Landform Lab Constructive and Destructive Processes Constructive processes build landforms through tectonic and depositional processes. Destructive processes break down landforms through weathering, erosion, and mass wasting. Tectonic processes include movements at plate boundaries, earthquakes, orogeny, deformation, and volcanic activity. Deposition is the accumulation or accretion of weathered and eroded materials. Weathering is the disintegration of rocks by mechanical, chemical, and biological agents. Erosion is the removal and transportation of weathered material by water, wind, ice, or gravity. Mass wasting is the rapid down-slope movement of materials by gravity. Other Agents and Processes that Affect Landform
Development Climate: temperature, precipitation, water cycle, atmospheric conditions Time: fast and slow rates of change People: influences on natural resources and earth surface processes Constructive Processes Constructive processes are responsible for physically building or constructing certain landforms. Constructive processes include tectonic and depositional processes and their landforms. Tectonic Landforms are created by massive earth movements due to tectonic and volcanic activity, and include landforms such as: mountains, rift valleys, volcanoes, and intrusive igneous landforms Depositional Landforms are produced from the deposition of weathered and eroded surface materials. Depositional landforms include features such as: beaches, deltas, flood plains, dunes,Floodplain alluvial fans, andatglacial The Stromboli Volcano erupting off deposits
the moraines. the coast of Sicily in the confluence of Mississippi and Mediterranean Sea. Arkansas Rivers. Source: wikimedia commons Copyright Google Earth 200 Destructive Processes Destructive processes create landforms through weathering and erosion of surface materials facilitated by water, wind, ice, and gravity. Mass-wasting events occur in areas where weathering and erosion is accelerated. Weathering is the disintegration and decomposition of rock at or near the Earths surface by mechanical, chemical, or biological weathering processes. Erosion is the removal and transportation of weathered or unweathered materials by water, wind, ice, and gravity. Mass-Wasting is a rapid period of weathering and erosion that removes and transports materials very quickly and is often triggered by an environmental stimuli. Mass wasting includes rock falls, landslides, debris and mud flows, slumps, and creep. Landforms formed by destructive processes include river and stream valleys, waterfalls, and glacial valleys. Tectonic Landforms
Mountains: Orogenesis and Deformation Folding Faulting Fractures Domes and Basins Horst and Graben Rift Valleys Major Mountain Ranges: Rocky Mountains Appalachian Mountains Himalayan Mountains Andes Mountains Orogenesis Orogenesis is the thickening of the continental crust and the building of mountains over millions of years and it translates from Greek as birth of mountains, (oros is the Greek word for mountain). Orogeny encompasses all aspects of mountain formation including plate tectonics, terrane accretion, regional metamorphism, thrusting, folding, faulting, and igneous intrusions. Orogenesis is primarily covered in the plate tectonics section of
the earth science education materials, but it is important to review for the landform section because it includes deformation processes responsible for mountain building. South Carolinas Blue Ridge Photo courtesy of SCGS, SCDNR Mountains and Inner Piedmont Region were formed by multiple orogenic events when rocks forming South Carolina were uplifted, metamorphosed, folded, faulted, and thrusted. More information on the Blue ridge mountains is included on the section for the Appalachian Mountain Range. Deformation Deformation processes deform or alter the earths crust by extreme stress or pressure in the crust and mantle. Most deformation occurs along plate margins from plate tectonic movements. Folding and faulting are the most common deformation processes. Folding occurs when rocks are compressed such that the layers buckle and fold.
Faulting occurs when rocks fracture under the accumulation of extreme stress created by compression and extensional forces. Both of these folds are in biotite-rich gneiss from the South Carolina Piedmont, the areas where the folds are most pronounced contain greater amounts of quartz from the granitic composition of the rock. The scale card shows us that the rock on the left contains smaller folds than the rock on the right. Photo: South Carolina Geological Survey Photo: South Carolina Geological Survey Folding Folding occurs when rocks are compressed or deformed and they buckle under the stress. The diagram below is a cartoon illustrating how rocks fold. The crest of the fold, where the rock layers slope downward form the anticline. The valley of the fold where the layers slope toward the
lower axis form the syncline. Folding Anticlines and synclines can take on slightly different geometries depending on the compressional forces that form them. Very intense compressional forces form tight isoclinal folds, less intense compressional forces produce open folds. Folds can be asymmetric, upright, overturned, or curved. A fold pushed all the way over onto its side is called recumbent. Twisting or tilting during rock deformation and compression can cause folds to form at different angles. Some folds are very small and can be viewed in hand held specimens, while other folds are as large as a mountain and can be viewed from aerial photos. Folding Anticline exposed along NJ Route 23 near Butler NJ. The man in the bottom of the photo helps show the scale of the folds.
Copyright USGS Overturned folds in the Table Rock gneiss in South Carolinas piedmont. The rock hammer in the photo is used for scale. SCGS photo Syncline valley between mountain peaks. Copyright Michael Lejeune Recumbent folds in limestone. Copyright Marli Miller, University of Oregon Faulting Faulting occurs when the rocks fail under deformation processes. A fault is a planar discontinuity along which displacement of the rocks occurs. There are four basic types of faulting: normal, reverse, strike-slip, and oblique. Normal Normal: rocks above the fault plane, or hanging wall, move down relative to the rocks below the fault plane, or footwall.
