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Articles 1351 - 1380 of 1880

Full-Text Articles in Earth Sciences

Land Use In The Tropical Karst - The Case Of Peruaçu, Januária And Jaiba; Se Brazil, Heinz Charles Kohler, Sergio Dos Anjos Ferreira Pinto, João Francisco De Abreu Jan 1999

Land Use In The Tropical Karst - The Case Of Peruaçu, Januária And Jaiba; Se Brazil, Heinz Charles Kohler, Sergio Dos Anjos Ferreira Pinto, João Francisco De Abreu

International Journal of Speleology

The karstic regions of the municipalities of Peruaçu, Januária and Jaiba present a variety of soil uses which are a function of the organization of the karstic relief. This relief system forms a rift, which received fluvial sediments deposition from the São Francisco River. The horst of the Peruaçu plateau is developed on limestone rocks of Late Proterozoic age with a high concentration of calcium carbonate. The South American Surface was formed on this and is today occupied by cattle ranching. In the graben, due to easy irrigation from underground karst waters and because of the nearby drainage system of …

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New Kinematic Models For Pacific-North America Motion From 3 Ma To Present, I: Evidence For Steady Motion And Biases In The Nuvel-1a Model, Charles Demets, Timothy H. Dixon Jan 1999

New Kinematic Models For Pacific-North America Motion From 3 Ma To Present, I: Evidence For Steady Motion And Biases In The Nuvel-1a Model, Charles Demets, Timothy H. Dixon

School of Geosciences Faculty and Staff Publications

We use velocities derived from 2–4.5 years of continuous GPS observations at 21 sites on the Pacific and North American plates along with a subset of the NUVEL-1A data to examine the steadiness of Pacific-North America motion since 3.16 Ma, the transfer of Baja California to the Pacific plate, and the magnitude of biases in the NUVEL-1A estimate of Pacific-North America motion. We find that Pacific-North America motion has remained steady since 3.16 Ma, but at rates significantly faster than predicted by NUVEL-1A. In the vicinity of Baja California, our GPS-derived model and recent seafloor spreading rates in the southern …

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Decelerating Nazca-South America And Nazca-Pacific Plate Motions, Edmundo O. Norabuena, Timothy H. Dixon, Seth Stein, Christopher G. A. Harrison Jan 1999

Decelerating Nazca-South America And Nazca-Pacific Plate Motions, Edmundo O. Norabuena, Timothy H. Dixon, Seth Stein, Christopher G. A. Harrison

School of Geosciences Faculty and Staff Publications

Space geodetic estimates of the rate of Nazca-South America convergence and Nazca-Pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average NUVEL-1A model. The implied rates of deceleration are consistent with longer term trends extending back to at least 20 Ma, about the time of initiation of Andes growth, and may reflect consequences of ongoing subduction and construction of the Andes, e.g., increased friction and viscous drag on the subducted slab as the leading edge of South America thickens.

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Impact Of Agricultural Land Use On Some Hungarian Karst Regions, Ilona Bárány-Kevei Jan 1999

Impact Of Agricultural Land Use On Some Hungarian Karst Regions, Ilona Bárány-Kevei

International Journal of Speleology

The karst regions are found in the medium altitude mountains of Hungary. Their land use types are natural and sustainable forestry, grazing and vineyards. In international comparison, Hungary belongs to those countries of Europe where arable land is abundant, therefore, in the future its extension has to be reduced. That means agricultural activity has to be restricted on the sensitive karst surfaces. This paper presents ways of sustainable forestry and other land use types for three karst regions of Hungary.

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Agricultural Use And Water Quality At Karstic Cuban Western Plain, Juan Reynerio Fagundo Castillo, Patricia González Hernandez Jan 1999

Agricultural Use And Water Quality At Karstic Cuban Western Plain, Juan Reynerio Fagundo Castillo, Patricia González Hernandez

International Journal of Speleology

In the paper some results of studies on the karstic aquifers of the western plain of Cuba are presented and discussed. The intensive exploitation of these aquifers for agriculture use and drinking water supply induces an increase of marine water intrusion, water salinisation and a progressive increase of chemical corrosion with a greater dissolution of carbonates. During the period of study (1983-1998) a trend in the deterioration of water quality was observed by means of a chronological series of hydrochloride content.

