Grenville belts and the rodinia supercontinent

The Proterozoic saw the development of many continental-scale orogenic belts, many of which have been recently recognized to be parts of global-scale systems that reflect the formation, breakup, and reassembly of several supercontinents. Paleoproterozoic orogens include the Wopmay in northern Canada, interpreted to be a continental margin arc that rifted from North America, then collided soon afterward, closing the young back arc basin. There are many 1.9-1.6-Ga orogens in many parts of the...

Lematre Georges 18941966 Belgian

Cosmologist Georges Lema tre is most famous for proposing the theory of the big bang in 1933. He was born July 17, 1894, in Charleroi, Belgium, where he studied civil engineering and obtained a Ph.D. for his dissertation, L'Approximation des fonctions de plusieurs variables r elles (Approximation of functions of several real variables). He was ordained in 1923 as a Catholic priest before moving to Cambridge, United Kingdom, to study astrophysics at St. Edmund's College. He then moved to the...

Juvenile island arc accretion

Many Archean granite-greenstone terranes are interpreted as juvenile island arc sequences that grew above subduction zones and later amalgamated during collisional orogenesis to form new continental crust. The island arc model for the origin of the continental crust is supported by geochemical studies that show the crust has a bulk composition similar to arcs. Island arcs are extremely complex systems that may exhibit episodes of distinctly different tectonics, including accretion of ophiolite...

Dynamics Of Stream Flow

Streams are dynamic systems and constantly change their channel patterns and the amount of water (discharge) and sediment being transported in the system. streams may transport orders of magnitude more water and sediment in times of spring floods, as compared with low-flow times of winter or drought. since streams are dynamic systems, as the amount of water flowing through the channel changes, the channel responds by changing its size and shape to accommodate the extra flow. For instance, in a...

Northern Hemisphere snow cover

Graphs of global average temperature, sea level, and snow cover for the past 160 years (Data from IPCC 2007) Spruce killed by spruce bark beetle near Homer, Alaska (Peter Essick Aurora Getty Images) Spruce killed by spruce bark beetle near Homer, Alaska (Peter Essick Aurora Getty Images) Northern and the Southern Hemispheres. Changes in the ice caps on Greenland and Antarctica show an increased outflow of glacial ice and meltwater, so melting of the polar ice caps is very likely contributing to...

The Hydrologic Cycle

The water cycle describes the sum of processes operative in the hydrosphere, a dynamic mass of liquid continuously on the move between the different reservoirs on land and in the oceans and atmosphere. The hydrosphere includes all the water in oceans, lakes, streams, glaciers, atmosphere, and groundwa-ter, although most water is in the oceans. The hydro-logic, or water, cycle encompasses all of the changes, both long- and short-term, in the Earth's hydrosphere. It is powered by heat from the...

Beauty And The Beach Rethinking Coastal Living

Civilized societies have built villages, cities, and industrial sites near the sea for thousands of years. Coastal settings offer beauty and commercial convenience but also invite disaster with coastal storms, tsunami, and rising sea levels. In 2004 and 2005 the world witnessed two furious incursions of the sea into heavily populated coastal regions, killing hundreds of thousands of people and causing trillions of dollars in damage. Coastal communities are experiencing early stages of a new...

Summary

Sea level is rising presently at a rate of one foot (0.3 m) per century, although this rate seems to be accelerating. This rising sea level will obviously change the coastline dramatically a one-foot (0.3-m) rise in sea level along a gentle coastal plain can be equated with a 1,000-foot (300-m) landward migration of the shoreline. The world will look significantly different when sea levels rise significantly. Many of the world's low-lying cities like New York, New orleans, London, Cairo, Tokyo,...

Radon

Radon is a poisonous gas released during radioactive decay of the uranium decay series. Radon is a heavy gas, and it presents a serious indoor hazard in every part of the country because it accumulates in poorly ventilated basements and well-insulated homes that are built on specific types of soil or bedrock rich in uranium minerals. Radon causes lung cancer, and since it is an odorless, colorless gas, its presence can go unnoticed in homes for years. However, the hazard of radon is easily...

Emission Nebulae

The sections above focused on the formation of stars from the collapse of interstellar dust clouds but did not focus on the effects these processes have on the surrounding intergalactic medium. Star formation as described above does not usually result in the formation of just one star, but rather a group or cluster of stars with similar characteristics and ages in a region that represents the original collapsed interstellar cloud. The more massive the original collapsed dust cloud, the more new...

Flash Floods

Flash floods result from short periods of heavy rainfall and are common near warm oceans, along steep mountain fronts in the path of moist winds, and in areas prone to thunderstorms. They are well known from the mountain and canyon lands of the U.S. desert Southwest and many other parts of the world. Some of the heaviest rainfalls in the United States have occurred along the Balcones escarpment in Texas. Atmospheric instability in this area often forms along the boundary between dry desert air...

Namib desert and the skeleton coast

Namibia's Atlantic coastline is known as the skeleton coast, named for the suffering and death that beset many sailors attempting to navigate the difficult waters swept by the cold Benguela current, which moves along the coast, and warm winds coming off the Namib and Kalahari Deserts. The coastline is littered with numerous shipwrecks, testifying to the difficult and often unpredictable nature of shifting winds and ocean currents. Giant sand dunes of the Namib sand sea reach to the coast, and...

