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Fluvial

Fluvial

The word fluvial is used in geography and earth science to refer to all topics related to flowing water. Fluvial usually refers to rivers, streams and sometimes through flow, overland flow and percolation. Fluvial may also refer to glaciers and oceans, though these are usually known as glacial, oceanic and coastal. Common applications are fluvial processes and fluvial landforms.

Fluvial Processes

- Erosion
- Saltation
- Solution
- Suspension

Fluvial Landforms

- bar
- basin
- beach
- cave
- cliff
- confluence
- delta
- estuary
- flood plain
- gorge and canyon
- gully
- island
- lake
- levee
- meander
- ox-bow lake
- pool
- riffle
- river
- spring
- stream
- stream terrace
- valley and vale
- waterfall
- watershed (see landforms for complete list) Category:Geomorphology Category:Hydrology

Geography

)]] Geography is the study of the locational and spatial variation of both natural and human phenomena on Earth. The word derives from the Greek words Ge (γη) or Gaea (γεια), both meaning "Earth", and graphein (γραφειν) meaning "to describe" and "to write". Modern geography is a diverse discipline that draws influence from almost every other arena of knowledge. Geographers engage with other disciplines according to their particular research interests and, while subjects such as biology and economics have a powerful influence, there are geographers who use concepts taken from subjects such as sociology, psychology and sports science, among many others. Within the discipline there have been many long-running tensions among those seeking to define geography - whether as a 'science' or as a 'humanity', as a 'systematic' subject or 'regional' specialism and so forth - which at various times have come close to destroying geography as an academic discipline. Whilst profound differences do exist among geographers, the dual concepts of space and place provide a commonality of interest, which gives the subject a unique identity.

Structure of geography

William Hughes - who taught the geography of the Holy Lands to divinity students at King's College London - defined geography in an address in 1863: :"Mere place names are not geography. To know by heart a whole gazeteer full of them would not, in itself, constitute anyone a geographer. Geography has higher aims than this: it seeks to classify phenomena (alike of the natural and of the political world insofar as it treats of the latter) to compare, to generalise, to ascend from effects to causes and in doing so to trace out the great laws of nature and to mark their influence upon man. In a word, geography is a science, a thing not of mere names, but of argument and reason, of cause and effect." This was a specific rejection of geography as a merely descriptive discipline and also defined it as inclusive of both the physical world and the human. Within the discipline, however, there are many areas of specialism. Modern geographers tend to specialise in one of the broad branches (or sub-branches). However, most introductory geography syllabuses seek to ensure that geographers have at least working knowledge of the main focus of each branch of the subject.

Physical geography

Physical geography (or physiogeography) focuses on geography as an Earth science. It aims to understand the physical layout of the Earth, its weather and global flora and fauna patterns. Many areas of physical geography make use of geology, particularly in the study of weathering and sediment movement. Physical Geography can be divided into the following broad categories:
- Geomorphology
- Hydrology
- Glaciology
- Biogeography
- Climatology
- Pedology (soil study)
- Coastal/Marine studies
- Geodesy
- Palaeogeography
- Environmental Geography and management
- Landscape ecology Exact lines between these different areas are often difficult to draw. Sometimes Oceanography is included as a branch within physical geography, but is now considered a separate subject in its own right. Related topics: Atmosphere - Archipelago - Continent - Desert - Island - Landform - Ocean - Sea - River - Lake - Ecology - Soil - Timeline of geography, paleontology - Geostatistics - Environmental science - Oceanography - Environmental studies

Human geography

Human geography is a branch of geography that focuses on the study of patterns and processes that shape human interaction with various environments. It encompasses human, political, cultural, social, and economic aspects. While the major focus of human geography is not the physical landscape of the Earth (see Physical geography) it is hardly possible to discuss human geography without referring to the physical landscape on which human activities are being played out, and environmental geography is emerging as a link between the two. Human geography can be divided into broad categories, such as:
- Economic geography
- Development geography
- Population geography or Demography
-
- Urban geography
- Social geography
- Behavioral geography
- Cultural geography
- Political geography, including Geopolitics
-
- Historical geography
- Regional science
- Strategic geography
- Military geography
- Feminist geography
- Distinction between these fields of study have become increasingly blurred over time and the above list should not be considered definitive. Related topics: Countries of the world - Country - Nation - State - Personal union - Province - County - City - Municipality - Central place theory - Urban morphology

Socio-environmental geography

During the time of environmental determinism, geography was defined not as the study of spatial relationships, but as the study of how humans and the natural environment interact. Though environmental determinism has died out, there remains a strong tradition of geographers addressing the relationships between people and nature. There are two main subfields of socio-environmental geography:
- cultural and political ecology (CAPE) and
- risk-hazards research.

Cultural and political ecology

Cultural ecology grew out of the work of Carl Sauer in geography and a similar school of thought in anthropology. It examined how human societies adapt themselves to the natural environment. Sustainability science has been one important outgrowth of this tradition. Political ecology arose when some geographers used aspects of critical geography to look at relations of power and how they affect people's use of the environment. For example, an influential study by Michael Watts argued that famines in the Sahel are caused by the changes in the region's political and economic system as a result of colonialism and the spread of capitalism.

Risk-hazards research

Research on hazards began with the work of geographer Gilbert F. White, who sought to understand why people live in disaster-prone floodplains. Since then, the hazards field has expanded to become a multidisciplinary field examining both natural hazards (such as earthquakes) and technological hazards (such as nuclear reactor meltdowns). Geographers studying hazards are interested in both the dynamics of the hazard event and how people and societies deal with it.

Historical geography

This branch seeks to determine how cultural features of the multifarious societies across the planet evolved and came into being. Study of the landscape is one of many key foci in this field - much can be deduced about earlier societies from their impact on their local environment and surroundings. ; What's in a name? Historical geography and the Berkeley School "Historical Geography" can indeed refer to the reciprocal effects of geography and history on each other. But in the United States, it has a more specialized meaning: This is the name given by Carl Ortwin Sauer of the University of California, Berkeley to his program of reorganizing cultural geography (some say all geography) along regional lines, beginning in the first decades of the 20th Century. To Sauer, a landscape and the cultures in it could only be understood if all of its influences through history were taken into account: Physical, cultural, economic, political, environmental. Sauer stressed regional specialization as the only means of gaining expertise on regions of the world. Sauer's philosophy was the principal shaper of American geographic thought in the mid-20th century. Regional specialists remain in academic geography departments to this day. But many geographers feel that it harmed the discipline in the long run: Too much effort was spent on data collection and classification, and too little on analysis and explanation. Studies became more and more area specific as later geographers struggled to find places to make names for themselves. This probably led in turn to the 1950s crisis in Geography which nearly destroyed it as an academic discipline.

