Hypogenic caves in France. Speleogenesis and morphology of the cave systems

2010 ◽  
Vol 181 (4) ◽  
pp. 327-335 ◽  
Author(s):  
Philippe Audra ◽  
Jean-Claude D’antoni-Nobecourt ◽  
Jean-Yves Bigot
Keyword(s):  
Water Table ◽  
Thermal Convection ◽  
Land Surface ◽  
Meteoric Water ◽  
Thermal Conditions ◽  
Development Trend ◽  
Oxidation Potential ◽  
Bedding Planes ◽  
The World ◽  
Iron Pool

Abstract Hypogenic caves develop by recharge from below, not directly influenced by seepage from the overlying land surface. Several processes of speleogenesis are combined, involving CO2 or H2S produced at depth. If the recharge from depth remains uniform, the growth of selected fissures is prevented, giving rise to maze cave systems with an upward development trend, which is defined as “transverse speleogenesis” [Klimchouk, 2003]. Hypogenic caves are much fewer than epigenic caves (i.e. developed downwards by meteoric water with aggressivity derived from soil). In France, as in the rest of the world, hypogenic caves were poorly recognized until recently because of their lower frequency, subsequent epigenic imprint often hiding the true origin, and the absence of a global conceptual model. However, about a hundred of hypogenic caves have been identified recently in France. The extreme diversity of hypogenic cave patterns and features is due to the variety of geological and topographic settings and types of flow. Thermal caves are a sub-set of hypogenic caves. Active thermal caves are few and small (Mas d’En Caraman, Vallon du Salut). Often, thermal influences only occur as point thermal infeeders into epigenic caves (Mescla, Estramar). In addition to the higher temperature, they may be characterized by CO2 (Madeleine) or H2S degassing, by warm water flowing in ceiling channels, or by manganese deposits. The Giant Phreatic Shafts locate along regional active faultlines. They combine all characteristics (thermal, CO2, H2S), due to the fast rising of deep water. The Salins Spring has been explored by scuba diving down to −70 m. Such a hyperkarstification is responsible for the development of the deepest phreatic shafts of the world: pozzo del Merro, Italy (−392 in). Inactive hypogenic caves may be recognized by their specific mineralization or by the presence of large calcite spar. Metallic deposits are due to the rising of deep waters that are warm, aggressive, and low in oxidation potential. Mixing with meteoric water generates Mississippi Valley Type (MVT) sulfidic ores. Iron deposits as massive bodies (Lagnes) or onto microbial media (Iboussières, Malacoste) making specific facies, such as “black tubes”, iron flakes, and iron pool fingers. Other frequent minerals are Mn oxides and Pb sulfur. In such low thermal conditions, calcite deposits occur as large spar in geodes or as passage linings. Other inactive hypogenic caves may also be recognized by characteristic patterns, such as mazes. The relatively constant recharge into confined karst aquifers suppresses fissure competition, so they enlarge at similar rates, producing a maze pattern. In horizontal beds, mazes extend centrifugally around the upwelling feeder. The juxtaposition of multiple discrete vertical feeders produces extended horizontal mazes. In gently tilted structures, 2D mazes extend below aquitards, or along bedding or more porous beds (Saint-Sébastien). In thick folded limestone the rising hypogenic flow alternatively follows joints and bedding planes, producing a 3D maze cave in a staircase pattern (Pigette). Isolated chambers are large cupola-like chambers fed by thermal slots. Thermal convection of air in a CO2-rich atmosphere causes condensation-corrosion that quickly produces voids above the water table (Champignons Cave). Sulfuric acid caves with replacement gypsum are produced by H2S degassing in the cave atmosphere. H2S oxidizes to H2SO4, which corrodes the carbonate rock and replaces it with gypsum. The strongest corrosion occurs above the water table, where sulfide degassing and thermal convection produce strong condensation-corrosion. Caves develop headward from springs and from thermo-sulfuric slots upward (Chevalley-Serpents System). The low-gradient main drains record base-level positions and even the slightest stages of water-table lowering (Chat Cave). Hypogenic speleogenesis provides better understanding of the distribution of karst voids responsible for subsidence hazards and the emplacement of minerals and hydrocarbons.

scholarly journals Hydrogeology of Brahmaputra Basin, India

2003 ◽  
Vol 28 ◽  
Author(s):  
Barendra Purkait
Keyword(s):  
Ground Water ◽  
Water Table ◽  
Land Surface ◽  
Flood Plain ◽  
Water Levels ◽  
The South ◽  
Drainage Pattern ◽  
The North ◽  
The World ◽  
Brahmaputra Basin

