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72-668: Tank Farm (sometimes Tuff Crater ) is the name of a volcanic explosion crater (or maar ) on the North Shore of Auckland , New Zealand, near the approaches to the Auckland Harbour Bridge . Part of the Auckland volcanic field , it was created by a series of explosive eruptions. Although its age is unknown it could be one of the older volcanoes in Auckland like its neighbours Onepoto and Lake Pupuke . Originally

144-408: A drop in the ground surface. In unconsolidated aquifers, groundwater is produced from pore spaces between particles of gravel, sand, and silt. If the aquifer is confined by low-permeability layers, the reduced water pressure in the sand and gravel causes slow drainage of water from the adjoining confining layers. If these confining layers are composed of compressible silt or clay, the loss of water to

216-402: A former lake bed, has experienced rates of subsidence of up to 40 centimetres (1 foot 4 inches) per year. For coastal cities, subsidence can increase the risk of other environmental issues, such as sea level rise . For example, Bangkok is expected to have 5.138 million people exposed to coastal flooding by 2070 because of these combining factors. If the surface water source

288-502: A freshwater lake, it later became a tidal lagoon when the sea levels rose after the last ice age . Tank Farm is mostly in its natural state, though some parts of the tuff ring were quarried and its name stems from the petrochemicals storage tanks located here during World War II. Tank Farm and neighbouring Onepoto were fresh water lakes when sea levels were lower using the Last Glacial Maximum . As sea levels rose,

360-1076: A global level, although priority chemicals will vary by country. There is a lot of heterogeneity of hydrogeologic properties. For this reason, salinity of groundwater is often highly variable over space. This contributes to highly variable groundwater security risks even within a specific region. Salinity in groundwater makes the water unpalatable and unusable and often occurs in coastal areas, for example in Bangladesh and East and West Africa. Municipal and industrial water supplies are provided through large wells. Multiple wells for one water supply source are termed "wellfields", which may withdraw water from confined or unconfined aquifers. Using groundwater from deep, confined aquifers provides more protection from surface water contamination. Some wells, termed "collector wells", are specifically designed to induce infiltration of surface (usually river) water. Aquifers that provide sustainable fresh groundwater to urban areas and for agricultural irrigation are typically close to

432-408: A home and then returned to the ground in another well. During cold seasons, because it is relatively warm, the water can be used in the same way as a source of heat for heat pumps that is much more efficient than using air. Groundwater makes up about thirty percent of the world's fresh water supply, which is about 0.76% of the entire world's water, including oceans and permanent ice. About 99% of

504-519: A long time without severe consequences. Nevertheless, over the long term the average rate of seepage above a groundwater source is the upper bound for average consumption of water from that source. Groundwater is naturally replenished by surface water from precipitation , streams , and rivers when this recharge reaches the water table. Groundwater can be a long-term ' reservoir ' of the natural water cycle (with residence times from days to millennia), as opposed to short-term water reservoirs like

576-620: A mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme . The name maar comes from a Moselle Franconian dialect word used for the circular lakes of the Daun area of Germany. The word evolved from its first use in German in the modern geological sense in 1819 and is now used in English and in the geological sciences as the term for the explosion crater, even if water from rainfall might always have drained from

648-714: A name taken from Hochstetter's (1864) map of the volcanoes of Auckland where a number of volcanoes, including Tank Farm, were each labelled "tuff crater" or "tuff craters". The name Tank Farm became popularised during World War II , when bulk fuel storage tanks were constructed adjacent to the crater. The crater is now surrounded by a 35-hectare nature reserve. 36°48′07″S 174°45′12″E  /  36.8020°S 174.7533°E  / -36.8020; 174.7533 Maar Maars range in size from 20 to 3,000  m (66 to 9,800  ft ) across and from 5 to 200 m (20 to 700 ft) deep. Most maars fill with water to form natural lakes. Most maars have low rims composed of

