Descripción: The previous analysis of the prehistoric slide phenomena in the main Andes of Neuquén Province in Argentina (36o-38oS), triggered the study of those located south of this la-titude. Therefore a new set of mass wasting deposits has been identified, whose trigger factors and corresponding tectonic framework, where they are located, differ from the northern slides. Their study was performed in three specific areas: Aluminé, Chapelco and Arroyo Limay Chico. Earth flows predominate in relation to slumps. The only exception is the Chapelco rock avalanche. Their occurrence seems to be related to the presence of Limay Chico member of the Caleufú Formation, whose lithology (expanding clays), particular rheology before water saturation, and particular disposition underlying basaltic lava and conglomeradic plains were conditioning factors. The trigger factor of the Present and prehistoric earth flows has been intense orographic precipitations. Water saturation reduced friction and cohesion in materials, incrementing water pore pressure and producing slope instabilities. Rotational slides are related to the slope basal erosion produced by lateral river migration and additionally to precipitations. Slope orientation has been important in determining location of main slides. Lateral slope release through the flanks of glacial valleys due to debutressing because of the glacial retire in the area, has produced instability and rock fracturation that led to slide phenomena. The Chapelco rock avalanche is particularly related to copious precipitations during postglacial times. Thus sliding main trigger factors south of 38oS differ from those pro-posed for the northern area where earthquakes dominated. Their specific age is still unknown, although their geomorphologic analysis allow to constraint a postglacial age for all these occurrences. However, temporal relationships are lacking for the specific case of the arroyo Limay Chico, beyond the glaciated area.

Descripción: Five prehistoric rock-avalanches are described in the northern cordilleran region of Neuquén Province, between 37°15′ and 37°30′S and between 70°55′ and 71°05′W. These slides and their deposits were not previously identified and moreover they were classified as glacial and glaciofluvial in origin. All of them are developed on volcanic-sedimentary deposits. They are named after local places: Cerro Piche Moncol, Cerro Guañaco, Cerro Coronal, Laguna Negra and Laguna Lauquen Mallin avalanches. The first three form a group of avalanches situated north of Reñileuvú creek, in the vicinity of the previously described Moncol rock-avalanche. Their break-away zones are located on the lateral slopes of a pre-existing deep glacial valley. The biggest rock-avalanche is the Cerro Piche Moncol and its deposits are due to the collapse of the southern flank of a volcanic edifice with a small caldera. The Cerro Guañaco, Cerro Coronal and Laguna Negra rock-avalanches began as a slump slide to evolving distally into a flow. The slides of Laguna Lauquen Mallín are big rock-block slides. Some local factors, principally contrasting lithology and physical properties, structural factors and more humid conditions during postglacial times favourable conditions for the loss of slope equilibrium. The authors suggest that these gravitational movements triggered by seismic shock. The age of these rock-avalanches is unknown but they must be younger than last local glaciation. © 2005 Asociación Geológica Argentina.

Descripción: Chemical trails have been shown to act as an orientation cue in some ant species. Here, I report that the trail-laying behaviour in the nectar-feeding ant, Camponotus rufipes, varies with the concentration of the sucrose solutions collected. Single workers collected solutions of different sucrose concentrations (5, 20, and 40 in weight) during 4 consecutive visits to the resource, and their trail-marking behaviour was recorded on soot-coated slides during their first and last visits. Results suggest that these chemical trails provide both an orientation cue between the nest and the food source, as previously suggested for Camponotus ants, as well as information about food quality. © 2011 Pablo E. Schilman.

Descripción: This paper reports the standardization of methods used for processing and embedding various vertebrate brains of different sizes in paraffin. Other technical details developed for avoiding frequent difficulties arising during laboratory routine are also reported. Some modifications of the Nissl and Klüver-Barrera staining methods are proposed. These modifications include: 1) a Nissl stain solution with a rapid and efficient action with easier differentiation; 2) the use of a cheap microwave oven for the Klüver-Barrera stain. These procedures have the advantage of permitting Nissl and Klüver-Barrera staining of nervous tissue in about five and fifteen minutes respectively. The proposed procedures have been tested in brains obtained from fish, amphibians, reptiles and mammals of different body sizes. They are the result of our long experience in preparing slides for comparative studies. Serial sections of excellent quality were regularly obtained in all the specimens studied. These standardized methods, being simple and quick, are recommended for routine use in neurobiological laboratories.

Descripción: In the region of the Main Andes of San Juan, exists a high concentration of landslide deposits that can originate natural dams. The outburst of these dams generated by slide is a common process in this morphology. The analyses of satellite imagery and air photos of previous years allow reconstructing the characteristics and the origin of the slides that formed those natural dams. In this region of the Main Andes, the rapid uplift and erosion of the mountain chain has created abrupt slopes and an internal structure in the materials that determined an increase of the susceptibility to the slope collapse without triggers as the seismic activity or precipitations. The objectives of the present work are (1) to analyze the causes that formed the natural dam and produced the landslide dam and development of the Los Erizos lagoon in the middle course of the Santa Cruz river; (2) the outburst of the dam and their consequent flood; and (3) the morphologic characteristic of the study region. The temporary comparison between air photos with satellite imageries indicates that the natural dam was generated by slip of the western hillside of the Santa Cruz mountain range, located below the Cerro Estrella. However, the constant water flow to the lagoon, has increased its water level until reaching the maximum benchmark of the dam, produced the beginning of the lake drainage and weakening of the dam causing the outburst and its consequent flood. Based on satellite imagery, a temporary analysis of the lagoon is presented, indicating that monitoring is an important tool to alert in the whole San Juan river basin for possible natural dikes, preventing hazards to the populations down water. The alluvium of November 12 of 2005, discharged 32.100.000 m3 in 67 minutes and traveled 254 km in less than 12 hours.