Mount St Helens 1980 and the Cascades Today

The most significant eruption in the contiguous united states in the past 90 years is that of Mount st. Helens in 1980, a mountain that had lain dormant for 123 years. The volcano is part of the active Cascade volcanic arc, a continental-margin arc built on the western coast of North America above where the minor Juan de Fuca plate is being subducted beneath North America. The arc is relatively small (about 1,200 miles, or 2,000 km, long), and stretches from Lassen Peak in California to Mount...

Rapid Changes In Ocean Circulation Patterns And Cumate Change

Some models of climate change show that patterns of ocean circulation can suddenly change and cause global climate conditions to switch from warm to cold, or cold to warm, over periods of a few decades. Understanding how fast climate can shift from a warm period to a cold, or cold to a warm, is controversial. The record of climate indicators is incomplete and difficult to interpret. Only 18,000 years ago the planet was in the midst of a major glacial interval, and since then global average...

Glaciation And Glacial Landforms

Glaciation is the modification of the land's surface by the action of glacial ice. When glaciers move over the land's surface, they plow up the soils, abrade and file down the bedrock, carry and transport the sedimentary load, steepen valleys, then leave thick deposits of glacial debris during retreat. In glaciated mountains a distinctive suite of landforms results from glacial action. Glacial stria- tions are scratches on the surface of bedrock, formed when a glacier drags boulders across the...

Darwins Theory Of EvOLUTION

When Darwin returned to London he was already a celebrity in some scientific circles, since his mentor Henslow had shared many of his geological notes and biological findings with colleagues. After visiting family and friends Darwin returned to Cambridge and studied his notes, data, and samples with the help of many colleagues and scientists recommended by Henslow. Together they cataloged his collections from around the world and discussed many of the possibilities suggested by his geological...

Glossopetrae

While waiting for these results to be published in the fall of 1666, an enormous great white shark that weighed about 2,800 pounds (1,270 kg) was captured and killed on a beach off Livorno. Ferdinando asked Steno to dissect its head, which was brought to Florence. Before a large audience, Steno carefully dissected away the skin and soft tissues and examined the nerves and the tiny brain. The excitement at the scene must have been incredible. The beast's teeth were almost three inches (7.6 cm)...

Structural geology And Plate Tectonics

The surface of the Earth is divided into 12 major and several minor plates that are in motion with respect to each other. Plate tectonics describes these relative motions, which are, to a first approximation, rigid body rotations. However, deformation of the plates does occur (primarily in belts tens to hundreds of kilometers in width along the plate boundaries), and in a few places, extends into the plate interiors. structural geology deals with these deformations, Hypsometric curve showing...

Further Reading

London Routledge, 1992. Erickson, Jon. Glacial Geology How Ice Shapes the Land. New York Facts On File, 1996. Intergovernmental Panel on Climate Change. Available online. URL http www.ipcc.ch index.htm. Accessed January 30, 2008. Kusky, T. M. Climate Change Shifting Deserts, Glaciers, and Climate Belts, The Hazardous Earth Set. New York Facts On File. 2008. Pluto The solar system has long been considered to have nine planets, including Mercury, Venus, Earth, Mars,...

Wind In Deserts

Wind plays a significant role in the evolution of desert landscapes. Wind erodes in two basic ways. Deflation is a process whereby wind removes material from an area, reducing the land surface. The process is akin to deflating a balloon below the surface of the ground, hence its name. Abrasion is a different process that occurs when particles of sand and other size grains are blown by the wind and impact one another. Exposed surfaces in deserts are subjected to frequent abrasion, which is...

The Greenhouse Effect

The term greenhouse effect refers to the Earth's climate as being sensitive to the concentrations of certain gases in the atmosphere. The concept was first coined by French physicist Edme Mariotte (1620-84) in 1681, who noted that light and heat from the Sun easily pass through a sheet of glass, but that heat from candles and other sources does not. This concept was then extended by French mathematician and physicist Joseph Fourier in 1824 to the atmosphere by noting that heat and light from...

Krakatau Indonesia 1883

Indonesia has seen catastrophic volcanic eruptions and associated tsunamis other than from Tambora. The island nation of Indonesia has more volcanoes than any other country in the world, with more than 130 known active volcanoes. These volcanoes have been responsible for about one-third of all the deaths attributed to volcanic eruptions and associated tsunamis in the world. Indonesia stretches for more than 3,000 miles (5,000 km) between southeast Asia and Australia, is characterized by very...

American Desert Southwest

The history of development the American desert southwest was crucially dependent on bringing water resources into this semiarid region. much of California, especially the Los Angeles region, was regarded as worthless desert scrubland until huge water projects designed by the Bureau of Land Reclamation diverted rivers and resources from all over the West. In the years between 1911 and 1923 the California water department under the leadership of William Mulholland quietly purchased most of the...

Major volcanic Eruptions and Climate Change

Some of the larger, more explosive volcanic eruptions that the planet has witnessed in the past few hundred years have ejected large amounts of ash and finer particles called aerosols into the atmosphere and stratosphere, and it may take years for these particles to settle down to Earth. They get distributed about the planet by high-level winds, and they block some of the Sun's rays, which lowers global temperatures. This happens because particles and aerosol gases in the upper atmosphere tend...

Evolution in the fossil record

The vast expanses of time needed to test models of evolution are provided by the fossil record, which extends back hundreds of millions of years for complex organisms, and billions of years for simple organisms. The first example of evolution described from the geologic record was in 1869, when German geologist Wilhelm Heinrich Waagen (1841-1900), who studied Jurassic ammonites, published his classic Die Formenreihe des Ammonites subradiatus (The Sequence of Form of the Ammonite's...