720-722: A permanently reduced capacity to hold water. The city of New Orleans, Louisiana is actually below sea level today, and its subsidence is partly caused by removal of groundwater from the various aquifer/aquitard systems beneath it. In the first half of the 20th century, the San Joaquin Valley experienced significant subsidence , in some places up to 8.5 metres (28 feet) due to groundwater removal. Cities on river deltas, including Venice in Italy, and Bangkok in Thailand, have experienced surface subsidence; Mexico City, built on

792-469: A volcanic crater, is a maar. The carbon dioxide -saturated Lake Nyos in northwestern Cameroon is another example, as is Zuñi Salt Lake in New Mexico , a shallow saline lake that occupies a flat-floored crater about 6,500 ft (2,000 m) across and 400 ft (120 m) deep. Its low rim is composed of loose pieces of basaltic lava and wall rocks ( sandstone , shale , limestone ) of

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864-642: Is Kagamiike Pond as well as many on the volcanic island of Miyake-jima , Izu Islands (Furumio, Mi'ike, Mizutamari, Shinmio). Koranga Maar and Numundo Maar are in Papua New Guinea . Kawah Masemo maar is on Mount Sempu volcano in Indonesia. The San Pablo Volcanic Field in the Province of Laguna on the island of Luzon in the Philippines contains maars. The Newer Volcanics Province in

936-399: Is a highly useful and often abundant resource. Most land areas on Earth have some form of aquifer underlying them, sometimes at significant depths. In some cases, these aquifers are rapidly being depleted by the human population. Such over-use, over-abstraction or overdraft can cause major problems to human users and to the environment. The most evident problem (as far as human groundwater use

1008-466: Is also subject to substantial evaporation, a groundwater source may become saline . This situation can occur naturally under endorheic bodies of water, or artificially under irrigated farmland. In coastal areas, human use of a groundwater source may cause the direction of seepage to ocean to reverse which can also cause soil salinization . As water moves through the landscape, it collects soluble salts, mainly sodium chloride . Where such water enters

1080-632: Is an additional water source that was not used previously. First, flood mitigation schemes, intended to protect infrastructure built on floodplains, have had the unintended consequence of reducing aquifer recharge associated with natural flooding. Second, prolonged depletion of groundwater in extensive aquifers can result in land subsidence , with associated infrastructure damage – as well as, third, saline intrusion . Fourth, draining acid sulphate soils, often found in low-lying coastal plains, can result in acidification and pollution of formerly freshwater and estuarine streams. Groundwater

1152-417: Is concerned) is a lowering of the water table beyond the reach of existing wells. As a consequence, wells must be drilled deeper to reach the groundwater; in some places (e.g., California , Texas , and India ) the water table has dropped hundreds of feet because of extensive well pumping. The GRACE satellites have collected data that demonstrates 21 of Earth's 37 major aquifers are undergoing depletion. In

1224-412: Is fresh water located in the subsurface pore space of soil and rocks . It is also water that is flowing within aquifers below the water table . Sometimes it is useful to make a distinction between groundwater that is closely associated with surface water , and deep groundwater in an aquifer (called " fossil water " if it infiltrated into the ground millennia ago ). Groundwater can be thought of in

1296-461: Is often cheaper, more convenient and less vulnerable to pollution than surface water . Therefore, it is commonly used for public drinking water supplies. For example, groundwater provides the largest source of usable water storage in the United States , and California annually withdraws the largest amount of groundwater of all the states. Underground reservoirs contain far more water than

1368-468: Is rapidly increasing with population growth, while climate change is imposing additional stress on water resources and raising the probability of severe drought occurrence. The anthropogenic effects on groundwater resources are mainly due to groundwater pumping and the indirect effects of irrigation and land use changes. Groundwater plays a central role in sustaining water supplies and livelihoods in sub-Saharan Africa . In some cases, groundwater

1440-560: Is susceptible to saltwater intrusion in coastal areas and can cause land subsidence when extracted unsustainably, leading to sinking cities (like Bangkok ) and loss in elevation (such as the multiple meters lost in the Central Valley of California ). These issues are made more complicated by sea level rise and other effects of climate change , particularly those on the water cycle . Earth's axial tilt has shifted 31 inches because of human groundwater pumping. Groundwater

