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Reassessment of the development and hazard of the Rampac Grande landslide, Cordillera Negra, Peru

Reassessment of the development and hazard of the Rampac Grande landslide, Cordillera Negra, Peru Background: The initial investigation analysed the complex Rampac Grande slope deformation from April 2009 (Landslides 8(3):309-320, 2011). The primary research in 2009 also identified an unrealistic explanation (raw mineral exploration) of the triggering of the landslide and the intention of the local authorities (from the administration centre of Carhuaz) to take measures to minimize the possible future risk to the local population. We also examined the adaptation measures introduced by the local authorities to reduce the risk for the local community. Findings: Unstable landslide material has been left after the 2009 event in the sources and transportation zone and several blocks were described as being only in a temporarily stable state. Landslide propagation could also follow the already existing lateral tension cracks identified in 2009. Areas of reactivation from 2012 were localized and triggering precipitation was evaluated. Conclusion: This study concluded that there is still a hazard of remobilization of specific parts of the landslide in Rampac Grande with potentially damaging effects on the buildings located close to the accumulation area. Keywords: Landslides, Natural hazards, Cordillera Negra, Peru Findings in Cordillera Negra after a significant rainy period dur- Introduction ing the El Niño of 1997/98 (Vilímek et al. 2000). The aim of this article is to describe the recent state of The area of Rampac Grande landslide is located within development of the catastrophic Rampac Grande com- sediments of Middle/Upper Cretaceous age (INGEM- plex landslide (Fig. 1) and to use newly available infor- MET 1995). The rocks contain argillite and schist mation to reassess the hazard level of this landslide for interlaid with sandstones, limestone and small amount the local community, because we suppose that this ex- of gypsum. Sediments are highly permeable due to perience might be useful for other landslide prone areas fracturing and their weathering (Gutierrez et al. 2004). in Calleyon de Huaylas (Department Ancash). This land- TheRampacGrandehas been classified as acomplex slide occurred on the 25th of April 2009 and was studied landslide with rotational character in the most upper by Klimeš and Vilímek (2011). Several slope deforma- part and significant translational character transform- tions were described in the close vicinity of the village of ing into flows in the middle and lower sections Rampac Grande in the past (e.g. Barrón 1972). Two (Klimeš and Vilímek 2011). The complex landslide ex- landslides were reported as having destroyed houses dir- aggeration is 383 m and maximum length and width ectly within the neighbouring Rampac Chico community are 863 and 450 m. (Zapata 1966). The surrounding area in general is land- Water infiltrates the landslide area through superficial slide prone, with several landslides also being identified sediments and deep gullies, which in some places cut up to 20 m into the massif enabling the water to reach dee- per layers of the bed rock. The topographic infiltration * Correspondence: vit.vilimek@natur.cuni.cz area of the complex landslide is only about 3 Km , but Department of Physical Geography and Geoecology, Faculty of Science, based on our field observations and morphology of the Charles University, Albertov St. 6, Prague 2 128 43, Czech Republic surrounding slopes, it may be more than twice as large Full list of author information is available at the end of the article © 2016 Vilímek et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 2 of 7 Fig. 1 An oblique photo of the complex landslide (after Klimeš and Vilímek, 2011). Different parts are categorized according to their prevailing character: a) scarp; b) hanging blocks in an unstable position; c) zone of depletion; d) stable part probably without any movement; e) and f) transport area; g) accumulation zone; h) stable part probably without any movement; i) detached rock block; j), k) and l) accumulation zones. Unstable blocks (1, 2, 3 and 4); partial landslides 1a, 2a as the topographic infiltration area. Observation of the geomorphological and geophysical data for the Ronco land- fissure spring at the NW border of landslide with mea- slide study (Northern Italy). They also stressed the necessity sured outflow of 0.07 l/s supports this opinion (Klimeš of diversesources in studyofcomplex landslides because of and Vilímek 2011). This water infiltration may occur the possible data uncertainty what is also true for our local- deeper into the massif. ity in the Cordillera Negra. All natural hazards in the department Ancash were There are several reasons why we returned to this area analysed (Vilímek et al. 2013) in terms