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Agriculture And Nature Conservation In The Moravian Karst (Czech Republic), Ivan Balák, Jozef Janèo, Leos Stefka, Pavel Bosák Jan 1999

Agriculture And Nature Conservation In The Moravian Karst (Czech Republic), Ivan Balák, Jozef Janèo, Leos Stefka, Pavel Bosák

International Journal of Speleology

Moravian karst is a narrow strip of limestone with long history of settlement, agricultural use and man impact to karst. It is naturally divided into smaller units - karst plateaus - separated by deep valleys (glens). Each plateau has different proportion of land use, i.e. the percentage of agricultural land, forests, etc. The agricultural land constitutes now up to 70% in the north and max. 30% in the centre and south of the total area of plateaus. Intensive agricultural use of the arable land since 60ties of this Century caused great impact to quality of soils and groundwater by overdoses …

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Land Use And Human Impact In The Dinaric Karst, Ivan Gams, Matej Gabrovec Jan 1999

Land Use And Human Impact In The Dinaric Karst, Ivan Gams, Matej Gabrovec

International Journal of Speleology

The article presents Dinaric karst, human impacts in the area, and its long history of deforestation, transformation into stony semi-desert, and a century long reforestation, where plans to restore the primary thick soil were just hoping against hope.

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Agriculture, Grazing And Land Changes At The Serra De Tramuntana Karstic Mountains, Ángel Ginés Jan 1999

Agriculture, Grazing And Land Changes At The Serra De Tramuntana Karstic Mountains, Ángel Ginés

International Journal of Speleology

Karst landforms are one of the most outstanding characteristics of the Serra de Tramuntana range on the island of Mallorca, especially regarding traditional farming and the landscape wilderness. Good examples of polje-like depressions, dolines, karstic gorges and karrenfields are widely distributed over the mountain range. Owing to karrenfields occupying a large surface area in the Serra to the exclusion of arable land, the traditional activity based on the repetitive burning of the Ampelodesmos mauritanica brushwoods for cattle-raising promotes hastening deforestation and soil removal.

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Impacts Of Agricultural Transformation On The Principal Karstic Regions Of France, Jean Nicod, Jean-Noël Salomon Jan 1999

Impacts Of Agricultural Transformation On The Principal Karstic Regions Of France, Jean Nicod, Jean-Noël Salomon

International Journal of Speleology

The recent extension of intensive agriculture on the karst plateaus has caused different types of impact: soil management, generalised and/or localised pollution. Yet paradoxically rural depopulation can also have negative impacts, which largely depend on the characteristics and the hydrological function of the different karst environments. They are often negative, particularly as far as the water quality is concerned, which is why protection measures are undertaken, either in a defined area for a catchment, or in the framework of regional parks. But this is not always the case, so it is appropriate to analyse the problem of karst pollution as …

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Agriculture, Landscape And Human Impact In Some Karst Areas Of Italy, Ezio Burri, Benedetta Castiglioni, Ugo Sauro Jan 1999

Agriculture, Landscape And Human Impact In Some Karst Areas Of Italy, Ezio Burri, Benedetta Castiglioni, Ugo Sauro

International Journal of Speleology

Italy is made up for about 1/5 of its surface by soluble rocks, which represent the arena of karst environments. The karst morpho-units, some hundreds, are mainly distributed inside the alpine structure of the Mediterranean mountains. A very large number of rock formations are present, different in facies, lithology, age, etc. Among these, carbonate rocks prevail, followed by gypsum and salt. Most of the carbonate rocks are limestones sedimented in a platform environment and they show a wide range of porosity, frequency of fractures and bedding planes. The climatic processes, the expression of some different sub-types of Mediterranean climate (from …