2. Reverse: rocks above the hanging wall moves up relative to the footwall 3. Strike-slip: rocks on either side of a nearly Reverse Geologists recognize faults byvertical looking for fault off-set rock layers in outcrops. plane move horizontally 1. Strike-Slip Faults may also be recognized by debris, breccia, clay, or rock fragments that break apart or are pulverized during the movement of the rocks along the fault plane. Fault gouge is a term used to describe the material produced by faulting. If a fault plane is exposed, there may be grooves, striations (scratches), and slickenslides (symmetrical fractures) that show evidence of the rocks movement. Large fault systems, such as the San Andreas fault can be seen from aerial imagery. Faulting
Faulting The San Andreas fault is the largest fault system in North America and it runs for nearly 780 miles through western California and in some places the width of the fault zone is 60 miles. The San Andreas fault is a transform boundary between the Pacific Plate on the west and the North American Plate to the east. The Pacific Plate is moving northwestward against the North American Plate. This motion generates earthquakes along the fault that pose significant hazards to people and alters the physical landscape. Photo: South Carolina Geological Survey These two faults are from South Carolinas Piedmont. These faults are evident by the off-set igneous intrusions in the rock. Offset in stream valley from San Andreas Fault movement Copyright Michael Collier Photo: South Carolina Geological Survey Domes and Basins Domes and basins are large, elongated folds formed by broad warping processes including mantle convection, isostatic adjustment, or swelling from a hot spot.
Upwarping produces domes, while downwarping produces basins. Geologists identify dome and basin structures by the stratified ages of the rock folds: Domes contain strata which increase in age toward the center as the younger layers are eroded from the top and sides. Basins contain strata which is youngest toward the center and the oldest rocks form the flanks or sides. This geologic map of the Michigan Basin illustrates the circular pattern of the sedimentary strata. The green color in the center of the map represents the youngest rocks which are Upper Pennsylvanian; and the rocks progressively increase in age toward the periphery where the reddish-orange colors represent the oldest rocks flanking this structure which are Ordovician and Cambrian age. Oldest Rocks (Ordivician and Cambrian) Youngest rocks (Upper Pennsylvanian) http://en.wikipedia.org/wiki/Michigan_Basin Horst and Graben: Basin and Range
Horst and graben topography is generated by normal faulting associated with crustal extension. The central block termed graben is bounded by normal faults and the graben drops as the crust separates. The graben forms an elongated valley that is bound by uplifted ridge-like mountainous structures referred to as horsts. Some horsts may tilt slightly producing asymmetric, tilted terrane or mountain ranges. In the Western United States, horst and graben fault sequences are described as Basin and Range topography. Basin and Range topography, Nevada. Copyright Marli Miller, University of Oregon Rift Valleys Rift valleys are fault structures formed by normal faults. Rising magma below the crust upwells, forcing the lithosphere to fracture, as it fractures and cracks, one or more faults cause the crustal rocks to separate forming a rift valley. Rift valleys can eventually form lakes or seas such as the Red Sea, which separates Africa from the Arabian Peninsula. Rift valleys can become inactive and fill in with volcanic material, such as the rift structure in the United States which extends from Lake Superior to Oklahoma. Rift Valleys in Africa East African Rift Valley Lake www.visibleearth.nasa.gov
Major Mountain Ranges of the World Antarctica: Antarctic Peninsula, Transantarctic Mountains Africa: Atlas, Eastern African Highlands, Ethiopian Highlands Asian: Himalayas, Taurus, Elburz, Japanese Mountains Australia: MacDonnell Mountains Europe: Pyrenees, Alps, Carpathians, Apennines, Urals, Balkan Mountains North American: Appalachians, Sierra Nevada, Rocky Mountains, Laurentides South American: Andes, Brazilian Highlands European Alps Rocky Mountains Andes Mountai ns Appalachian Mountains
Himalaya Mountains Rocky Mountains The Rocky Mountains, which extend from British Columbia to Texas were formed by the Laramide Orogeny 40-80 million years ago; however, there is still active uplift today. Colorados Front Range, the Sangre de Cristo Mountains of Colorado and New Mexico, the Franklin Mountains in Texas, and Wyomings Bighorn Mountains are all part of the Rocky Mountain Range.The Rocky Mountains contain some of the most beautiful scenery in North America and are home to hundreds of parks and recreational areas including Rocky Mountain National Park, Yosemite National Park, Glacier National Park, and Grand Tetons National Park. Source: USGS The Laramide Orogeny was characterized by intense tectonic activity resulting from a series of compressional and extensional events. The subduction of the Pacific Ocean Plate caused compressional forces in the continental plate, and pushed the oceanic plate downward. Following subduction of the oceanic plate, upwelling and extensional forces caused the literal uplift of the continental bedrock and formed of the Rocky Mountains. The lower crust in this region of upwelling and uplifting is relatively thin and
stretches under pressure. The upper crust is very brittle and deforms easily. As a result the upper crust is characterized by large angular tilted faults blocks which form the Rocky Mountains we see today. Copyright Dr. Roger Slatt, University of Oklahoma Appalachian Mountains The Appalachian Mountains extend along the eastern margin of North America from Alabama to Maine in the United States, and through the southeastern provinces of Canada to Newfoundland. The Appalachian Mountains were formed during the Paleozoic Era from several orogenic episodes, the Taconic Orogeny (Ordovician ~480 mya), followed by the Acadian Orogeny (Devonian ~400 mya), and lastly the Alleghany Orogeny (Permian ~ 300 mya). Each of these major orogenic episodes involved multiple events of folding, faulting, metamorphism, emplacements of igneous intrusions, and uplift. The Appalachian Mountains are divided into four major provinces: Piedmont, Blue Ridge, Valley and Ridge, and Appalachian Waterfall carved into Plateau. valley of Blue Ridge Province of the Appalachians near the
South Carolina and North Carolina border. www. maps.google.com Source: USGS Source: SCGS This is an aerial view of the Susquehanna River in Pennsylvania flowing through the folded and faulted Valley and Ridge Province of the Appalachian Mountains. Andes Mountains The Andes Mountains began forming during the Jurrasic period (~200 mya) when plate tectonics forced the oceanic Nazca plate to subduct beneath the continental South American plate. The subduction zone between the plate margins marks the Peru-Chile ocean trench which is 26,500 ft (8,065 meters) below sea level. Tectonic forces along this active continental margin are forcing the ongoing uplift, folding, faulting, and thrusting of bedrock forming the Andes Mountains. The Andes are the longest mountain range on land and they extend along the entire western coast of South America. They are divide into three sections: (1)
