1,716 research outputs found
Ground penetrating radar surveys in a karst area for identification of geomorphological hazards.
Many coastal areas along the apulian coastlines (SE Italy) are intensely affected by sinkhole problems, which
periodically cause damage to the main infrastructures, including the coastal roads and sparse settlements. Torre
Castiglione is a locality situated at the boundary between the provinces of Lecce and Taranto, on the Jonian sea.
Several sinkholes have in time affected the province road 340, which is a very important communication route
during the summer, due to the tourist vocation of the area. Proximity of the site to the sea results in the mixing
between sea water and fresh water, which determines a higher aggressivity toward the carbonate rock mass, and
development of karst features and landforms, including caves. Due to the above reasons, the whole coastal sector
is classified as with high geomorphological hazard.
Aimed at investigating such hazard, a variety of direct and indirect surveys have been performed in the last years.
Geological surveys, carried out through detailed field surveys, highlighted the presence of multi-storey cave
systems, which upward stoping might eventually produce the formation of sinkholes. As concerns geomorphology,
the population of identified sinkholes (more than 50) has been morphometrically characterized by measuring their
depth, length, and width.
The present contribution focuses on the geophysical surveys performed in the area. In detail, Ground Penetrating
Radar (GPR) surveys have been carried out, due to the good resolution and the high penetration of the electromagnetic
signal in geological settings characterized by presence of carbonate rocks. However, the presence of
a karst aquifer in the area causes problems in the absorbing capacity of the signal. The main goal of this study
is the analysis of the subsoil, aimed at testing the capability of GPR in a karst setting. A GSSI instrument was
used, with antennae of 400 MHz, 200MHz and 100 MHz. The surveys were addressed to evaluate the capability
of the method in such a setting, and to verify the velocity of propagation of the electromagnetic waves. Some
scanlines were addressed to investigate, in particular, a sinkhole crossing the province road 340, by carrying out
GPR profiles with a 200 MHz antenna at 90ns and 120 ns. The signal appeared to penetrate the subsoil at velocity
of about 8 cm/ns. Elaboration of the data pointed out a series of cavities along the rural road running parallel to
province road 340. In addition, the GPR survey highlighted the presence of complex karst systems at different
depths, with cave size on the order of some tens of meters. A likely alignment in the cave direction seems to be
shown, too
Natural and anthropogenic hazards in karst areas of Albania
International audienceIn Albania, about one quarter of the country is occupied by outcroppings of soluble rocks; thus, karst represents an important and typical natural environment. Today karst areas are seriously threatened by a number of hazards, of both natural and anthropogenic origin. Many problems are related to agricultural practices: the use of heavy machinery, ever-increasing in recent years, results at many sites in destruction of the original karst landscapes. Use of pesticides and herbicides, in addition, causes the loss of karst ecosystems of great biological relevance, as has been observed in the Dumre district, where about 80 lakes of karst origin are present in the evaporites of Permian-Triassic age. Agricultural practice performed on slopes with medium to high gradient is a further factor which greatly predispose the slopes to erosion. The cave heritage of Albania (estimated so far in about 1000 caves) is at risk because of the uncontrolled quarrying activities which determine the total or partial destruction of karst caves, including many of naturalistic, archaeological and speleological interest. Many caves have also become sites of illegal disposal of solid and liquid wastes, which causes pollution of the karst ecosystems and of the aquifer therein present, with heavy negative consequences on the quality of water. Even though most of the cases here mentioned are related to anthropogenic activities, the natural hazards, such as subsidence phenomena, floods, and the development of sinkholes, have not to be disregarded
Implementation of computation codes in geostructural surveys to evaluate rock mass stability aimed at the protection of cultural heritage
Instability of rock masses is a frequent problem in Italy, which territory is naturally predisposed to
a variety of geological hazards. Therefore, issues related to the study of rock masses have always
been of primary importance, since their consequences directly affect human lives and the
urbanized areas, causing severe losses to society. In order to identify the areas most susceptible to
gravity-related phenomena in such settings, the traditional approaches are often not sufficient,
and need to be integrated by new tools and techniques aimed at properly and quantitatively
describe the structural arrangement of rock masses. These include the use of close range remote
sensing techniques. It is now many years that various attempts have been made to standardize
processes to extract volumetric shapes from digital data, in order to individuate geometrical
features in point clouds and, eventually, to identify discontinuities on rock outcrops.