1512-400: Is the most accessed source of freshwater around the world, including as drinking water , irrigation , and manufacturing . Groundwater accounts for about half of the world's drinking water, 40% of its irrigation water, and a third of water for industrial purposes. Another estimate stated that globally groundwater accounts for about one third of all water withdrawals , and surface water for

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1584-456: Is used for irrigation. Occasionally, sedimentary or "fossil" aquifers are used to provide irrigation and drinking water to urban areas. In Libya, for example, Muammar Gaddafi's Great Manmade River project has pumped large amounts of groundwater from aquifers beneath the Sahara to populous areas near the coast. Though this has saved Libya money over the alternative, seawater desalination,

1656-531: The Auckland volcanic field has other easily accessible maars such as the Mangere Lagoon , Orakei Basin , Panmure Basin , and Pukaki Lagoon . Elsewhere a recent example, only 4000 years old, is Lake Rotokawau in the Bay of Plenty Region . Groundwater This is an accepted version of this page Groundwater is the water present beneath Earth 's surface in rock and soil pore spaces and in

1728-1123: The Butajiri - Silti -Volcanic Field, Ethiopia, the Bayuda Volcanic Field in the Sudan and Lake Nyos in the Oku Volcanic Field in Cameroon). In Saudi Arabia the Al Wahbah crater formed as a result of a maar eruption. In Japan there are maars in the Kirishima - Yaku volcanic field in the Kirishima-Yaku National Park on Kyushu . These include the several maars of the Ibusuki volcanic field such as Lake Unagi . On Honshu in Myōkō-Togakushi Renzan National Park there

1800-651: The Eifel region of Germany (where they were originally described), and in other geologically young volcanic regions of Earth. Elsewhere in Europe, La Vestide du Pal, a maar in the Ardèche department of France, is easily visible from the ground or air. Kilbourne Hole and Hunt's Hole, in southern New Mexico near El Paso, Texas , are maars. The Crocodile Lake in Los Baños in the Philippines, though originally thought to be

1872-803: The Province of Ciudad Real . Active maars were commonplace in Fife and Lothian , Scotland during the Carboniferous period. The location of one such maar was Elie Ness. Active maar volcanoes are mainly known outside Europe. In the US there are numerous maar areas, such as in Alaska ( Ukinrek maars , Nunivak in the Bering Sea ); in Washington ( Battle Ground Lake ); in Oregon ( Fort Rock basin with

1944-585: The Punjab region of India , for example, groundwater levels have dropped 10 meters since 1979, and the rate of depletion is accelerating. A lowered water table may, in turn, cause other problems such as groundwater-related subsidence and saltwater intrusion . Another cause for concern is that groundwater drawdown from over-allocated aquifers has the potential to cause severe damage to both terrestrial and aquatic ecosystems – in some cases very conspicuously but in others quite imperceptibly because of

2016-883: The Swabian Jura and the Albvorland (the Swabian Volcano) there are maar-forming volcanoes. Because the over 350 eruption points were only active in the Upper Miocene 17 to 11 million years ago, all the maars, apart from the dry maar, Randecker Maar and the Molach, are only detectable geologically. In the Ore Mountains near Hammerunterwiesenthal , the Hammerunterwiesenthal Maar formed about 30 million years ago during

2088-407: The fractures of rock formations . About 30 percent of all readily available fresh water in the world is groundwater. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table . Groundwater is recharged from

2160-442: The hydraulic pressure of groundwater in the pore spaces of the aquifer and the aquitard supports some of the weight of the overlying sediments. When groundwater is removed from aquifers by excessive pumping, pore pressures in the aquifer drop and compression of the aquifer may occur. This compression may be partially recoverable if pressures rebound, but much of it is not. When the aquifer gets compressed, it may cause land subsidence,

2232-405: The vadose zone below plant roots and is often expressed as a flux to the water table surface. Groundwater recharge also encompasses water moving away from the water table farther into the saturated zone. Recharge occurs both naturally (through the water cycle ) and through anthropogenic processes (i.e., "artificial groundwater recharge"), where rainwater and/or reclaimed water is routed to