Physical Properties Of GalaxIES

The observable universe presents an estimated minimum of 100 billion galaxies, and many of these have billions of stars in them. Most of these galaxies are located far from Earth and the Milky Way Galaxy, and thus are difficult to observe closely. To measure distances to and sizes of these distant galaxies one must use some objects, such as planetary nebulae or certain kinds of supernovae that have known brightnesses, and then use their apparent brightness to measure their distance from Earth....

Siberian Taiga Forest And Global Carbon Sink

The northern third of Asia, stretching from the Ural Mountains in the west to the Pacific coast into the east, is known as siberia. The southern border of Siberia is generally taken to be the Kazakh steppes in the southwest, the Altai and sayan Mountains in the south, and the Mongolian steppes in the southeast. This region occupies approximately 3,000,000 square miles (7,500,000 km2). The western third of Siberia is occupied by the Siberian lowland, stretching from the Urals to the Yenisei...

Groundwater Dissolution

Groundwater also reacts chemically with the surrounding rocks it may deposit minerals and cement together grains, causing a reduction in porosity and permeability, or form features like stalagtites and stalagmites in caves. In other cases, particularly when acidic water moves through limestone, it can dissolve the rock, forming caves and underground tunnels. sinkholes form where these dissolution cavities intersect the surface of the Earth. Groundwater dissolution leads to the development of a...

Ophiolite accretion

Ophiolites are a distinctive association of allochtho-nous rocks interpreted to form in a variety of plate tectonic settings such as oceanic spreading centers, back arc basins, forearcs, arcs, and other extensional magmatic settings including those in association with plumes. A complete ophiolite grades downward from pelagic sediments into a mafic volcanic complex generally made of mostly pillow basalts, underlain by a sheeted dike complex. These are underlain by gab-bros exhibiting cumulus...

Atmospheric evolution

Considerable uncertainty exists about the origin and composition of the Earth's earliest atmosphere. Many models assume that methane and ammonia dominated the planet's early atmosphere, instead of nitrogen and carbon dioxide, as it is presently. The gases that formed the early atmosphere could have come from outgassing by volcanoes, from extraterrestrial sources (principally cometary impacts), or, most likely, both. Alternatively, comets may have brought organic molecules to Earth. A very large...

Magnetosphere

The magnetosphere encompasses the limits of the Earth's magnetic field, as confined by the interaction of the solar wind with the planet's internal magnetic field. The natural undisturbed state of the Earth's magnetic field is broadly similar to a bar magnet, with magnetic flux lines (of equal magnetic intensity and direction) coming out of the south polar region, and returning back into the north magnetic pole. The solar wind, consisting of supersonic H+ and 4He2+ ions expanding away from the...

Greenstonegneiss Contact Relationships

An important problem in many greenstone belt studies is determining the original structural relationships between greenstone belts and older gneiss terrains. In pre-1990 studies the significance of early thrusting along thin fault zones went unrecognized, leading to a widespread view that many greenstone belts simply rest in depositional contact over older gneisses, or that the older gneisses intruded the greenstone belt. While this may be the case in a few examples, it is difficult to...

Of metallic ore deposits

Most metallic ores form by one of several main processes, including concentration by hydrothermal fluids, crystallization from an igneous magma, meta-morphic processes that move fluids and chemical components in rocks from place to place, weathering, sorting by water in streams, or other surficial processes that can remove some elements from a rock or soil while concentrating other elements. Many of the ores of metallic minerals occur as compounds of the sulfide ion, S2-, with the metals...

Natural Gas and Gas Hydrate Eruptioninduced Tsunamis

The continental shelves and slopes around most continents are the sites of deposition of very thick piles of sediments. River deltas such as the Mississippi delta may add even more sediments to these environments, in some cases forming piles of sediment that are 10 miles (16 km) thick, deposited over many millions of years. Natural gas is produced in submarine sediments by the anaerobic decay of organic matter that becomes buried with the sediments. The gas produced by the decay of these...

Cosmic microwave background radiation

In 1964 two American scientists, Arno Penzias and Robert Wilson, were working on a project at Bell Laboratories in New Jersey to identify and eliminate sources of interference with satellite communications. In their work they accidentally stumbled on one of the most important finds in astronomy and astrophysics of the century. While Penzias and Wilson were examining the radiowave emissions from the Milky Way Galaxy using microwave wavelengths, they discovered a background hiss that would not go...

Plate Tectonics Supercontinents And Life

Plate tectonic motions, especially the supercontinent cycle, profoundly affect the distribution and evolution of life on Earth. Plate tectonic activity such as rifting, continental collision, and drifting continents affects the distribution of life-forms, the formation and destruction of ecological niches, and radiation and extinction blooms. Plate tectonic effects also can induce sea level changes, initiate periods of global glaciation, change the global climate from hothouse to icehouse...

Love Canal Is Not For Honeymooners

Love Canal is not a place many people would choose to visit on a honeymoon. Love Canal was a quiet neighborhood in Niagara Falls, New York, that became infamous as one of the most horrific toxic waste dumps in the country. The history of Love Canal began in the 1890s, when entrepreneur William T. Love envisioned building a canal that would connect the two levels of the Niagara River, above and below the falls, for generating electricity and, eventually, as a shipping canal. He dug about a mile...

Further Resources

Natural Disasters. 3rd ed. Boston McGraw-Hill, 2002. A college freshman-level book about natural disasters, listing causes and examples. Abrahams, A. D., and A. J. Parsons. Geomorphol-ogy of Desert Environments. Norwell, Massachusetts Kluwer Academic Publishers for Chapman and Hall, 1994. This is a comprehensive textbook, describing the wide range of landforms and processes in desert environments. Ahrens, C. D. Meteorology Today, An Introduction to Weather, Climate, and the...