We present an attempt to develop and experimentally implement an application of computation
codes and software control via command line, to carry out geomechanical investigations on rock
masses, starting from 3D surveys. The final goal is to provide reliable results on the likely
instability processes in surface and underground settings, as a contribution to the mitigation of
the related risks. For this aim, a novel approach is proposed: in order to combine user observation
made in situ and on digital results of scanning, our attention was focused on developing nonautomatic
methods, which could allow, giving a tolerance angle for both dip and dip direction, the
extraction of discontinuities on well-structured datasets representing point clouds. This approach
could be considered a fully supervised type of classification, because the user can specify the
query by placing a numerical input representing an interval of tolerance in degrees; then, it has as
output a cluster of planar surfaces belonging to the given interval for each set. The code,
organized in a basic software called GEODS (alpha version), which runs on Windows operating
systems, also utilizes the results to represent the rocky surfaces on charts and stereographic
projections, and is able to calculate standard deviation and mean values of the classified clusters.
It is useful to identify the density of each identified discontinuity and to evaluate potential
kinematics as well, based on geometric relationships, through analyses carried by a skilled user.
This approach was tested at the Cocceio cave, in Campania, southern Italy: this site has historical
importance since the Roman age. Reused during World War II, it is now part of a redevelopment
project of the Phlegraean Fields, an area renowned for its natural beauty, which includes
numerous archaeological sites. At the cave, with this new method, we were able to recognize an
additional set, with minor frequency than the other sets, and which was not identified during
previous studies.
As a final result, it is thus expected to contribute in an innovative way to the implementation of
alternative and accurate methods in structural analysis and the geomechanical characterization of
rock masses
The evolutionary state of the southern dense core Cha-MMS1
Aims: Our goal is to set constraints on the evolutionary state of the dense
core Cha-MMS1 in the Chamaeleon I molecular cloud. Methods: We analyze
molecular line observations carried out with the new submillimeter telescope
APEX. We look for outflow signatures around the dense core and probe its
chemical structure, which we compare to predictions of models of gas-phase
chemistry. We also use the public database of the Spitzer Space Telescope (SST)
to compare Cha-MMS1 with the two Class 0 protostars IRAM 04191 and L1521F,
which are at the same distance. Results: We measure a large deuterium
fractionation for N2H+ (11 +/- 3 %), intermediate between the prestellar core
L1544 and the very young Class 0 protostar L1521F. It is larger than for HCO+
(2.5 +/- 0.9 %), which is probably the result of depletion removing HCO+ from
the high-density inner region. Our CO(3-2) map reveals the presence of a
bipolar outflow driven by the Class I protostar Ced 110 IRS 4 but we do not
find evidence for an outflow powered by Cha-MMS1. We also report the detection
of Cha-MMS1 at 24, 70 and 160 microns by the instrument MIPS of the SST, at a
level nearly an order of magnitude lower than IRAM 04191 and L1521F.
Conclusions: Cha-MMS1 appears to have already formed a compact object, either
the first hydrostatic core at the very end of the prestellar phase, or an
extremely young protostar that has not yet powered any outflow, at the very
beginning of the Class 0 accretion phase.Comment: Accepted by Astronomy & Astrophysics as a letter, to appear in the
special issue on the APEX first result
TIMASSS : The IRAS16293-2422 Millimeter And Submillimeter Spectral Survey: Tentative Detection of Deuterated Methyl Formate (DCOOCH3)
High deuterium fractionation is observed in various types of environment such
as prestellar cores, hot cores and hot corinos. It has proven to be an
efficient probe to study the physical and chemical conditions of these
environments. The study of the deuteration of different molecules helps us to
understand their formation. This is especially interesting for complex
molecules such as methanol and bigger molecules for which it may allow to
differentiate between gas-phase and solid-state formation pathways. Methanol
exhibits a high deuterium fractionation in hot corinos. Since CH3OH is thought
to be a precursor of methyl formate we expect that deuterated methyl formate is
produced in such environments. We have searched for the singly-deuterated
isotopologue of methyl formate, DCOOCH3, in IRAS 16293-2422, a hot corino
well-known for its high degree of methanol deuteration. We have used the
IRAM/JCMT unbiased spectral survey of IRAS 16293-2422 which allows us to search
for the DCOOCH3 rotational transitions within the survey spectral range (80-280
GHz, 328-366 GHz). The expected emission of deuterated methyl formate is
modelled at LTE and compared with the observations.} We have tentatively
detected DCOOCH3 in the protostar IRAS 16293-2422. We assign eight lines
detected in the IRAM survey to DCOOCH3. Three of these lines are affected by
blending problems and one line is affected by calibration uncertainties,
nevertheless the LTE emission model is compatible with the observations. A
simple LTE modelling of the two cores in IRAS 16293-2422, based on a previous
interferometric study of HCOOCH3, allows us to estimate the amount of DCOOCH3
in IRAS 16293-2422. Adopting an excitation temperature of 100 K and a source
size of 2\arcsec and 1\farcs5 for the A and B cores, respectively, we find that
N(A,DCOOCH3) = N(B,DCOOCH3) ~ 6.10^14 /cm2. The derived deuterium fractionation
is ~ 15%, consistent with values for other deuterated species in this source
and much greater than that expected from the deuterium cosmic abundance.
