10.4 Water’s Effect on Shaping Earth’s Surface Water is always moving due to the water cycle Quick changes can happen due to floods, storms or tsunamis Slower changes occur due to glaciers, run-off and rivers Water helps in weathering, erosion and deposition Weathering is the breaking down of rock into smaller pieces Physical weathering (aka mechanical) - rocks broken down by force, but still remain as the same kind of rocks Chemical weathering - rocks broken down by chemicals into different types of matter Erosion is the movement of pieces of broken rock to another location Deposition is the dropping, and building up, of pieces of rock (eg. river deltas) See page 386 - 388 (c) McGraw Hill Ryerson 2007
Weathering by Water and Ice Physical weathering Occurs most quickly where the climate includes high levels of precipitation and large temperature changes (between night and day, and also from season to season) Ice wedging (aka frost wedging) weathers rocks due to the expansion of water as it freezes Chemical weathering Occurs most quickly where climate is warm, there is high levels of rainfall and pollution Water + oxygen = much chemical weathering, including rusting aka oxidation Plants also aid in chemical weathering Lichens, decomposing plants See page 389 (c) McGraw Hill Ryerson 2007
Weathering by Water and Ice (continued) Chemical weathering also occurs underground Water + carbon dioxide = carbonic acid, which dissolves rock Groundwater becomes acidic, and reacts with calcium carbonate in some rocks to dissolve the rocks Limestone has high levels of carbonate Over time, large spaces are created underground Sinkholes, caves and karst are formed this way See page 390 (c) McGraw Hill Ryerson 2007
Erosion by Water and Ice Moving water breaks down rock into sediment Sediment can be eroded far away and deposited V-shaped valleys are carved by flowing water Rapids create more weathering as water moves faster Ocean waves continually erode shoreline Gravity can cause landslides and avalanches Erosion by ice Glaciers once covered all of BC (2 km deep, 10 000 years ago) leave striations (scratch marks) on rocks form U-shaped valleys can move large rocks long distances See pages 392 - 393 (c) McGraw Hill Ryerson 2007
Glacial Effects Arête Cirque Fiord Hanging Valley Horn (or fjord) Narrow ridge (high ground) between two cirques Bowl-shaped valley at the head of a glacier A narrow inlet of ocean between steep cliffs carved by glaciers U-shaped valley cut off by a bigger valley created by a larger glacier Pyramid-shaped peak located between three cirques See page 394 Images from http://pubs.usgs.gov/of/2004/1216/a/a.html (c) McGraw Hill Ryerson 2007
Deposition by Water and Ice After erosion, sediments are eventually deposited A delta forms where a river empties into a calm basin Glaciers deposit many different forms of sediment Erratic Esker Moraine Outwash Large boulder deposited on the ground by a glacier Winding ridge of material deposited by a stream running under a glacier Ridge of rocky material deposited by a glacier, are found at the sides and farthest advance of a glacier. Material deposited by water from melting glaciers See page 395 Take the Section 10.4 Quiz Images from http://pubs.usgs.gov/of/2004/1216/a/a.html (c) McGraw Hill Ryerson 2007