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Lesson 8 Aim: What is physical weathering? IV. Weathering: breaking down rocks Physical Weathering (a.k.a. mechanical weathering) - Physical weathering breaks down rocks without changing their composition 1. Frost Action a) When water freezes, it expands about 9 percent b) In places where T constantly goes above and below 32°F (here!): - water seeps into cracks in rocks, concrete, roadway - water freezes and expands, making cracks larger - repeats until pieces break off c) At high altitudes: large rocks are exposed, in spring and summer the temperature drops below freezing every night. Result: boulder field- large areas of broken rock. If cliff: collects at bottom d) Causes roads to warp, pushes rocks to surface each spring, creates potholes, cracks concrete Q: Why is it important to remove plants growing in concrete? 2. Plant Action - Soil and water get into the cracks in rocks and concrete - Plant seeds and spores fall into cracks, grow - First: moss and lichen. When they die, soil more fertile. - Then: weeds - Roots grow, breaking rock apart 3. Pressure Unloading - Rock deep under the crust is under pressure, creates joints (cracks) and strain (line of weakness) in the rock. - Pressure (weight of material above) keeps the rock from splitting - Rock comes to the surface: due to earthquake, erosion (material worn away: water? wind? etc.), landslide, frost action, etc. - Sudden removal of pressure causes rock to split V. Chemical Weathering: objects on Earth's surface react with an agent and change into a new substances DNQ: Why do some people fall on the sidewalk? DI EARTH SCIENCE 1 DO NOW 1. What are sediments? _________________________________________________________________________ 2. What are three major ways of turning rocks into sediments? _________________________________________________________________________ 3. Why are we interested in learning why rocks becoming sediments? _________________________________________________________________________ EARTH SCIENCE 1 CLASSWORK 1. a) Why do the Park Department turn off water to unheated restrooms and water fountains? _________________________________________________________________________ b) What are some ways to winterize an unheated vacation home in Vermont? _________________________________________________________________________ 2. Why are plants undesirable in the concrete joints or near a building? _________________________________________________________________________ 3. What may happen if people take apart the pyramid or the stonehedge? _________________________________________________________________________ 4. Weathering a) What is physical weathering? _________________________________________________________________________ b) What is chemical weathering? _________________________________________________________________________ c) How do physical and chemical weathering compare? _________________________________________________________________________ 5. a) How many seismic stations is required to locate an earthquake epicenter? _________________________________________________________________________ b) Explain your answer for the minimal number of seismic stations? _________________________________________________________________________ NAME__________________________________________________________________ EARTH SCIENCE 1 H.W. 4-8 READ: EARTH SCIENCE Pages 149-151 1. Define weathering _________________________________________________________________________ _________________________________________________________________________ 2. Physical Weathering a) What is frost action? _________________________________________________________________________ _________________________________________________________________________ b) How do boulder fields form? _________________________________________________________________________ _________________________________________________________________________ c) Why would there be no frost action in Antarctica, even though there is ice all year around? _________________________________________________________________________ _________________________________________________________________________ d) Why are there pieces of rock at the bottom of a cliff face? _________________________________________________________________________ _________________________________________________________________________ e) Why must you pull weeds out of the concrete in front of your house? _________________________________________________________________________ _________________________________________________________________________ f) What is pressure unloading? _________________________________________________________________________ _________________________________________________________________________