DCOOCH3, if its tentative detection is confirmed, should now be considered in
theoretical models that study complex molecule formation and their deuteration
mechanisms. Experimental work is also needed to investigate the different
chemical routes leading to the formation of deuterated methyl formate
A multi-disciplinary approach combining geological, geomorphological and geophysical data for mapping the susceptibility to sinkholes
The Salento region of southern Italy has a great number of active sinkholes, related to both natural and anthropogenic
cavities. The presence of sinkholes is at the origin of several problems to the built-up environment, due
to the increasing population growth and development pressures. In such a context, the detection of cavities, and
therefore the assessment of the sinkhole hazard presents numerous difficulties. Multidisciplinary – approach,
comprising geological, geomorphological and geophysical analyses, is therefore necessary to obtain comprehensive
knowledge of the complex phenomena in karstic areas. Geophysical methods can also be of great help to
identify and map the areas at higher risk of collapse. In this case it is important to identify the features related to
the underground voids, likely evolving to sinkholes, by contrasts in physical properties such as density, electrical
resistivity, and so on, with the surrounding sediments. At the same time, identification of the presence of sinkholes
by geophysical methods has to adapt to the different geological conditions, so that there is not the possibility to
use the same techniques everywhere.
At this aim, the present paper illustrates the advantages of integrating geological and geomorphological surveys
with surface geophysical techniques such as seismic, geoelectrical and ground penetrating radar methods for
the identification of sinkhole-prone areas. The present work illustrates the results concerning a sinkhole system
at Nociglia (inland Salento, southeastern Italy) where the shallow phreatic speleogenesis operates close to the
water table level with formation of karst conduits and proto-caves whose evolution occurs through successive
roof collapse, formation of wide caverns and sinkhole development at the surface. All of this creates serious
problems to the nearby infrastructures, including a province road that has often been threatened by the sinkhole
development.
Geological and geomorphological analyses provided the basic data necessary to constitute a framework to
understand the mechanism of sinkholes formation and at the same time to guide the choice of the most suitable
geophysical techniques, and the interpretation of the measurements as well. The different geophysical methods
are eventually discussed in order to point out their ability to locate the main karst conduits and caves
H2CO and CH3OH maps of the Orion Bar photodissociation region
A previous analysis of methanol and formaldehyde towards the Orion Bar
concluded that the two molecular species may trace different physical
components, methanol the clumpy material, and formaldehyde the interclump
medium. To verify this hypothesis, we performed multi-line mapping observations
of the two molecules to study their spatial distributions. The observations
were performed with the IRAM-30m telescope at 218 and 241 GHz, with an angular
resolution of ~11''. Additional data for H2CO from the Plateau de Bure array
are also discussed. The data were analysed using an LVG approach.
Both molecules are detected in our single-dish data. Our data show that CH3OH
peaks towards the clumps of the Bar, but its intensity decreases below the
detection threshold in the interclump material. When averaging over a large
region of the interclump medium, the strongest CH3OH line is detected with a
peak intensity of ~0.06K. Formaldehyde also peaks on the clumps, but it is also
detected in the interclump gas. We verified that the weak intensity of CH3OH in
the interclump medium is not caused by the different excitation conditions of
the interclump material, but reflects a decrease in the column density of
methanol. The abundance of CH3OH relative to H2CO decreases by at least one
order of magnitude from the dense clumps to the interclump medium.Comment: 11 pages, accepted for publication in A&
CO and CH3OH observations of the BHR71 outflows with APEX
Context : Highly-collimated outflows are believed to be the earliest stage in
outflow evolution, so their study is essential for understanding the processes
driving outflows. The BHR71 Bok globule is known to harbour such a
highly-collimated outflow, which is powered by a protostar belonging to a
protobinary system. Aims : We aimed at investigating the interaction of
collimated outflows with the ambient molecular cloud by using molecular
tracers. Methods : We mapped the BHR71 highly-collimated outflow in CO(3-2)
with the APEX telescope, and observed several bright points of the outflow in
the molecular transitions CO(4-3), 13CO(3-2), C18O(3-2), and CH3OH(7-6). We use
an LVG code to characterise the temperature enhancements in these regions.
Results : In our CO(3-2) map, the second outflow driven by IRS2, which is the
second source of the binary system, is completely revealed and shown to be
bipolar. We also measure temperature enhancements in the lobes. The CO and
methanol LVG modelling points to temperatures between 30 and 50K in the IRS1
outflow, while the IRS2 outflow seems to be warmer (up to 300K).Comment: 4 pages, 5 Figures, accepted by A&A Letters, to appear in the APEX
First results special issu
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