This lecture will help you understand: Earth s Many Landforms. Earth s Many Landforms. Crustal Deformation. Earth s Many Landforms 10/18/2011

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1 Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science Chapter 24 EARTH S SURFACE LAND AND WATER This lecture will help you understand: A survey of Earth s landforms Folds and faults and how they are classified The different types of mountains The topography of the ocean floor Earth s water and where it is found The different erosive agents that sculpt Earth s surface Earth s Many Landforms Earth consists of seven continents: Africa, Antarctica, Asia, Australia, Europe, North America, and South America Continental elevations vary between Mt. Everest (8848 m) Dead Sea shores ( 400 m) Earth s Many Landforms Earth has three oceans: The Pacific Ocean Largest, deepest, and oldest The Atlantic Ocean Coldest and saltiest The Indian Ocean Smallest BUT, the oceans are all connected In reality, there is just one big ocean. Earth s Many Landforms Continental land features High mountains, plateaus, lowland plains Ocean features Deep trenches to mid-ocean ridge system Tectonic force and landforms Folds, faults, mountains Erosive force and landforms Valleys, canyons, deltas, and floodplains Crustal Deformation Deformation is a general term that refers to all changes from the original form and/or size of a rock body. Most crustal deformation occurs along plate margins. How rocks deform: Rocks subjected to stresses begin to deform. 1

Crustal Deformation Compressional stress convergent plate boundary Pushing together of rock masses Tensional stress divergent plate boundary Pulling apart of rock masses Shear stress transform

2 Crustal Deformation Compressional stress convergent plate boundary Pushing together of rock masses Tensional stress divergent plate boundary Pulling apart of rock masses Shear stress transform fault-plate boundary Rock masses sliding past one another Crustal Deformation Elastic deformation Size and shape deform, but rock returns to original form when stress is removed Fracture Elastic limit of rock exceeded; rock breaks Colder, surface rock Plastic deformation Elastic limit of rock exceeded; shape changed permanently folds Warmer, subsurface rock Folds During crustal deformation, rocks are often bent into a series of wave-like undulations called folds. Characteristics of folds: Most folds result from compressional stresses that shorten and thicken the crust. Folds Anticlines upfolded or arch-shaped rock layers. Oldest rock layers at the fold core, rock layers get younger away from core. Synclines downfolds or trough-shaped rock layers. Youngest rocks at the fold core, rock layers get older away from the core. Faults Strength of rock exceeded Faults are fractures with displacement. Sudden fault movement causes most earthquakes. Faults classified by relative displacement Dip-slip (vertical), strike-slip (horizontal), or oblique Dip-Slip Faults Dip-slip fault movement is up or down Footwall rock below the fault surface where a miner could stand. Hanging wall rock above the fault surface where a miner could hang a lamp. Normal fault: hanging wall moves down relative to footwall tension Reverse fault: hanging wall moves up relative to footwall compression 2

Dip-Slip Faults Strike-Slip Faults Displacement is horizontal, right-lateral, or left-lateral depending on direction of

Facing the fault: Block on opposite side of fault moves to the right (right-lateral) Block on opposite side of fault moves to

lithosphere, accommodates motion between two tectonic plates San Andreas Fault zone major transform fault separating Pacific

strike-slip fault Move vertically as in a dip-slip fault Oblique faulting occurs when tensional and shear forces or

3 Dip-Slip Faults Strike-Slip Faults Displacement is horizontal, right-lateral, or left-lateral depending on direction of movement. Facing the fault: Block on opposite side of fault moves to the right (right-lateral) Block on opposite side of fault moves to the left (left-lateral) Strike-Slip Faults Transform fault-plate boundary: Large strike-slip fault that cuts through the lithosphere, accommodates motion between two tectonic plates San Andreas Fault zone major transform fault separating Pacific Plate and North American Plate Strike-Slip Faults Oblique-Slip Faults Faults with combined motion: Move horizontally as in a strike-slip fault Move vertically as in a dip-slip fault Oblique faulting occurs when tensional and shear forces or compressional and shear forces exist. Mountains Mountains are thick sections of crust elevated with respect to the surrounding crust. Mountains are classified according to their structural features: Folded Mountains Upwarped Mountains Fault-Block Mountains Volcanic Mountains 3

