Transcript landscapes
LANDSCAPES LANDFORMS • Surficial features formed by: Mountain Building Erosion/Sedimentation Geomorphology: defined GEO (earth) MORPH (shape) OLOGY (study of) Geomorphology: The scientific study of landscapes and the processes that shape them. Geomorphology: basics • What is a landscape? – • A surface composed of an assemblage of subjectively defined components. What is a landform? – A landscape component that can be observed in its entirety "Distinct association of landforms, as operated on by geological processes, that can be seen in a single view." - Glossary of Geology "Any physical, recognizable form or feature on the earth's surface, having a characteristic shape, and produced by natural causes; it includes major forms such as a plain, plateau, or mountain, and minor forms such as a hill, valley, slope, esker, or dune. Taken together, the landforms make up the surface configuration of the earth." - Glossary of Geology Landform Description • Landforms are described using the following terms: – Topography: The general configuration of varying heights that gives shape to the Earth’s Surface. – Elevation: Height of landscape features above and below sea level. – Contours: Lines that connect equal points of elevation which show the distribution of elevations in an area. – Relief: The difference between the highest and lowest elevations in an area. Landform Examples • Mountain: Large mass of rock that projects well above its surroundings due to tectonic activity. • Plauteau: Large, broad, flat areas of appreciable elevation above the neighboring terraine formed due to regional uplift by tectonic activity. • Mesa: Small platueau formed from differential weathering of bedrock of varying hardness. • Anticlines • Synclines Landform Examples • Badlands: Deeply gullied features formed from fast erosion of easily erodible shales and clays. • Cuestas: Assymetrical ridges in a tilted aand eroded series of beds with alternating weak and strong resistance to erosion. – One side has a long gentle slope. – Other side has a steep slope. • Hogback: Narrow ridges formed by layers of erosion-resistant sedimentary rocks that are tectonically turned up so that the beds are vertical or nearly so. United States Physiographic Regions United States Physiographic Regions • The U.S. Physiographic Regions are based on landscape features, which are mostly controlled by the geology of the regions. United States Physiographic Regions United States Physiographic Regions • LAURENTIAN UPLAND – • ATLANTIC PLAIN – • Areas 20-22 PACIFIC MOUNTAIN SYSTEM – • Areas 16-19 INTERMONTANE PLATEAUS – • Areas 14 & 15 ROCKY MOUNTAIN SYSTEM – • Areas 11-13 INTERIOR HIGHLANDS – • Areas 4-10 INTERIOR PLAINS – • Areas 2 & 3 APPALACHIAN HIGHLANDS – • Area 1 Areas 23-25 ALASKA – Areas 26-28 LANDSCAPE MECHANISMS Landscape Mechanisms • The interaction of Earth’s internal and external heat engines controls landscapes. – Internal Heat Engine (Endogenic Process) • Plate tectonics • Mountain Building • Constructive Process – External Heat Engine (Exogenic Process) • Sun: Affects Climate (Wind, Temperature, Precipitation) • Weathering and Erosion • Destructive Process Endogenic Landforms Exogenic Landforms Exogenic Process Sedimentary Cycle is Subcycle Within Rock Cycle • Weathering: Parent rock breaks apart into smaller rocks. • Erosion: Rocks become individual grains. • Transportation: Material is transported by wind, water or gravity. • Deposition: Material comes to rest in new location and often additional material piles up on top. Weathering and Erosion Weathering Weathering • The breakdown of the materials of Earth’s crust into smaller pieces due to Physical and Chemical Processes. Physical Processes Physical Weathering • Process by which rocks are broken down into smaller pieces by external conditions. • Types of Physical weathering – Frost heaving and Frost wedging – Plant roots – Friction and impact – Burrowing of animals – Temperature changes Frost Wedging Frost Heaving Plant Roots Friction and Repeated Impact Burrowing of Animals Temperature Changes Chemical Processes Chemical Weathering • The process that breaks down rock through chemical changes. • The agents of chemical weathering – Water – Oxygen – Carbon dioxide – Living organisms – Acid rain Water • Water weathers rock by dissolving it Oxygen • Iron combines with oxygen in the presence of water in a processes called oxidation • The product of oxidation is rust Carbon Dioxide • CO2 dissolves in rain water and creates carbonic acid • Carbonic acid easily weathers limestone and marble Living Organisms • Lichens that grow on rocks produce weak acids that chemically weather rock Acid Rain • Compounds from burning coal, oil and gas react chemically with water forming acids. • Acid rain causes very rapid chemical weathering Erosion Erosion • The process by which water, ice, wind or gravity moves fragments of rock and soil. Water Erosion • Rivers, streams, and runoff Ice Erosion • Glaciers Wind Erosion Mass Movements • Landslides, mudslides, slump and creep landslide clip.mpeg Mass Wasting is any Down Slope Movement Due to Gravity Soil Creep is a Form of Mass Movement Mass Wasting Balance Between Mountain Building and Erosion Mechanisms Effect on Landforms • Negative Feedback: When mountain building slows and erosion starts to dominate. – Elevation is in balance between the rate of tectonic uplift and the rate of erosion. • Positive Feedback: When mountain summits become higher due to erosion. – Due isostatic rebound – the upward movement of the Earth’s surface due to surface erosion of valleys. i.e., Ice Berg Feedback Between Climate and Topography • Climate (Rainfall & Temperature): Affects the rate at which water dissolves minerals in rock and soil: – – – – Rain that falls on bedrock and soil. Infiltration of water into the soil. Mass Wasting Rivers and Glaciers • Topography: High elevation and relief enhance the mechanical break up of rocks. Effect of Climate & Topography on Landforms • Climate – – – – Rain that falls on bedrock and soil. Infiltration of water into the soil. Mass Wasting Rivers and Glaciers • Topography – – – – – Freezing and thawing Gravity Flow of rivers Mechanical Weathering: high elevations Chemical Weathering: low elevations Models of Landscape Evolution Models of Landscape Evolution • Originally thought to occur in two phases – Phase 1: Tectonic Uplift – Phase 2: Erosion • :Present models support simultaneous tectonic processes and erosion. • Key element is time – Appalachian Mountains (Older) – Rocky Mountains (Younger) – Landscapes achieve dynamic equilibrium over time THE END