Abstract. This paper presents the results of lahar modelling in the town of Villa La Angostura (Neuquén-Argentina) based on the Two-Phase-Titan modelling computer code. The purpose of this exercise is to provide decision makers with a useful tool to assess lahar hazard during the 2011 PuyehueCordón Caulle Volcanic Complex eruption. The possible occurrence of lahars mobilized from recent ash falls that could reach the city was analysed. The performance of the TwoPhase-Titan model using 15 m resolution digital elevation models (DEMs) developed from optical satellite images and from radar satellite images was evaluated. The output of these modellings showed inconsistencies that, based on field observations, were attributed to bad adjustment of the DEMs to real topography. Further testing of results using more accurate radar-based 10 m DEM, provided more realistic predictions. This procedure allowed us to simulate the path of flows from Florencia, Las Piedritas and Colorado creeks, which are the most hazardous streams for debris flows in Villa La Angostura. The output of the modelling is a valuable tool for city planning and risk management especially considering the glacial geomorphic features of the region, the strong urban development growth and the land occupation that has occurred in the last decade in Villa La Angostura and its surroundings.

The seasonal dynamics of Acartia tonsa and the invader Eurytemora americana were analysed in relation to the environmental variability occurring from April to November in the Bahía Blanca Estuary. Twice a month, the abundance of eggs, nauplii, copepodites and adults was examined and some environmental variables were recorded. Multivariate statistics (CCA) was applied to analyse the data of variables. Acartia tonsa eggs and nauplii diminished from April–May and they were almost absent between June and September, although a small larval peak could be detected from the end of July to October. All the stages of this species increased in number through spring. Eurytemora americana was registered as from June and only nauplii larvae were observed, with a peak increase during September. Copepodites and adults were observed as from July, increasing in number until peaking at the end of September. The number of all stages of this species decreased abruptly, the whole population disappearing from the plankton. The A. tonsa developmental stages were most positively correlated with temperature, photoperiod and other light variables whereas those of E. americana showed positive correlations with chlorophyll-a and salinity. The gradients of the main environmental factors likely give rise to a certain niche separation facilitating the coexistence of the two copepod populations within the period studied.

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Some interaction processes at the sediment-water and sediment-atmosphere interfaces were analyzed for each season of the year using mass aerodynamic formulas. Data were collected from Puerto Cuatreros tidal flats (Bahia Blanca estuary, Argentina) during an entire year (2000). The soil temperature was measured every 10 min by a thermistor chain at three levels below the sediment surface (-0.05,-0.15 and-0.25 m). Water and air temperatures, solar radiation and meteorological data were registered simultaneously, resulting i~ annual means of 14.07°C (soil at-0.15 m), 13.69°C (air) and 14.51°C (water). Atmospheric and tidal conditions regulated the mudflat's thermal behavior. The soil temperature vertical profiles showed a diurnal and semidiurnal cycle due to the influence of these factors. The diurnal thermal amplitude at-0 .05 m reached 14.6°C on 20 February 2000, but only 2.8°C on 1 July 2000. Most fluctuations of sediment temperatures were observed in the first 15 cm, with vertical gradients of 0.82°C cm-1 during summer. In order to obtain the soil heat capacity, the granulometric composition of a' sediment column was analyzed. Soil heat fluxes during a typical summer and winter day were compared. A net heat gain in the soil was observed during the summer day (+ 840.6 kJ m-2) and an inverse situation was found in winter, with a diurnal heat exchange of-768.6 kJ m-2 •

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