The Ganga-Brahmaputra river system together forms one of the largest deltas in the world comprising some 59570 sq km. The waterpower resources of the Brahmaputra have been presumed to be the fourth biggest in the world being 19.83 x 103 m3s1. The entire lower portion of the Brahmaputra consists of a vast network of distributary channels, which are dry in the cold season but are inundated during monsoon. The catchment area of the entire river is about 580,000 sq km, out of which 195,000 sq km lies in India. The maximum discharge as measured at Pandu in 1962 was of the order of 72800 m3 s-1 while the minimum was 1750 m3 s-1 in 1968. The drainage pattern in the valley is of antecedent type while the yazoo drainage pattern is most significant over the composite flood plain to the south of the Brahmaputra. The Brahmaputra valley is covered by Recent alluvium throughout its stretch except a few isolated sedimentary hills in the upper Assam, inselbergs/bornhardt of gneissic hills in the Darrang, Kamrup and Goalpara districts and a few inlying patches of Older Alluvium in the Darrang and Goalpara districts. The basin is very unstable. The present configuration of the basin is the result of uplift and subsidence of the Precambrian crystalline landmasses. Four geotectonic provinces can be delineated in the N-E India through which the Brahmaputra flows. These are bounded by major tectonic lineaments such as the basement E-W trending Dauki fault, a NE-SW trending structural feature of imbricate thrusts known as 'belt of Schuppen' and the NW-SE trending Mishmi thrust. Hydrogeologically, the Brahmaputra basin can be divided into two distinct categories, viz(a) dissected alluvial plain and (b) the inselberg zone. The first category is rep resented in the flood plain extending from the south of Sub-Himalayan piedmont fan zone in the north to right upto the main rock promontory of Garo Hills and Shillong Plateau. The inselberg zone is characterized by fractured, jointed and weathered ancient crystalline rocks with interhill narrow valley plains, consisting of thin to occasionally thick piles of assorted sediments. From the subsurface lithological data, two broad groups of aquifers are identified. These are i) shallow water table and ii) deeper water table or confined ones, separated by a system of aquicludes. The shallow aquifer materials, in general, consist of white to greyish white, fine grained micaceous sand and the thickness ranges from 1.2 to 10.3 m. The sand and clay ratio varies from 1: 2.5 to 1:26. The bedrock occurs at depth ranges of 30.4 to 39.5 m. The materials of the deeper aquifers comprise grey to greyish white, fine to medium grained sand. The sand and clay ratio varies from 1:2 to 1:7. The effective size of the aquifer materials varies from 0.125 to 0.062 mm with uniformity co-efficient around 4.00, porosity 38 to 42%, co-efficient of permeability 304 to 390 galls per day/0.3m2. The ground water is mildly alkaline with pH value 6.5 to 8.5, chloride 10 to 40 ppm, bi-carbonate 50 to 350 ppm, iron content ranges from a fraction of a ppm to 50 ppm. Total dissolved solids are low, hardness as CaCo3 50 to 300 ppm, specific conductance at 25 °C 150 to 650 mhos/cm. The yield from shallow aquifers is 1440 litres to 33750 litres/hour and for deeper aquifers ~ 1700 litres/hour at a drawdown of 13.41 m, specific capacity 21 litres/minute. The temperatures of ground water are 23°-25° C during winter, 24°-26° C during pre-monsoon and 27°- 28° C during peak monsoon. The general hydraulic gradient in the north bank is 1:800 whereas in the south bank it is 1: 300-400 The Tertiary sediments yield a range of water from 200 to 300 l.p.m whereas the yield from the Older Alluvium is 500 to 700 1.p.m. The estimated transmissibility and co-efficient of storage is of the order of ~ 800 1.p.m/ m and 8.2 x 10-3 respectively. Depths to water levels range from 5.3 to 10m below land surface (b.l.s). In the Younger or Newer Alluvium, ground water occurs both under water table and confined conditions. Depths to water levels vary from ground level to 10 m b.l.s. Depth to water ranges from 6 m b.l.s. to 2 m above land surface. The yield of the deep tubewells ranges from 2 to 4 kl/minute for a drawdown of 3 m to 6 m. The transmissibility of the aquifers varies from 69 to 1600 l.p.m/m and the storage co-fficient is of the order of 3.52 x 10-2.

scholarly journals Structure, Diversity, and Environmental Determinants of High-Latitude Threatened Conifer Forests

