New Horizons | EPFL Graph Search

New Horizons (« Nouveaux Horizons » en français) est une sonde de l'agence spatiale américaine (NASA) dont l'objectif principal est l'étude de la planète naine Pluton et ses satellites, ce qui a été réalisé à la mi-juillet 2015. Après de légères modifications de trajectoire, elle a pu explorer , un autre corps de la ceinture de Kuiper, et pourrait éventuellement en étudier un autre (restant à découvrir). New Horizons est la première mission spatiale qui explore cette région du Système solaire. Du fait de leur éloignement, on dispose de très peu d'informations sur les corps célestes qui s'y trouvent, car ceux-ci sont à peine visibles avec les meilleurs télescopes. Or leurs caractéristiques sont susceptibles de fournir des informations importantes sur le processus de formation du Système solaire. La sonde spatiale New Horizons a été conçue pour fonctionner dans les conditions hostiles de cette région, très éloignée de la Terre et du Soleil. L'architecture de l'engin spatial et le déroul

Spatial analysis of karst conduit networks and determination of parameters controlling the speleogenesis along preferential lithostratigraphic horizons

Marco Filipponi

The main objective of this thesis is to improve the understanding of the position and characteristics of karst conduits within a rock massif. Such a characterisation is an important issue in civil engineering and in hydrogeology. Today in practice dissolution voids are considered as random in most cases. However, it is obvious for karst researchers that dissolution void distribution is not random, but defined by parameters controlling the speleogenesis. We developed a method to analyse the 3D geometry of cave systems in order to demonstrate from a statistical point of view that karst conduits position is not random. The analysis of several among the largest cave systems in the World (more than 1500 km of analysed cave conduits) confirmed for the first time quantitatively that the development and position of karst conduits under phreatic conditions is strongly related to a restricted number of so called inception horizons. An inception horizon – a concept introduced by Lowe (1992) – is a part of a lithostratigraphic succession that is particularly susceptible to the effects of the earliest cave forming processes by virtue of physical, lithological or chemical deviation from the predominant carbonate facies within the formation. We demonstrate that probably less than 10 % of the existing bedding partings of a limestone sequence are inception horizons and guide more than 70 % of the phreatic conduits. Our analysis clearly confirms that the influence of these horizons onto the 3D geometry of cave systems is high. Based on the 3D analysis of cave systems as well as on field verifications, 18 inception horizons in six cave systems have been selected for field characterisation and sampling in order to identify the properties and processes that makes these particular lithostratigraphic horizons favourable to karstification. Around 200 rock samples from the horizons and the surrounding rock mass have been analysed. The results evidence that inception horizons have a thickness of some centimetres to decimetres and that it is possible to distinguish between 3 types of inception horizons: Inception horizons where the cave inception took place within the inception horizon (type 1); characterized by a slightly higher primary permeability, pyrite and quartz contents and lower matrix contents than the surrounding rock mass. Usually, fractures propagate through or occur within these horizons. Inception horizons where the cave inception took place at the contact with the inception horizon (type 2); characterized by a lower primary permeability and carbonate contents, but higher pyrite contents than the surrounding rock mass. Fractures usually are ending at these horizons. Inception horizons where the cave inception took place along bedding plane fractures (type 3); already a slippage of just a few millimetres, striation, brecciation and surface irregularities enhance openings along the sliding plane and cause a significant increase in permeability. Furthermore it can be assumed that for the inception of horizons of type 1 the primary permeability will be the relevant factor at beginning of karstification, whereas both the matrix and the pyrite contents are the key factors during the later phases of cave inception and gestation. Whereas for further cave development the total carbonate content will be crucial. For inception horizons of type 2, we can assume that the low primary permeability, the clogging of the pores by the clay minerals, the high content of pyrite (production of aggressive solutions within the horizon that concentrates the dissolution along the contact to the surrounding rock) and the ending of the fractures at the horizon are responsible for the enhanced karstification at the contact during cave inception and gestation phases. Using simple hydrogeological numerical modelling we show that an epigenic karstic rock massif can be subdivided into four speleogenetic zones: 1) vadose cave development zone above the water table, 2) the phreatic cave development and 3) gestation zone within the first tens of metres of the phreatic zone and 4) below them the inception zone. Each of these zones is characterized by typical speleogenetic processes as well as dissolution void distribution. Further, it was possible to explain and reproduce schematically the 3D pattern of different cave systems by using the position and orientation of the inception horizons and the history of the landscape evolution (i.e. the re- and discharge area). This forward analysis provides a first idea of the geometry of the conduits as well as a better understanding of the development of a karst system in time and space (vertical section). Finally, we evaluated the feasibility to combine the improved inception horizon hypothesis, to predict inception horizons, with other current applied methods to improve the prediction of dissolution voids. Furthermore, we proposed a scientific based risk assessment for underground engineering proposes. Essentially, it is now evidenced that it is possible to quantify the probability of karst occurrences inside a karst massif by reconstructing the hydrogeolgical history and identifying the few inception horizons that guide the karstification at a regional scale.