Southern Andes in Argentina and Chile, (2) Central Andes including the Chilean and Peruvian cordilleras an parts of Bolivia, and (3) Northern sections in Venezuela, Columbia, and Ecuador, including to parallel ranges the Cordillera Occidental and the Cordillera Oriental. The Andes Mountains contain many active volcanoes, including Cotopaxi in Ecuador, one of the largest active volcanoes in the world. http:visibleearth.nasa.go v/ European Alps The European Alps began forming during the Alpine Orogeny (~ 20-120 mya) with the collision of the African Plate moving northward into the European Plate. This motion is still active today as the Alps continue to uplift, fold, fault, and accrete. The Alps are the largest mountain range in Europe and they extend from Austria and Slovenia in the east, through Italy, Switzerland, Germany, and France in the west. Major orogenic events involved recumbent folding and thrust faulting of crystalline basement rocks that today form some of the highest peaks in the Alps. The Alps were one of the first mountain ranges to be studied by geologists African Plate and as a result many geomorphic terms,
Austriaespecially those relating to glaciation and Germany alpine environments, were first defined in the European Alps. European Plate Switzerland s p Al an e op Sloveni r France u Italy a E http://en.wikipedia.org/wiki/Matterhorn Modified from: http://en.wikipedia.org/wiki/Alps The Matterhorn, on the border between Switzerland an Italy, is one of the most familiar mountains in the world and is a popular climbing site. The continentcontinent collision resulted in the peak of the Matterhorn containing bedrock from the African Plate while the lower portions contain bedrock from the European Plate. Himalaya Mountains Himalaya orogeny began 45-54 million years ago from the collision between the India and Eurasian Plates and is still active today.
When two continental plates collide, the Earths crust at the plate boundaries is folded, faulted, overthrusted, uplifted forming an extensive continental mountain range. Today, the Himalayas separate the Indian sub-continent from the Tibetan Plateau and they are recognized as the tallest above sea level mountains on Earth. The Himalayas contain 10 of the tallest mountain peaks on Earth >8,000 meters , including Mount Everest with a peak of 8850 meters (29,035 ft). In addition, the Himalayas include three major individual mountain ranges, the Karakoram, Hindu Kush, and Toba Kakar. Shallow, intermediate, and deep earthquakes are associated with this zone, The name Himalaya is from and scientists predict that several major earthquakes will occur in the region Sanskirt, and it means the abode Continental Continental Plate to millions of people. posing a significant hazard of snow. Hima for snow and Collision alaya for abode. www.usgs.gov http://en.wikipedia.org/wiki/ Image:Himalayas.jpg Volcanic Landforms: Extrusive Igneous
Cinder Cones Shield Volcanoes Strato (Composite)Volcanoes Lava Domes Caldera Volcanic Necks Volcanic Hot-Spots Cinder Cones Cinder cones are relatively small cone shaped hills (< 2000 ft of relief) formed by the accumulation of cinders and ash during volcanic eruptions. The cinders form from bursting bubbles of gas in the magma that eject lava into the air. The summit my be truncated or bowl-shaped where the magma emerges from a single central vent or volcanic neck. Cinder cones are formed from an accumulation of ejected tephra and scoria rocks. Tephra and scoria occur in a range of different sizes from fine ashes to large volcanic rock fragments. Once the magma is ejected into the air, it cools, hardens, and is deposited on
the summit or slopes of the cinder cone. The pyroclastic tephra and scoria rocks are produced from gas-rich basaltic magma, and is usually reddish-brown to black in color. Cinder cones generally form from a single volcanic episode and are rarely associated with eruptions lasting more than a decade. Cinder cones can be found in combination with shield and strato volcanos and can occur at convergent or divergent plate boundaries. Cinder cones are the most common type of volcano and often occur in large numbers within a region forming volcano fields. Flagstaff Arizona contains a volcanic field of nearly 600 cinder cones. Cinder cones have an easily recognizable hill shape form with relatively steep 30-40 degree slopes. This angle represents the steepest angle maintained by unconsolidated, loose material and is commonly referred to as the angle of repose. This image is of an older cinder cone with small caldera depression on Copyright Larry Fellows, USGS the summit. Shield Volcanoes
Shield volcanoes are broad shaped mountain landforms built by the accumulation of fluid basaltic lava. Their slopes are often very gentle and may be < 5 degrees, and their summits, or peaks, are relatively flat. They received their name because their gently domed form resembles the exterior of a warriors shield. Most shield volcanoes originate from the ocean floor and have grown to form islands or seamounts. Hawaii and the Galapagos Islands are examples of shield volcanoes that formed in the ocean and emerged as mountainous, island landforms. Magma, or lava, discharges from both the summit and rifts along the slopes. Most lava that forms shield volcanoes erupts as a flow from fissures; however, occasional high intensity pyroclastic ejections may occur. Shield volcanoes usually have either smooth, ropy pahoehoe lava, or blocky, sharp aa lava. Shield volcanoes form the largest volcanoesMauna on Earth. Loa Volcano on Hawaii is a shield volcano and the lava flow below illustrates a typical eruption for a shield volcano. Photo: D. Little, USGS Courtesy USGS Hawaiian Volcano Observatory Strato Volcanoes Strato-volcanoes, also referred to as composite cones, are large, nearly symmetrical mountainous landforms, formed by a combination of lava flows and intense pyroclastic eruptions. Eruptions are violent and the ejected material is primarily a gas-rich, high viscosity (resistance to flow) magma with an andesitic composition. Eruptions can also produce extensive ash deposits. Most strato volcanoes are located along the ring of fire which is a geographic zone
that rims the Pacific Plate where it is in contact with the Eurasian, North American, and Indo-Australian Plate. Mount Well-known St. Helens strato 1980 volcanoes eruption occur in the Andes, the Cascade Range of the United States and Canada (including Mount St. Helens, Mount Ranier, and Mount Garibaldi), and the volcanic islands of the western Pacific from the Aleutian Islands to Japan, the Philippines, and New Zealand. USGS Cascades Volcano Observatory Caldera Calderas are bowl-shaped collapse depressions formed by volcanic processes. Calderas most likely result from one of three collapse type events: 1. Collapse of the summit following an explosive eruption of silica-rich pumice and ash pyroclastics 2. Collapse of the summit following the subterranean or fissure drainage of the magma chamber