History of geography

:See main article: History of geography History of geography The Greeks are the first known culture to actively explore geography as a science and philosophy. Mapping by the Romans as they explored new lands added new techniques. During the Middle Ages, Arabs such as Idrisi, Ibn Batutta, and Ibn Khaldun maintained the Greek and Roman techniques and developed new ones. Following the journeys of Marco Polo, interest in geography spread throughout Europe. The great voyages of exploration in 16th and 17th centuries revived a desire for both accurate geographic detail, and more solid theoretical foundations. This period is also known as Great Geographical Discoveries. By the 18th century, geography had become recognized as a discrete discipline and became part of a typical university curriculum in Europe (especially Paris and Berlin). Over the past two centuries the quantity of knowledge and the number of tools has exploded. There are strong links between geography and the sciences of geology and botany, as well as economics, sociology and demographics. In the West during the 20th century, the discipline of geography went through four major phases: environmental determinism, regional geography, the quantitative revolution, and critical geography.
Geographic techniques
As spatial interrelationships are key to this synoptic science, maps are a key tool. Classical cartography has been joined by a more modern approach to geographical analysis, computer-based geographic information systems (GIS).
- Cartography studies the representation of the Earth's surface with abstract symbols (map making). Although other subdisciplines of geography rely on maps for presenting their analyses, the actual making of maps is abstract enough to be regarded separately. Cartography has grown from a collection of drafting techniques into an actual science. Cartographers must learn cognitive psychology and ergonomics to understand which symbols convey information about the Earth most effectively, and behavioral psychology to induce the readers of their maps to act on the information. They must learn geodesy and fairly advanced mathematics to understand how the shape of the Earth affects the distortion of map symbols projected onto a flat surface for viewing. It can be said, without much controversy, that cartography is the seed from which the larger field of Geography grew. Most geographers will cite a childhood fascination with maps as an early sign they would end up in the field. mathematics
- Geographic Information Systems deals with the storage of information about the Earth for automatic retrieval by a computer, in an accurate manner appropriate to the information's purpose. In addition to all of the other subdisciplines of geography, GIS specialists must understand computer science and database systems. GIS has so revolutionized the field of cartography that nearly all mapmaking is now done with the assistance of some form of GIS software.
- Geographic quantitative methods deal with numerical methods peculiar to (or at least most commonly found in) geography. In addition to spatial analyses, you are likely to find things like cluster analysis, discriminant analysis, and non-parametric statistical tests in geographic studies.
- Geographic qualitative methods, or ethnographic research techniques, are used by human geographers. In cultural geography there is a tradition of employing qualitative research techniques also used in anthropology and sociology. Participant Observation and in-depth interviews provide human geographers with qualitative data. In their study geographers use four interrelated approaches:
- Systematic - Groups geographical knowledge into categories that can be explored globally
- Regional - Examines systematic relationships between categories for a specific region or location on the planet.
- Descriptive - Simply specifies the locations of features and populations.
- Analytical - Asks why we find features and populations in a specific geographic area.
Related fields

Urban and regional planning
Urban planning and regional planning use the science of geography to assist in determining how to develop (or not develop) the land to meet particular criteria, such as safety, beauty, economic opportunities, the preservation of the built or natural heritage, etcetera. The planning of towns, cities and rural areas may be seen as applied geography although it also draws heavily upon the arts, the sciences and lessons of history. Some of the issues facing planning are considered briefly under the headings of rural exodus, urban exodus and Smart Growth.
Regional science
In the 1950s the regional science movement arose, led by Walter Isard to provide a more quantitative and analytical base to geographical questions, in contrast to the more qualitative tendencies of traditional geography programs. Regional Science comprises the body of knowledge in which the spatial dimension plays a fundamental role, such as regional economics, resource management, location theory, urban and regional planning, transport and communication, human geography, population distribution, landscape ecology, and environmental quality.
Reference

See also

- List of geography topics
- Geographical terms
- List of countries
- Geography reference tables
- Map
- Geographical renaming
- Geographic magazines
- National Geographic Society (United States)
- National Geographic Bee (United States)
- Point of Beginning
- Royal Geographical Society (United Kingdom)
External links

- [http://www.confluence.org/ Confluence.org - A work in progress, involving travelling to every point on the globe where the lines of longitude and latitude intersect and taking a photograph in each direction.]
- [http://www.aag.org/ Association of American Geographers]
- [http://www.gisuser.com/ GISuser.com, information-rich portal about GIS]
- [http://www.populationdata.net/ PopulationData.net]
- [http://www.freemaps.de/ Free Maps Germany]
- [http://www.ericdigests.org/1996-4/high.htm Using Literature To Teach Geography in High Schools. ERIC Digest.]
- [http://ericdigests.org/1992-5/geography.htm Teaching Geography at School and Home. ERIC Digest.]
- [http://ericdigests.org/1996-1/geography.htm The National Geography Content Standards. ERIC Digest.]
- [http://www.geo-guide.de Geo-Guide] extensive list of academic resources on geography and earth science
- [http://www.geopium.org Geopium: Geopolitics of Illicit Drugs in Asia]
- [http://www.nationalgeographic.com/ National Geographic Online]
- [http://www.rgs.org Royal Geographical Society]
- [http://www.rcgs.org Royal Canadian Geographical Society]
- [http://www.canadiangeographic.ca Canadian Geographic]
- [http://hypergeo.free.fr Hypergeo : Geographical Encyclopedia]
- [http://www.rare-maps.com/links.cfm Antique and Rare Maps - Art Source International] - Links to rare and antique maps and to cartography resources.
- [http://www.mapinfo.com/ MapInfo GIS Software]
- Category:School subjects als:Geografie ko:지리학 ms:Geografi ja:地理学 simple:Geography th:ภูมิศาสตร์