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2304-552: The Eifel and Volcanic Eifel there are numerous dry maars: The following volcanic features are often colloquially referred to as a "maar" or "maar lake", although they are not, strictly speaking, maars: In Germany there are also several maars outside of the Eifel. A well-known example is the Messel pit , a former maar lake near Messel in the county of Darmstadt-Dieburg and which is known for its well preserved fossils . In addition in

2376-715: The Oligocene; the maar measures 2 kilometres from east to west and 1.4 kilometres from north to south. The Chaîne des Puys in France contains numerous maars; Lake Albano in the Alban Mountains is a complex maar, and there is also a submarine maar ( Kolumbo ) near Santorini in Greece. The Campo de Calatrava Volcanic Field in Spain contains numerous maars; a typical example being the maar of Hoya del Mortero at Poblete in

2448-567: The States of South Australia and Victoria , Australia, has numerous maars, such as Mount Gambier , Mount Schank and Tower Hill , whose complex system of nested maars is enclosed by one of the largest maars in the world. Foulden Maar in Otago , New Zealand , is an important fossil site, but there are many more maars in New Zealand. As already mentioned these include Lake Pupuke , but

2520-561: The age of groundwater obtained from different parts of the Great Artesian Basin, hydrogeologists have found it increases in age across the basin. Where water recharges the aquifers along the Eastern Divide , ages are young. As groundwater flows westward across the continent, it increases in age, with the oldest groundwater occurring in the western parts. This means that in order to have travelled almost 1000 km from

2592-405: The aquifer reduces the water pressure in the confining layer, causing it to compress from the weight of overlying geologic materials. In severe cases, this compression can be observed on the ground surface as subsidence . Unfortunately, much of the subsidence from groundwater extraction is permanent (elastic rebound is small). Thus, the subsidence is not only permanent, but the compressed aquifer has

2664-525: The aquifers are likely to run dry in 60 to 100 years. Groundwater provides critical freshwater supply, particularly in dry regions where surface water availability is limited. Globally, more than one-third of the water used originates from underground. In the mid-latitude arid and semi-arid regions lacking sufficient surface water supply from rivers and reservoirs, groundwater is critical for sustaining global ecology and meeting societal needs of drinking water and food production. The demand for groundwater

2736-598: The atmosphere and fresh surface water (which have residence times from minutes to years). Deep groundwater (which is quite distant from the surface recharge) can take a very long time to complete its natural cycle. The Great Artesian Basin in central and eastern Australia is one of the largest confined aquifer systems in the world, extending for almost 2 million km . By analysing the trace elements in water sourced from deep underground, hydrogeologists have been able to determine that water extracted from these aquifers can be more than 1 million years old. By comparing

2808-510: The atmosphere through evapotranspiration , these salts are left behind. In irrigation districts, poor drainage of soils and surface aquifers can result in water tables' coming to the surface in low-lying areas. Major land degradation problems of soil salinity and waterlogging result, combined with increasing levels of salt in surface waters. As a consequence, major damage has occurred to local economies and environments. Aquifers in surface irrigated areas in semi-arid zones with reuse of

2880-930: The capacity of all surface reservoirs and lakes in the US, including the Great Lakes . Many municipal water supplies are derived solely from groundwater. Over 2 billion people rely on it as their primary water source worldwide. Human use of groundwater causes environmental problems. For example, polluted groundwater is less visible and more difficult to clean up than pollution in rivers and lakes. Groundwater pollution most often results from improper disposal of wastes on land. Major sources include industrial and household chemicals and garbage landfills , excessive fertilizers and pesticides used in agriculture, industrial waste lagoons, tailings and process wastewater from mines, industrial fracking , oil field brine pits, leaking underground oil storage tanks and pipelines, sewage sludge and septic systems . Additionally, groundwater