3. Collapse of a large area following the discharge of silica-rich pumice and ash along ring fractures that may or may not have been previously active volcanoes Crater Lake in Oregon is an example of a 700 year old caldera that formed from the eruption and collapse of Mount Mazama. Today it is filed in with rainwater and forms a lake. A small cinder cone, named Wizard Island, formed inside the caldera and today it emerges as an island in the lake. Many of the calderas on Hawaiian volcanoes formed after the magma drained through fissures in the central magma chamber and the summit eventually collapses. Yellowstone National Park contains a caldera that is >43 miles across and was formed by an intense pyroclastic eruption that ejected ash fragments as far as the gulf of Mexico. Crater Lake in Oregon is the collapsed caldera of Mount Mazama and is now filled in with water. Wizard Island is a volcanic cone in the middle of the lake. Crater Lake is the deepest lake in the United States at 1,932 feet deep! Copyright Larry Fellows, USGS Lava Domes Lava domes are rounded, steep-sided mounds built by very viscous magma that is resistant to flow and builds up forming a dome.
The magma does not move far from the vent before cooling and it crystallizes in very rough, angular basaltic rocks. A single lava dome may be formed by multiple lava flows that accumulate over time. This lava dome began forming after the Mount St. Helens eruption in 1980. Geologists set up a monitoring station to measure the growth of this lava dome and recorded that it is growing at a rate of about 40 feet per year. CopyrightLyn Topinka Volcanic Hot Spots Volcanic hot-spots occur where a mass of magma ascends toward the earths surface as a mantle plume, releasing basaltic magma that generates volcanic activity at a locally specific site. Hot-spots do not occur along plate boundaries but instead form as intraplate volcanic features characterized by magma upwelling. Once a hot spot is generated it may stay active for millions of years. Hot spots may produce thermal effects in the ground water and the crust producing geothermal power often in the form of steam. In Iceland and Italy geothermal power is used to generate electricity for industrial and municipal use. The Hawaiian Islands formed over the last 5 million years from a hot spot in the Pacific Ocean. As the Pacific plate moves over the hotspot, it generates a chain of islands that as seamounts above the oceans surface. Hot spot activity is currently most active Nihauemerge Kauai on the big island, Hawaii.
Oahu Oldest Islands Pa ci fi Molokai Maui Lanai c Pl at e Kahoolawe M ov em Hawaii en t Youngest Islands www.maps.google.com www.usgs.gov
Volcanic Necks Volcanic necks are remnant cooled lava pipes that are exposed after the exterior volcanic mountain is weathered and eroded. Volcanic necks are a good example of differential weathering. The magma cooled in the interior pipes is more resistant than the ejected deposits that accumulate on the exterior. As a result, when the volcanic mountain erodes, it leaves behind the remnant more resistant volcanic neck. Shiprock is a volcanic neck of a solidified lava core from a dormant 40-million year old volcano. Its elevation is 7,178 feet above sea level with a local relief of 1,800 feet. It lies southwest of the town of Shiprock, New Mexico, and was named after 19th -century clipper ships. Copyright Michael Collier Volcanic Landforms: Intrusive Igneous Batholiths Plutons
Laccoliths Dikes Sills Source: USGS Batholith Batholiths are massive igneous intrusions that form linear bodies that extend for hundreds of kilometers across the landscape and can be several kilometers thick. Some batholiths may incorporate groups of smaller plutons in addition to their massive structure. Batholiths form below the earths surface as intrusions of magma emplaced during tectonic processes. Following emplacement they may be uplifted and exposed by weathering and erosion processes. Some batholiths are metamorphosed by heat and pressure. For example, many of the batholiths in the Appalachian Mountains are metamorphosed igneous intrusions. Half Dome is a granitic igneous intrusion that forms an impressive mountain peak that is part of the greater Sierra Nevada Batholith in Yosemite National Park. The Half Dome shape was carved by glacial erosion. The Sierra Nevada Batholith, which includes Half Dome, Mt. Whitney, and El Capitan, became exposed as the mountains uplifted and
weathering and erosion removed the material surrounding the batholith. Copyright Bruce Molnia at Terra Photographics Plutons Plutons are intrusive igneous rocks which form below the Earths surface and are surrounded by sedimentary or metamorphic rocks. Plutons are formed as magma forces its way up through other rocks and solidifies before reaching the surface. Some plutons are remnant magma chambers that once fueled volcanic activity. Plutons become exposed on the landscape as the other rocks surrounding them are removed by weathering and erosion. Some plutons appear as small or large hills while others appear as tabular, flat rock exposures. Enchanted Rock is a large granitic pluton in the Llano Uplift of the Texas Hill Country Region that is part of a larger igneous batholith. http://en.wikipedia.org/wiki/Image:Enchanted_rock_2006.jpg Sills, Laccoliths, and Dikes
Sills and laccoliths are igneous intrusions that form near the earths surface. They are concordant features meaning that they form parallel to existing strata or structures. Sills form near the surface from very fluid magma that cools quickly they are usually mostly basaltic rocks with an aphanitic (fine-grained) texture. Laccoliths are similar to sills, accept they are formed by more viscous magma which collects in a lens shape prior to cooling as a concordant igneous intrusion near the surface. This process may force the overlaying strata to form a slightly domed structure over the bulging laccolith. Dikes are tabular intrusions of igneous rock that form when magma injects into fractures. Dikes are discordant features, meaning that they cut through layers of rock. Magma can force the rock apart separating the fracture. The cooled magma can range in thickness from centimeters to kilometers and may be more resistant to erosion than the surrounding rocks enabling them to protrude The dark linear outward amidst their surroundings. feature in this image is an exposed dike that is more resistant to weathering and erosion than the http://en.wikipedia.org/wiki/sill surrounding
Salisbury Craig is an exposed sill landscape. north of Edinburg, Scotland that forms a resistant cap on this hill top. 34 River Systems Lakes and Dams Braided Rivers Meandering Rivers River Canyons Waterfalls Flood plains Alluvial Fans Photo: SCGS The Congaree River in South Carolina is home to Congaree National Park which is a large flood plain ecosystem that protects some of the oldest and largest bottomland hardwood forests in the nation. Almost every year the Congaree River floods the National Park providing water, sediments, and nutrients that support the incredible growth of the forest and rich biodiversity of organisms.