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H₂O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at springs or extracted from artificial borings in the ground, or wells. Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow. Other water sources are the rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant ocean or seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs. Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the pollutor. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

The impact of water on human culture

Water is considered a purifier in most religions, including Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the daily Salah can only be done after ablution (Wodoo), that is, washing parts of the body in clean water. In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess. Alternatively, gods can be patrons of particular springs, river or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids. The Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic stuff of the universe. Water was considered cold and moist. In the theory of the four bodily humours, water was associated with phlegm. Water was also one of the Five Elements in traditional Chinese philosophy, along with earth, fire, wood, and metal. A common misconception about water is that it is a powerful conductor of electricity. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize (two water molecules become one hydroxide anion and one hydronium cation), but only at a very slight, almost immeasurable level. Pure water can also be electrolized into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. Many bottled water companies exploit another common misconception, advertising both purity and taste, even though pure water is tasteless.

External links

- [http://www.lsbu.ac.uk/water/phase.html Phase diagrams of water]
- [http://www.publicforuminstitute.org/issues/oceans/index.htm Oceans and Water Issues Page]
- [http://www.greenfacts.org/water-disinfectants/index.htm Scientific Facts on Water disinfectants] A faithful summary by GreenFacts of a leading scientific consensus report on Drinking Water Disinfectants published by the International Programme on Chemical Safety of the WHO.
- [http://www.hkc22.com/residentialwater.html Residential water problems and markets] Study paper from Helmut Kaiser Consultancy
- [http://www.hkc22.com/watermarketsworldwide.html Water markets worldwide] Study paper from Helmut Kaiser Consultancy
- [http://www.worldwaterforum.org/ World Water Forum]
- [http://www.unesco.org/water/wwap/ World Water Assessment Program]
- [http://unesdoc.unesco.org/images/0012/001295/129556e.pdf United Nations' World Water Development Report]
- [http://www.gemswater.org/ United Nations GEMS/Water Programme]
- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.wateraid.org/ WaterAid]
- [http://www.sahra.arizona.edu/newswatch/ SAHRA—Global Water Newswatch]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.c-win.org/ California Water Impact Network (C-WIN)]
- [http://news.bbc.co.uk/2/hi/science/nature/3752590.stm BBC: The water debate]
- [http://www.geocities.com/tapvsbottled/ Tap Water Vs Bottled Water] - Interesting site providing facts about tap and bottled water.
- [http://www.emagazine.com/september-october_2003/0903feat1.html E the Environmental Magazine piece on bottled water] (Oct 2003).
- [http://www.iapws.org/ International Association for the Properties of Water and Steam]
- [http://ga.water.usgs.gov/edu/watercycle.html US Geological Survey: Comprehensive discussion of the water cycle, in many languages]
- [http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]
- [http://www.water.org.uk/home/resources-and-links/water-for-health/ask-about/adults Water requirements in adults]
- [http://www.hkc22.com/environmentaltechnology.html/ Climate change raises markets for environmental technology, drinking water and clean energies]

References

- OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
- Category:Beverages Category:Hydrology Category:Materials Category:Natural resources Category:Nutrition zh-min-nan:Chúi als:Wasser ko:물 ja:水 ms:Air simple:Water th:น้ำ

Stream

A stream is a body of water with a detectable current, confined within a bed and banks. Stream is also an umbrella term used in the scientific community for all flowing natural waters. An analogy is often drawn between time and a stream; see timestream. The study of streams and waterways in general is known as surface hydrology and is important in environmental geography or environmental geology.

Types of water streams

environmental geology ; River: A large natural stream, which may be a waterway. ; Creek (North America and Australia): A small natural stream. Rarely navigable and may be intermittent. Often pronounced "crick". ; Creek (UK and India): A tidal inlet, typically in a saltmarsh or mangrove swamp. Alternatively, between enclosed and drained, former saltmarshes or swamps. In these cases, the stream is the tidal stream, the course of the sea-water through the creek channel on each of the flood and ebb. ; Tributary: A contributory stream, or a stream that does not reach the sea but joins another river (a parent river). Sometimes also called a branch or fork. ; Brook: A stream that crosses between two other bodies of water, thus "brooking" them. It is usually small and easily forded. forded forded

Other names for streams

In the United Kingdom, there are several regional names for a stream:
- Beck is used in Yorkshire, Lancashire and Cumbria.
- Brook is used in the Midlands.
- Burn is used in Scotland and North East England.
- Stream is limited to Southern England. In North America:
- Kill in New York and New Jersey comes from a Dutch language word, as in Peekskill (Peek's Kill), Fishkill (Fish Kill), and Fresh Kills.
- Branch, fork, or prong can refer to tributaries that share the same name as the main stream.

Parts of a stream

; Confluence: The point at which the two streams merge. If the two tributaries are of approximately equal size, the confluence may be called a fork. ; Run: A fairly smooth flowing segment of the stream. ; Pool: A segment where the water is deeper and slower moving. ; Riffle: A segment where the flow is shallower and more turbulent. ; Source: The spring from which the stream originates or other point of origin of a stream. ; Headwater: The part of a stream or river close to its source. The word is commonly used in the plural where there is no single point source. ; Channel: A depression created by constant erosion, that carries the stream's flow. ; Floodplain: Flatlands on either side of the stream that are subject to seasonal flooding. ; Bed: The bottom of the stream. ; Mouth: The point at which the stream discharges, possibly via an estuary or delta, into a static body of water such as a lake or ocean. ; Thalweg: The river's longitudinal section, or the line joining the deepest point in the channel at each stage from source to mouth. ; Wetted perimeter: The line on which the stream's surface meets the channel walls. ; Spring: The point at which a stream emerges from an underground course through unconsolidated sediments or through caves. A stream can, especially with caves, flow aboveground for part of its course, and underground for part of its course. ; Waterfall or cascade: The fall of water where the stream goes over a sudden drop called a nickpoint; some nickpoints are formed by erosion when water flows over an especially resistant stratum, followed by one less so. The stream expends kinetic energy in "trying" to eliminate the nickpoint.