Emergence Of Photosynthesis

The first single-celled organisms were heterotrophs they could not manufacture their own food. These organisms consumed the inorganically formed amino acids or other chemicals existing in their immediate environment. These early organisms received energy from these amino acids by fermentation, the processes of breaking down food molecules (sugars) through a series of chemical steps, into carbon dioxide and alcohol. When photosynthesis began, organisms became able to manufacture their own food...

Continental Interior Midlatitude Deserts

Some places on Earth are so far from ocean moisture sources that by the time weather systems reach them, most of the moisture they carry has already fallen. This effect is worsened if the weather systems must rise over mountains or plateaus to reach these areas, because cloud systems typically lose moisture as they rise over mountains. These remote areas therefore have little chance of receiving significant rainfall. The most significant deserts in this category are the Taklimakan-Gobi region...

Himalaya Mountains

The Himalaya Mountains were formed during the Tertiary continent-continent collision between India and Asia and contain the tallest mountains, as well as those exhibiting the greatest vertical relief over short distances, in the world. The range extends for more than 1,800 miles (3,000 km) from the Kara-koram near Kabul, Afghanistan, past Lhasa, Tibet, to Arunachal Pradesh in the remote Assam Province of India. Ten of the world's 14 peaks that rise to more than 26,000 feet (8,000 m) are located...

Early Paleozoic History

One of the greatest changes in Earth history is marked by the Precambrian-Phanerozoic transition. At this time the Earth witnessed the first widespread appearance of organisms with hard shells, and there was a huge adaptive radiation unparalleled in the rest of Earth history. By this time most of the cratons on the planet had formed and large continents existed, and plate tectonics had already been through several supercontinent cycles. The history of the early Paleozoic can be interpreted from...

Andesitic Magma

The average composition of the continental crust is andesitic, or somewhere between the composition of basalt and rhyolite. Laboratory experiments show that partial melting of wet oceanic crust yields an andesitic magma. Most andesites today are erupted along continental margin convergent boundaries where a slab of oceanic crust is subducted beneath the continent. Remember that oceanic crust is dry, but after it forms it interacts with seawater, which fills cracks to several miles (kilometers)...

Hadley cell

Hadley cells are the globe-encircling belts of air that rise along the equator and drop moisture as they rise in the Tropics. As the air moves away from the equator at high elevations, it cools, becomes drier, then descends at 15-30 N and S latitude, where it either returns to the equator or moves toward the poles. The locations of the Hadley cells move north and south annually in response to the changing apparent seasonal movement of the Sun. High-pressure systems form where the air descends,...

Volcanic Eruptioninduced Tsunamis

Some of the largest recorded tsunamis have been generated by volcanic eruptions. These may be associated with the collapse of volcanic slopes, debris and ash flows that displace large amounts of water, or submarine eruptions that explosively displace water above the volcano. Approximately 20 percent of volcanic-induced tsunamis form when volcanic ash or pyroclastic flows hit the ocean, displacing large amounts of water, and 20 percent form from earthquakes associated with the eruption. About 15...

Pluton Emplacement Mechanisms

The volume of magma that intruded the Earth's crust in some plutons and batholiths is enormous. All the magma in these plutons had to create space in the crust for it to intrude into, since the plutons typically intrude into preexisting continents. Geologists have long speculated on how such large volumes of magma intrude the crust, and what relationships these magmas have on the style of volcanic eruption. One mechanism that may operate is assimilation, where the magma melts surrounding rocks...

Drainage Systems

A drainage basin is the total area that contributes water to a stream, and the line that divides different drainage basins is known as a divide (such as the continental divide) or interfluve. Drainage basins are the primary landscape units or systems concerned with the collection and movement of water and sediment into streams and river channels. Drainage basins consist of a number of interrelated systems that work together to control the distribution and flow of water within the basin....

Types Of Satellite Imagery

Satellite imagery forms one of the basic tools for remote sensing. The types of satellite images available to the geologist, environmental scientist, and others are expanding rapidly, and only the most common in use are discussed here. The Earth Resources Technology Satellite (ERTS-1), the first unmanned digital imaging satellite, was launched on July 23, 1972. Four other satellites from the same series, later named Landsat, were launched at intervals of a few years. The Landsat spacecraft...

The 1992 Flores Indonesia Tsunami

One of the more deadly tsunamis in recent history hit the island of Flores, located in Indonesia several hundred miles from the coast of northern Australia near the popular resort island of Bali. The tsunami hit on December 12, 1992, and was triggered by a magnitude 7.9 earthquake, with the earthquake faulting event lasting for a long 70 seconds. The tsunami had run-up heights of 15 to 90 (4-27 m) feet along the northeastern part of Flores Island, where more than 2,080 people were killed and at...

Movement of glaciers

When glacial ice becomes thick enough, it begins to flow and deform under the influence of gravity. The thickness of the ice must be great enough to overcome the internal forces that resist movement, which depend on the temperature of the glacier. The thickness at which a glacier starts flowing also depends on the steepness of the slope on which it flows thin glaciers can move on steep slopes, whereas to move across flat surfaces, glaciers must become very thick. The flow is by creep, or...