35 Standards: 3-3.5, 3-3.6, 3-3.8 Standards: 5-3.1 Standards: 8-3.7, 8-3.9 Dams and Lakes Dams are control structures on rivers which store and release river water from a lake (reservoir) according to specific operating regimes. Some dams are run-of-river structures which continually release the same amount of water entering the reservoir, while others are operated as storage facilities for regulated control on water releases. Although 70 percent of the earth is covered with water, only about 2.5 percent is freshwater, by building dams with reservoirs people are able to store the freshwater and use it as needed. Dams provide water for drinking, irrigation, hydro-electric power, river navigation, flood control, recreation, and many other needs. Dams disconnect river channels and can function as local base level controls on stream gradient and store sediment from transporting downstream. They also act as barriers to migrating species, such as fishDam:
traveling upstream toPowell spawn, and and the controlled Lake Murray and Saluda Lake Glen Canyon water Dam: releases alter the downstream ecology of river systems and their floodplains. Saluda River, South Carolina Colorado River, Arizona www.sceg.com Photo: Paul R. Kucher 36 Table of Contents Braided
Braided river patterns occur in high-energy environments that contain an excessive sediment load that is deposited on the bed of the channel. The stream loses the capacity to transport the sediments and it forces its way through the accumulation of sediments forming an interwoven network of channels. The islands between the braided channels are ephemeral and dynamic. The sediment is continually remobilized, transported and deposited, leaving minimal time for vegetation to establish, as a result they are rarely vegetated. Braided channels tend to be wide and shallow with defined banks that are higher than the mid-channel islands. Braided channels occur downstream of areas with high sediment loads. Their sediment textures vary from silts, sands, and gravels depending on the sediment source. This is the braided Resurrection River in Alaska. The sediment load consists primarily of silt that has been eroded and weathered from glacial debris. Braided river patterns may also be referred to as anastomosing. Copyright Marli Miller, University of Oregon
Meandering Meandering river patterns are low-gradient, sinuous channels that contain multiple, individual meander bends that are laterally migrating across the flood plain. As they migrate or move across the flood plain they are continuously eroding, transporting, and depositing alluvial sediments. Meandering rivers and their hydrologic conditions create a variety of depositional and erosional landform features that collectively form the flood plain valley. The primary features of meandering channels are the aggrading pointbar deposit on the inside of a meander bend and eroding cut bank along the outside of the bend. As the channel migrates laterally across the flood plain, sediments are eroded from the outer cutbank and deposited on the inner pointbar. Thismeander is an aerial viewthese of thecutOccasionally, meandering channels cut-off entire bends; meandering and offs are incorporated into the flood plain as oxbow lakes Congaree
or in-filledRiver channels. 2006 Aerial imagery: http://www.dnr.sc.gov/GIS/gisdata.html flood plain in Congaree National Park, South Carolina. This image uses infrared colors instead of true colors; the infrared reflectance causes healthy vegetation to show up as a reddish-pink color, instead of the green we expect to see. The bottom right of the image includes a recently cut off meander bend and oxbow lake. Flood plains Flood plains are the landform adjacent to the river channel that is influenced by modern river processes. Flood plains are constructive, depositional landforms created by stream flow and sediment deposition. Flood plain environments are composed of a mosaic of different landform features including cutbanks, pointbars, natural levees, crevasse channels and crevasse splays, infilled channels and oxbow lakes, backswamps, and
occasionally yazoo tributaries and other flood plain channels. This aerial view of the Mississippi River Valley contains many typical floodplain features. The darker, green areas are floodplain forest and they likely flood the most frequently and thus are not developed with agriculture or housing. The surrounding patchwork represents agricultural fields and other developed lands that are probably at a higher elevation formed by natural or artificial Cutbank Pointbar Infilled Channel Oxbow Lakes Copyright 2008 Google Flood Plains
Cutbanks form along the outer convex margin of meander bends. Cutbanks , unlike most floodplain landforms are actually erosional features formed by the lateral movement of the channel across the flood plain. Flood plain sediments are eroded from the cutbank and deposited on pointbar surfaces. Pointbars are concave, depositional landforms that form opposite of the eroding cutbanks, and they develop in concert with the laterally migrating river channel. Pointbars are typically composed of sands, gravel, silts, and clay deposits, that form arcuate, meander-scroll ridges. Natural levees are depositional landforms formed from the vertical accumulation of sediments deposited during flood events. Natural levees form topographically higher surfaces adjacent to the river channel, that generally consist of stratified, well-sorted sands, silts, and clays. Natural levees deposits are thickest and coarsest close to the channel and they become progressively thinner, and finer with increasing distance from the channel. Crevasse channels and splays are breaches in the natural levee that result in the fanshaped deposition of flood deposits, beyond or over levee deposits. Crevasse channels can produce flooding in backswamp areas, even before the levees are submerged by floodwaters. Oxbow lakes or infilled channels form when a meander bend is cut off from the main river and abandoned in the floodplain. Abandoned meanders can occur in various stages from flooded oxbow lakes to being completely infilled with sediment deposits. Backswamps are typically low-lying areas of the floodplain beyond the natural levee deposits. Backswamps contain the finest-textured flood plain deposits and may even develop organic-rich soils from the forest litter. They often form along the margins or edge of the floodplain, and are usually influenced by connections to the groundwater. Yazoo tributaries are stream networks that enter the floodplain but the natural levee Flood Plains Oxbow