of frequency of and by using field research and a comparative study of recurrence (in the period 1971-2009). The analyses re- photos we tried to reassess the landslide hazard. In gen- vealed that the most frequent type of natural hazard was eral we consider the area as being unstable because “alluvion” (a local term for debris flow), followed by some material has been left in the transportation zone; floods and extreme rainfall. If we group various forms of moreover some blocks are still in only a temporarily mass movement together, they comprise a dominant stable state. The rainy seasons following 2009 were portion among natural hazards. A major portion of nat- analysed and compared with the triggering conditions in ural hazards are generated by the direct impacts of 2008/2009. Landslide propagation could follow the extreme hydrometeorological events. already existing lateral tension cracks identified in 2009. The research carried out on landslides which maintains a state of marginal instability (e.g. Carey et al. 2015) revealed Methods the importance of the relationship between the level of We carried out field research focusing on the use of pre- groundwater and pore water pressure. With respect to the viously gathered data (Klimeš and Vilímek 2011) to fact, that our area of study does not allow us to equip the assess the processes (their type and intensity) that oc- landslide like in less remote areas, we are looking at the in- curred within the landslide since the first investigations fluence of precipitation on slope movement reactivation. and also to collect new information, which may be For instance Longoni et al. (2016) combined geological, useful in evaluating the recent hazard level that the Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 3 of 7 landslide imposes on the local community. In order to achieve this we first compared field photographs from the primary research (July 2009) with recent ones (May 2014) to identify processes ongoing within the landslide and in its close surrounding. Four pairs of pictures (Figs. 2, 3, 4 and 5) are presented here to reveal the main morphological changes; we tried to take the pictures from more or less the same distance and angle. The rainy seasons following 2009 were analysed and compared with landslide triggering conditions in 2008/ 2009. The precipitation record was analysed from the point of view of cumulative data as well as short term precipitation. Unfortunately, no station exists directly around the landslide. We had to use the Yungay (22 km to the NW, 2 530 m a.s.l.) and Huaráz (27 km to the SE, 3 050 m a.s.l.) stations, which are both available on www.senamhi.gob.pe. Electric resistivity tomography (ERT) was used to in- vestigate subsurface conditions within and outside the 2009 landslide, searching for potential sliding planes sus- ceptible to reactivation. We constructed one profile across the main scarp (Fig. 1) in a place where we sus- pected possible future sliding activity due to the location of a spring just below the main scarp. We used a 4point Fig. 3 a from 2009, b from 2014. A new flow accumulation was placed on the body of the complex landslide from 2009 – this time it arrived from a ravine located in the close vicinity of the complex landslide light hp 10w (Grinat et al. 2010) instrument with 27 electrodes on three chains with a 3 m electrode spacing and maximum depth penetration of 12 m. Different ar- rangements of electrodes (e.g. Schlumberger, Wenner and dipole-dipole) were used and the obtained apparent resistivity values were processed in RES2DINV software using the least-squares inversion method in order to represent the true resistivity of the subsurface. We per- formed a maximum five iterations, keeping the root mean square (RMS) error below 10 %. Results Precipitation data analysis The deep-seated movement at the end of the 2008/09 rainy season was due to significant cumulative precipita- tion, reaching 950 mm, with the precipitation reaching a total of 229.6 mm during March 2009 (Klimeš and Vilímek 2011). During the periods 2011/12, 2012/13 and 2013/14 the monthly totals during the rainy season were much lower, with the highest being between 100 and 200 mm at the Yungay station (January to March). The Fig. 2 a from 2009, b from 2014. Some material in the source area level of precipitation in March 2013 reached only has been washed out down the slope since 2009 205.7 mm and January 2013 was rather dry. Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 4 of 7 Fig. 5 a from 2009, b from 2014. The erosion activity in the Fig. 4 a from 2009, b from 2014. The younger photo (b) shows direction of tensional crack in the lateral parts of the complex fresh vegetation on the surface of the flow from 2009, but also a landslide is possible to see by comparing pictures a) and b) young accumulation in the right part of the depositional area According to Mejía and Meza (2012) complex land- precipitation and that the triggering event during the 19th slide reactivation occurred on the 19th of April 2012 at of April (or the day before) was not registered at the near- 9.00. First of all we checked short term precipitation, est stations. The fact that there large differences in short because the reactivation affected only surficial part of term precipitation were registered at both stations in the the former complex landslide from 2009. Surprisingly, past can be documented in Table 1. the short term precipitation was very low at both of the nearest stations in the surrounding area (daily amount Areas of reactivation of 6.1 mm at the Yungay station and 2.3 mm at the Some areas of the Rampac Grande landslide were reacti- Huaráz station). One week precipitation totals reached vated but the activity could not be compared with the 45.1 mm in Huaráz and 35.9 mm in Yungay; 30 day to- 2009 event. We identified remobilization of the landslide tals were 142 mm in Yungay and 177.5 in Huaráz. These material in the scarp area—‘a’ (Fig. 1) which was consid- rainfall intensities were reached several times per year ered as being highly unstable by Klimeš and Vilímek during the last decade and therefore they seem unlikely (2011). In addition to Mejía and Meza (2012), local people to be responsible for this reactivation. For instance, the confirmed the sliding of this material, which probably oc- precipitation record for the 9th of March 2012 reached curred during the 2013/14 rainy season. The reactivation 48.9 mm (see Table 1) and no reactivation was reported. also involved the head scarp, which retreated by at least Also the other months during the rainy season were with- out any exception from the average—for Yungay station: Table 1 Some examples of variation in daily precipitation between February total 136.6 mm; January total 91 mm and for the 2 nearest stations to the landslide locality in Rampac Grande Huaraz station: February total 142.6 mm; January total Station 19/11/2010 9/3/2012 24/3/2012 4/1/2014 104,3 mm. To explain the reactivation during the 19th of Yungay 40.2 mm 7.5 mm 27.5 mm 0 mm April 2012 (Mejía and Meza 2012) we assume that there Huaraz 1.1 mm 48.9 mm 2 mm 27.5 mm must be a large difference in the volumes of short term Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 5 of 7 1 m. We were not able to distinguish the accumulation of to the left of the transportation zone (Fig. 2a,b). Pro- the slide material from the original one. cesses responsible for this remobilization are mainly The main reactivation in Rampac Grande happened water erosion starting as sheet erosion and propagating during the 19th of April 2012 (Mejía and Meza, 2012) to rill and gully forming erosion. The most prominent and is probably based on the intensive, short term pre- gully formed along the east side of the landslide (‘e’, ‘k’ in cipitation which activated only the near surface layers in Fig. 1) reaching a depth of up to 6 m in the accumula- zone ‘c’ (Fig. 1). Remobilisation of accumulation pro- tion area. This gully re-established the main drainage duced two smaller debris flows which we identified in which existed before the landslide formation (Klimeš the eastern as well as western part of the landslide and Vilímek 2011) and now drains the whole landslide area—‘k’ and ‘g’ (Fig. 1). body. A similar process is responsible for considerable Geophysical research across the main landslide scarp removal of the material from the western part of the revealed the highly variable properties of the slide mass landslide (‘b’ in Fig. 1) and in the place where the irriga- with regions of higher resistivity probably formed by tion channel crosses the landslide. A freshly looking more compact rocks and low resistivity patches which debris flow (200 m long) with a source area outside the could be related to a spring observed some 10 m to the landslide probably appeared during the 2013/14 rainy sea- east of the profile. Sharp transition of resistivity values son. It deposited a thin layer (0.4 m) of material reaching from high to low across short depth along with modelled the main landslide accumulation area (‘l’ in Fig. 1). geometry of this boundary suggest presence of water Along the incision of the ‘traditional’ stream, an saturated material which may. It may represent possible accumulation of new material was deposited in the future sliding plane of a shallow (approximately 6 m accumulation part of the landslide (Fig. 4a,b). We deep) landslide (Fig. 6). Due to the limited depth pene- assume it was deposited by reactivation in 2012. The tration, the main sliding plane could not be identified. major process involved the removal of material from A comparison of historical photographs (from 2009) the landslide area is water erosion—flows with high revealed a large remobilization of the landslide material sediment loads. Fig. 6 The ERT profile (Schlumberger electrode array) across the main