Technical Note Landslides (2012) 9:417–432 Rosa María Mateos I Inmaculada García-Moreno I Jose Miguel Azañón DOI 10.1007/s10346-011-0290-8 Received: 10 December 2010 – Accepted: 1 August 2011 Freeze thaw cycles and rainfall as triggering factors Published online: 20 August 2011 © Springer-Verlag 2011 of mass movements in a warm Mediterranean region: the case of the Tramuntana Range (Majorca, Spain) Abstract Between 2008 and 2010, the island of Majorca (Spain) minima at −6.8°C, which are anomalous values in the mild experienced the coldest and wettest winters of the last 40 years. Mediterranean climate. The result was that 34 mass movements Accumulated rainfall was twice the average and values of intense were triggered (Table 1), distributed along the Tramuntana Range rainfall up to 296 mm/24h were recorded, very similar to those (Fig. 1), namely 14 rockfalls, 1 rock avalanche and 15 earth slides– calculated for a return period of 100 years. Additionally, high earth flows (Cruden and Varnes 1996). There are also records of four precipitation coincided with anomalous, low temperatures, with karstic collapses, which shall not be analysed in this study as they abundant snowfall and freezing in the highest zones of the require a distinct analysis. Tramuntana Range, in the northwest sector of the island. As a result, The mass-movement inventory covering this period was carried 34 mass movements were recorded on the range, which seriously out with the support from the Emergency and Road Maintenance affected the road network in an area of great importance for tourism, Services, which informed us of every occurrence as such, and most of as it welcomes 8.5 million visitors each year. Fourteen rockfalls, 1 rock the movements were dated. Others were reported by private avalanche, 15 landslides and 4 karstic collapses were inventoried. The individuals, and the remaining cases were located during two geological structure, formed by a series of NW overlapping thrusts, helicopter flights over the range. As Table 1 shows, some of them determines the distribution as well as the failure pattern of the could not be dated with precision. For each of them, a detailed report movements. Thus, the northern face of the range registered 68% of was written with information regarding size, type of failure, runout, the mass movements: nine rockfalls with planar failure took place as materials involved, damage, etc. well as all the landslides recorded. Likewise, south-facing slopes have Fortunately, there were no deaths, but there were numerous been affected by longer runout rockfalls with a wedge-type failure. cases of damage to dwellings, holiday apartment blocks, barns and The thorough analysis of the meteorological data shows that most of power stations etc., and especially the road network in the range, the movements have taken place after antecedent rainfall over most significantly the numerous blockages on the Ma-10 road, which 800mm. Additionally, the rockfalls have also occurred after several caused significative economic losses in the different tourist sites, freeze–thaw cycles, being a determining and unusual factor in this valued at up to €6M. warm region. Intense rainfall >90 mm/24h also caused rockfalls as This study aims to contribute to the examination of different well as exceptional very intense rainfall >120 mm/24h caused parameters that condition the spatial and temporal distribution of the landslides. The results aim to contribute to the design of an early slope movements that have taken place. To accomplish this, the warning system coordinating emergency, infrastructure services and following specific goals were set: (1) to establish the prominent role of meteorological centres in a region of high risk. the mountain range’s geological structure in the spatial distribution of the landslides and rockfalls, as well as in the failure pattern of the Keywords Landslides . Rockfalls . Rainfall . Freeze–thaw latter; (2) to determine the influence of meteorological factors in cycles . High risk . Early warning system triggering the movements. Relationships were established between theintensityofdailyrainfallaswellasthepreviousrainfallandthe Introduction start of both kinds of slope movements recorded. To do this, data on The island of Majorca, located in the western Mediterranean, has a the daily rainfall and minimum temperature at the 36 weather variety of different geomorphological domains, most prominently the stations distributed along the entire mountain range were analysed, Tramuntana Range (1,100 km2) in the northwestern part of the island from the 1st of October 2008 until the 9th of May 2010. The purpose is (Fig. 1). The steep topography of this chain, which is linked to its to set a series of thresholds for the initiation of the movements. These geological complexity and Mediterranean climate, determines intense values have been checked against the ones obtained