Characteristics of streams

kinetic energy ; Ranking : Streams in geographic terms are awarded order designations. A stream of the first order is a blue-line stream which does not have any other blue-line stream feeding into it. A stream of the second order is one which is formed by the joining of two or more blue-line streams. A third-order stream is one below the confluence of two or more second-order streams; a fourth-order stream is formed by the confluence of at least two third-order streams, and so forth. ; Gradient : The gradient of a stream is a critical factor in determining its character, and is entirely determined by its base level of erosion. The base level of erosion is the point at which the stream either enters the ocean, a lake or pond, or enters a stretch in which it has a much lower gradient, and may be specifically applied to any particular stretch of a stream. : In geologic terms, the stream will erode down through its bed to achieve the base level of erosion throughout its course. If this base level is low, then the stream will rapidly cut through underlying strata and have a steep gradient, and if the base level is relatively high, then the stream will form a flood plain and meanders. ; Meander : Meanders are looping changes of direction of a stream caused by the erosion and deposition of bank materials. These may be somewhat sine-wave in form. Typically, over time, the meanders don't disappear but gradually migrate downstream. : If some resistant material slows or stops the downstream movement of a meander, a stream may erode through the neck between two legs of a meander to become temporarily straighter, leaving behind an arc-shaped body of water termed an oxbow lake or bayou. A flood may also result in a meander being cut through in this way. ; Profile : Typically, streams are said to have a particular profile, beginning with steep gradients, no flood plain, and little shifting of channels, eventually evolving into streams with low gradients, wide flood plains, and extensive meanders. The initial stage is sometimes termed a "young" stream, and the later state a "mature" or "old" stream. However, a stream may meander for some distance before falling into a "young" stream condition.

Intermittent and ephemeral streams

meander In the United States, an intermittent stream is one that only flows for part of the year and is marked on topographic maps with a line of blue dashes and dots. A wash or desert wash is normally a dry streambed in the deserts of the American Southwest which flows only after significant rainfall. Washes can fill up quickly during rains, and there may be a sudden torrent of water after a thunderstorm begins upstream, such as during monsoonal conditions. These flash floods often catch travellers by surprise. A blue-line stream is one which flows for most or all of the year and is marked on topographic maps with a solid blue line. In Australia, an intermittent stream is usually called a creek, and marked on topographic maps with a solid blue line. Generally, streams that form only during and immediately after precipitation are termed ephemeral.

Watersheds

The entire basin drained by the stream is termed the watershed. Every watershed is made up of smaller watersheds, while most watersheds are parts of larger watersheds. For instance, the Continental Divide in North America divides the Atlantic Ocean watershed from the Pacific Ocean watershed, but the Atlantic Ocean watershed may be first divided into the Atlantic Ocean drainage and the Gulf of Mexico drainage. This delineation within the United States is termed the Eastern Continental Divide. The Gulf of Mexico watershed may be divided into Mississippi River basin and a number of smaller watersheds, such as the Tombigbee River watershed. The Mississippi River watershed includes the Ohio River watershed, which in turn includes the Kentucky River watershed, and so forth.

Percolation

In chemistry and materials science, percolation proto-typically concerns the movement and filtering of fluids through porous materials. During the last three decades, percolation theory, an extensive mathematical model of percolation, has brought new understanding and techniques to a broad range of topics in physics and materials science.

Applications of percolation theory

Among the applications are the study of percolation of petroleum and natural gas through semi-porous rock; here the theory has helped predict and improve the productivity of natural gas and oil wells. In two dimensions, the percolation of water through a thin tissue (such as toilet paper) has the same mathematical underpinnings as the flow of electricity through two-dimensional random networks of resistors. In chemistry, chromotography can be understood with similar models. The propagation of a tear or rip in a sheet of paper, in a sheet of metal, or even the formation of a crack in ceramic bears broad mathematical resemblance to the flow of electricity through a random network of electrical fuses. Above a certain critical point, the electrical flow will cause a fuse to pop, possibly leading to a cascade of failures, resembling the propagation of a crack or tear. The study of percolation helps indicate how the flow of electricity will redistribute itself in the fuse network, thus modeling which fuses are most likely to pop next, and how fast they will pop, and what direction the crack may curve in. Examples can be found not only in physical phenomena, but also in biological and ecological ones (evolution), and also in economic and social ones (see diffusion of innovation). Percolation can be considered to be a branch of the study of dynamical systems or statistical mechanics. In particular, percolation networks exhibit a phase change around a critical threshold.

Ocean

:For other uses see Ocean (disambiguation) Ocean (disambiguation)] Ocean (from Okeanos, Greek for river, the ancient Greeks noticed that a strong current flowed off Gibraltar, and assumed it was a great river); covers almost three quarters (71%) of the surface of the Earth, and nearly half of the world's marine waters are over 3000 m deep. This global, interconnected body of salt water, called the World Ocean, is divided by the continents and archipelagos into the following four bodies, from the largest to the smallest: the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, and the Arctic Ocean, and, according to some authorities such as International Hydrographic Organization(IHO), a fifth ocean, the Southern Ocean. Some geographers and some governments but not the US, recognize the IHO as defining official water body names and boundaries. (The US authority is the United States Board on Geographic Names.) The IHO officially sanctioned the Southern Ocean name only in 2000, but its definition by a line of latitude (with IHO members widely disputing which line of latitude) has left its acceptance as a fifth ocean open to question. The National Geographic Society and some other leading geographers and cartographers continue to use "South Pacific", "South Atlantic", and "Indian" Ocean for the waters around Antarctica. A few Oceanographers recognize only four oceans also, treating the Arctic Ocean (or the Arctic Sea) as a part of the Atlantic Ocean. Smaller regions of the oceans are called seas, gulfs, straits and other names. Geologically, an ocean is an area of oceanic crust covered by water. Oceanic crust is the thin layer of solidified volcanic basalt that covers the Earth's mantle where there are no continents. From this point of view, there are three "oceans" today: the World Ocean, and the Black and Caspian Seas that were formed by the collision of Cimmeria with Laurasia. The Mediterranean Sea is very nearly its own "ocean", being connected to the World Ocean through the Strait of Gibraltar, and indeed several times over the last few million years movement of the African Continent has closed the strait off entirely, making the Mediterranean a fourth "ocean". (The Black Sea is connected to the Mediterranean through the Bosporus, but this is in effect a natural canal, cut through continental rock some 7000 years ago, rather than a piece of oceanic sea floor like the Strait of Gibraltar.) The area of the World Ocean is 361 million km², its volume is 1370 million km³, and its average depth is 3790 m. Nearly half of the world's marine waters are over 3000 m deep. This does not include seas not connected to the World Ocean, such as the Caspian Sea. The total mass of the hydrosphere is about 1.4 × 10²¹ kg, ca. 0.023 % of the Earth's total mass. See sea water for a detailed discussion of ocean water composition, most notably its salinity.

