Carrera de Ingeniería Geológica

The Alpine glaciers are sensitive to climate fluctuation, and glacier mass balance may be used as a proxy indicator of the regional climate change impacts. An indirect methodology is presented for determining the distribution of mass balance at high spatial resolution using remote sensing and ground stakes measurements. The method is based on the snowline determination as a proxy of the equilibrium line altitude (ELA) and the key of the transfer is the activity coefficient (db/dz) for the annual mass balance calculation. Three outlet glaciers well suited in the French Alps (ground stakes) were selected to evaluate the accuracy of the method for a short period (7 cycles) and extended for a longest period (15 cycles) for a glacier with limited ground measurements. The computed distribution of mass-balance compares well (R 2 =0.90) with mass-balance measurements made at stakes installed along the glacier centre line for the short period.

Numerous glaciological data have been obtained from measurements carried out on Glacier d'Argentière, Mont Blanc area, France, since the beginning of the 20th century. Moreover, data on annual mass balance, ice-flow velocity, thickness variation and length fluctuation have been obtained from yearly measurements performed since 1975. This dataset provides an excellent opportunity to analyze the relationships between surface mass balance and dynamic response over time periods during which net mass balance changed from positive to negative. Following a positive specific-net-balance period between 1960 and 1981, the ablation zone experienced a large increase in thickness and ice-flow velocities. Conversely, the highly negative specific-net-balance period since 1982 has led to strong thinning, deceleration and retreat of the tongue. The response of these observed dynamics to surface mass balance is analyzed from ice-flux calculations performed on three transverse cross-sections. Our results reveal that the ice fluxes are largely accommodated by ice-flow velocities. Velocity fluctuations are synchronous over the entire area studied. In the largest part of the glacier, no compressing/ extending flow change has been observed over the last 30 years and thickness changes are solely driven by surface mass-balance changes. However, on the tongue of the glacier, thickness changes do not depend on surface mass balance but are mainly driven by changes in the longitudinal strain rate.

The longest continuous glaciological mass-balance time-series in the intertropical zone of South America goes back to 1991 on Glaciar Zongo, Bolivia. Photogrammetric and hydrological data have been used to (i) check the specific net balance over long periods and (ii) extend the mass-balance time series over the last 50 years. These data reveal a bias in the glaciological mass balance which can be explained by the field-measurement sampling network. Our study shows a large temporal variability of the surface mass balances in the ablation area and reveals strong relationships between independent surface mass-balance data coming from selected ablation areas with numerous data. It demonstrates the very large contribution (80%) of low-elevation ranges (one-third of the surface) to the specific mass balance and, consequently, the importance of the reduction of the area of the tongue. With these new results, Glaciar Zongo offers the longest and most accurate mass-balance series in any Andean country. The dataset shows that Glaciar Zongo experienced a relatively steady state over the period 1956-75, with even a slight mass gain over 1963-75, and a rapid and continuous decrease since then.

Under tropical conditions, water discharge from glaciers is crucial for water resources in the dry season, as it is the case for La Paz, Bolivia (16 • S). In the current study, the glacier water supply of La Paz city has been assessed at annual and seasonal time-scale for the first time thanks to the mass balance analysis of 70 glaciers located within the drainage basins of La Paz between 1963 and 2006. The ice melting has contributed to about 15% of the water resources of the city at an annual scale, 14% in the humid season and 27% in the dry season. Despite the loss of about the half of the glaciers areas during this period, the runoff at La Paz did not change significantly. It reveals that ice melting rise compensated the surface areas decrease. Contrary, assuming that glaciers disappear in the future and precipitation does not change in the catchment areas, the runoff should diminish by about 12% at annual scale, 9% during the humid season and 24% during the dry season.

The longest and most continuous series of measurements of mass balance in the Intertropical Zone correspond to Zongo glacier, Bolivia. Measurements, which were initiated in 1991, were taken using both the hydrological and glaciological methods. Comparison of these results show discrepancies in the mass balances obtained. In order to verify the mass balances derived from both methods, a new mass balance was performed using the photogrammetric method, results of which were compared with the existing glaciological and hydrological methods. This comparison showed that the hydrological and photogrammetric methods are equivalent. However, these results disagree with the glaciological method. This difference is attributed to a lack of measurements using the glaciological method in areas of difficult access on Zongo glacier. In these areas, the glaciological method simply used interpolation to estimate the specific net mass balance. The final results of this three-method comparison show tha...

ABTRACT : The Voellmy avalanche basal friction parameters are retrieved from high rate positioning of artificially released avalanches. Two dense snow avalanches were triggered at the Lautaret full-scale test site on December 19th 2012 and February 13th 2013. Their fronts were tracked thanks to an accurate photogrammetric system. Couples of images were acquired at 1 frame per second with 2 APS-C DSLR synchronized cameras set at 800 meters from the avalanche track. 9 control points are used for image orientation and the typical precision for this measurement is around 0.2m for any point of the avalanche front. For the two avalanches, velocities are determined on several points of the front along different directions orthogonal to the flow. In order to retrieve rheological parameters of the avalanche, the front is considered as a hydraulic intumescence and the relation between its velocity and the avalanches properties is developed in the sliding block model framework. The Voellmy fri...

