Page 460 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

424 part III The earth–Atmosphere Interface
separated and the production of heavy crude oil results. As of 2012, about 770 km2 near Fort McMurray, Alberta, were disturbed by surface mining.
Once such oil is removed, tailings— the unwanted by-product—remain. About 1.25 m3 of tailings are created for each barrel of oil (159 litres) produced. The tailings are mixed with water and vari- ous chemical by-products, and collected in settling ponds. Solid materials in the tailings settle as the water evaporates. Over decades, the ponds fill up and the producers are charged with reclaiming and revegetating the land. Successful rec- lamation projects are experimental and only a few reclaimed hectares have re- ceived official certification so far from the Alberta government.
Tailing ponds are basins surrounded by dikes covering tens of square kilome- tres. Also, there are former mine pits that result from the extraction of oil sands.
In addition to concerns about slow seepage of liquids through dikes, questions
have been raised about the stability of older dikes, and the possibility of a cata- strophic failure and release of toxic mate- rial into the adjacent Athabasca River.
For deeper deposits, the method used is in situ extraction, which requires less human-mass movement than sur- face mining. In this process steam is in- jected underground, where it heats the bitumen and separates it from sand. The oil is then pumped to the surface. Significant quantities of water are used and polluted in this process. In northern Alberta, in situ methods are used for the majority of oil sands deposits that are distributed over more than 142 000 km2 at depths that are impractical for surface mining.
Visit www.oilsands.alberta.ca and www.pembina.org/oil-sands to learn more about oil sands and environmental impacts related to both surface mining and in situ mining of this resource, includ- ing scarification—one of the topics dis- cussed later in this chapter.
geosystems now online Failure of a retaining wall around an ash-pond at the Kingston coal-fired power plant in Tennessee in 2008, released 4.13 million m3 of toxic ash into the surrounding environ- ment. To learn more about this disaster, see www.epakingstontva.com and go to Chapter 14 of the MasteringGeogra- phy website (www.masteringgeography .com) for resources and activities. In 2010, a similar event occurred in western Hungary at an aluminum oxide plant, sending a torrent of chemical waste over land and into waterways (see www.npr.org/blogs/ thetwo-way/2010/10/05/130351938/ redsludge-from-hungarian-aluminum-plant- spill-anecological-disaster); and in 2014, a breach of a mine tailings pond at Mount Polley, British Columbia, released 8 million m3 of tailings into Polley and Quesnel Lakes (see www.env.gov.bc.ca/ eemp/incidents/2014/mount-polley/).
As mentioned in earlier chapters, the exogenic processes at work on Earth’s landscapes include weathering, erosion, transportation, and depo- sition of materials. In this chapter and the four chapters that follow, we look at exogenic agents and their handi- work: weathering and mass-movement processes, river systems and their landforms, landscapes shaped by waves and wind, and landforms worked by ice and gla- ciers. All of these are subjects of geomorphology, the science of the origin, development, and spatial distribu- tion of landforms. Whether your preference is for hiking in the mountains or wandering along a river, for visit- ing sand dunes in the desert or catching waves along a coastline—or perhaps you live in a place where glaciers once carved the land—there is something of interest for you in these chapters.
We begin our study of Earth’s exogenic systems with weathering, the process that breaks down rock by disin- tegrating it into mineral particles or dissolving it into water. Weathering produces an overall weakening of surface rock, which makes it more susceptible to other exogenic processes. The difference between weathering and erosion is important: Weathering is the breakdown of materials, whereas erosion includes the transport of weathered materials to different locations.
Along with the earthquakes and volcanoes that were the focus of Chapter 13, many events related to exogenic processes are often in the news: for example, a debris avalanche in Austria or Pakistan, a landslide in China or Turkey, a debris flow in the Okanagan Valley, British Columbia, or a mudslide in Washington State. In 2008, the world watched as Haiti was deluged by three hurri- canes that caused massive landslides and mudflows from deforested mountain slopes. Then, in 2010, Haiti suffered
more landslides, caused by the earthquake described in Focus Study 13.1.
In this chapter: We look at physical (mechanical) and chemical weathering processes that break up, dissolve, and generally reduce the landscape. Such weathering re- leases essential minerals from bedrock for soil formation and enrichment. In limestone regions, chemical weather- ing produces sinkholes, caves, and caverns. In these karst environments, water has dissolved enormous under- ground areas that are still being discovered by scientists and explorers. In addition, we examine types of mass movements and discuss the processes that cause them.
Landmass Denudation
Denudation is any process that wears away or rearranges landforms. The principal denudation processes affecting surface materials include weathering, mass movement, erosion, transportation, and deposition, as produced by moving water, air, waves, and ice—all influenced by the pull of gravity.
Interactions between the structural elements of the land and the processes of denudation are complex. They represent an ongoing opposition between the forces of weathering and erosion and the resistance of Earth materials.
The iconic 15-story-tall Delicate Arch in Utah is dramatic evidence of this conflict (Figure 14.1). An as- sortment of weathering processes have worked in com- bination with the differing resistances of the rocks to produce this delicate sculpture—an example of differential weathering, where a more resistant cap rock protects sup- porting strata below.