landside scarp. The dashed black line shows the suggested slip surface of the shallow landslide below the main scarp where the spring is also shown Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 6 of 7 Geomorphological characteristics believes that the landslide occurred due to mineral ex- The main changes in the landscape evolution of the ploration; there are no signs informing of the danger the landslide area are connected with fluvial erosion. The landslide still possess (e.g. new material in the accumula- un-vegetated surface began to be modulated by rill ero- tion area) and only minor technical measures were taken sion and the former water drainage created just after the to try to stabilize the landslide. Unfortunately, no landslide event is specified by deep-ward erosion (up to changes have been made in the settlement and several 5 m). The identification of types and intensity of fluvial houses are directly endangered by a similar event to erosion is important because it works as a destabilising 2009 (see Fig. 1). Also, there are no signs warning the process for possible future mass movements. Many local inhabitants that the landslide area still poses a open cracks were identified on the eastern margin of danger to them and they should be ready to evacuate or the complex landslide but not in the uppermost part. should consider this hazard when using the land for Future propagation of cracks will destabilise the side agriculture or when living directly below the landslide. areas (Fig. 5). The local community begun to grow small trees over Removal of the landslide material which occurs mainly the landslide accumulation where the slope inclination is by water erosion results in steepening of the slopes lower and some small areas are covered by crops (ac- within the scarp and upper transportation area of the cording to the field visit in 2014); nevertheless, the dens- landslide and also creates longer slopes below landslide ity of the vegetation cover is still low. Moreover, the parts that were described as unstable in 2009 (numbers local community has begun to utilize the landslide area 1, 2, 3 and 4 in Fig. 1). We consider this process to be (e.g. establishing fields, planting fruits, and crossing it especially dangerous in the case of three individual land- with cattle) for everyday use, which may strengthen their slides (numbers 1, 2, 3 and 4 in Fig. 1) as landslides 1 understanding of the landslide as an integral part of their and 2 are exposed to continuous and quite intensive environment. Such a mental image does not contribute unloading at their toes. They have clear scarps with towards vulnerability reduction. evidence of vertical movements of 5 m (landslide 1) and To change these unfavourable conditions with respect 7 m (landslide 2), which occurred during 2009. There to possible future landslide risk mitigation, development are also two temporarily stable landslides (1a, 2a on project of the Czech Development Agency will be conduct Fig. 1) just next to them. Along with the toe unloading, during 2016. It aims on landslide hazard dissemination we assume that weathering of the loosened landslide among the local inhabitants, identification hazardous and material mainly along the shear planes further dimin- safe areas around the landslide placing evacuation signs to ishes their stability. Considering these recent processes show the proper evacuation rotes in case of the landslide and the long history of landsliding in this area, we con- reactivation. Simple but reliable manual tape extensom- sider it highly probable that landslide 1 or 2 (Fig. 1) will eter monitoring of the most dangerous landslide parts undergo major movement in the next 50 years. will be also established involving also placement of rain Mapping of tension cracks (4 on Fig. 1) suggests a gauge station on convenient site near the landslide. The deep discontinuity crossing the narrow ridge to the east provincial government of Carhuaz is involved and sup- of the Rampac Grande landslide. Possible future propa- ports these activities. gation of these cracks may result in mobilization of approximately 25,000 m of the estimated volume of the Discussion rocks causing a smaller scale disaster than the landslide The uncertainty of the precipitation analysis is not only in 2009. Recent knowledge does not allow us to estimate due to the small differences of the positions between the the hazard degree of such a scenario. Nevertheless, the landslide head scarp and the rain gauge stations (eleva- 2009 landslide proves it is feasible; therefore, we recom- tion and position inside the valley) but also the local mend establishing a long term project of monitoring of differences in the precipitation records even within short this part of the landslide, whose main requirement is a distances because of the high mountains in the sur- positive approach of the local community and their roundings. During the time