Origins

The Oceans of the world most likely originated by comets striking the Earth.

Exploration

salinity Travel on the surface of the ocean through the use of boats dates back to prehistoric times, but only in modern times has extensive underwater travel become possible. The deepest point in the ocean is the Mariana Trench located in the Pacific Ocean near the Northern Mariana Islands. It has a maximum depth of 10,923 m (35,838 ft) [http://www.rain.org/ocean/ocean-studies-challenger-deep-mariana-trench.html]. It was fully surveyed in 1951 by the British naval vessel, "Challenger II" which gave its name to the deepest part of the trench, the "Challenger Deep". Much of the bottom of the world's oceans is unexplored and unmapped. A global image of many underwater features larger than 10 km was created in 1995 based on gravitational distortions of the nearby sea surface.

Climate

One of the most dramatic forms of weather occurs over the oceans: tropical cyclones (also called "typhoons" and "hurricanes" depending upon where the system forms). Ocean currents greatly affect Earth's climate by transferring warm or cold air and precipitation to coastal regions, where they may be carried inland by winds. The Antarctic Circumpolar Current encircles that continent, influencing the area's climate and connecting currents in several oceans.

Ecology

The oceans are home to the majority of plant and animal life on Earth. These lifeforms include:
- fish
- cetacea such as whales, dolphins and porpoises,
- cephalopods such as the octopus
- crustaceans such as lobsters and shrimp
- marine worms
- plankton
- krill

Economy

The oceans are essential to transportation: a huge portion of the world's goods are moved by ship between the world's seaports. Important ship canals include the Saint Lawrence Seaway, Panama Canal, and Suez Canal.

Ancient oceans

Continental drift has reconfigured the Earth's oceans, joining and splitting ancient oceans to form the current oceans. Ancient oceans include:
- Panthalassa, the vast world ocean that surrounded the Pangaea supercontinent.
- Tethys Ocean, the ocean between the ancient continents of Gondwana and Laurasia.
- Iapetus Ocean, the southern hemisphere ocean between Baltica and Avalonia.

Ocean rowing

Extraterrestrial oceans

Earth is the only known planet with liquid water on its surface, and is certainly the only such in our own solar system. However, liquid water is thought to be present under the surface of several natural satellites, particularly the Galilean moons of Europa, and, with less certainty, its fellows Callisto and Ganymede. Other icy moons may have once had internal oceans that have now frozen, such as Triton. The planets Uranus and Neptune may also possess large oceans of liquid water under their thick atmospheres, though their internal structure is not well understood at this time. There is currently much debate over whether Mars once had an ocean of water in its northern hemisphere, and over what happened to it if it did; recent findings by the Mars Exploration Rover mission indicate it had some long-term standing water in at least one location, but its extent is not known. Liquid hydrocarbons are thought to be present on the surface of Titan, though it may be more accurate to describe them as "lakes" rather than an "ocean". The distribution of these liquid regions will hopefully be better known after the full analysis of data from the Huygens probe of the Cassini-Huygens space mission, which dropped onto Titan's surface in January 2005. Titan is also thought likely to have a subterranean water ocean under the mix of ice and hydrocarbons that forms its outer crust.

Oceans in film

- In the movie Muppet Treasure Island, a non-specific ocean is featured, and referred to as the "Big Blue Wet Thing". Oceans have also been featured in many other movies such as Free Willy. To list more, click edit beside "Oceans on Film"

External links

- [http://www.oceanexplorer.noaa.gov/ Ocean Explorer] - An educational and reference resource from NOAA
- [http://news.bbc.co.uk/2/hi/science/nature/4033555.stm Science taps into ocean secrets]
- [http://www.palomar.edu/oceanography/salty_ocean.htm Why is the ocean salty?]
- [http://ioc.unesco.org/oceanteacher/resourcekit/M3/Formats/Geography/OceansSeas.htm Official IHO boundaries of Oceans and Seas]
- [http://www.thehydrogenexpedition.com The Hydrogen Expedition] The first circumnavigation of the globe in a hydrogen fuel cell powered boat
- [http://www.coreocean.org Coreocean]
- [http://www.nopp.org/ NOPP - The National Oceanographic Partnership Program] Category:Bodies of water Category:Oceanography zh-min-nan:Hái-iûⁿ ko:대양 ms:Lautan ja:大洋 simple:Ocean th:มหาสมุทร

Glacial

:This article is about the geographical formation. For the professional wrestler, see Ray Lloyd A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. A glacier is formed by multi-year ice accretion in sloping terrain. Glacier ice is the largest reservoir of fresh water on Earth, and second only to the oceans as the largest reservoir of total water. Glaciers can be found on every continent except Australia. Geologic features associated with glaciers include end, lateral, ground and medial moraines that form from glacially transported rocks and debris; U-shaped valleys and corries (cirques) at their heads, and the glacier fringe, which is the area where the glacier has recently melted. cirques

