Transcript Slide 1
Water Erosion: How do processes involving water change Earth’s surface? Part 1 1 What is the MAJOR agent of erosion that has shaped Earth’s land surface? moving water 2 Water moving over land’s surface is called runoff. Runoff may cause sheet erosion. 3 The amount of water runoff in an area depends on 5 main factors: 4 Factors that affect Runoff 1. The amount of rain an area receives. *More rain = more runoff 2. Vegetation - grasses, shrubs & trees reduce runoff. *More vegetation=less runoff 3. Type of soil - some soils absorb more water than others 4. Shape of the land – steep slopes have more run-off, which causes more erosion 5. How people use the land – parking lots & crop removal increase run-off. 5 Runoff overtime: How does runoff over time affect the land and water? 6 Rills & Gullies As runoff travels across the soil, rills form. Rills are tiny grooves in the soil that grow larger forming gullies. A gully is a large groove or channel in the soil that carries runoff after a storm. It moves soil & rocks. Gullies only contain water after it rains. 7 Streams & Rivers Gullies join together to form a larger channel called a stream. Water continuously flows here and rarely dries up. Small streams may be called creeks or brooks. Small streams flow together to form a large stream called a river. 8 Rill, Rill erosion at a construction site. Image by M. Mamo, Labels added by UNL Gully, Stream Gully erosion in a pasture. Image by NRCS Stream 9 Tributaries Streams grow together by getting water from tributaries. A tributary is a stream or river that flows into a larger river. Tributaries collect their water from the drainage basin or watershed. An example: The Missouri & Ohio rivers are tributaries of the Mississippi river. 10 Rivers & Tributaries http://images.google.com/imgres?imgurl=http://knol.google.com/k/-/-/3ajhc7zrwtav1/c1ssz4/figure-1%2520(2).bmp&imgrefurl=http://knol.google.com/k/neworleans-the-geologic-difficulties-with-the-big-easy-part-1&usg=___SPqqMAUDGF2VVgD-x0Wwvs5xk=&h=394&w=432&sz=31&hl=en&start=5&um=1&tbnid=ShJceJzlrtYlWM:&tbnh=115&tbnw=126&prev=/images%3Fq%3DMississippi%2Briver%2Band%2Bits%2 11 Btributaries%26hl%3Den%26um%3D1 Rivers: * cause erosion and create valleys, waterfalls, flood plains, meanders and oxbow lakes. *form on steep mountain slopes. 12 How do they flow? Quickly and follow a narrow path How do they erode? Rapidly The result is that rivers form deep, V-shaped valleys. 13 Valleys http://www.google.com/imgres?imgurl=http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/r chambers/GeoBytes%2520GCSE%2520Blog%2520Resources/Images/Rivers/Vshapedvalley.jpg&imgrefurl=http://geobytesgcse.blogspot.com/2006/11/upper-course-of-river-v-shapedvalleys.html&usg=__Hp8C8YOunbWzJy9E7kbQcOiURzA=&h=308&w=411&sz=47&hl=en&start=0&zoom=1 &tbnid=giwF1FppYFy8zM:&tbnh=116&tbnw=154&ei=kk2TfKtEMH68AbI__2tBA&prev=/images%3Fq%3Dvshaped%2Bvalley%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D1280%26bih%3D531%26tbs%3Disch: 10%2C35&um=1&itbs=1&iact=hc&vpx=247&vpy=77&dur=701&hovh=194&hovw=259&tx=161&ty=116&o ei=g0k2TbG1L4T58Aa8nOC7Aw&esq=12&page=1&ndsp=22&ved=1t:429,r:1,s:0&biw=1280&bih=531 http://images.travelpod.com/users/theboy_picot/3.1149265860.580x-nice-v-shapedvalley.jpg 14 Features of rivers: What features are formed by erosion along a river? 15 Waterfalls Occur where? Where a river meets an area of hard & slowly eroding rock Then flows over softer rock downstream. How does softer rock erode? The softer rock erodes away faster. What results from this erosion? A waterfall develops. 16 Waterfalls Waterfalls at the Plitvicka Jezera National Park in Croatia Minnehaha Falls, Minneapolis Minnesota http://images.google.com/imgres?imgurl=http://realestate-inminnesota.com/images/Minneapolis.jpg&imgrefurl=http://realestate-inminnesota.com/&usg=__kBYWaWcelJlCsNAEDq6zr8eLY=&h=599&w=800&sz=162&hl=en&start=5&um=1&tbnid=WO5G4jC_rIKDMM:&tbnh=107&tbnw=143&prev=/images%3Fq%3Dminnehaha%2Bfalls,%2B 17 mn%26ndsp%3D18%26hl%3Den%26sa%3DG%26um%3D1 Flood Plain What is a flood plain? A wide valley in which a river flows What happens to the land during a flood? The water in the river over flows its banks into this wide river valley area. 18 Flood Plain 19 Meanders What are meanders? Loop-like bends in the course of a river. Where & how do they occur? They occur as the outer bank of a river is eroded & deposits are dropped on the inner bank of the bend in a river. 20 Example: The southern stretch of the Mississippi River meanders on a wide, gently sloping flood plain area. 21 Mississippi River Meanders http://images.google.com/imgres?imgurl=http://www.ecology.info/img/MississippiRiver.jpg&imgrefurl=http://www.ecology.info/article.aspx%3Fcid%3D12%26id%3D10&usg=__B9CvpJJ70Ydm7HE2LjHs3GW76Ec=&h=450&w=600&sz=57& hl=en&start=8&tbnid=Q3zaqdFNmc7QVM:&tbnh=101&tbnw=135&prev=/images%3Fq%3Dmeanders%26gbv%3D2%26hl%3Den%26sa%3DG 22 Oxbow Lakes What is an oxbow lake? A meander that has been cut-off from the river. They may form when a river floods as high water finds a straighter path downstream . As flood waters fall, sediments dam up the ends of the meander and a lake forms. 23 Oxbow Lakes http://muller.lbl.gov/travel_photos/AmazonWebPages/AmazonWebPages-Images/1.jpg 24