EPFL2009

The diffuse infiltration of road runoff: an environmental improvement

Michaël Bensimon, Aurèle Parriaux, Pascal Piguet

The Laboratory of Engineering and Environmental Geology (GEOLEP) has been mandated by Swiss authorities (Swiss Federal Road Office FedRO) to test a new road runoff management concept. This concept promotes the diffuse infiltration of road runoff into infiltration slopes designed for this purpose. Soils retain particles and contaminants; this lowers the road impact on the environment and simultaneously improves aquifer recharge. This concept has to be adapted to aquifer vulnerability and traffic conditions. Thus, a real-scale experimental station was designed and built in Switzerland to assess the feasibility of this new concept. This station allowed the testing of two lysimeters composed of 80cm of A and B- horizons. Water and chemical fluxes were measured at the lysimeter bases. Road runoff was sampled in a distinct collector. Infiltration of road runoff into the local aquifer was monitored thanks to six piezometers. Water quality and quantity were therefore measured at each step of the infiltration process. Results provided by 112 natural events showed that soil horizons accommodated road runoff flows. The least favourable conditions for contaminant retention are encountered during thunderstorms, when high concentrations of substances deposited on the road are remobilised within a short time and rapidly percolates through soil horizons. Thus, three artificial events were designed to mimic heavy thunderstorms. Concentrations measured in road runoff notably decreased after soil filtration. Substances with high distribution coefficients Kd (low mobility) had concentrations reduced to lower values (1/1000 to 1/10,000), while those with high mobility retained similar concentrations even after soil filtration. However, these mobile substances exhibited low concentrations in the underlying aquifer due to dilution. This innovative road runoff management concept can thus be readily implemented outside groundwater protection zones where aquifers are slightly vulnerable; it undoubtedly lowers the environmental impact of roads, does not endanger road integrity, and locally increases aquifer recharge.

2008

Real-time projections of cholera outbreaks through data assimilation and rainfall forecasting

Enrico Bertuzzo, Flavio Finger, Damiano Pasetto, Andrea Rinaldo

Although treatment for cholera is well-known and cheap, outbreaks in epidemic regions still exact high death tolls mostly due to the unpreparedness of health care infrastructures to face unforeseen emergencies. In this context, mathematical models for the prediction of the evolution of an ongoing outbreak are of paramount importance. Here, we test a real-time forecasting framework that readily integrates new information as soon as available and periodically issues an updated forecast. The spread of cholera is modeled by a spatially-explicit scheme that accounts for the dynamics of susceptible, infected and recovered individuals hosted in different local communities connected through hydrologic and human mobility networks. The framework presents two major innovations for cholera modeling: the use of a data assimilation technique, specifically an ensemble Kalman filter, to update both state variables and parameters based on the observations, and the use of rainfall forecasts to force the model. The exercise of simulating the state of the system and the predictive capabilities of the novel tools, set at the initial phase of the 2010 Haitian cholera outbreak using only information that was available at that time, serves as a benchmark. Our results suggest that the assimilation procedure with the sequential update of the parameters outperforms calibration schemes based on Markov chain Monte Carlo. Moreover, in a forecasting mode the model usefully predicts the spatial incidence of cholera at least for one month ahead. The performance decreases for longer time horizons yet allowing sufficient time to plan for deployment of medical supplies and staff, and to evaluate alternative strategies of emergency management.