Forests ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 775
Author(s):  
Carlos Esse ◽  
Francisco Correa-Araneda ◽  
Cristian Acuña ◽  
Rodrigo Santander-Massa ◽  
Patricio De Los Ríos-Escalante ◽  
...  
Keyword(s):  
Water Table ◽  
Environmental Variables ◽  
National Park ◽  
High Water ◽  
Forest Communities ◽  
Competitive Effect ◽  
Forest Patches ◽  
Last Glaciation ◽  
The World ◽  
Local Topography

Pilgerodendron uviferum (D. Don) Florin is an endemic, threatened conifer that grows in South America. In the sub-Antarctic territory, one of the most isolated places in the world, some forest patches remain untouched since the last glaciation. In this study, we analyze the tree structure and tree diversity and characterize the environmental conditions where P. uviferum-dominated stands develop within the Magellanic islands in Kawésqar National Park, Chile. An environmental matrix using the databases WorldClim and SoilGrids and local topography variables was used to identify the main environmental variables that explain the P. uviferum-dominated stands. PCA was used to reduce the environmental variables, and PERMANOVA and nMDS were used to evaluate differences among forest communities. The results show that two forest communities are present within the Magellanic islands. Both forest communities share the fact that they can persist over time due to the high water table that limits the competitive effect from other tree species less tolerant to high soil water table and organic matter. Our results contribute to knowledge of the species’ environmental preference and design conservation programs.

scholarly journals Real-time monitoring of nitrate transport in the deep vadose zone under a crop field – implications for groundwater protection

2016 ◽  
Vol 20 (8) ◽  
pp. 3099-3108 ◽  
Author(s):  
Tuvia Turkeltaub ◽  
Daniel Kurtzman ◽  
Ofer Dahan
Keyword(s):  
Real Time ◽  
Water Table ◽  
Vadose Zone ◽  
Land Surface ◽  
Agricultural Land ◽  
Root Zone ◽  
Isotopic Signature ◽  
Nitrate Transport ◽  
Mass Migration ◽  
Crop Field

Abstract. Nitrate is considered the most common non-point pollutant in groundwater. It is often attributed to agricultural management, when excess application of nitrogen fertilizer leaches below the root zone and is eventually transported as nitrate through the unsaturated zone to the water table. A lag time of years to decades between processes occurring in the root zone and their final imprint on groundwater quality prevents proper decision-making on land use and groundwater-resource management. This study implemented the vadose-zone monitoring system (VMS) under a commercial crop field. Data obtained by the VMS for 6 years allowed, for the first time known to us, a unique detailed tracking of water percolation and nitrate migration from the surface through the entire vadose zone to the water table at 18.5 m depth. A nitrate concentration time series, which varied with time and depth, revealed – in real time – a major pulse of nitrate mass propagating down through the vadose zone from the root zone toward the water table. Analysis of stable nitrate isotopes indicated that manure is the prevalent source of nitrate in the deep vadose zone and that nitrogen transformation processes have little effect on nitrate isotopic signature. The total nitrogen mass calculations emphasized the nitrate mass migration towards the water table. Furthermore, the simulated pore-water velocity through analytical solution of the convection–dispersion equation shows that nitrate migration time from land surface to groundwater is relatively rapid, approximately 5.9 years. Ultimately, agricultural land uses, which are constrained to high nitrogen application rates and coarse soil texture, are prone to inducing substantial nitrate leaching.

scholarly journals Hover Surf Drone

2019 ◽  
Vol 8 (2) ◽  
pp. 564-566
Keyword(s):  
Land Surface ◽  
Autonomous Vehicle ◽  
Technological Growth ◽  
The World

The technological growth leads to various advanced inventions in the world, which makes the work ease. In this rush-up generation, we must adopt to an ease and the faster way to reach our destination on time without any troubles. Hence flying is the only way of faster transportation without any interference. However airplanes, Jets, helicopters etc helps us; Hover surf is a drone type flying model which flies over the sky with shorter distance from the land surface. Even it acts as an autonomous vehicle which can be operated or travelled by a person. Hover surf works under the principle of a flying drone

Introduction

2000 ◽  
Author(s):  
Peter J. Cook ◽  
Chris M. Carleton
Keyword(s):  
Land Surface ◽  
18Th Century ◽  
Science And Technology ◽  
World Ocean ◽  
Trade Routes ◽  
Peaceful Settlement ◽  
The World ◽  
Comprehensive Framework ◽  
Settlement Of Disputes ◽  
First Time