2952-511: The crater after the formation event. This extension in meaning was due to recognising that the lake may no longer exist. Since maar lakes are formed after initially ground or subsurface water interacts with a magma intrusion to create an explosion crater, the name came to be used for the crater type as well. The present definition of the term relates to both its common and scientific discourse use in language over two centuries. Depending upon context there may be other descriptors available to use in

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3024-491: The current population growth rate. Global groundwater depletion has been calculated to be between 100 and 300 km per year. This depletion is mainly caused by "expansion of irrigated agriculture in drylands ". The Asia-Pacific region is the largest groundwater abstractor in the world, containing seven out of the ten countries that extract most groundwater (Bangladesh, China, India, Indonesia, Iran, Pakistan and Turkey). These countries alone account for roughly 60% of

3096-765: The explosive reaction that occurs when magma comes into contact with permafrost . Hydromagmatic eruptions are increasingly explosive when the ratio of water to magma is low. Since permafrost melts slowly, it provides a steady source of water to the eruption while keeping the water to magma ratio low. This produces the prolonged, explosive eruptions that created these large maars. Examples of the Seward Peninsula maars include North Killeak Maar, South Killeak Maar, Devil Mountain Maar and Whitefish Maar. Maars occur in western North America, Patagonia in South America,

3168-404: The extended period over which the damage occurs. The importance of groundwater to ecosystems is often overlooked, even by freshwater biologists and ecologists. Groundwaters sustain rivers, wetlands , and lakes , as well as subterranean ecosystems within karst or alluvial aquifers. Not all ecosystems need groundwater, of course. Some terrestrial ecosystems – for example, those of

3240-407: The extent, depth and thickness of water-bearing sediments and rocks. Before an investment is made in production wells, test wells may be drilled to measure the depths at which water is encountered and collect samples of soils, rock and water for laboratory analyses. Pumping tests can be performed in test wells to determine flow characteristics of the aquifer. The characteristics of aquifers vary with

3312-420: The geological sciences such as the term tuff ring or maar-diatreme volcanoes. These last are volcanoes produced by explosive eruptions that cut deeply into the country rock with the maar being " the crater cut into the ground and surrounded by an ejecta ring ". A 2011 geological clarification of a maar is " Maar volcanoes are distinguished from other small volcanoes in having craters with their floor lying below

3384-472: The geology and structure of the substrate and topography in which they occur. In general, the more productive aquifers occur in sedimentary geologic formations. By comparison, weathered and fractured crystalline rocks yield smaller quantities of groundwater in many environments. Unconsolidated to poorly cemented alluvial materials that have accumulated as valley -filling sediments in major river valleys and geologically subsiding structural basins are included among

3456-404: The globe includes canals redirecting surface water, groundwater pumping, and diverting water from dams. Aquifers are critically important in agriculture. Deep aquifers in arid areas have long been water sources for irrigation. A majority of extracted groundwater, 70%, is used for agricultural purposes. In India, 65% of the irrigation is from groundwater and about 90% of extracted groundwater

3528-416: The ground surface (within a couple of hundred metres) and have some recharge by fresh water. This recharge is typically from rivers or meteoric water (precipitation) that percolates into the aquifer through overlying unsaturated materials. In general, the irrigation of 20% of farming land (with various types of water sources) accounts for the production of 40% of food production. Irrigation techniques across

3600-536: The hollow. The largest known maars are found at Espenberg on the Seward Peninsula in northwest Alaska. These maars range in size from 4 to 8 km (2.5 to 5.0 mi) in diameter and a depth up to 300 m (980 ft). These eruptions occurred in a period of about 100,000 years, with the youngest (the Devil Mountain Maar) occurring about 17,500 years ago. Their large size is due to

3672-640: The latter is the Eckfelder Maar . Near Steffeln is the Eichholzmaar (also called the Gussweiher ) which has dried out during the last century and is being renaturalised into a maar. In some cases the underlying rock is so porous that maar lakes are unable to form. After winters of heavy snow and rainfall many dry maars fill partially and temporarily with water; others contain small bogs or often artificial ponds that, however, only occupy part of

