Pere Oller

Dendrochronological study of the Canal del Roc Roig avalanche path: first results of the Aludex project in the Pyrenees

Abstract Historical data about ancient avalanches are scarce in the Pyrenees. Dendrochronology can provide new data about past avalanches and their return period, but up to now little research has been carried out with this purpose. The Aludex project aims to obtain information about the frequency and extent of extreme avalanches, using a dendrochronological and a nivo-meteorological approach. In this paper, we present the results of a dendrochronological study of the Canal del Roc Roig avalanche path which was affected by two extreme avalanches in February 1996. This first dendrochronological study has permitted us to assess the tree-ring signals due to avalanche events in 53 out of 132 dated trees. The trees presented a variety of responses to the 1996 avalanche events. It is shown that the type of tree-ring signal depends on tree age. The methodology has proved successful in detecting the 1996 and 1972 documented avalanche events, and provided outstanding evidence of undocumented past events such as one in 1930.

Using vegetation to characterize the avalanche of Canal del Roc Roig, Vall de Nuria, eastern Pyrenees, Spain

Abstract Avalanche hazard maps of high accuracy are difficult to produce. For land-use planning and management purposes, a good knowledge of extreme run-out zones and frequencies of avalanches is required. In the present work, vegetation recognition (especially focused on Pinus uncinata trees) and dendrochronological techniques are used to characterize avalanches that have occurred in historical times, helping to determine both the extent of large or extreme avalanches and their occurrence in time. Vegetation was studied at the Canal del Roc Roig (eastern Pyrenees, Spain) avalanche path. The avalanches descending this path affect the railway that reaches the Vall de Núria resort and the run-up to the opposite slope. During winter 1996, two important avalanches affecting this path were well documented. These are compared with the results of the vegetation study, consisting of an inventory of flora, the recording of vegetation damages along eight transverse profiles at different altitudes on the path and a dendrochronological sampling campaign. The data obtained contributed to a characterization of the predominant snow accumulation in the starting zone, the 1996 avalanches and the range of frequencies of large avalanches. Also, traces of avalanches that increase the path mapped in the avalanche paths map published by the Institut Cartogràfic de Catalunya in 2000 were identified, improving the initial existing information.

Avalanche mapping and related G.I.S. applications in the Catalan Pyrenees

The Avalanche Risk Project for the Catalan Pyrenees was started in 1986 by theServei Geològic de Catalunya and theDpt. de Geologia Dinàmica, Geofísica i Paleontologia. One of the aims of this project is to carry out the “Map of Probable Avalanche Paths”, which is a thematic map in where the land areas affected by avalanches are represented. This information is the result of: 1) aerial photointerpretation, 2) field work: observations of the avalanche effects and interviews to the inhabitants and people who work in the mountain areas. All the descriptive complementary information about each avalanche zone has been stored in a database, thus constituting the avalanche Cadastre. A Geographic Information System (G.I.S.) is an informatic system which can acquire, store and manipulate data that describe the land surface. The Cadastre and Map of Probable Avalanche Paths constitutes a complex document. It is also a basic document to perform further analysis, risk maps and defense actions, so it must have the following characteristics: easy to update, possibility to combine with other documents and to exploit as a source of diverse informations. Therefore, a G.I.S. is the most appropriate tool to store, manage, analyze and restore this avalanche data. The area of the Catalan Pyrenees that has been mapped and automated until now is also presented.

Slushflows at El Port del Comte, northeast Spain

Slushflows were first recorded in the Iberian Peninsula on 18 December 1997. Three slushflows were released at the ski resort of El Port del Comte, in the Catalan Pyrenees, northeast Spain, during intense rainfall. Two of the slushflows originated on the pistes, and the third affected another piste. Three ski lifts were damaged. This paper analyzes the hydrogeological characteristics of the massif, the geomorphic features of the terrain and the meteorological and snowpack conditions that caused the release of the slushflows. Mans role in triggering the slushflows by compacting snow on the pistes is also considered. Drainage control for reducing the hazard is outlined, taking into consideration the low frequency of the phenomenon.

Tracking Past Snow Avalanches in the SE Pyrenees

Winter 1995–1996 was an exceptional snow avalanche season in the Pyrenees. Nuria Valley, at the SE Pyrenees, registered four avalanches that reached a rack railway that runs along the valley floor. One of these avalanche paths, Canal del Roc Roig, was studied by dendrochronological means. Muntan et al. (2004) reported tree-ring evidence for two previously known snow avalanches and provided striking evidence for one undocumented event that occurred in 1929–1930. Subsequently, to unveil past avalanches more extensive research based on a higher sample density was carried out. The results of this research are outlined here.

The Geological Hazard Map of Catalonia 1:25,000. A Tool for Geohazards Mitigation

We present the Geological Hazard Prevention Map of Catalonia 1:25,000 (MPRG25M), and in detail, the procedure carried out for landslide hazard determination. As a component of the Geoworks of the Geological Institut of Catalonia (IGC), the MPRG25M is a multi-hazard map at 1:25,000 scale conceived to be used for land use planning. It includes the representation of evidence, phenomena, susceptibility and natural hazards of geological processes. These are the processes generated by external geodynamics (such as slope, torrent, snow, coastal and flood dynamics) and internal (seismic) geodynamics. The information is displayed by different maps on each published sheet. The map is intended to enable government and individuals to have an overview of the territory with respect to geological hazards, identifying areas where it is advisable to carry out detailed studies in case of action planning.