As pointed out in the Foreword, the United Nations Convention on the Law of the Sea (the Convention) is, by any measure, a remarkable document, which for the first time provides a comprehensive framework of governance for a large part of the world ocean. It covers such issues as delimitation, environmental impact and management, scientific research, economic and commercial issues, and technology transfer and provides a regime for the peaceful settlement of disputes. The resolution of disputes is especially important, given that there are 151 coastal States, all with sovereign rights to the adjacent seas and shelf. Under the Convention, those rights cover a total area of about 60 million km2 or around 20% of the world ocean within the 200-nauticalmile (M) limit. But there is perhaps an additional 5% (15 million km2) which lies beyond the 200-M limit, to which sovereign rights may also extend under the terms of the Convention. Up to 54 coastal States may be able to claim extensions of their continental shelf beyond 200 M (figure 1.1). What is intended is that over the next 10 years or so, nations will document and lay claim to an area of around 75 million km2, equal to more than half the Earth's land surface. Viewed against the background of human history and land conquest extending over thousands of years, the magnitude of the undertaking is extraordinary. What is also remarkable is the key role that science and technology will play. Science and technology have always played a role in exploration and documentation of the oceans in the past. The development of an accurate chronometer by Harrison in the 18th century was critical to developing an accurate means of establishing longitude (Sobel, 1995). This in turn made it possible to accurately chart the oceans for the first time, which then enabled nations to lay claim to newly explored areas, establish trade routes, document marine hazards, and exploit ocean resources. Parts of the world's territorial sea baselines are and will continue to be based on 19th-century data. As will be evident from this book, such data are sufficiently important in some areas that we have felt it necessary to document just how those "historical data" were gathered so that we can establish their reliability.

International Activities Related to Dryland Degradation Assessment and Drought Early Warning

2005 ◽  
Author(s):  
Ashbindu Singh
Keyword(s):  
Land Degradation ◽  
Land Surface ◽  
Food Production ◽  
Agricultural Productivity ◽  
Economic Productivity ◽  
Adequate Diet ◽  
The World ◽  
Sub Saharan ◽  
Drought Early Warning ◽  
Land Degradation And Desertification

Land degradation usually occurs on drylands (arid, semiarid, and dry subhumid areas). According to the United Nations Convention to Combat Desertification held in Paris in 1994 (UNCCD, 1999), drylands are defined as those lands (other than polar and subpolar regions) where the ratio of annual precipitation to potential evapotranspiration falls within the range of 0.05–0.65. Land degradation causes reduction in the biological or economic productivity of those lands that may support cropland, rangelands, forest, and woodlands. Land degradation threatens culturally unique agropastoral and silvopastoral farming systems and nomadic and transhumance systems. The consequences of land degradation are widespread poverty, hunger, migration, and creation of a potential cycle of debt for the affected populations. Historical awareness of the land degradation was cited, mainly at the local and regional scales, by Plato in the 4th century B.C in the Mediterranean region, and in Mesopotamia and China (WRI, 2001). The occurrence of the “dust bowl” in the United States during the 1930s affected farms and agricultural productivity, and several famines and mass migrations, especially in Africa during the 1970s, were important landmarks of land degradation in the 20th century. It is estimated that more than 33% of the earth’s land surface and 2.6 billion people are affected by land degradation and desertification in more than 100 countries. About 73% of rangelands in dryland areas and 47% of marginal rain-fed croplands, together with a significant percentage of irrigated croplands, are currently degraded (WRI, 2001). In sub-Saharan Africa, land degradation is widespread (20–50% of the land) and affects some 200 million people. This region experiences poverty and frequent droughts on a scale not known anywhere else in the world. Land degradation is also severe and widespread in Asia, Latin America, as well as other regions of the globe. Continuous land degradation is accelerating the loss of agricultural productivity and food production in the world. Over the next 50 years, food production needs to triple in order to provide a nutritionally adequate diet for the world’s growing population. This will be difficult to achieve even under favorable circumstances.

scholarly journals Subsea cable key challenges of an intercontinental power link: case study of Australia–Singapore interconnector

2020 ◽  
Author(s):  
Jeremy Gordonnat ◽  
James Hunt
Keyword(s):  
Southeast Asia ◽  
Land Surface ◽  
High Carbon ◽  
High Demand ◽  
High Carbon Content ◽  
Holistic View ◽  
Demand Growth ◽  
The World ◽  
Renewable Energy Generation