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3744-518: The local hydrogeology , may draw in non-potable water or saltwater intrusion from hydraulically connected aquifers or surface water bodies. This can be a serious problem, especially in coastal areas and other areas where aquifer pumping is excessive. Subsidence occurs when too much water is pumped out from underground, deflating the space below the above-surface, and thus causing the ground to collapse. The result can look like craters on plots of land. This occurs because, in its natural equilibrium state,

3816-768: The maars of Big Hole , Hole-in-the-Ground , Table Rock ); in Death Valley National Park , California ( Ubehebe Crater ); in Nevada ( Soda Lakes ); as well as the maars of the White Rock Canyon , Mount Taylor , the Potrillo volcanic fields ( Kilbourne Hole and Hunt's Hole ), and Zuñi Salt Lake in New Mexico. In Central Mexico, the Tarascan volcanic field contains several maars in

3888-412: The most productive sources of groundwater. Fluid flows can be altered in different lithological settings by brittle deformation of rocks in fault zones ; the mechanisms by which this occurs are the subject of fault zone hydrogeology . Reliance on groundwater will only increase, mainly due to growing water demand by all sectors combined with increasing variation in rainfall patterns . Groundwater

3960-436: The necessary powers, to send up numerous volcanic eruptions to plague the hot-tempered man and his wife Matakerepo. The two eruptions that were eventually fatal to the couple were said to be at the sites of what is now called Tank Farm and Onepoto Domain respectively. Consequently, the former was named Te Kopua o Matakamokamo, and the latter Te Kopua o Matakerepo. The local council uses the name Tuff Crater for this volcano -

4032-671: The open deserts and similar arid environments – exist on irregular rainfall and the moisture it delivers to the soil, supplemented by moisture in the air. While there are other terrestrial ecosystems in more hospitable environments where groundwater plays no central role, groundwater is in fact fundamental to many of the world's major ecosystems. Water flows between groundwaters and surface waters. Most rivers, lakes, and wetlands are fed by, and (at other places or times) feed groundwater, to varying degrees. Groundwater feeds soil moisture through percolation, and many terrestrial vegetation communities depend directly on either groundwater or

4104-470: The other two thirds. Groundwater provides drinking water to at least 50% of the global population. About 2.5 billion people depend solely on groundwater resources to satisfy their basic daily water needs. A similar estimate was published in 2021 which stated that "groundwater is estimated to supply between a quarter and a third of the world's annual freshwater withdrawals to meet agricultural, industrial and domestic demands." Global freshwater withdrawal

4176-683: The percolated soil moisture above the aquifer for at least part of each year. Hyporheic zones (the mixing zone of streamwater and groundwater) and riparian zones are examples of ecotones largely or totally dependent on groundwater. A 2021 study found that of ~39 million investigated groundwater wells 6-20% are at high risk of running dry if local groundwater levels decline by a few meters, or – as with many areas and possibly more than half of major aquifers  – continue to decline. Fresh-water aquifers, especially those with limited recharge by snow or rain, also known as meteoric water , can be over-exploited and depending on

4248-426: The pre-eruptive surface ". Maar lakes , also referred to simply as maars , occur when groundwater or precipitation fills the funnel-shaped and usually round hollow of the maar depression formed by volcanic explosions. Examples of these types of maar are the three maars at Daun in the Eifel mountains of Germany . A dry maar results when a maar lake dries out, becomes aggraded or silted up . An example of

4320-423: The same terms as surface water : inputs, outputs and storage. The natural input to groundwater is seepage from surface water. The natural outputs from groundwater are springs and seepage to the oceans. Due to its slow rate of turnover, groundwater storage is generally much larger (in volume) compared to inputs than it is for surface water. This difference makes it easy for humans to use groundwater unsustainably for

4392-416: The source of recharge in 1 million years, the groundwater flowing through the Great Artesian Basin travels at an average rate of about 1 metre per year. Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer . This process usually occurs in