4 Folded Mountains Mountains mostly occur at convergent plate boundaries crustal thickening causes uplift. Compression folds, thickens, and shortens the crust isostatic t ti uplift Continental collision creates highest mountains Himalayas India and Eurasia Appalachians North America and Africa Upwarped Mountains Broad upwarping of deeper rock deforms overlying sedimentary rock, producing roughly circular structures domes. Older rocks are in the center, and younger rocks are on the flanks. The Black Hills of South Dakota are a large, domed structure generated by upwarping. Fault-Block Mountains Fault-block mountains occur within large areas of broad uplift. Overall force is usually compression. But crust is also stretched in such settings, like a balloon is stretched when inflated. Another example: When a tree branch is bent, compression occurs on the inside of the bend and tension occurs on the outside of the bend. Fault-Block Mountains Normal faults in stretched crust let huge blocks drop downward. Block left standing is the mountain. Broad uplift continues. The Sierra Nevada Mountains The Grand Teton Mountains The Basin and Range Province The Great Basin, geographically Covers most of Nevada and parts of Arizona, California, and Utah Volcanic Mountains Volcanic mountains formed by eruptions of lava, ash, and rock fragments. Opening at the summit of a volcano: Crater: steep-walled depression at the summit, less than 1 km in diameter Caldera: summit depression greater than 1 km diameter, produced by collapse following a massive eruption Vent an opening connected to the magma chamber via a pipe Volcanic Mountains Shield volcano: Broad, large, slightly dome-shaped volcano Composed primarily of basaltic lava Mild eruptions of large volumes of lava Mauna Loa on Hawaii Cinder cone: Ejected lava (mainly cinder-sized) fragments Steep slope angle, small in size Sunset Crater in Arizona 4

Volcanic Mountains Composite cone: Large, classic-shaped volcano (thousands of feet high and several miles wide at base) Composed of interbedded lava flows and alternating layers of ash, cinder, and

5 Volcanic Mountains Composite cone: Large, classic-shaped volcano (thousands of feet high and several miles wide at base) Composed of interbedded lava flows and alternating layers of ash, cinder, and mud Many are located adjacent to the Pacific Ocean (Mount Fuji, Mount St. Helens) Very violent, explosive volcanic activity (Mt. Vesuvius) Volcanic Mountains Most volcanoes form near plate boundaries where converging plates meet. About 75% of the world s volcanoes are found in the Ring of Fire that encircles the Pacific Ocean. Volcanic Mountains Hot spots stationary, deep, very hot. Hot mantle rock moves upward by convection. Hot spot volcanism: Partial melting occurs near the surface Localized volcanism in the overriding plate In oceanic crust, basaltic magma produced Hawaiian Islands In continental crust, granitic magma produced Yellowstone National Park Earth s Waters Earth is 71% covered by water: ~97% is saltwater in the oceans; ~3% is fresh water. ~2% is frozen in ice caps and glaciers. ~1% is liquid fresh water in groundwater, and water in rivers, streams, and lakes. A small amount is water vapor. Earth s waters are constantly circulating. The driving forces are: Heat from the Sun Force of gravity Earth s Waters The hydrologic cycle is the set of processes that controls the circulation of water on Earth. Processes involved in the hydrologic cycle: Evaporation Precipitation Infiltration Runoff Earth s Waters Water that goes from the ocean back to the ocean completes a hydrologic cycle. The journey is not always direct, and water can flow as: Streams, rivers, and groundwater Water can also be frozen in ice caps and glaciers 5

The Ocean Floor Ocean floor encompasses continental margins and deep ocean basins. Continental margins are between shorelines and deep ocean basins.