Types of glaciers

cirques There are two main types of glaciers: alpine glaciers, which are found in mountain terrains, and continental glaciers, which are associated with ice ages and can cover large areas of continents. Most of the concepts in this article apply equally to alpine glaciers and continental glaciers. A temperate glacier is one where liquid water is present at least part of the year. Polar glaciers are always below the freezing point. The smallest alpine glaciers form in mountain valleys and are referred to as valley glaciers. Larger ice layers can cover an entire mountain, mountain chain or even a volcano; this type is known as an ice cap. Ice caps feed outlet glaciers, tongues of ice that extend into valleys below, far from the margins of those larger ice masses. Outlet glaciers are formed by the movement of ice from a polar ice cap, or an ice cap from mountainous regions, to the sea. The largest glaciers are continental ice sheets, enormous masses of ice that are not affected by the landscape and extend over the entire surface, except on the margins, where they are thinnest. Antarctica and Greenland are the only places where continental ice sheets currently exist. These regions contain vast quantities of fresh water. The volume of ice is so large that if the Greenland ice sheet melted, it would cause sea levels to rise some six meters all around the world. If the Antarctic ice sheet melted, sea levels would rise up to 65 meters. Plateau glaciers resemble ice sheets, but on a smaller scale. They cover some plateaus and high-altitude areas. This type of glacier appears in many places, especially in Iceland and some of the large islands in the Arctic Ocean, and throughout the northern Pacific Cordillera from southern British Columbia to western Alaska. Tidewater glaciers are glaciers that flow into the sea. As the ice reaches the sea pieces break off, or calve, forming icebergs. Most tidewater glaciers calve above sea level, which often results in a tremendous splash as the iceberg strikes the water. If the water is deep, glaciers can calve underwater, causing the iceberg to suddenly explode up out of the water. The Hubbard Glacier is the longest tidewater glacier in Alaska and has a calving face over ten kilometers long. Yakutat Bay and Glacier Bay are both popular with cruise ship passengers because of the huge glaciers descending to them. Piedmont glaciers occupy broad lowlands at the base of steep mountains, and form when one or more alpine glaciers surge from the confining walls of mountain valleys. The size of piedmont glaciers varies greatly: among the largest is the Malaspina Glacier, which extends along the length of the southern coast of Alaska. It covers more than 5,000 km² of the coastal plain at the foot of the Saint Elias range. And it is only a part of the much bigger Kluane Icecap, which spans the Mount St. Elias and Chugach groups of mountain ranges all the way from the Malaspina Glacier to the Copper River and well into the southwestern Yukon, as well as southeast from the Malaspina towards the Iskut River in British Columbia. The highest alpine glacier in the world is the Siachen Glacier, which is also a zone of political conflict between India and Pakistan.

Formation of glaciers

Siachen Glacier The snow which forms glaciers is subject to repeated freezing and thawing, which changes it into a form of granular ice called névé. Under the pressure of the layers of ice and snow above it, this granular ice fuses into denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice. Glacial ice contains minute air bubbles as a result, giving it a distinctive blue tint due to Rayleigh scattering. The lower layers of glacial ice flow and deform plastically under the pressure, allowing the glacier as a whole to move slowly like a viscous fluid. Glaciers do not need a slope to flow, being driven by the continuing accumulation of new snow at their source. The upper layers of glaciers are more brittle, and often form deep cracks known as crevasses as they flex. These crevasses make travel over glaciers dangerous. Glacial meltwaters flow throughout and underneath glaciers, carving channels in the ice similar to caves in rock and also helping to lubricate the glacier's movement. In the summer, the melted ice from the glacier alone may be enough to create a stream, and while the glacier may be a barren waste of dense ice, fertile land is often nearby.

Anatomy of a glacier

cave The upper part of a glacier that receives most of the snowfall is called the accumulation zone. As a rule of thumb, the accumulation zone accounts for 60-70% of the glacier's surface area. The depth of ice in the accumulation zone exerts a downward force sufficient to cause deep erosion of the rock in this area. After the glacier is gone, this often leaves a bowl or amphitheater-shaped depression called a cirque. On the opposite end of the glacier, at its foot or terminal, is the deposition or ablation zone, where more ice is lost through melting than gained from snowfall and sediment is deposited. The place where the glacier thins to nothing is called the ice front. The altitude where the two zones meet is called the equilibrium line. At this altitude, the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. The downward erosive forces of the accumulation zone and the tendency of the ablation zone to deposit sediment also cancel each other out. Erosive lateral forces are not canceled; therefore, glaciers turn v-shaped river-carved valleys into u-shaped glacial valleys. The "health" of a glacier is defined by the area of the accumulation zone compared to the ablation zone. Healthy glaciers have large accumulation zones. Several non-linear relationships define the relation between accumulation and ablation. The worldwide shrinking of 70% of glaciers [http://www.grida.no/climate/ipcc_tar/wg1/064.htm] is among the evidence for global warming. Approximately 30% of glaciers are advancing. Even in very cold climates, there may be unglaciated areas, which receive too little precipitation to form permanent ice. This was the case in most of Siberia, central and northern Alaska and all of Manchuria during glacial periods of the Quaternary, and occurs today in that part of the Andes between 19°S and 27°S above the hyperarid Atacama Desert where, although the mountains reach 6700 metres above sea level, the cold Humboldt Current competely suppresses precipitation. During ice ages, continental glaciers may be as much as 1500 meters thick. A more extreme instance of glacial growth may have occurred during the Snowball Earth period. In the past several centuries the Earth's glaciers have generally been retreating, often dramatically.

Glacial motion

Earth Ice behaves like an easily breaking solid until its thickness exceeds about 50 meters (160 ft). Below that depth the increased pressure causes ice to become plastic and flow. The glacial ice is made up of layers of molecules stacked on top of each other, with relatively weak bonds between the layers. When the stress exceeds the inter-layer binding strength, the layers start to slide past each other. Another type of movement is basal gliding. In this process, the whole glacier moves over the terrain on which it sits, lubricated by thawed ice. As the pressure increases toward the base of the glacier, the melting point of water decreases, and the ice melts. Friction between ice and rock and geothermal heat from the Earth's interior also contribute to thawing. The top 50 meters of the glacier are more rigid. In this section, known as the fracture zone, there are no layers which slide past each other; instead the ice mostly moves as a single unit. Ice in the fracture zone moves over the top of the lower section. When the glacier moves through irregular terrain, cracks form in the fracture zone. These cracks can be up to 50 meters deep, at which point they meet the plastic flow underneath that seals them.

Speed of glacial movement

The speed of glacial displacement is partly determined by friction. Friction makes the ice at the bottom of the glacier move slower than the upper portion. In alpine glaciers, friction is also generated at the valley's side walls, which slows the edges relative to the center. This has been confirmed by experiments in the 19th century, in which stakes were planted in a line across an alpine glacier, and as time passed, those in the center moved further. Mean speeds vary; some have speeds so slow that trees can establish themselves among the deposited scourings. In other cases they can move as fast as many meters per day, as is the case of Byrd Glacier, an overflowing glacier in Antarctica which moves 750-800 meters per year (some 2 meters (6 ft) per day), according to studies using satellites. Many glaciers have periods of very rapid advancement called surges.[http://www.geog.leeds.ac.uk/research/glaciology/maths.htm] These glaciers exhibit normal movement until suddenly they accelerate, then return to their previous state. During these surges, the glacier may reach velocities up to 1000 times greater than normal.