In-situ measurements of glacial mass balance are scarce at the global scale. The World Glacier Monitoring Service compiles data from 110 of the 100,000 existing glaciers contained in the World Glacier Inventory. To better understand the climate-glacier relationship at a regional scale, and to study the influences of both morphological (exposure, slope, elevation) and meteorological parameters on glacial changes, a spatialization of measurements of glaciological parameters (mass balance, equilibrium line altitude) is necessary. For such an aim, remote-sensing techniques appear to be well adapted. This study presents a method to reconstruct annual glacier mass balance using optical remote-sensing images. This method, based on the indentification of the snow line on satellite images recorded at the end of the hydrological year, has been first developped and validated on French Alpine glaciers. On these glaciers, the snow line can be condisered as a good indicator of the equilibrium lin...

ABTRACT : The Voellmy avalanche basal friction parameters are retrieved from high rate positioning of artificially released avalanches. Two dense snow avalanches were triggered at the Lautaret full-scale test site on December 19th 2012 and February 13th 2013. Their fronts were tracked thanks to an accurate photogrammetric system. Couples of images were acquired at 1 frame per second with 2 APS-C DSLR synchronized cameras set at 800 meters from the avalanche track. 9 control points are used for image orientation and the typical precision for this measurement is around 0.2m for any point of the avalanche front. For the two avalanches, velocities are determined on several points of the front along different directions orthogonal to the flow. In order to retrieve rheological parameters of the avalanche, the front is considered as a hydraulic intumescence and the relation between its velocity and the avalanches properties is developed in the sliding block model framework. The Voellmy friction parameters in the accelerating, steady and decelerating phases are quantified and discussed.

Poststreptococcal sequelae, especially acute rheumatic fever/rheumatic heart disease continues to occur in significant proportions in many parts of the world, especially in less developed countries. An important factor in the study of rheumatic heart disease is the human genetic susceptibility to the disease. The aim of the present study was to detect the most prevalent HLA class I and class II types associated with risk of rheumatic heart disease in Egyptian children. Our study was performed on 100 patients with rheumatic valvular heart diseases and 71 control subjects. Patients were recruited from the Heart Institute, Embaba, Egypt. HLA typing for HLA class I was performed by serotyping and HLDR allele genotyping was performed using INNO-LiPA kits. In the study of HLA class I, there was a statistically significant increase in the B5 allele (P = 0.03; odds ratio, 3.46 [1.12–10.72]) in patients compared to controls, while B49 and B52 alleles (P = 0.004 and P = 0.02) were found in controls only. There was a statistically significant increase in HLA DR* 04-02, 3.46 (1.12–10.72) and HLA DR *10-0101 5.75 (1.27–25.98) in patients. Meanwhile HLA DR*1309120 was found only in controls (P = 0.02). Our study provides further information on the genetic predisposition for rheumatic valvular disease and the protective genotypes in rheumatic heart disease. Further insight into the molecular mechanisms of the disease will be a useful tool for predicting clinical outcome in those patients and, thus, potentially offer new means and approaches to treatment and prophylaxis, including a potential vaccine.

The histological parameters of Helicobacter pylori (H. pylori) gastritis are dependent on the virulence factor profile of the microbe, which includes the cytotoxins vacA (vacuolating cytotoxin A) and cagA (cytotoxinassociated gene A) as well as the duration of infection. The virulence factor genotypes vacA and cagA were assessed by the line probe reverse hybridization assay INNO-LiPA and correlated with the histological parameters of H. pylori infection, in particular intestinal metaplasia (IM) as well as with the patient's age. A total of 120 patients were analyzed; 47 patients with IM in the antrum and 73 control patients without this alteration. The vacA s1 cagA þ genotype (high virulence) correlated with the presence of antral IM, a more intense acute inflammation in both antrum and corpus and the formation of ulcer. The vacA m1 genotype (high virulence) correlated with a more intense acute inflammation in only the corpus as well as more prominent Russell bodies in the antrum. H. pylori strains with the vacA s2 m2 cagAÀ genotype (low virulence) were rarely found in these conditions (all P o0.05). No correlation with the virulence status was found for the type and extent of IM, the intensity of chronic inflammation, the formation of lymphoid follicles and the microbial density. Furthermore, patients with IM were 7 years older than their counterparts without (Po0.05). Finally, there was a trend for more virulent vacA s1 m1 cagA þ strains to be found in younger individuals (P40.05). The virulence genotype of the microbe is an important determinant for the severity of the gastritis and the formation of antral IM. Age is an additional factor for the development of IM.