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Interaction Between Karst, Water And Agriculture Over The Climatic Gradient Of Israel, Amos Frumkin Jan 1999

Interaction Between Karst, Water And Agriculture Over The Climatic Gradient Of Israel, Amos Frumkin

International Journal of Speleology

The dry climate of Israel and the karstic nature of its rocks have always imposed human innovation for utilisation of water resources and agriculture. Large perennial karst springs are available only in the lowlands, but sophisticated water supply systems were built both in the lowland and highland regions. Marl layers interbedded within carbonates give rise to local perched springs and allow terrace construction. Deforestation has taken place for some 4000 years, causing intense soil erosion, but terraces have reduced this impact.

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Land Use In The Karstic Lands In The Mediterranean Region, Ibrahim Atalay Jan 1999

Land Use In The Karstic Lands In The Mediterranean Region, Ibrahim Atalay

International Journal of Speleology

Karstic lands have special importance in terms of soil formation and land-use. Soil appears only on the flat and slightly undulating karstic lands, while soils are found along the cracks and bedding surfaces between the layers on the hilly karst areas although these lands are rocky in appearance. Karstic lands in the hilly area are not conducive to cultivation. But rocky areas create a favourable habitat for the growth of forests except in an arid climate. Because the tree roots easily follow and develop along the cracks in the limestone. As a general rule soil erosion does not occur on …

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Environmental Vulnerability And Agriculture In The Karstic Domain: Landscape Indicators And Cases In The Atlas Highlands, Morocco, Brahim Akdim, Mohammed Amyay Jan 1999

Environmental Vulnerability And Agriculture In The Karstic Domain: Landscape Indicators And Cases In The Atlas Highlands, Morocco, Brahim Akdim, Mohammed Amyay

International Journal of Speleology

After the brief presentation of the major karstic areas in Morocco, the article focused essentially on the Atlas mountains to investigate the impact of the agriculture on the natural systems equilibrium. Socio-economic changes (demographic pressure, escalation of the landscape use, utilisation of new techniques in water harvesting, etc...) have sometimes fathered mechanisms of degradation. Many indicators seem to reflect these mechanisms. The pedologic indicators, soil erosion, the hydrologic and geomorphic indicators, are apprehended to demonstrate existent correlation between different variables and the often negative impacts of land over-use in the karstic domain of the Middle Atlas.

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Karst And Agriculture In Australia, David Gillieson, Mia Thurgate Jan 1999

Karst And Agriculture In Australia, David Gillieson, Mia Thurgate

International Journal of Speleology

Much of the development and degradation of karst lands in Australia has occurred in the last two centuries since European settlement. Recent prolonged El Niño events add further climatic uncertainty and place real constraints on sustainable agriculture. The lower southeast of South Australia is perhaps the one area in Australia where karst, and particularly karst hydrology, impinge on the daily lives of the community in that pollution and overexploitation of the aquifer are readily apparent to the local population. Effluent from intensive dairy farms, piggeries and cheese factories enters the karst and has caused concern over pollution of water supplies. …

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Stochastic Methods For Evaluating The Potential For Wetland Rehydration In Covered-Karst Terranes, Christian David Langevin Oct 1998

Stochastic Methods For Evaluating The Potential For Wetland Rehydration In Covered-Karst Terranes, Christian David Langevin

USF Tampa Graduate Theses and Dissertations

Augmentation with reclaimed water is one method for rehydrating wetlands damaged by water-level declines. Augmentation with reclaimed water has been proposed for rehydrating a wetland in the covered-karst terrane of west-central Florida. There is concern because reclaimed water may contain harmful agents that could flow from the wetland 1.4 km to a municipal wellfield that withdraws 30,000 m3/day. Estimates of groundwater flow velocities were calculated from the results of detailed field studies at the wetland. Results indicate that groundwater flows downward in the surficial aquifer at rates of 0.1 to 0.2 m/day and horizontally in the Floridan aquifer …

