PDF: /pdf/seka_pdf9592.pdf

Abstract:

Bell holes are vertical, cylindrical voids, higher than they are wide, with circular cross sections and smooth walls found in the ceilings of dissolutional caves primarily from tropical and subtropical settings. They range in size from centimeter to meters in height and width. The origin of bell holes has been controversial, with two proposed categories: vadose mechanisms including bat activity, condensation corrosion, and vadose percolation; and phreatic mechanisms including degassing and density convection.
Crooked Island, Bahamas has a number of caves with bell holes of unusual morphology (up to 7 m high and 1.5 m in diameter), commonly in tight clusters, requiring significant bedrock removal in a small area. In many cases, numerous bell holes are open to the surface, which requires that up to a meter or more of surface denudation has occurred since the bell hole first formed.
Surface intersection has little impact on the phreatic mechanisms, which were time limited to cave genesis from 119 to 131 ka ago, but greatly reduces the time window for later vadose mechanisms, which need to have been completed before bell hole intersection by surface denudation.
The Crooked Island observations suggest that bell hole development occurred syngenetically with flank margin cave development under phreatic conditions. Because flank margin caves develop under slow flow conditions, vertical convection cell processes are not disrupted by turbulent lateral flow and bell holes formed as a vertical phreatic dissolution signature.

  PDF: /pdf/seka_pdf9591.pdf

Abstract:

The Edwards Aquifer is a large karst aquifer located in south-central Texas USA. The Index Well J-17, in which water levels in the aquifer are continuously monitored since 1934, detected distinctly the March 11, 2011 Honshu, Japan earthquake (9.0 magnitude). The Edwards Aquifer fluctuated approximately 0.3 meters (1 foot) during the initial response and continued to oscillate for approximately two hours after the event.

  PDF: /pdf/seka_pdf9533.pdf

Abstract:

The tracing technique has been recently used in karstified Zagros structural belt in northern Iran. A tracer study (uranine injection) was conducted in Jurassic limestone of the Poshte-Naz area in the Alborz belt to evaluate aquifer parameters and hydraulic relations between a large (about 100 m in diameter) sinkhole and springs. A main goal of the project was to find out the source of turbidity of the Emarate drinking water supply spring (SP4) in rainy seasons. Eight springs, three wells and the Neka River were selected for monitoring and totally 989 samples in 107 days were collected. In order to select reliable sampling stations, hydrochemical analysis of major ions was carried out and for better interpretation of concentration-time curve, spring discharge was also measured. The results of the tracing by sampling water indicated only a hydraulic connection between the injection point and the Sange-Nou spring (SP8) and, whereas the charcoal bags analysis revealed tracer exits also from spring SP1, SP3, SP4, SP5, SP8, in wells W1 and W2, and in the Neka River. This paper discuses concentration/time curves from charcoal bags for qualitative analysis and tracer exit curves for quantitative analysis.

  PDF: /pdf/seka_pdf9576.pdf

Abstract:

Comparative tracer testing may be used to evaluate the vulnerability of groundwater to specific contaminants by comparing reactive tracer response to that of a simultaneously injected non-reactive “conservative” substance. Conversely, knowledge of tracer reaction with specific materials permits information about subsurface heterogeneity to be inferred. A series of tests completed in the vadose zone overlying a limestone aquifer employed a cocktail of particles along with reactive and
non-reactive solute tracers to investigate transport rates between the ground surface and monitoring points approximately 10 m below ground. Short pulse tests revealed both solutes and particulate contaminants could travel at rates of over 10 m/h. Comparison of particle (microorganisms) and non-reactive solute tracer breakthrough revealed that particle tracers experience pore exclusion resulting in higher peak relative concentrations which arrive earlier than those of the solute. Prolonged tracer injection during subsequent experiments confirmed the response observed and illustrated that over 40 % of flow paths between
injection and monitoring points were inaccessible to particles, but could allow solutes to pass through them. Similarly, the difference in response between various reactive tracers demonstrated tracers reached monitoring points via multiple flow paths and suggests geochemical heterogeneity plays an important role in influencing tracer behaviour. The results of this investigation highlight the complexity of water flow through the epikarst and the vulnerability of groundwater in karst aquifers to contamination when soil cover is thin to absent.

  PDF: /pdf/seka_pdf9532.pdf

Abstract:

Papua New Guinea is one of the world’s most active seismic areas. On the surface, huge landslides are found on mountainsides and steep canyons slopes. Underground large passages and megadolines result mainly from the erosion of soft limestones by underground streams, but seismic movements may accelerate their evolution. Morphological characteristics were derived from statistical data and field observations.

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The 16th Sinkhole Conference: Register and Help the People of Puerto Rico!

in Miscellaneous by Super User
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Call for the 2020 EuroSpeleo Protection Label

in Miscellaneous by News Manager
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