Jame, vrtače in razpoke na eogenem krasu na Floridi, prostorska analiza z orodji GIS

The correlation between surface and subsurface karst development was explored by comparing the directionality and spatial distribution of karstic depressions around twenty-two select caves in the eogenetic karst of Florida. Orientations of cave passages and major axes of depressions around cave centrelines imply varying degrees of correlation between them. Spatial distribution of karstic depressions was studied by standard deviational ellipses of sinkhole centroids and nearest neighbour orientations around caves using spatial statistics tools of ArcGIS. An overall analysis of the data shows close connections between some caves and the surrounding sinkholes in terms of their orientation and spatial distribution, suggesting the importance of fracture systems in the development of karst.Z analizo smeri in prostorske porazdelitve vrtač v okolici 22 izbranih jam na eogenem krasu na Floridi smo raziskovali povezavo med površinskim in podzemnim razvojem krasa. Primerjava smeri jamskih rovov in glavnih osi vrtač v okolici jam kaže na različno stopnjo povezave med njimi. Prostorsko porazdelitev vrtač smo raziskovali z orodji prostorske statistike v okolju ArcGIS, pri tem smo uporabili elipse standardnih odklonov centroidov vrtač in smeri osi vrtač, najbližjih sosedov izbranih jamskih rovov. Celotna analiza podatkov je pokazala tesno povezanost med nekaterimi jamami in okoliškimi vrtačami z vidika njihove orientacije in lege, kar kaže na pomen razpoklinskih sistemov za razvoj krasa

Large-scale wind structures in OB supergiants: a search for rotationally modulated H\alpha variability

We present the results of a long-term monitoring campaign of the H\alpha line in a sample of bright OB-supergiants (O7.5-B9) that aims at detecting rotationally modulated changes potentially related to the existence of large-scale wind structures. A total of 22 objects were monitor ed during 36 nights spread over 6 months in 2001-2002. Coordinated broad-band photometric observations were also obtained for some targets. Conspicuous evidence for variability in H\alpha is found for the stars displaying a feature contaminated by wind emission. Most changes take place on a daily time-scale, although hourly variations are also occasionally detected. Convincing evidence for a cyclical pattern of variability in H\alpha has been found in 2 stars: HD 14134 and HD 42087 (periodic signals are also detected in other stars, but independent confirmation is required). Rotational modulation is suggested from the similarity between the observed recurrence time-scales (in the range 13-25 days) and estimated periods of stellar rotation. We call attention to the atypical case of HD 14134 which exhibits a clear 12.8-d periodicity both in the photometric and in the spectroscopic data sets. This places this object among a handful of early-type stars where one may observe a clear link between extended wind structures and photospheric disturbances. Further modelling may test the hypothesis that azimuthally-extended wind streams are responsible for the patterns of spectral variability in our target stars.Comment: 18 pages, accepted for publication in MNRA

Bright OB stars in the Galaxy IV. Stellar and wind parameters of early to late B supergiants

We apply the NLTE atmosphere code FASTWIND to perform a spectroscopic study of a small sample of Galactic B-supergiants from B0 to B9. By means of the resulting data and incorporating additional datasets from alternative studies, we investigate the properties of OB-supergiants and compare our findings with theoretical predictions. As a result we find that due to the combined effects of line- and wind-blanketing, the temperature scale of Galactic B-supergiants needs to be revised downwards, by 10 to 20 percent, the latter value being appropriate for stronger winds. In fair accordance with recent results, our sample furthermore indicates a gradual decrease in wind terminal velocities over the bi-stability region, where the limits of this region are located at lower temperatures than the predicted ones. Introducing a distance-independent quantity Q' related to wind-strength, we also show that this quantity is a well defined, monotonically increasing function of Teff outside this region. Inside and from hot to cool, the mass loss rate changes by a factor (in between 0.4 and 2.5) which is (much) smaller than the predicted factor of 5. All this indicates that the decrease in wind terminal velocity over the bi-stability region is not over-compensated by an increase of mass loss rate, as frequently argued (provided the wind-clumping properties on both sides of this region do not differ substantially).Comment: 23 pages and 14 figures accepted for publication in A & A; the Fig. 1 title and the last para of Sec. 4.1 modified; a new reference adde