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Gps Measurement Of Surface Deformation Around Soufriere Hills Volcano, Montserrat From October 1995 To July 1996, Glen S. Mattioli, Timothy H. Dixon, Frederic Farina, Ellen S. Howell, Pamela E. Jansma, Alan L. Smith Sep 1998

Gps Measurement Of Surface Deformation Around Soufriere Hills Volcano, Montserrat From October 1995 To July 1996, Glen S. Mattioli, Timothy H. Dixon, Frederic Farina, Ellen S. Howell, Pamela E. Jansma, Alan L. Smith

School of Geosciences Faculty and Staff Publications

Global Positioning System geodesy was used to measure surface deformation on Soufriere Hills volcano, Montserrat from October 6, 1995 to July 1, 1997 during initial dome growth and gravitational collapse. Our data from this period show non-axially symmetric horizontal displacements, and decreasing subsidence as a function of radial distance from the former topographic high of the volcanic edifice. Forward modeling suggests that surface deformation is caused by a shallow vertical dike (< 3 km), which expanded approximately 1 m, coupled with a deflating Mogi source at about 6 km depth. These inferred source parameters are in good agreement with independent observations of regional dike widths and preemption magma storage depth.

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Gps Measurements Across The Northern Caribbean Plate Boundary Zone: Impact Of Postseismic Relaxation Following Historic Earthquakes, Fred F. Pollitz, Timothy H. Dixon Jun 1998

Gps Measurements Across The Northern Caribbean Plate Boundary Zone: Impact Of Postseismic Relaxation Following Historic Earthquakes, Fred F. Pollitz, Timothy H. Dixon

School of Geosciences Faculty and Staff Publications

GPS measurements in the northern Caribbean suggest that the rate of Caribbean plate motion relative to North America is about 10 mm/yr faster than predicted by global plate motion model NUVEL-1A. Several of the key sites used in the GPS study are located in the Dominican Republic, near the rupture zones of large earthquakes in 1946 and in the previous two centuries. Postseismic relaxation of the crust and upper mantle is a possible explanation for the plate velocity discrepancy. We explore a range of fault mechanisms and crustal and mantle rheology to place an upper bound on postseismic relaxation effects. …

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A Preliminary Assessment Of Wave, Current, And Sediment Interactions On The Louisiana Shoreface Adjacent To The Isles Dernieres, David A. Pepper, Gregory W. Stone, Ping Wang Jan 1998

A Preliminary Assessment Of Wave, Current, And Sediment Interactions On The Louisiana Shoreface Adjacent To The Isles Dernieres, David A. Pepper, Gregory W. Stone, Ping Wang

Geology Faculty Publications

The Louisiana coast is generally characterized as a low wave-energy environment where sediment transport is dominated by the influence of the Mississippi and the Atchafalaya Rivers. Winter cold fronts, however, generate waves and currents that have a significant impact on a variety of Louisiana’s coastal environments, although field data regarding their influence on the inner shelf are extremely sparse. During a 12-d period that included the passage of two cold fronts, waves and near-bed currents were measured on the Louisiana inner-shelf (depth-8 m) using a sophisticated bottom-mounted instrumentation system. Bottom boundary layer parameters were then calculated using wave-current interaction models, …

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Lave Caves Of Kilimanjaro. Mawenzi Lava Tubes, Clive Ward Jan 1998

Lave Caves Of Kilimanjaro. Mawenzi Lava Tubes, Clive Ward

International Journal of Speleology

This is the first short report on the exploration of lava tubes in the upper part of Kilimanjaro. The area seems to be extremely interesting from vulcanospeleological point of view.