Moraines

Glacial moraines are formed by the deposition of material from a glacier and are exposed after the glacier has retreated. These features usually appear as linear mounds of till, a poorly-sorted mixture of rock, gravel and boulders within a matrix of a fine powdery material. Terminal or end moraines are formed at the foot or terminal end of a glacier, lateral moraines are formed on the sides of the glacier, and medial moraines are formed down the center. Less obvious is the ground moraine, also called glacial drift, which often blankets the surface underneath much of the glacier downslope from the equilibrium line. Glacial meltwaters contain rock flour, an extremely fine powder ground from the underlying rock by the glacier's movement. Other features formed by glacial deposition include long snake-like ridges formed by streambeds under glaciers, known as eskers, and distinctive streamlined hills, known as drumlins. Stoss-and-lee erosional features are formed by glaciers and show the direction of their movement. Long linear rock scratches (that follow the glacier's direction of movement) are called glacial striations, and divots in the rock are called chatter marks. Both of these features are left on the surfaces of stationary rock that were once under a glacier and were formed when loose rocks and boulders in the ice were transported over the rock surface. Transport of fine-grained material within a glacier can smooth or polish the surface of rocks, leading to glacial polish. Glacial erratics are rounded boulders that were left by a melting glacier and are often seen perched precariously on exposed rock faces after glacial retreat. The most common name for glacial sediment is moraine. The term is of French origin, and it was coined by peasants to describe alluvial embankments and rims found near the margins of glaciers in the French Alps. Currently, the term is used more broadly, and is applied to a series of formations, all of which are composed of till.

Drumlins

till Drumlins are asymmetrical hills with aerodynamic profiles made mainly of till. Their heights vary from 15 to 50 meters and they can reach a kilometer in length. The tilted side of the hill looks toward the direction from which the ice advanced (stoss), while the longer slope follows the ice's direction of movement (lee). Drumlins are found in groups called drumlin fields or drumlin camps. An example of these fields is found east of Rochester, New York, and it is estimated that it contains about 10,000 drumlins. Although the process that forms drumlins is not fully understood, it can be inferred from their shape that they are products of the plastic deformation zone of ancient glaciers. It is believed that many drumlins were formed when glaciers advanced over and altered the deposits of earlier glaciers.

Glacial erosion

Rocks and sediments are added to glaciers through various processes. Glaciers erode the terrain principally through two methods: abrasion and plucking. plucking As the glacier flows over the bedrock's fractured surface, it softens and lifts blocks of rock that are brought into the ice. This process is known as plucking, and it is produced when subglacial water penetrates the fractures and the subsequent freezing expansion separates them from the bedrock. When the water expands, it acts as a lever that loosens the rock by lifting it. This way, sediments of all sizes become part of the glacier's load. Abrasion occurs when the ice and the load of rock fragments slide over the bedrock and function as sandpaper that smoothens and polishes the surface situated below. This pulverized rock is called rock flour. This flour is formed by rock grains of a size between 0.002 and 0.00625 mm. Sometimes the amount of rock flour produced is so high that currents of meltwaters acquire a grayish color. Another of the visible characteristics of glacial erosion are glacial striations. These are produced when the bottom's ice contains large chunks of rock that mark trenches in the bedrock. By mapping the direction of the flutes the direction of the glacier's movement can be determined. The velocity of a glacier's erosion is variable. The differential erosion undertaken by the ice is controlled by four important factors:
- Velocity of glacial movement
- Thickness of the ice
- Shape, abundance and hardness of rock fragments contained in the ice at the bottom of the glacier
- Relative ease of erosion of the surface under the glacier. Material that becomes incorporated in a glacier are typically carried as far as the zone of ablation before being deposited. Glacial deposits are of two distinct types:
- Glacial till: material directly deposited from glacial ice. Till includes a mixture of undifferentiated material ranging from clay size to boulders, the usual composition of a moraine.
- Fluvial and outwash: sediments deposited by water. These deposits are stratified through various processes, such as boulders being separated from finer particles. The larger pieces of rock which are encrusted in till or deposited on the surface are called glacial erratics. They may range in size from pebbles to boulders, but as they may be moved great distances they may be of drastically different type than the material upon which they are found. Patterns of glacial erratics provide clues of past glacial motions.

Glacial valleys

glacial erratics glacial erratics. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades.]] Before glaciation, mountain valleys have a characteristic "V" shape, produced by downward erosion by water. However, during glaciation, these valleys widen and deepen, which creates a "U"-shaped glacial valley. Besides the deepening and widening of the valley, the glacier also smoothes the valley due to erosion. This way, it eliminates the spurs of earth that extend across the valley. Because of this interaction, triangular cliffs called truncated spurs are formed. Many glaciers deepen their valleys more than their smaller tributaries. Therefore, when the glaciers stop receding, the valleys of the tributary glaciers remain above the main glacier's depression, and these are called hanging valleys. In parts of the soil that were affected by abrasion and plucking, the depressions left can be filled by paternoster lakes, from the Latin for "Our Father", referring to a station of the rosary. At the head of a glacier is the corrie, which has a bowl shape with escarped walls on three sides, but open on the side that descends into the valley. In the corrie, an accumulation of ice is formed. These begin as irregularities on the side of the mountain, which are later augmented in size by the coining of the ice. After the glacier melts, these corries are usually occupied by small mountain lakes called tarns. There may be two glaciers separated by a diving ridge. This, located between the corries, is eroded to create an arête. This structure may result in a mountain pass. Glaciers are also responsible for the creation of fjords (deep coves or inlets) and escarpments that are found at high latitudes. With depths that can exceed 1,000 metres caused by the postglacial elevation of sea level and therefore, as it changed the glaciers changed their level of erosion. sea level

Arêtes and horns

An arête is a narrow crest with a sharp edge. Pointed pyramidal peaks are called horns. Both features may have the same process behind their formation: the enlargement of cirques from glacial plucking and the action of the ice. Horns are formed by cirques that encircle a single mountain. Arêtes emerge in a similar manner; the only difference is that the cirques are not located in a circle, but rather on opposite sides along a divide. Arêtes can also be produced by the collision of two parallel glaciers. In this case, the glacial tongues cut the divides down to size through erosion, and polish the adjacent valleys.