lake Infilled Channel Na tu ra lL ev ee Both of these images are GIS-based models from the Congaree River floodplain in Congaree National Park. The image on the left is a clip from a flood model that shows the depth of flooding during a large flood event. The natural levee adjacent to the channel is one of the topographically highest features and it floods the least. The abandoned meanders and back swamps are topographically lower and flood more frequently and to greater depths. The channel networks fill up with water connecting the oxbow lakes to the main stem river. The image below is from a high resolution digital elevation model (DEM) of a floodplain. The DEM is useful for mapping the different landform features Crevasse on a floodplain. Channels Meander-Scroll ridges River Terraces
River terraces are older remnant flood plain surfaces that are higher in elevation than the modern flood plain. They may occur on one or both sides of the valley. Terraces are formed when the river channel cuts down into the flood plain and laterally erodes the alluvial valley, carving a new river channel and flood plain entrenched within the older flood plain surfaces. Down cutting can occur because of hydrologic or sedimentary changes in the headwaters or valley gradient changes caused by a retreating sea-level and lowered or extended base-level. Terraces can also form from tectonics and valley uplifting. Terraces are generally isolated from the more recent river processes and may only flood during 100 or 500 year flood events. River terraces are often Terrace 1 they contain artifacts from historic colonies archeological hot spots because This river has gone through that used the river and flood plain. Terrace 2 Terrace 3 Terrace 4 River Channel and Modern Flood Plain CopyrightLouis Maher, University of Wisconsin several different episodes of down cutting and rejuvenation.
The modern flood plain is preceded by four different terraces that all reflect distinct periods of environmental conditions or valley gradients, each different from the other. Over time, it is possible that the river will down-cut again abandoning a fifth terrace. Waterfalls Waterfalls occur where there is resistant bedrock, abrupt changes in bedrock resistance, or along fractures or faults in the bedrock. Less resistant materials are weathered more quickly than resistant rocks, creating stair-stepped ledges or drop offs where waterfalls occur. Less resistant rocks may also form pools between resistant rocks that form waterfalls. Faults and fractures often provide natural pathways for the downslope movement of water. The location of the waterfalls origin may be referred to as a knick-point, continued weathering by the stream flow causes the knick-point to slowly migrate upstream. Most waterfalls in South Carolina occur along streams in the Blue Ridge, Piedmont, and the along the Regional Fall Line where there are rock layers of varying This waterfall was formed by differential resistance. weathering between the softer shale and Lower White Water harder more resistant limestone. Falls in the Jocassee Gorges area of
South Carolina drops nearly 200 ft. Here, the Toxaway Gneiss forms a resistant bedrock that the Lower White Water River flows over before draining into Lake Jocasse. Copyright Marli Miller, University of Oregon Photo: SCGS Alluvial Fans Alluvial fans are fan-shaped fluvial deposits that accumulate at the base of stream where it flows out from a steep gradient and enters into a lower-gradient flood plain or valley setting. The stream enters the valley carrying a higher capacity sediment load than it can continue to carry, and as a result it deposits the sediments as an alluvial fan. Alluvial fans generally form in arid environments with a high sediment load and where there is minimal vegetation to disrupt
the fan formation. Alluvial fans may form from a single high-flow event or from the accumulation of multiple events. This alluvial fan is carrying a high sediment load from material weathered from the mountains. The dark line along the edge of the fan is a road. Because the road is not buried by recent deposits it suggest that this fan is not currently as active as it was in the past. Copyright Marli Miller, University of Oregon Coastal Landforms Coastal landforms include a diverse array of shoreline and nearshoreline features, as well as some coastal plain landforms far removed from the modern ocean by long term sea-level changes. This section will explore both constructive and destructive landforms formed by current coastal processes, as well as marine related landforms that were formed during periods of higher sea level. Littoral Zone Beaches Barrier Islands Beach Ridges Spits
Deltas Coastal Cliffs Marine Terraces Wave-Cut Scarps Hawaiian coastline Photo source: SCGS Beaches Beaches are depositional landforms along the coastal area where sediment is transported and deposited by waves and currents. Although the sediment along the beach is continually being mobilized there is an overall net accretion of deposition. The width of the beaches vary from one location to another and from one shoreline to another. In some locations a shoreline might even lack a beach altogether. Most beaches are dominated by sand-sized quartz grains, and shells or shell fragments. However, this can be highly variable depending on the landscape that drains into the ocean and near-shore sediment sources. For example, some beaches in the Hawaiian islands consist of coarse, red and black rock fragments formed by weathered lava; and in France and Italy many beaches consist of pebbles and cobbles. Sediment movement along the beach is referred to as beach drift, and it generally follows long shore currents traveling along a directional trend produced
as waves approach the shallower water in the surf zone near the shoreline. Beaches often stabilize shorelines by absorbing or deflecting wave and current energy. During large storms, such as hurricanes, beaches can experience extensive erosion, and it can be years before they are replenished. Beaches provide numerous recreational activities and are a popular destination for vacationers. Photo: SCGS Barrier Islands Barrier islands, also referred to as barrier beaches, are long, narrow, depositional landforms, that form parallel to the coastline and may or may not connect to the mainland. They are the first line of protection against hurricane storm surge. They are generally composed of quartz sands, and they form along coasts where there is a substantial supply of sand entering the ocean from Coastal Plain rivers. Barrier islands often form where tidal process are minimal. The landward side of the barrier islands may contain tidal flats, marshes, swamps, lagoons, coastal dunes, and beaches.