Proposal Of Seafloor Spreading

Hess contemplated these many unexpected discoveries in relation to the theory of continental drift proposed by the German meteorologist and geophysicist Alfred Wegener in 1912. After noticing that the east coast of south America and the west coast of Africa fit together like pieces of a jigsaw puzzle and collecting additional fossil evidence, Wegener concluded that the continents had once been connected, but split and drifted thousands of miles apart. Wegener offered no explanation for the...

IvErgent Plate Boundaries In The Oceans The Midocean Ridge System

Some continental rifts may evolve into midocean ridge-spreading centers. The world's best example of where this transition can be observed is in the Ethiopian Afar, where the East African continental rift system meets juvenile oceanic spreading centers in the Red Sea and Gulf of Aden. Three plate boundaries meet in a wide plate boundary zone in the Afar, including the African Arabian boundary (Red Sea spreading center), the Arabian Somalian boundary (Gulf of Aden spreading center), and the...

Coastal Wetlands And Marshes

Many bays, estuaries, and coastal tidal flats are bordered inland by a vegetated intertidal area containing grasses or shrublike mangrove swamps. mangroves do not tolerate freezing conditions so are found only at low latitudes, whereas salt marshes are found at all latitudes. These coastal wetlands or salt marshes host a range of water salinities, from salty and brackish to nearly fresh. As estuaries age or mature, they tend to become progressively filled in first by tidal flats, then by salt...

Chile Earthquake and Tsunami

The great magnitude 9.5 Chilean earthquake of May 22, 1960, generated a huge tsunami that killed more than 1,000 people near the earthquake epicenter and almost 1,000 more as the wave propagated across the Pacific Ocean. This tsunami was generated along the convergent boundary between the small Nazca oceanic plate in the Pacific Ocean and southern South America. This part of the Ring of Fire convergent boundary generates more tsunamogenic earthquakes than anywhere else on the planet, unleashing...

Granitic Magma

Granitic magmas are very different from basaltic magmas. They have about 20 percent more silica, and the minerals in granite include quartz (Si02) and the complex minerals mica (K,Na,Ca) (Mg,Fe,Al)2 AlSi4 O10 (OH,F)2 and amphibole ((Mg,Fe,Cah (Mg,Fe,Al)5 (si,Al)8 o22(oH)2), which both have a lot of water in their crystal structures. Also, granitic magmas are found almost exclusively in regions of continental crust. From these observations it is inferred that the source of granitic magmas is...

Big Thompson Canyon Colorado 1976

Big Thompson Canyon is a popular recreation area about 50 miles (80 km) northwest of Denver, in the Front Ranges of the Rocky Mountains. On July 31, 1976, a large thunderhead cloud had grown over the front ranges, and it suddenly produced a huge cloudburst (rainfall) instead of blowing eastward over the plains as it normally does. Approximately 7.5 inches (0.2 m) of rain fell in a four-hour period, an amount approximately equal to the average yearly rainfall in the area. The steep topography...

Rocky Coasts

Rocky coastlines are most common along many convergent tectonic plate boundaries and on volcanic islands, but may also be found on recently deglaci-ated coasts and along other uplifted coasts such as southern Africa and recently uplifted coasts such as along the Red sea. Rocky coasts are the most common type of coastline in the world, forming on the order of 75 percent of the world's coasts. The morphology of rocky coastlines is determined mainly by the type of rock, its internal structure and...

Intrusive Igneous Bodies

Once magmas are formed from melting rocks deep within the Earth, they rise to intrude the crust and may take several forms. A pluton is a general name for a large cooled igneous intrusive body in the Earth. The name of the specific type of pluton is based on its geometry, size, and relations to the older rocks surrounding the pluton, known as country rock. Concordant plutons have boundaries parallel to layering in the country rock, whereas discordant plutons have boundaries that cut across...

Basaltic Magma

Partial melting in the mantle leads to the production of basaltic magma, which forms most of the oceanic crust. By looking at the mineralogy of the oceanic crust, which is dominated by the minerals olivine (mg2sio4), pyroxene (mg,Fesi2o6), and feldspar (KAlsi3o8), it is concluded that very little water is involved in the production of the oceanic crust. These minerals are all anhydrous, that is without water in their structure. Therefore partial melting of the upper mantle without the presence...

Coal

The most abundant fossil fuel, coal is a combustible rock that contains more than 50 percent (by weight) carbonaceous material formed by the compaction and induration of plant remains. Coal is a black sedimentary rock that consists chiefly of Oil platform off California coast (Susan Quinland-Stringer, Shutterstock, Inc.) Oil platform off California coast (Susan Quinland-Stringer, Shutterstock, Inc.) decomposed plant matter, with less than 40 percent inorganic material. Most coal formed in...

Giant landslideinduced Tsunamis in Hawaii

Many volcanic islands, such as those of the Hawaiian chain in the Pacific, Reunion in the Indian Ocean, and the Canary Islands and Tristan da Cunha in the Atlantic, are built through a combination of volcanic flows adding material to a small area in the center of the island. Frequent submarine landslides cause the islands to collapse, spreading the rocks from these flows across a wide area. Undersea mapping of the Hawaiian chain using sonar systems that can produce detailed views of the...

Black dwarf stage

As the white dwarf continues to cool, its surface becomes less and less luminous until it becomes a cold, dark, carbon-rich, burned-out sphere floating in space. Even as it cools, the black dwarf no longer contracts. This is because its atoms are so dense that they are in the electron degenerate state and cannot be squeezed together any further. Therefore most solar-sized stars end up as dense, cold, dark, Earth-sized objects, perpetually cooling in space. such is the fate of most solar-sized...