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4464-680: The states of Michoacán and Guanajuato . In Nicaragua is the maar of Laguna de Xiloa, part of the Apoyeque volcano. From South America, there are known maars in Chile (e.g. Cerro Overo and Cerro Tujle in northern Chile). Jayu Khota is a maar in Bolivia . The maar of Birket Ram lies on the Golan Heights ; further south maars occur in Africa ( Bilate Volcanic Field and Haro Maja in

4536-497: The subsurface. The high specific heat capacity of water and the insulating effect of soil and rock can mitigate the effects of climate and maintain groundwater at a relatively steady temperature . In some places where groundwater temperatures are maintained by this effect at about 10 °C (50 °F), groundwater can be used for controlling the temperature inside structures at the surface. For example, during hot weather relatively cool groundwater can be pumped through radiators in

4608-462: The surface; it may discharge from the surface naturally at springs and seeps , and can form oases or wetlands . Groundwater is also often withdrawn for agricultural , municipal , and industrial use by constructing and operating extraction wells . The study of the distribution and movement of groundwater is hydrogeology , also called groundwater hydrology . Typically, groundwater is thought of as water flowing through shallow aquifers, but, in

4680-430: The technical sense, it can also contain soil moisture , permafrost (frozen soil), immobile water in very low permeability bedrock , and deep geothermal or oil formation water. Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults . It is likely that much of Earth 's subsurface contains some water, which may be mixed with other fluids in some instances. Groundwater

4752-408: The unavoidable irrigation water losses percolating down into the underground by supplemental irrigation from wells run the risk of salination . Surface irrigation water normally contains salts in the order of 0.5 g/L or more and the annual irrigation requirement is in the order of 10,000 m /ha or more so the annual import of salt is in the order of 5,000 kg/ha or more. Under

4824-781: The underlying diatreme , as well as chunks of ancient crystalline rocks blasted upward from great depths. Maars in Canada are found in the Wells Gray-Clearwater volcanic field of east-central British Columbia and in kimberlite fields throughout Canada. Another field of maars is found in the Pali-Aike Volcanic Field in Patagonia , South America. and in the Sudanese Bayuda Volcanic Field . The Auckland volcanic field in

4896-713: The urban area of Auckland , New Zealand, has several maars, including the readily accessible Lake Pupuke in the North Shore suburb of Takapuna . Arizona 's Meteor Crater was for many years thought to be a maar of volcanic origin but it is now known to be an impact crater . In the Volcanic Eifel there are about 75 maars. Both lake-filled and dry maars are typical, though the latter are more common. The last eruptions took place at least 11,000 years ago, and many maars are older, as evidenced by their heavy erosion and less obvious shapes and volcanic features. In

4968-528: The waters of the Waitematā Harbour breached the tuff rings of the craters, becoming tidal lagoons. Its Maori name is Te Kopua o Matakamokamo , meaning 'the basin of Matakamokamo'. Matakamokamo is an ancestral figure in Maori oral tradition who, during a domestic argument, is said to have inadvertently cursed the goddess of fire, Mahuika. As punishment, the goddess called on the parent god Mataoho , who had

5040-519: The world's liquid fresh water is groundwater. Global groundwater storage is roughly equal to the total amount of freshwater stored in the snow and ice pack, including the north and south poles. This makes it an important resource that can act as a natural storage that can buffer against shortages of surface water , as in during times of drought . The volume of groundwater in an aquifer can be estimated by measuring water levels in local wells and by examining geologic records from well-drilling to determine

5112-420: The world's total groundwater withdrawal. Groundwater may or may not be a safe water source. In fact, there is considerable uncertainty with groundwater in different hydrogeologic contexts: the widespread presence of contaminants such as arsenic , fluoride and salinity can reduce the suitability of groundwater as a drinking water source. Arsenic and fluoride have been considered as priority contaminants at

5184-402: Was probably around 600 km per year in 1900 and increased to 3,880 km per year in 2017. The rate of increase was especially high (around 3% per year) during the period 1950–1980, partly due to a higher population growth rate, and partly to rapidly increasing groundwater development, particularly for irrigation. The rate of increase is (as per 2022) approximately 1% per year, in tune with

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