Similar to beaches, barrier islands form in relation to, long-shore current processes and overtime adjust to sea-level changes. Classic examples of barrier islands include North Carolinas Outer Banks and Texass Padre Island. Both of these barrier islands have National Park Service lands that preserve natural coastal processes and protect plant and wildlife habitat from human impacts. Image: NOAA Deltas Deltas form where the mouth of a river meets its ultimate base level at the ocean or sea. As the rivers velocity decreases, it looses the capacity to carry its sediment load and the resulting deposits form a delta. Delta shapes and forms vary depending on tidal influences, waves, currents, sediment type and quantity, river discharge, and the stream gradient near the outlet. The most common types of deltas include bird-foot, estuarine, and arcuate. Not all rivers form deltas, for example the Amazon deposits its sediment load directly into the ocean onto an underwater seaward sloping continental shelf. The Columbia River in the northwest United States, lacks a delta altogether, because the currents are too strong and erosive for the A bird-foot delta contains a large Mississippi River Delta: Bird-Foot Delta
sediments to deposit. channel with multiple smaller distributary channels draining off from the main channel and depositing sediments. They generally form with rivers that have a high sediment load and flow into an area with minimal tidal influences. This false-color infrared image provides a satellite view of the Mississippi River delta. This delta has shifted positions several times over the last 5000 years in relation to changes in the Mississippi River. Scientist recognize atleast 7 distinct deltas. The most recent began forming 500 years ago Deltas Nile River and Arcuate Delta The Nile River forms an arcuate fanshaped delta where it drains into the Mediterranean Sea. It is one of the largest deltas in the world; however, it is currently disappearing because the upstream Aswan High Dam is storing water and sediments and preventing them from being deposited in the delta. As a result the delta is eroding and saltwater is encroaching into freshwater. Other typical arcuate deltas include the Danube River where it enters the Black Sea in Romania, and
the Ganges and Indus River Deltas An estuary delta is formed where a river meets the ocean and sediments from the river are filling in the estuary. Estuaries contain a brackish mixture of freshwater and saltwater, and they have a moderate to strong tidal influence. Estuarine deltas are a common deltaic landform and they occur in several rivers along the western and eastern United States coasts, the Seine River in France, and the Tiber River in Italy. The ACE Basin of South Carolina, named for the Ashepoo, Combahee, and Edisto Rivers, protects nearly 150,00 acres of undeveloped ACE Basin: Estuarine Delta estuary habitat. Continental Shelf and Slope The continental shelf is a submerged extension of the continental crust that slopes gently outward from the modern shoreline to the deep ocean basin. The continental shelf varies in width from being almost non-existent along some continental margins to extending outward for nearly 1500 kilometers (930 miles) in other places. On average it extends outward for about 80 kilometers (50 miles) and has an average slope of about 1 degree (2 meters/kilometer or 10 feet/mile).
Ocean floor features including continental shelf and slope. This diagram provides a good illustration of how the shelf is a shallow extension of the continental crust. Source: NASA, Visible Earth A digital elevation model (DEM) of the continental shelf and slope near Los Angeles, California. Rift Zone Rift zones are fault structures formed by normal faults along active boundaries. Rising magma below the crust upwells, forcing the lithosphere to fracture, as it fractures and cracks, one or more faults occur causing the rock layers to separate forming a rift valley. Rift valleys can eventually form lakes or seas such as the Red Sea, which separates Africa from the Arabian Peninsula. Rift Valleys in Africa Red Sea Lake Victoria Copyright 2008 Google Earth Continental Shelf and
Slope: areas of turquoise colored continental crust around the continental margins Mid-Atlantic Ridge Aleutian Trench Juan de Fuca Ridge Mid-Ocean Ridges: boundary between divergent plate margins, indicates areas of sea-floor spreading East African Rift Valley and Red Sea Puerto Rico Trench Central America Trench Mariana Trench East Pacific Rise Tonga
Trench Kuril Trench Japan Trench Phillipine Trench Java-Sunda Trench Peru-Chile Trench Kermadec Trench Pacific-Antartic Ridge Ocean Basin: all of the submerged ocean floor beyond continental shelf and slope, but excluding trenches. South Sandwich Trench Rift Zone: tectonically active areas of rifting that create new seas
Indian Ridge Trenches: deep, narrow features along active margins, trenches are dark blue markings located on the map next to a pink star Glacial Landforms Glaciers are large masses of moving ice. Because glaciers are frozen they are part of the Earths cryosphere, which accounts for 77 percent of all Earths freshwater. Glaciers are very sensitive to the slightest temperature changes. Over Earths geologic history the spatial extent and size of glaciers has expanded and shrunk numerous times. As a result, glacial landforms can be found in locations that currently have no active glaciers or glaciation processes. Presently, glacial landforms occur in two distinct geographic regions, high latitude polar environments and high altitude mountain environments. In thisGlacier section we will explore Alpine Valley in Alaska. glacial landforms from their present context and from a historic look into the past.