Trade wind or hadley cell deserts

Many of the world's largest and most famous deserts are located in two belts between 15 and 30 North and south latitude. Included in this group of deserts are the sahara, the world's largest desert, and the Libyan Desert of North Africa. Other members of this group include the Syrian Desert, Rub' al-Khali (Empty Quarter), and Great Sandy Desert of Arabia the Dasht-e-Kavir, Lut, and Sind of southwest Asia the Thar Desert of Pakistan and the Mojave and Sonoran Deserts of the united States. In the...

Stratigraphy strati cation cyclothem

Stratigraphy is the study of rock strata or layers, especially with concern for their succession, age relationships, lithologic composition, geometry, distribution, correlation, fossil content, and other aspects of the strata. The main aim of stratigraphy is to understand and interpret the rock record in terms of paleoenvironments, mode of origin of the rocks, and the causes of similarities and differences between different stratigraphic units. Because sedimentary rocks are laid down one on top...

Erosion Sediment Transport And Deposition In FluvIAL systems

Most energy in streams is dissipated by turbulent flow, but a small part of a stream's energy is used to erode and transport sediments downstream. Streams carry a variety of materials as they make their way to the sea, and the way this material is eroded and transported depends on the energy balance in the stream. These materials range from minute dissolved particles and pollutants to giant boulders moved only during the most massive floods. The bed load consists of the coarse particles that...

Hazards to Humans

From the descriptions of mass-wasting processes and specific events above, it should be apparent that mass wasting presents a significant hazard to humans. The greatest hazards are from building on mountain slopes, which when oversteepened may fail cata-strophically. The fastest moving flows present the greatest threat to human life, with examples of the debris avalanches at Vaiont, Italy, in 1963, Nevados Huascaran, Peru, in 1962 and 1970, and the Leyte, Philippines, disaster of 2006 providing...

Pelagic nektonic planktonic

The lithosphere to drifting and cooling of the lithosphere. The cooling of the lithosphere beneath the passive margin leads to gradual subsidence, typically without the dramatic faulting that characterized the rifting and Red Sea stages of the margin's evolution. Volcanism wanes, and sedimentation on the margins evolves to exclude evaporites, favoring carbonates, mudstones, sandstones, and deltaic deposits. The overall thickness of passive margin sedimentary sequences can grow to 9 or even 12.5...

Scientific ContnBUTIONS

Galileo was one of the first scientists to state clearly that the laws of nature could be explained mathematically. In his book The Assayer, published in Rome in 1623, Galileo wrote that the universe is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures. Galileo was driven by testing assertions by scientists, philosophers, and religious figures through experimentation and mathematics, and this passion and reason in his character led...

The Origin Of Magma

Magmas come from deep within the Earth. The processes of magma formation at depth and its movement to the surface have been the focus of research for hundreds of years. The temperature generally increases with depth in the Earth, since the surface is cool and the interior is hot. The geothermal gradient is a measure of how temperature increases with depth in the Earth, and it provides information about the depths at which melting occurs and the depths at which magmas form. The differences in...

Monitoring of Active Landslides

What are the signs that need to be watched for that may warn of an imminent mass-wasting event Areas that have previously suffered mass-wasting events may be most prone to repeated events, so geomor-phological evidence for ancient slumps and landslides should be viewed as a warning. It is recognized that seismic activity and periods of heavy rainfall destabilize slopes and are times of increased hazards. Activity of springs can be monitored to detect when the slopes may be saturated and...

Nicaragua Tsunami

The west coast of Nicaragua and Central America is a convergent margin where oceanic crust of the Cocos plate (a small plate attached to the Pacific Ocean plate) is being subducted beneath the western edge of the Caribbean plate. A volcanic arc with active volcanoes, earthquakes, and steep mountains has formed above this convergent margin subduction zone. The area is prone to large earthquakes in the forearc and to explosive volcanic eruptions and also suffers from many hurricanes, landslides,...

Precambrian Cratons And Shields

The core of South America is made of its Precam-brian cratons, including the Guiana and Brazilian (also called the Amazonian) shields and the Rio de la Plata craton. These cratonic blocks also formed central regions of several past supercontinents including Gondwana and Rodinia. The Guiana shield has rocks as old as 3.4 billion years, and other major groups of rocks formed at 1.5 and 0.9 billion years ago. Highland regions of the Guiana shield, called the Guiana Highlands, are characterized by...

Turkey 1999 magnitude

On August 17, 1999, a devastating earthquake measuring 7.4 on the Richter scale hit heavily populated areas in northwestern Turkey at 3 02 a.m. local time. The epicenter of the earthquake was near the industrial city of Izmit about 60 miles (100 km) east of Istanbul, near the western segment of the notorious North Anatolian strike-slip fault. The earthquake formed a surface rupture more than 75 miles (120 km) long, along which offsets were measured between four and 15 feet (1.5-5 m). This was...

Amazon river

The Amazon is the world's second-longest river, stretching 3,900 miles (6,275 km) from the foothills of the Andes to the Atlantic Ocean. The Amazon begins where the Ucayali and Maranon tributaries merge, and it drains into the Atlantic near the city of Belem. The Amazon carries the most water and has the largest discharge of any river in the world, averaging 150 feet (45 m) deep. Its drainage basin amounts to about 35 percent of south America, covering 2,500,000 square miles (6,475,000 km2)....