AbstractThe high potential for renewable energy generation in Australia, in particular solar and wind, and the high carbon content of Southeast Asian electricity and projected demand growth create favourable conditions for a HVDC power link between Australian and Southeast Asia. Such an interconnector would link predominantly solar farms located in northern Australia, known for its highest insolation levels in the world, to Singapore given its central location within Southeast Asia, high reliance on natural gas for its power generation, high demand growth and limited renewable potential and land surface. The current paper presents a holistic view of the key challenges of an Australia–Singapore power link related to its length, in the order of 3200 km, the water depth of sections crossing the Timor Trough and Indonesian waters, up to 1900 m, and the manufacturing and logistic issues of extensive length of cable to be deployed in a part of the world distant from the main manufacturing facilities. This very ambitious project will require a unique integrated contracting strategy involving multiple HVDC cable suppliers, marine heavy transport companies and cable installation contractors to effectively deliver this project within a sensible timeframe.

scholarly journals A process-based <i>Sphagnum</i> plant-functional-type model for implementation in the TRIFFID Dynamic Global Vegetation Model

2019 ◽  
Author(s):  
Richard Coppell ◽  
Emanuel Gloor ◽  
Joseph Holden
Keyword(s):  
Water Table ◽  
Primary Productivity ◽  
Photosynthetically Active Radiation ◽  
Land Surface ◽  
Net Primary Productivity ◽  
Type Model ◽  
Surface Model ◽  
Dynamic Global Vegetation Model ◽  
Active Radiation ◽  
Global Vegetation

Abstract. Peatlands are important carbon stores and Sphagnum moss represents a critical peatland genus contributing to carbon exchange and storage. However, gas fluxes in Sphagnum-dominated systems are poorly represented in Dynamic Global Vegetation Models (DGVMs) which simulate, via incorporation of Plant Functional Types (PFTs), biogeochemical and energy fluxes between vegetation, the land surface and the atmosphere. Mechanisms characterised by PFTs within DGVMs include photosynthesis, respiration and competition and, in more recent DGVMs, sub-daily gas-exchange processes regulated by leaf 10 stomata. However, Sphagnum, like all mosses, are non-vascular plants and do not exhibit stomatal regulation. In order to achieve a level of process detail consistent with existing vascular vegetation PFTs within DGVMs, this paper describes a new process-based non-vascular-PFT model that is implemented within the TRIFFID DGVM used by the JULES land surface model. The new PFT model was tested against extant published field and laboratory studies of peat assemblage-net primary productivity, assemblage-gross primary productivity, assemblage respiration, water-table position, incoming 15 photosynthetically active radiation, temperature, and canopy dark respiration. The PFT model’s parameters were roughly tuned and the PFT model easily produced curves of the correct shape for peat assemblage-net primary productivity against water-table position, incoming photosynthetically active radiation and temperature, suggesting that it replicates the internal productivity mechanism of Sphagnum for the first time. Minor modifications should also allow it to be used across a range of other bryophytes enabling this non-vascular PFT model to have enhanced functionality.

Global Overview of Tropical Dry Forests

2020 ◽  
pp. 1-23
Author(s):  
G. N. Tanjina Hasnat ◽  
Mohammed Kamal Hossain
Keyword(s):  
Climate Change ◽  
Endangered Species ◽  
Land Surface ◽  
Forest Type ◽  
Conservation Status ◽  
Tropical Dry Forests ◽  
Land Conversion ◽  
Dry Period ◽  
Dry Forests ◽  
The World

Forests cover almost one-third of the Earth's land surface. Tropical dry forests are the second-most-important forest type in the world covering approximately 42% of tropical and sub-tropical forest area. The main features of these forests are their deciduousness, a prolonged dry period extending 3-9 months, and little annual precipitation of 250-2,000 mm. Tropical dry forests are found in five of the eight realms in the world. More than half of the forests are distributed in the Americas, with other portions in Africa, Eurasia, Australia, and Southeast Asia. The forests are unique in nature, and provide shelter to a huge number of endemics and endangered species. Among woody plant species, about 40% are not found anywhere in the world. These forests are now the most threatened among all forest types. The conservation status of these forests is endangered. Deforestation, rapid civilization, land conversion, fire, and climate change are the major threats. Proper management with time-oriented policy could be helpful to restore these forests and protect the existing remnant areas.

Hydrogeological controls of water table-land surface interactions

2016 ◽  
Vol 43 (18) ◽  
pp. 9653-9661 ◽  
Author(s):  
E. Bresciani ◽  
P. Goderniaux ◽  
O. Batelaan
Keyword(s):  
Water Table ◽  
Land Surface ◽  
Surface Interactions
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