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Lava Caves Of Grande Comore, Indian Ocean: An Initial Reconnaissance, September 1997, Gregory J. Middleton Jan 1998

Lava Caves Of Grande Comore, Indian Ocean: An Initial Reconnaissance, September 1997, Gregory J. Middleton

International Journal of Speleology

What are believed to have been the first speleological investigations in the Comoros Islands were carried out on Grande Comore island between 7 and 13 September 1997. A number of caves were located with the help of local informants and the more significant ones surveyed. Exploration of some caves was not able to be completed. The potential for further significant discoveries is believed to be high.

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Hollow Volcanic Tumulus Caves Of Kilauea Caldera, Hawaii County, Hawaii, William R. Halliday Jan 1998

Hollow Volcanic Tumulus Caves Of Kilauea Caldera, Hawaii County, Hawaii, William R. Halliday

International Journal of Speleology

In addition to lava tube caves with commonly noted features, sizable subcrustal spaces of several types exist on the floor of Kilauea Caldera. Most of these are formed by drainage of partially stabilized volcanic structures enlarged or formed by injection of very fluid lava beneath a plastic crust. Most conspicuous are hollow tumuli, possibly first described by Walker in 1991. Walker mapped and described the outer chamber of Tumulus E-1 Cave. Further exploration has revealed that it has a hyperthermic inner room beneath an adjoining tumulus with no connection evident on the surface. Two lengthy, sinuous hollow tumuli also are …

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"Pit Craters", Lava Tubes, And Open Vertical Volcanic Conduits In Hawaii: A Problem In Terminology, William R. Halliday Jan 1998

"Pit Craters", Lava Tubes, And Open Vertical Volcanic Conduits In Hawaii: A Problem In Terminology, William R. Halliday

International Journal of Speleology

Almost from the 1849 publication of the term pit crater, volcanologists have disagreed about the parameters differentiating these features from other vertical volcanic structures. Kaluaiki is a jameo giving entry to Thurston Lava Tube in Hawaii Volcanoes National Park. Long-standing misidentification of it as a pit crater is an example of misunderstandings arising from the lack of a clear definition of pit crater. In general, pit craters are unrelated to lava tube caves genetically, but two special cases are discussed. One probably is genetically related to a rift tube deep below the surface; the other is a complex of a …

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Lava Tube Remelt By Radiant Heat And Burning Gasses, Kevin Allred Jan 1998

Lava Tube Remelt By Radiant Heat And Burning Gasses, Kevin Allred

International Journal of Speleology

Some volcanologists assume that interior surfaces of hot lava tubes can commonly be remelted by burning gases and radiant heat. Pending further data, this appears to be unlikely.

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The Origin Of Tubular Lava Stalactites And Other Related Forms, Kevin Allred, Carlene Allred Jan 1998

The Origin Of Tubular Lava Stalactites And Other Related Forms, Kevin Allred, Carlene Allred

International Journal of Speleology

Tubular lava stalactites are often found in lava tubes. Field observations, sample analysis, and comparative studies indicate that these are segregations extruded during cooling from partially crystallized lava al about 1,070 - 1,000 °C. Retrograde boiling (gas pressure) within the lava provides a mechanism to expel the interstitial liquid. In addition to tubular lava stalactites, a variety of other lava features can also result, such as lava helictites, lava coralloids, barnacle-like stretched lava, runners, runner channels, and some lava blisters and squeeze-ups.

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The 1981 Eruptive Fissure On Mt. Etna: Considerations On Its Exploration And Genesis, Angelo Leotta, Marco Liuzzo Jan 1998

The 1981 Eruptive Fissure On Mt. Etna: Considerations On Its Exploration And Genesis, Angelo Leotta, Marco Liuzzo

International Journal of Speleology

This paper is targeted to an analysis of features common to various fissure caves on Mt. Etna, Sicily. The Authors report the preliminary results of the exploration carried out in the 1981 eruptive fissure, the technical problems met during the exploration, the flow trends and the different courses of the molten material inside the fissure, the particular morphologies. A genetic model is proposed, different from those characterising the lava tube cave genesis, and links are suggested between the various fissures and the main tectonic stress systems operating on Mt. Etna, as well as the morpho-structural conditions of the volcanic edifice …

