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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter 10 Weathering and Mass Wasting Visualizing Physical Geography by Alan Strahler and Zeeya Merali Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter Overview Weathering Mass Wasting Processes and Landforms of Arctic and Alpine Tundra Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Weathering Weathering: all the processes that physically disrupt or chemically decompose a rock at or near the Earth?s surface Two types of weathering: 1. Physical weathering 2. Chemical weathering Weathering produces regolith Physical weathering: breakup of massive rock (bedrock) by physical forces at or near the Earth?s surface Regolith: layer of mineral particles that lies above bedrock Weathering Regolith ? Highly weathered rock Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Weathering Physical Weathering Physical weathering (mechanical weathering) fractures bedrock Frost Action: water expands when it freezes, and fractures rock ? Dominant process in arctic and high-mountain environments Joints: fractures in bedrock Granular disintegration: rocks break up grain by grain Talus: fragments of rock at the base of a cliff Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Weathering Physical Weathering Salt-crystal growth: Water evaporates from sandstone pores, leaving salt crystals behind. Crystals grow and disintegrate rock. ? Occurs in arid and semiarid regions Canyon de Chelly, Arizona Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Weathering Physical Weathering Unloading: rock is exposed at the surface, releasing pressure, so rock expands slightly Sheeting structure: rock joints in layers parallel to surface, forming exfoliation domes Other possible processes of physical weathering: ?Temperature change ?Plant roots ?Critters North DomeRoyal Arches Half Dome Yosemite NP Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Weathering Chemical Weathering Chemical Weathering: chemical change in rock minerals through exposure to the atmosphere and water ? Most effective in warm, moist climates ? Hydrolysis ? water breaks down minerals ? Oxidation ? metals combine with O2 (rust) ? Carbonic acid action ?Dissolves limestone, creating caverns ?Weathers buildings, tombstones ? Soil acids weather basalt Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Mass Wasting Mass Wasting: spontaneous downhill movement of soil, regolith, and bedrock under the influence of gravity Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Mass Wasting Slopes Bedrock: solid rock layer under soil and regolith, which is relatively unchanged by weathering A. Soil & regolith blanket bedrock with a few rock outcrops. B. Residual regolith accumulates at footslope as colluvium. C. Sediments along stream, water carried, are alluvium. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Mass Wasting Slopes Soil Creep: extremely slow downhill movement of soil and regolith Earthflow: moderately rapid downhill flow of water-saturated soil, regolith, or weak shale Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Creep up close Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Mass Wasting Mudflow and Debris Flood Mudflow: flowing mixture of water and soil or regolith that flows rapidly downhill Lahar: volcanic mudflow Debris flood or debris flow: very watery mudflow Alpine debris avalanche: debris flow on steep slopes in mountainous regions 1970 debris avalanche in Peru, buries the town of Yungay on the western edge of the Nevado Huscarán. 13_25.JPG Debris avalanche triggered by 1979 earthquake in Alaska covers portions of the Cascade Glacier west of the St. Elias Range. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Mass Wasting Landslide Landslide: rapid sliding of large masses of bedrock on steep mountain slopes or from high cliffs Set off by: ? earthquakes ? sudden rock failures ? oversteepening of slope 1995 slide in La Conchita, CA, also site of a 2005 mudslide Event. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Mass Wasting Induced Mass Wasting Mass wasting can be induced by human activities: excavation, adding water to slopes, extracting mineral resources, many other earth-moving activities Palos Verdes, CA Kayford Mountain West Virginia Kentucky Strip Mine Montana Strip Mine Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Mass Wasting Mass Wasting?After the Deluge Hurricanes can bring huge volumes of water on to the landscape, leading to debris avalanches and mudslides Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Processes and Landforms of Arctic and Alpine Tundra Permafrost Permafrost: soil, regolith, and bedrock at a temperature below 0º C, found in cold climates ? Periglacial: environment near glacial ice ? Permafrost reaches a depth of 300 to 450 m near 70º N ? Ground ice: water frozen in pore spaces ? Active layer: freezes and thaws with the seasons ? Permafrost table: upper surface of the permanently frozen zone Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Processes and Landforms of Arctic and Alpine Tundra Permafrost Ice wedges form as ice accumulates in cracks in the sediment Ice-wedge polygons: ice wedges interconnected in a system of polygons Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Processes and Landforms of Arctic and Alpine Tundra Permaforst Pingo: conspicuous conical mound or circular hill, with a core of ice, found on tundra where permafrost is present Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Processes and Landforms of Arctic and Alpine Tundra Environmental Problems of Permafrost Human activities degrade the permafrost environment ? Thermal erosion: surface layer removed, so the thaw extends deeper into the ground ? Thermokarst: natural surface removed over large areas of tundra?ground subsidence results in depressions and lakes ?Ground may subside ?Buildings may collapse ? Buildings must be insulated ? Pipelines must be placed aboveground Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Processes and Landforms of Arctic and Alpine Tundra Patterned Ground and Solifluction Annual freezing and thawing sorts particles by size, producing rings of coarse fragments Stone polygons Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Processes and Landforms of Arctic and Alpine Tundra Patterned Ground and Solifluction Solifluction: a type of earthflow found in arctic permafrost regions caused by soil that is saturated with water and then deformed into terraces Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Processes and Landforms of Arctic and Alpine Tundra Alpine Tundra Most periglacial processes and form of arctic tundra are also found in high alpine tundra Processes and Landforms of Arctic and Alpine Tundra Climate Change in the Arctic ? By 2100, arctic temperatures may rise by 4º C to 8º C ? Annual precipitation may increase by 20% ? Active layer of permafrost will deepen over broad areas ?Roads and pipelines disrupted ?Populations of animals fluctuate ?Hunting season shorter for native peoples ? Boreal forest will migrate poleward ? Forest productivity will decline from drought, insects, disease, fire Pattie PowerPoint Presentation