6 The Ocean Floor Ocean floor encompasses continental margins and deep ocean basins. Continental margins are between shorelines and deep ocean basins. Continental shelf shallow; underwater extension of the continent. Continental slope marks boundary between continental and oceanic crust. Continental rise wedge of accumulated sediment at base of continental slope. The Ocean Floor The ocean bottom is not flat, it is etched with deep canyons, trenches, crevasses. Underwater mountains rise upward from the seafloor. The deep-ocean basin: Basalt from seafloor spreading plus thick accumulations of sediment Abyssal plains, ocean trenches, and seamounts The Ocean Floor The deep-ocean basin: Abyssal plains flattest part of the ocean floor due to accumulated sediment Ocean trenches long, deep, steep troughs at subduction zones Seamounts elevated seafloor from volcanism Mid-ocean ridges: Sites of seafloor spreading (volcanic and tectonic activity) A global mid-ocean ridge system winds all around the Earth The Ocean Floor The deepest parts of the ocean are at the ocean trenches near some of the continents. The shallowest waters are in the middle of the oceans around underwater mountains (mid-ocean ridge system). Ocean Waves Characteristics of waves waves get their energy from the wind. The crest is the peak of the wave. The trough is the low area between waves. Wave height is the distance between a trough and a crest. Wavelength is the horizontal distance between crests. Wave period is the time interval between the passage of two successive crests. Ocean Waves Height, length, and period of a wave depend on: Wind speed Length of time wind has blown Fetch the the distance that the wind has traveled across open water 6

Ocean Waves Wave of oscillation: Wave energy moves forward, not water Occurs in the open sea in deep water Wave of translation: Shallow water; depth about one-half wavelength wave begins to feel

mineral salts, dissolved gases, and decomposed biological material. Salinity: the proportion of salts to pure water.

7 Ocean Waves Wave of oscillation: Wave energy moves forward, not water Occurs in the open sea in deep water Wave of translation: Shallow water; depth about one-half wavelength wave begins to feel bottom Wave grows higher as it slows and wavelength shortens Steep wave front collapses, wave breaks Turbulent water goes up the shore and forms surf Ocean Water Ocean water is a complex solution of mineral salts, dissolved gases, and decomposed biological material. Salinity: the proportion of salts to pure water. ~35 grams salts per 1000 grams of water Salinity and temperature control density Salty, cold water is denser than less salty, warmer water Ocean Water Salinity is variable: Salinity decreases as fresh water enters the ocean: Runoff from streams and rivers Precipitation Melting of glacial ice Salinity increases as fresh water leaves the ocean: Evaporation Formation of sea ice Earth s Fresh Water Only ~3% of Earth s water is fresh. Of the 3%, ~85% is frozen in ice sheets and glaciers ~14% is groundwater ~0.8% is in lakes and reservoirs, soil moisture, and rivers ~0.04% is water vapor Surface Water Surface water includes streams, rivers, lakes, and reservoirs. Infiltration of water is controlled by: Intensity and duration of precipitation Prior wetness condition of the soil Soil type Slope of the land Nature of the vegetative cover Surface Water The land area that contributes water to a stream is called the drainage basin. Drainage basins are separated by drainage divides. The largest drainage divides are continental divides. 7

8 Groundwater Water beneath the ground exists as groundwater and soil moisture. Groundwater occurs in the saturated zone water has filled all pore spaces. Soil moisture is above the saturated zone in the unsaturated zone pores filled with water and air. The water table is the boundary between these two zones. Groundwater The depth of the water table varies with precipitation and climate. Zero in marshes and swamps, hundreds of meters in some deserts. At perennial lakes and streams, the water table is above the land surface. The water table tends to rise and fall with the surface topography. Groundwater Factors that influence storage and movement of groundwater: Porosity: ratio of open space in soil, sediment, or rock to total volume of solids plus voids the amount of open space underground. Greater porosity equals more potential to store greater amounts of groundwater. Particle size, shape, and sorting influence porosity. Soil with rounded particles of similar size has higher porosity than soil with various sizes. Groundwater Permeability Degree to which groundwater can flow through a porous material higher permeability, greater potential for fluid flow. Sediment packing and connectedness of pores influences permeability example of clay and sandstone: Both have high porosity, but clay s small, flattened sediment grains makes for tighter packing and smaller pores. Water cannot flow easily through small pores so clay has low permeability. Groundwater Aquifers are reservoirs of groundwater. Aquifers generally have high porosity and high permeability. Aquifers underlie the land surface in many areas; they are a vital source of fresh water. It is important to keep this vital source of fresh water clean and contaminant free. Surface Processes Earth s surface is worn away by the processes of erosion. Agents of erosion include: Gravity Water Wind Ice 8