by other authors slope dynamics with the consequent movements of all categories in Mediterranean regions close to the Balearic Islands; and (3) to (Mateos 2002; Mateos and Azañón 2005). The main income of the determine the influence of low temperatures in the failures linked to island of Majorca comes from tourism (83% of its GDP), as it rocky massifs and to determine the influence of freeze–thaw cycles welcomes 8.5 million visitors each year. The vast urban development prior to the failure, processes which are very scantly documented in that the Tramuntana region has undergone in the past 30 years has warm Mediterranean regions. considerably increased the risk originating from mass movements. During the hydrological years 2008 to 2010, Majorca experi- Slope movements on the island of Majorca: background enced one of the coldest and wettest winters in living memory. Not Practically all the slope movements recorded on Majorca have taken only did the accumulated rainfall show twice the average recorded place in the Tramuntana Range. The variety of lithologies cropping values, this period also witnessed the highest rates of intense rainfall out in this mountain chain determines a wide range of slope (up to 296 mm/24 h) since instrumental records have been available movements. Landslides and earth flows are frequent phenomena, (1944). These rainy episodes have also coincided with cold periods in primarily affecting soft sediments from the Late Triassic (Keuper), which several days elapsed with temperatures around 0°C and made up of clays with gypsum, as well as an entire series of loamy Landslides 9 & (2012) 417 Technical Note Fig. 1 Location of the island of Majorca in the western Mediterranean and the Tramuntana Range on the northwest extreme of the island. The location of the 34 mass movements registered, as well as the location of the weather stations used in this study, is shown over the digital elevation model materials from the Palaeogene and Neogene that occasionally rockfall on the Valldemossa area razed and buried a large extension outcrop along the mountain range. The most prominent movements of cropland, leaving reports in the daily news. More recently, include the Fornalutx landslide which took place on the 17th December numerous rockfalls have made the news as well, such as the one in 1924 (Mateos et al. 2009), affecting an area of around 150,000 m2. Cala de Banyalbufar (1993), which affected several fishing huts However, the most important mass movement in the Balearic (Ferrer et al. 1997) and the rockfall in Son Matge (Valldemossa) in Islands, because of both its dimensions and the damage it caused, 2005, in which one of the most important archaeological sites from was the Biniarroi landslide in spring 1721, with later local reactiva- Majorca’s prehistory was buried (Mateos and Azañón 2005). The tions in 1816, 1857 and 1943. This landslide affected an area measuring main traffic arteries in the mountain range, both road and rail, have around 300,000 m2 and totally modified the original topography in often been intercepted by slope movements (Mateos 2006), trigger- the region (Mateos and Giménez 2007;Mateosetal.2008). ing serious circulation problems as well as major economic losses. Rockfalls are the most frequent slope movements in the The historical compilation of the slope movements on the island Tramuntana Range due to the predominance of Jurassic rocky (Mateos 2002, 2006), as well as the record of those that have occurred massifs made up of limestone and dolostone. Historically, there are more recently, reveals that all processes have taken place after short records of several major rockfalls. On the 16th March 1857, a huge intense and/or continuous rainfall. Nevertheless, there is no evidence 418 Landslides 9 & (2012) Table 1 Slope movements inventory Inventory number name and date Type Damage 0. Cala Deià (29 Oct. 2008) L Power station 1. Puig Tomir (27 Nov. 2008) R Track Lluc-Pollença 2. Sa Calobra (03 Dec. 2008) L Ma-10 road 3. Es Verger (15 Dec. 2008) L Es Verger road 4. Es Verger (15 Dec. 2008) C Es Verger road 5. Cala Tuent (15 Dec. 2008) L Cala Tuent road 6. Son Cocó (19 Dec. 2008) RA Pine wood 7. Gorg Blau (31 Dec. 2008) R Ma-10 road 8. Cantera (Dec. 2008–Jan. 2010) L Drystone wall 9. Carretera Banyalbufar (Jan. 2009) L Ma-10 road 10. Biniforani (05 Jan. 2009) R Pine wood and drystone walls 11. Biniaraix (06 Jan. 2009) R Small building 12. Port de Valldemossa (07 Jan. 2009) R Port Valldemossa road 13. Crestatx (Jan. 2009) C Housing development street 14. Edificio Siesta. Calvià (08 Jan. 2009) L Building 15. Son Alberti (23 Jan. 2009–Jan. 2010) R Small building 16. Casa Puigpunyent (14 Sept. 2009) R Dwelling 17. Carretera Estellencs (15 Jan. 2010) R Ma-10 road 18. Búger (Jan. 2010) C Old road Búger-Sa Pobla 19. Costa d’en Blanes (Jan. 2010) R Dwellings 20. Carretera Estellencs (Jan. 2010) L Pine wood 21. Costa Cala Estellencs (Jan.