Astronomical Forcing of the Climate

Medium-term climate changes include those that alternate between warm and cold on timescales of 100,000 years or fewer. These medium-term climate changes include the semiregular advance and retreat of the glaciers during the many individual ice ages in the past few million years. Large global climate oscillations that have been recurring at approximately a 100,000-year periodicity at least for the past 800,000 years have marked the last 2.8 Ma. The warm periods, called interglacial periods,...

Running Water As An Erosive Agent

Water is an extremely effective erosional agent, including when it falls as rain and runs across the surface in finger-sized tracks called rivulets, and when it runs in organized streams and rivers. Water begins to erode as soon as the raindrops hit the surface the raindrop impact moves particles of rock, breaking them free from the surface and setting them in motion. During heavy rains the runoff is divided into overland flow and stream flow. Overland flow is the movement of runoff in broad...

Cretaceoustertiary Boundary

The Cenozoic began after a major extinction at the Cretaceous-Tertiary boundary, marking the boundary between the Mesozoic and Cenozoic Eras. This extinction event was probably caused by a large asteroid impact that hit Mexico's Yucat n Peninsula near Chicxulub at 66 million years ago. Dinosaurs, ammonites, many marine reptile species, and a large number of marine invertebrates suddenly died off, and the planet lost about 26 percent of all biological families and numerous species. Some...

The Alpine Mountain Chain

The Alps form an arcuate or curved mountain system of south-central Europe, about 497 miles (800 km) long and 93 miles (150 km) wide, stretching from the French Riviera on the Mediterranean coast, through southeastern France, switzerland, southwestern Germany, Austria, and former Yugoslavia (serbia). The snow line in the Alps is approximately 8,038 feet (2,450 m), with many peaks above this permanently snowcapped or hosting glaciers. The longest glacier in the Alps is the Aletsch, but many...

Metamorphic Changes

Compressing a piece of paper would cause the flat dimensions to orient themselves perpendicular to the direction of compression. Likewise, when a metamor-phic rock is compressed or stressed, the platy minerals, such as chlorite and micas, orient themselves so that their long dimensions are perpendicular to the maximum compressive stress. The planar fabric that results from this process is known as a foliation. slaty cleavage is a specific type of foliation in which the parallel arrangement of...

Kinds Of metamorphic ROCKS

The names of metamorphic rocks are derived from their original rock type, their texture, and mineral assemblages. shales and mudstones have an initial mineral assemblage of quartz, clays, calcite, and feldspar. slate is the low grade metamorphic equivalent of shale and, with recrystallization, is made of quartz and micas. At intermediate grades of metamorphism, the mica grains grow larger so that individual grains become visible to the naked eye and the rock is called a phyllite. At high grades...

Darwin Charles

His ideas on the transmutation of species and natural selection were conceived in 1838 but not published until 1859. These ideas were used to build the modern concept of evolution and form some of the basic foundations of biology by offering viable explanations for the diversity of life, expressed in his famous book On the Origin of Species, published in 1859. His ideas are widely accepted by the scientific community but are often still attacked by religious...

Collisions

Collisions are the final products of subduction. There are several general varieties of collisions. They may be between island arcs and continents, such as the ordovician Taconic orogeny in eastern North America, or they may juxtapose a passive margin on one continent and an Andean margin on another. More rarely, collisions between two convergent margins occur above two oppositely dipping subduction zones, with a contemporary example extant in the Molucca Sea of Indonesia. Finally, collisions...

Geomorphology

China is geomorphologically diverse, consisting of about 33 percent mountains, 25 percent plateaus (including Tibet), 20 percent basins, and 10 percent hilly terrain. In general, the land surface slopes from the high regions including Tibet in the west, to the 1,100-mile (1,800-km) coastline in the east. Satellite image of Asia (M-Sat Ltd. Photo Researchers, Inc.) There are three main physiographic provinces of China based on elevation. The Tibetan, or Qinghai-Xizang Plateau, in the south rises...

Correlation of rocks

If a geologist has studied a stratigraphic unit or system in one location and figured out conditions on the Earth at that point when the rock was deposited, this information can be related to the rest of the planet or simply to nearby areas. In order to accomplish this task, the geologist first needs to determine the relative ages of strata in a column, then estimate the absolute ages relative to a fixed time scale. One can determine correlations between stratigraphic units locally using...

Detection of Incipient Sinkholes

Some of the damage from sinkhole formation could be avoided if the location and general time of sinkhole formation could be predicted. At present it may be possible to recognize places where sinkholes may be forming by monitoring for the formation of shallow depressions and extensional cracks on the surface, particularly circular depressions. Building foundations can be examined regularly for new cracks, and distances between slabs on bridges with expansion joints can be monitored to check for...

Atmospheric Shock Waves

The effect that an asteroid or meteor has on the Earth's atmosphere depends almost completely on the size of the object. Weak meteors that are up to about 30-90 feet (10-30 m) in diameter usually break up into fragments and completely burn up in the atmosphere before they hit the Earth's surface. The height in the atmosphere that these meteors break up depends on the strength of the meteor body, with most comets and carbonaceous chondrites of this size breaking up above 19 miles (30 km)....

Nevada del Ruiz Colombia 1985

The most deadly volcanic-induced disaster of modern times occurred in a relatively minor volcanic eruption in the Andes Mountains of South America. The Nevada del Ruiz volcano in Colombia entered an active phase in November 1984 and began to show rhythmically repeating harmonic earthquake tremors on November 10, 1985. At 9 37 p.m. that night a large Plinian eruption sent an ash cloud several miles into the atmosphere, and this ash settled on the ice cap on top of the mountain. This ash together...