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Guano Mining In Kenyan Lava Tunnel Caves, Jim W. Simons Jan 1998

Guano Mining In Kenyan Lava Tunnel Caves, Jim W. Simons

International Journal of Speleology

Commercial mining of bat guano for agricultural fertilizer only became possible in Kenya through discovery of major deposits in the lava tunnel caves of Mt. Suswa and the North Chyulu Hills in the early 1960’s. This paper provides historical information leading up to the guano mining, describes the cave deposits, outlines the mining under-takings, and provides information on the guano producing bats and insect faunas. The results of guano analyses, details of the tonnages extracted and sold to recipients between 1966 to 1984, and some benefits which resulted from its use on crops are given. A brief outline of attempts …

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Chemical Deposits In Volcanic Caves Of Argentina, Carlos Benedetto, Paolo Forti, Ermanno Galli, Antonio Rossi Jan 1998

Chemical Deposits In Volcanic Caves Of Argentina, Carlos Benedetto, Paolo Forti, Ermanno Galli, Antonio Rossi

International Journal of Speleology

During the last Conference of the FEALC (Speleological Federation of Latin America and Caribbean Islands) which was held in the town of Malargue, Mendoza, in February 1997, two volcanic caves not far from that town were visited and sampled for cave mineral studies. The first cave (Cueva del Tigre) opens close to the Llancanelo lake, some 40 kms far from Malargue and it is a classical lava tube. Part of the walls and of the fallen lava blocks are covered by white translucent fibres and grains. The second visited cave is a small tectonic cavity opened on a lava bed …

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Lava Caves Of The Republic Of Mauritius, Indian Ocean, Gregory J. Middleton Jan 1998

Lava Caves Of The Republic Of Mauritius, Indian Ocean, Gregory J. Middleton

International Journal of Speleology

In their Underground Atlas, MIDDLETON & WALTHAM (1986) dismissed Mauritius as: “very old volcanic islands with no speleological interest”. Recent investigations indicate this judgement is inaccurate; there are over 50 significant caves, including lava tube caves up to 687 m long (one 665 m long was surveyed as early as 1769) and 35 m wide. Plaine des Roches contains the most extensive system of lava tube caves with underground drainage rising at the seashore. Notable fauna includes an insectivorous bat and a cave swiftlet (Collocalia francica), the nests of which are unfortunately prized for ‘soup”. The caves …

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Sheet Flow Caves Of Kilauea Caldera, Hawaii County, Hawaii, William R. Halliday Jan 1998

Sheet Flow Caves Of Kilauea Caldera, Hawaii County, Hawaii, William R. Halliday

International Journal of Speleology

Terminal lobes of sheet flows of pahoehoe lava sometimes form three-dimensional nests, initially separated by partitions consisting of accreted "skins” of each lobe. Melting breaks down these partitions, forming a uniform flow unit. In Kilauea Caldera we have found and mapped sizable drained cavities in low-slope sheet flows. Their general pattern includes three-dimensional nests, with partially melted septa evident in some examples. Christmas Cave is the most extensive found to date, with 632 meters surveyed on two levels. It is located at the lower end of an inflated sheet flow tongue which underwent local deflation as a result of drainage …

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Tectonic Caves Of Solai In The Kenyan Rift Valley, Robert A. Davis Jan 1998

Tectonic Caves Of Solai In The Kenyan Rift Valley, Robert A. Davis

International Journal of Speleology

Tectonic caves at Solai, Kenya, were explored in 1970. These lie in a complex geological area of the Great Rift Valley in columnar-faulted ignimbrite. Fissures are presumed to have been widened by later tectonic activity -e.g. the major earthquake of January, 1928. The caves and exploration are briefly described. Questions of formation, drainage and possibilities of steam reservoirs are discussed.

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