Sheepback rock

Some rock formations in the path of a glacier are sculpted into small hills with a shape known as roche moutonnée or sheepback. An elongated, rounded, asymmetrical, bedrock knob produced can be produced by glacier erosion. It has a gentle slope on its up-glacier side and a steep to vertical face on the down-glacier side. The glacier abrades the smooth slope that it flows along, while rock is torn loose from the downstream side and carried away in ice. Rock on this side is fractured by combinations of forces due to water, ice in rock cracks, and structural stresses.

Alluvial stratification

The water that rises from the zone of ablation moves away from the glacier and carries with it fine eroded sediments. As the speed of the water decreases, so does its capacity to carry objects in suspension. The water then gradually deposits the sediment as it runs, creating an alluvial plain. When this phenomenon occurs in a valley, it is called a valley train. alluvial plain Alluvial plains and valley trains are usually accompanied by basins known as kettles. Glacial depressions are also produced in till deposits. These depressions are formed when large ice blocks are stuck in the glacial alluvium and after melting, they leave holes in the sediment. Generally, the diameter of these depressions does not exceed 2 km, except in Minnesota, where some depressions reach up to 50 km in diameter, with depths varying between 10 and 50 meters.

Deposits in contact with ice

When a glacier reduces in size to a critical point, its flow stops, and the ice becomes stationary. Meanwhile, meltwater flows over, within, and beneath the ice leave stratified alluvial deposits. Because of this, as the ice melts, it leaves stratified deposits in the form of columns, terraces and clusters. These types of deposits are known as deposits in contact with ice. When those deposits take the form of columns of tipped sides or mounds, which are called kames. Some kames form when meltwater deposits sediments through openings in the interior of the ice. In other cases, they are just the result of fans or deltas towards the exterior of the ice produced by meltwater. When the glacial ice occupies a valley it can form terraces or kame along the sides of the valley. A third type of deposit formed in contact with the ice is characterized by long, narrow sinuous crests composed fundamentally of sand and gravel deposite by streams of meltwater flowing within, beneath or on the glacier ice. After the ice has melted these linear ridges or eskers remain as landscape features. Some of these crests have heights exceeding 100 meters and their lengths surpass 100 km.

Loess deposits

Very fine glacial sediments or rock flour is often picked up by wind blowing over the bare surface and may be deposited great distances from the original fluvial deposition site. These eolian loess deposits may be very deep, even hundreds of meters, as in areas of China and the midwestern United States.

Isostatic rebound

loess This rise of a part of the crust is due to an isostatic adjustment. A large mass, such as a glacier, depresses the Earth's crust. After the glacier melts, the crust begins to rise to its original position. This is post-glacial rebound and is currently occurring in measurable amounts in Scandinavia and the Great Lakes region of the United States.

Ice ages

:Main article: Ice age.

Ice age divisions

A quadruple division of the Quaternary glacial period has been established for North America and Europe. These divisions are based principally on the study of glacial deposits. In North America, each of these four stages was named for the state in which the deposits of these stages were well exposed. In order of appearance, they are the following: Nebraskan, Kansan, Illinoisan, and Wisconsinan. This classification was refined thanks to the detailed study of the sediments of the ocean floor. Because the sediments of the ocean floor, in contrast to that of the Earth's surface, are less affected by stratigraphic discontinuities, they are useful to determine the climatic cycles of the planet. In this matter, geologists have come to identify over twenty divisions, each of them lasting approximately 100,000 years. All these cycles fall within the Quaternary glacial period. During its peak, the ice left its mark over almost 30% of Earth's surface, covering approximately 10 million km² in North America, 5 million km² in Europe and 4 million km² in Siberia. The glacial ice in the Northern hemisphere was double that found in the Southern hemisphere. This is because in the South Pole the ice cannot advance beyond the Antarctic landmass. It is now believed that the most recent glacial period began between two and three million years ago, in the Pleistocene era.

Causes of ice ages

Little is known about the causes of glaciations. Generalized glaciations have been rare in the history of Earth. However, the Ice Age of the Pleistocene was not the only glaciative event, since tillite deposits have been identified. Tillite is a sedimentary rock formed when glacial till is lithified. These deposits found in strata of differing age present similar characteristics as fragments of fluted rock, and some are superposed over bedrock surfaces of channeled and polished rock or associated with sandstone and conglomerates that have features of alluvial plain deposits. Two Precambrian glacial episodes have been identified, the first approximately 2 billion years ago, and the second (Snowball Earth) about 600 million years. Also, a well documented record of glaciation exists in rocks of the late Paleozoic (of 250 million years of age). Although there are several scientific hypotheses about the determining factors of glaciations, the two most important ideas are plate tectonics and variations in Earth's orbit (Milankovitch cycles).

Plate tectonics

Because glaciers can form only on dry land, plate tectonics suggest that the evidence of previous glaciations is currently present in tropical latitudes due to the drift of tectonic plates from tropical latitudes to circumpolar regions. Evidence of glacial structures in South America, Africa, Australia, and India support this idea, because it is known that they experienced a glacial period near the end of the Paleozoic Era, some 250 million years ago. The idea that the evidence of middle-latitude glaciations is closely related to the displacement of tectonic plates was confirmed by the absence of glacial traces in the same period for the higher latitudes of North America and Eurasia, which indicates that their locations were very different than today. Climatic changes are also related to the positions of the continents, which has made them vary in conjunction with the displacement of plates. That also affected ocean current patterns, which caused changes in heat transmission and humidity. Since continents drift very slowly (about 2 cm per year), similar changes occur in periods of millions of years. A study of marine sediment that contained climatically sensitive microorganisms until about half a million years ago were compared with studies of the geometry of Earth's orbit, and the result was clear: climatic changes are closely related to periods of obliquity, precession, and eccentricity