Copyright Bruce Molnia, Terra Photographics Ice sheets and Alpine Glaciers Ice Field and Ice Caps Piedmont Glacier Tidal Glaciers and Icebergs Glacial U-shaped Valleys Fjords Hanging Valleys Cirques and Cirque Glaciers Artes, Horns, Cols Lateral and Medial Moraines End and Terminal Moraines Paternoster Lakes Kettles Erratics Drumlins
Outwash Plain Glaciers Glaciers are large masses of flowing ice formed by the accumulation and compaction of recrystallized melted snow. Glacial landforms are divided into two broad categories which occur in distinct geographic regions: ice sheets which occur high latitude polar environments and alpine glaciers which occur in high altitude mountain environments. Ice sheets are high latitude polar glaciers that cover extensive areas of continental landmasses, for this reason they are also referred to as continental glaciers. Glacial ice sheet formation requires long periods of extremely low temperatures, which allows snow to collect over vast areas covering the underlying terrain. The accumulation of snow forms dense layers that are thousands of meters thick. Antarctica and Greenland are both almost completely covered by glacial ice sheets. Alpine glaciers are long, linear glaciers that occupy high altitude mountain valleys, for this reason they are also referred to as valley glaciers. Alpine glaciers flow down valley, and increase in size as they accumulate and absorb smaller tributary glaciers from the mountainous terrain. Alpine glaciers can be found all around the world, and presently occur in may of the major mountain ranges in the world including the Rockies, Andes, and Himalayas. Alpine glaciers may also occur in highlatitude, polar or arctic mountains, such as those in Alaska. Geomorphologists often refer to glaciers as rivers of ice because like rivers, continental and alpine glaciers flow down-valley through the landscape eroding, transporting, and depositing weathered materials along their the path. It is this combination processes that
forms the diverse array of constructive and destructive glacial landforms. Tidal Glaciers and Icebergs Tidal glaciers are the portion of either alpine or continental glaciers which spill out into the sea and float on the surface of the saltwater. The glacial ice over the water breaks by calving off into large icebergs. Icebergs are large floating blocks of ice that calved off from tidal glaciers. Icebergs usually calve off along crevasses or cracks in the ice, but can also fail from a combination of melting and gravitational pull. Icebergs vary in size and thickness, and some reach heights more than 100 feet! The icebergs in the front of the photo calved of from the tidal glacier in the background. The portion of the icebergs exposed above the water is often only a third of their entire size, the other two-thirds is submerged below the water. Copyright Bruce Molnia, Terra Photographics Glacial U-Shaped Valleys
Glacial valleys are formed by the abrasive action of glacial ice as it slowly carves a u-shaped path through the mountainous valleys. Prior to the formation of the glacier, most valleys are initially formed as a v-shaped stream valley eroded by flowing water. Once the valleys becomes occupied by the glacier, the glacial ice spreads from one side of the valley to the other, completely filling in the valley floor and up the hill slopes. As the glaciers moves down-valley it abrasively erodes the pre-formed v-shaped stream valley into a u-shaped glacial valley. The Alaska's Woodworth Glacier, on the left is beginning to retreat and expose a glacial u-shaped valley beneath the melting ice. The Sierra Nevada landscape with Yosemite Valley pictured below, presently only contains glaciers in the highest elevations, but many of the prominent u-shaped valleys, reveal past evidence of glacial erosion. Copyright Bruce Molnia, Terra Photographics Source: Wikimedia Commons 56 Fjords
Fjords are flooded troughs that form where glacial u-shaped valleys intersect the ocean and the sea floods inland filling up the valley. Fjords can form during active glaciation or post-glaciation depending on sea-level. When a glacier intersects the ocean, the glacier can continue to erode and carve the valley below sea-level. The water that fills in above the glacier and floods the valley forms a fjord. Fjords can also form post-glaciation byisrising sea-level or changes in in the On the left a glacier intersecting a fjord elevation along the coastline fromOcean melting Pacific office. Estero de las Montanas in Chile, South America. Below is an aerial view of the Prince William Sound and Cascade Glacier fjord in Alaska. Copyright Michael Collier, USGS Copyright 2008 Google Hanging Valleys
Hanging valleys are abrupt, cliff-like features that are formed at the confluence where smaller tributary glaciers merge with larger valley glaciers. The scour of the larger glacier carves the valley into a u-shape, removing the original gradient of the tributary confluence, as a result the tributary valley is left stranded or hanging above the larger valley. Hanging valleys are only visible after the glacier melts and reveals the underlying topography. Hanging valleys are often the sight of dramatic plunging waterfalls. These images show hanging valleys in two different periods. Below the tributary glacier is retreating and a waterfall begins to form. The image on the right is of a post-glacial hanging valley, Bridal Falls in Yosemite National Park. Hanging Valley Copyright Bruce Molnia, Terra Photographics Lateral and MedialKennicott Moraines Glacier shows off multiple medial moraines as it Moraines are formed by the deposition of
descends Mount Blackburn in the glacial till as the glacier melts. Moraines are Wrangell-St. Elias National Park in defined by where the glacial till was Alaska. deposited relative to the moving, melting glacier. Lateral moraines are long linear ridges of glacial till deposited along the side of the glacier parallel to its direction of movement. Medial moraines are long linear ridges that form along the contact where tributary glaciers with lateral moraines merge to join larger valley glaciers (makes a Y-like formation). Medial moraines form were the glaciers merge together the till deposits become incorporated as dark ridges of sediment oriented down valley and aligned parallel through the middle of the glacier. Copyright Michael Collier, USGS