9 The Work of Gravity Mass movement the downslope movement of Earth material (rock, soil, debris, land), due to gravity. Rapid movement: Debris avalanche, rock fall, rock slide, landslide, debris flow Evidence: concave scars, debris, buried structures Slow movement: Soil creep, rock slump Evidence: broken retaining walls, bent tree trunks The Work of Surface Water Running water shapes Earth s surface in two opposing ways: fast water transports sediment, slow water deposits sediment. Streamflow two types of flow; stream speed Laminar flow slow and gentle Turbulent flow fast and rapid Factors that determine velocity: Gradient, or slope Channel characteristics (shape and size) Discharge volume of water moving past a given point in a certain amount of time The Work of Surface Water Stream erosion: Loosely consolidated particles are lifted by abrasion and dissolution. Stronger currents lift particles more effectively: Stronger currents have higher energy Lift and transport more and bigger particles Turbulent versus laminar flow Downward limit to stream erosion: The lowest point to which a stream can erode is called base level. The Work of Surface Water Two general types of base level: Ultimate (sea level) Local or temporary (lake, etc.) Raising base level causes deposition Lowering base level l causes erosion Transportation of sediment by streams: Capacity: maximum load a stream can transport controlled by stream discharge Competence: maximum particle size a stream can transport controlled by stream velocity The Work of Surface Water Decreased velocity causes sediment deposition competence and capacity reduced, sediment drops out of flow. Stream sediments (alluvium) are generally well sorted. Natural levees form parallel to stream channel by successive floods Alluvial fans develop where a high-gradient stream abruptly leaves a narrow valley Deltas form when stream enters an ocean, bay, or lake creates new land The Work of Groundwater Flowing groundwater can alter and change features at the surface: Land subsidence Caves and caverns Sinkholes 9

The Work of Groundwater Land Subsidence: Extreme groundwater withdrawal by pumping from wells can result in lowering of the land land subsidence.

The clays leak water to the sand, then when water is pumped out, the clays shrink and compact, causing subsidence.

10 The Work of Groundwater Land Subsidence: Extreme groundwater withdrawal by pumping from wells can result in lowering of the land land subsidence. Land subsidence is especially prevalent in aquifers made of sandy sediments and interbedded clays. The clays leak water to the sand, then when water is pumped out, the clays shrink and compact, causing subsidence. The Work of Groundwater Caverns and caves The dissolving action of groundwater eats away at rock limestone in particular. Rainwater chemically reacts with CO 2 in the air and soil, producing carbonic acid. The acidified water seeps into rock (especially limestone), partially dissolving it. Such action has carved out magnificent caves and caverns (a cavern is a large cave). The Work of Groundwater Sinkholes are funnel-shaped cavities in the ground that are open to the sky; they are formed similar to caves. They can also be formed from conditions of drought and the over withdrawal of groundwater. The Work of Wind Wind blows everywhere, but its impact on sculpting the land is minor. Impact is greatest where: Strong winds blow frequently Vegetation is sparse or absent Plant roots keep particles together Plants deflect wind and shelter particles Surface particles are small Small particles are more easily lifted and transported The Work of Glaciers Glaciers are powerful agents of erosion. A glacier is like a plow as it scrapes and plucks up rock and sediment. Glaciers are also powerful agents of deposition. A glacier is like a sled as it carries its heavy load to distant places. The Work of Glaciers A glacier is an accumulation of snow and ice thick enough to move under its own weight. Two types of glaciers: Alpine Continental Alpine glaciers develop in mountainous areas, generally confined to individual valleys. Cascades, Rockies, Andes, Alps, Himalayas Erosional landforms: cirque, arête, horn, hanging valley, U-shaped valley 10

11 The Work of Glaciers Continental Glaciers: Spread over large areas Antarctica, Greenland, Alaska Erosional landforms Roches moutonees, striations Depositional landforms Moraine, kame, esker, drumlin 11

Earth s Many Landforms. Earth s Many Landforms. Earth s Many Landforms. Crustal Deformation. Crustal Deformation 10/22/2014

Earth s Many Landforms. Earth s Many Landforms. Earth s Many Landforms. Crustal Deformation. Crustal Deformation 10/22/2014 Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science Chapter 24 EARTH S SURFACE LAND AND WATER Earth s Many Landforms Earth consists of seven continents: Africa, Antarctica, Asia, Australia, Europe,