Evaluating susceptibility of karst dolines (sinkholes) for collapse in Sango, Tennessee, USA

Dolines or sinkholes are earth depressions that develop in soluble rocks complexes such as limestone, dolomite, gypsum, anhydrite, and halite; dolines appear in a variety of shapes from nearly circular to complex structures with highly curved perimeters. The occurrence of dolines in the studied karst area is not random; they are the results of geomorphic, hydrologic and chemical processes that have caused partial subsidence, even total collapse of the land surface, when voids and caves are present in the bedrock and the regolith arch overbridging these voids is unstable. In the study area, the majority of collapses occur in the regolith (bedrock cover) that bridges voids in the bedrock. Because these collapsing dolines can damage property and cause even the loss of lives, there is a need to develop methods for evaluating karst hazards; such methods can be used by planners and practitioners for urban and economic development, especially in regions with a growing population. The purpose of this project is threefold: 1) to develop a karst feature database, 2) to investigate critical indicators associated with doline collapse, and 3) to design a doline susceptibility model for potential doline collapse based on external morphometric data. The study revealed the presence of short range spatial dependence in the distribution of the dolines’ morphometric parameters such as circularity, geographic orientation of the main doline axes and the length-to-width doline ratios; therefore, geostatistics can be used to spatially evaluate the susceptibility of the karst area for doline collapse using the probability of occurrence of these critical parameters. The partial susceptibility estimates were combined into final spatial probabilities enabling the identification of areas where undetected dolines may cause significant hazards

Land use changes and groundwater quality in Florida

Abstract Land use changes around 26 karstic cave–spring systems in Florida were evaluated using geographic information system. Located in the unconfined or semiconfined zones of the Floridan aquifer, some of the cave–spring systems are directly connected to the surficial land use processes by sinking streams, whereas others receiving diffuse recharge are still vulnerable to contamination due to a thin sandy cover overlying the aquifer. Comparison of nitrate-producing land use practices between 2004 and 2013–2014 shows increasing risks of groundwater contamination in the Floridan aquifer. Proliferation of septic systems and wastewater treatment sites due to growing residential areas, increased use of fertilizers for farming and landscaping stand out as major causes of nitrate overload in the both surface and groundwater

Karst features on the Withlacoochee River, near Valdosta, Georgia

The Withlacoochee River of South Georgia crosses an area of karst landscape before it flows south into the Suwannee River in Florida. This limestone karst is particularly well-developed ~5 km northwest of Valdosta Georgia. At this location the Withlacoochee River crosses an area of widespread sinkhole development. Some of these sinkholes occur directly in the riverbed. Field studies by both the USGS and by faculty at Valdosta State University have shown that during periods of intense drought the water in the Withlacoochee River is completely consumed as 100% of the water flows into the sinks. Additionally, a small segment of the downstream portion of the river reverses flow and flows north into the sink area. When the river is at drought conditions many karst features can be observed both in and near the dry Withlacoochee channel. These karst features include disappearing streams, solution cavities, whirlpools, sinkholes, and caves. This also provides an excellent opportunity to observe conventional stream landforms such as channel features, depositional features, and flow features. During periods of higher rainfall, the Withlacoochee will return to normal flow. The USGS has studied groundwater flow in this are and has found that significant and rapid communication exists between the river and the underlying aquifer systems, including the important Floridan Aquifer

MULTIWAVELENGTH SPECTROSCOPY OF THE STABLE SHELL STAR HD-193182

HD 193182 is one of the most interesting ''stable shell stars'' and presents stable shell features which seems to be constant over decades. In this research we analyzed optical, ultraviolet and near-infrared spectra of this little-studied shell star. In the meantime we applied model calculations to the measured spectral parameters of HD 193182 in order to present a more complete view of its stellar and envelope characteristics