Altaids

The Altaid orogenic belt stretches across southern Russia and several former soviet Republics including Kazakhstan, Uzbekistan, Mongolia, and parts of China. This huge, poorly known mountain system forms about half of northern Asia and is bounded by the Siberian (Angara) and Russian cratons in the north and by the Alpine-Himalaya mountains, Tarim, and North China blocks in the south. The Urals bound the Altaids in the west, and the Baikal Mountains bound them in the east. There are two main...

Geological And Agricultural Studies

Hutton toured a little, and his interest in chemistry grew into a love of geology and mineralogy. Between 1752 and 1753 he lived with a farmer in Norfolk, England, where he was fascinated by the rows of black flints embedded in the white chalk. He spent time gazing at heaps of seashells on the east coast and noticed chalk and foreign stones embedded in cliffs to the north. In the west he observed red-colored chalk in the strata. With such geological variety above ground, he wondered what was...

Windblown Sand And Dust

Most people think of deserts as areas with lots of big sand dunes and continual swirling winds of dust storms. But really dunes and dust storms are not as common as depicted in popular movies, and rocky deserts are more common than sandy deserts. For instance, only about 20 percent of the Sahara is covered by sand the rest is covered by rocky, pebbly, or gravel surfaces. Sand dunes are locally very important in deserts, however, and wind is one of the most important processes in shaping deserts...

Relationship Of Supercontinents Lower Mantle Convection And The Geoid

Some models for the formation and dispersal of supercontinents suggest a link between mantle convection, heat flow, and the supercontinent cycle. Stationary supercontinents insulate the mantle, causing it to heat up, because the cooling effects of subduction and seafloor spreading are absent. As the mantle then heats up, convective upwelling is initiated, causing dynamic and isostatic uplift of the continent, injection of melts into the continental crust, and extensive crustal melting. These...

Nickel

Nickel deposits are typically found as concentrations in lateritic soils or in association with sulfide minerals in ultramafic magmatic rocks. Nickel occurs often with platinum group elements and has geochemi-cal affinities that make it occur with sulfide minerals such as pyrite, chalcopyrite, and pyrrhotite in ultamafic rocks such as komatiites. Other nickel deposits are found in tropical regions, where lateritic weathering leaches away many elements, leaving just the residual material such as...

Diamonds Are Forever

Diamonds are the most precious of all stones, adorning many engagement rings, necklaces, and other jewelry. They are admired for their hardness, clarity, beauty, and ability to divide light into its component colors. Diamonds, it is said, are forever. Diamonds are stable crystalline forms of pure carbon that form only at high pressures in cool locations in the Earth's mantle. Their origin is restricted, therefore, to places in the subcontinental mantle where these conditions exist, between 90...

At divergent plate boundaries

Although divergent boundaries are all similar in that they are places where the crust and entire lithosphere are breaking and moving apart, there are large differences in the processes that allow this extension to occur. Some of these different processes act in different places, while others may work together to produce the extension and associated sinking (subsidence) of the land surface. There are three main end-member models for the mechanisms of extension and subsidence in continental...

Convergent Plate Boundaries

Oceanic lithosphere is being destroyed by sinking back into the mantle at the deep ocean trenches in a process called subduction. As the oceanic slabs sink downward, they experience higher temperatures that cause the release of water and other volatiles from the subducting slab, generating melts in the mantle wedge overlying the subducting slab. These melts then move upward to intrude the overlying plate, where the magma may become contaminated by melting through and incorporating minerals and...

Geophysics And Isostacy

Isostacy is the principle of hydrostatic equilibrium applied to the Earth, referring to the position of the lithosphere essentially floating on the asthenosphere, similar to how low-density ice floats at a certain level on water, depending on the relative densities of the water and ice. Isostatic forces are of major importance in controlling the topography of the Earth's surface. There are several different models for how topography is supported, referred to as isostatic models. The simplest...

Bending Of Rocks

The bending or warping of rocks is called folding. Monoclines are folds in which both sides are horizontal, which often form over deeper faults. Anticlines are upward-pointing arches that have the oldest rocks in the center, and synclines are downward-pointing arches, with the oldest rocks on the outside edges of the structure. Though many other geometric varieties of folds exist, most are variations of these basic types. The fold hinge is the region of maximum curvature on the fold, whereas...

SODIUM cycle

One of the most important geochemical cycles is the sodium cycle. sodium is one of the major constituents of crustal rocks, sediments, and ocean water, and moves from each of these reservoirs to the other over long geological times. sodium is dissolved from crustal rocks such as granite by rainwater, then streams and rivers carry it in solution to the sea. sodium (Na) and chlorine (Cl) are the two most abundant elements carried in solution in ocean water. They combine to form the mineral halite...

Groundwater Contamination

Natural groundwater is typically rich in dissolved elements and compounds derived from the soil, regolith, and bedrock through which the water has migrated. Some of these dissolved elements and compounds are poisonous, whereas others are tolerable in small concentrations but harmful in high concentrations. Human and industrial waste contamination of the groundwater is increasing, and the overuse of groundwater resources has caused groundwater levels to drop and has led to other problems,...

Changes in Ground level

During earthquakes, blocks of earth shift relative to one another. This may result in changes in ground level, base level, the water table, and high-tide marks. Particularly large shifts have been recorded from some of the historically large earthquakes, such as the magnitude 9.2 Alaskan earthquake (1964) and the Sumatra earthquake (2004). In 1964 an area more than 600 miles (1,000 km) long in south central Alaska recorded significant changes in ground level, including uplifts of up to 12 yards...