING THINGS Some living things produce acids. Lichen and mosses grow on rocks and produce weak acids that can weather rocks. What causes chemical weathering? REACTIONS WITH ACIDS IN GROUND WATER REACTIONS WITH ACIDS IN LIVING THINGS 11
Checking for understanding: What are factors that causes chemical weathering? One thing that causes chemical weathering is. How can oxygen cause chemical weathering? Oxygen can cause chemical weathering by. How acid precipitation cause chemical weathering? Acid precipitation can cause chemical weathering by. How can acids in ground water cause chemical weathering? Acids in ground water can cause chemical weathering by. How can acids in living things cause chemical weathering? Acids in living things can cause chemical weathering by. Place the correct cards into the table base on the different types of weathering be sure of your answers before gluing it on. 12
Erosion and Deposition by Water CONTINUATION How does flowing water change Earth s surface? Rivers and other bodies of flowing water carry million of tons of rocks and soil across the U.S.. http://earthobservatory.nasa.gov/iotd/view.php?id=79677 13
How does flowing water change Earth s surface? BY EROSION Rivers and streams erode soil, rock, and sediment. Sediment is tiny grains of broken-down rock. Eroded materials in streams may come from stream s own bed and banks or from runoff. Over time, erosion causes streams to widen and deepen. BY DEPOSITION After streams erode rock or soil, they eventually deposit their load downstream. Deposition occurs when gravity s pull is greater than the push of flowing water or wind. A stream deposits materials along its bed, banks, and mouth, which can form different landforms. How does flowing water change Earth s surface? BY EROSION BY DEPOSITION 14
What factors relate to a stream s ability to erode material? Some streams are able to erode large rocks, while others can erode only very fine sediment. A stream s gradient, discharge, and load are the three main factors that control what sediment a stream can carry. What factors relate to a stream s ability to erode material? GRADIENT Gradient is the measure of the change in elevation over a certain distance. Gradient is similar to the steepness of a slope. Water in stream with a high gradient moves very rapidly because of the downward pull of gravity. This gives the water a lot of energy to erode rock and soil. Energy of erosion is also called erosive energy. LOAD Materials carried by a stream are called stream s load. The size of the particles in a stream s load is affected by the stream s speed. Fast-moving streams can carry large particles. A stream that has a load of large particles has a higher erosion rate. 15
What factors relate to a stream s ability to erode material? GRADIENT LOAD What factors relate to a stream s ability to erode material? DISCHARGE The amount of water that stream carries in a given amount of time is called discharge. The discharge of a stream increases when a major storm occurs or when warm weather rapidly melts snow. As the stream s discharge increases, its erosive energy, speed, and load increase. 16
What landforms can streams create? A stream is formed when water erodes soil and rock to make a channel. A channel is the path that the stream follows. As the stream continues to erode rock and soil, the channel gets wider and deeper. Over time, different landforms can form such as: Canyons and Valleys Floodplains Deltas and Alluvial Fans Canyons and Valleys by Erosion Six million years ago, Earth s surface in the area now known as the Grand Canyon was flat. The Colorado River cut down into the rock and formed the Grand Canyon over millions of years. Canyons and valleys are created by the flow of water through streams and rivers. As the water moves, it erodes rock and sediment from the stream bed. The flowing water can cut through rock, forming steep canyons and valleys. 17
Canyons and Valleys by Erosion CANYON VALLEY Floodplains by Deposition When a stream floods, a layer of sediment is deposited over the flooded land. Many layers of deposited sediment can form a flat area called a floodplain. Sediment contains nutrients needed for plant growth, because of this, floodplains are often fertile. A stream can may run straight in some parts and curve in other parts. Curves and bends form a twisting, looping pattern in a stream channel called meanders. During a flood, a stream may cut a new channel that bypasses a meander. The cut-off meander forms a crescent-shaped lake which is called an oxbow lake. 18
Floodplains by Deposition FLOODPLAINS MEANDER AND OXBOW LAKE Deltas and Alluvial Fans by Deposition When a stream empties into a body of water, such as a lake or an ocean, its current slows and it deposits its load. Streams often deposit their loads in a fan-shaped pattern called delta. Over time, sediment builds up in a delta, forming a new land. A similar process occurs when a stream flows onto a flat land surface from mountains or hills. On land, the sediment forms an alluvial fan. An alluvial fan is a fan-shaped deposit that forms on dry land. 19
Deltas and Alluvial Fans by Deposition DELTAS ALLUVIAL FAN What landforms are made by groundwater erosion? Movement of water underground can also cause erosion. Groundwater is the water located with the rocks below Earth s surface. Acidic groundwater can cause rocks to dissolve. When this occurs, it forms caves. Carves are formed by erosion but they show signs of deposition. Water can drip through cracks leaving behind icicle-shaped deposits called stalactites and stalagmites. 20
What forces shape a shoreline? A shoreline is the place where land and a body of water meet. Ocean waves crashing against the shoreline have a great deal of energy. Strong waves erode material. Gentle waves deposit materials. Ocean water has currents, or stream like movements of water. Currents can also erode and deposit materials. What forces shape a shoreline? WAVES Waves play a major part in building up and breaking down a shoreline. The first part of the shoreline that waves meet are the headlands. A huge amount of energy is released when waves crash into headlands, causing the land to erode. Waves with very little energy deposits material rather than erode. CURRENTS A longshore current is when water travels almost parallel to the shoreline very near the shore. Long shore currents are caused by waves hitting the shore at an angle. 21
What coastal landforms are made by erosion? Sea Cliffs Wave-cut Platforms Sea Caves Arches Stacks What coastal landforms are made by erosion? SEA CLIFFS AND WAVE-CUT PLATFORMS Sea cliff forms when waves erode and undercut rock to make steep slopes. As a sea cliff erodes above the waterline, a bench of rock usually remains beneath the water at the cliff s base. This bench is called a wavecut platform. SEA CAVES, ARCHES, AND STACKS Waves can cut deeply into the cracks and form large holes. When the holes continue to erode, they become sea caves. As sea caves further erode it becomes a sea arch. When the top of the sea arch collapses, its sides become sea stacks. 22
What coastal landforms are made by erosion? SEA CLIFFS AND WAVE-CUT PLATFORMS SEA CAVES, ARCHES, AND STACKS What coastal landforms are made by deposition? Waves and currents carry materials such as sand, rock, dead coral, and shells. These materials are often deposited on shorelines where they form a beach. A beach is an area of shoreline that is made up of material deposited by waves and currents. 23
What coastal landforms are made by deposition? BEACHES Not all beaches are made of sand. The size and shape of beach material depend on far the material has traveled from its source. Size and shape also depend on the type of material and how it is eroded. Stormy seas: beaches may be made of pebbles and boulders. SANDBARS AND BARRIER ISLANDS A sandbar is an underwater or exposed ridge of sand, gravel, or shell materials. A barrier island is a long, narrow island, usually made of sand, that forms parallel to the shoreline a short distance offshore. What coastal landforms are made by deposition? BEACHES SANDBARS AND BARRIER ISLANDS 24