when the Yungay station active involvement in the monitoring. registered very high short-term precipitation (see Table 1) the Huaráz station which is 48 km away from Yungay Interaction of the community and natural hazards showed only low amounts per day (and also no signifi- Despite the large attention the event attracted in the cant rains occurred a few days before or after). This days following its occurrence and the largely proper res- means that the local differences in precipitation in such cue action of the local authorities, all of the governmen- a high mountain area are very significant, and we cannot tal organizations on various different levels failed to take be completely sure of the exact triggering totals of pre- any effective action to lower the possible future risk cipitation. Similar situation we already described in an- caused by the event. The local community still largely other part of Peruvian Andes (Vilímek et al. 2006). Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 7 of 7 Conclusion Zone on a North Sea Island, Extended abstracts. Zurich: 16th European Meeting of Environmental and Engineering Geophysics. Five years on from the main Rampac Grande landslide Gutierrez FM et al 2004. Mapa de peligro, plan de usos del suelo y medidas de only small reactivations have been identified; neverthe- mitigacion ante desastres, ciudad de Carhuaz. Unpublished report Proyecto less, several parts of the complex landslide were unstable INDECI PNUD PER/02/051, Carhuaz, Ancash, Peru, p. 222 INGEMMET: Carta Geologica del Peru, Map 19-h Carhuaz, M 1:100 000, 1995, Lima in 2009 and continuing fluvial erosion enhanced this Klimeš J, and Vilímek V 2011. A catastrophic landslide near Rampac Grande in the hazard. The comparison of precipitation revealed that Cordillera Negra, northern Peru. Landslides 8(3): 309–320. the reactivation identified by local people as taking place Longoni L, Papini M, Brambilla D, Arosio D, and Zanzi L 2016. The role of the special scale and data accuracy on deep-seated gravitational slope deformation on the 19th of April 2012 did not match any enormous modeling: The Ronco landslide, Italy. Geomorphology 253: 74–82. precipitation event at the nearest stations. Mejía JMS, Meza LR. Informe No. 102 – PMS/DATYDC. Informe Tecnico de Defensa The anthropogenic measures are both positive and Civil, Unpublished report,2012,p.6 Vilímek V, Zapata ML, and Stemberk J 2000. Slope movements in Callejón de negative. The revegetation could be considered as posi- Huaylas, Peru. Acta Univ Carol Geogr 35(Supplementum): 39–51. tive measure even if it is not sufficient. The negative Vilímek V, Klimeš J, Vlčko V, and Carreño R 2006. Catastrophic debris flows near influences unfortunately prevail e.g. a simple water pipe- Machu Picchu village (Aguas Calientes), Peru. Environ Geol 50(7): 1041–1052. Vilimek V, Hanzlík J, Sládek I, Šandová M, Santillán N 2013 . The Share of Landslides in line is crossing the landslide body and in the case of any the Occurrence of Natural Hazards and the Significance of El Niño in the Cordillera rupture the concentration of water into the landslide Blanca and Cordillera Negra Mountains, Peru. – In Sassa K, Rouhban B, area will be a problem, and on the other hand the local Briceno S, McSaveney M, He B (eds.): Landslides: Global Risk Preparedness, 133-148, Springer, 385 p. people avoid the possibility of concentrating the water Zapata ML 1966. Deslizamento de tierras en Rampac Chico (Carhuaz). Unpublished flow out from the landslide area (western margin). They report Electroperu S.A., Glaciology y Seguridad Lagunas, Huarás, Ancash, Peru. I- have also not refused any directly endangered houses Geotec-002, p 4 (Fig. 1) and have even not informed the local residents about the hazard. The wrong idea about the triggering factor in the village is still evident—they are afraid of mining, the effects of which have not been confirmed and are not too worried about high precipitation, which will be of greater importance in the future (especially during El Niňo). It seems that the local population are not sufficiently educated about the landslide hazard and do not reflect it in their everyday lives, which creates negative conditions for future disasters. Competing interests The authors declare that they have no competing interests. Authors’ contributions All of authors performed the field research. Vít Vilímek analysed the precipitation and Jan Klimeš with Marco Zapata Torres carried out the geophysical investigation. All of the authors drafted, read and approved the final manuscript. Acknowledgements This work was carried out thanks to the support of the long-term conceptual development research organisation RVO: 67985891. Author details Department of Physical Geography and Geoecology, Faculty of Science, Charles University, Albertov St. 6, Prague 2 128 43, Czech Republic. Institute of Rock Structure and Mechanics, Academy of Sciences, V Holešovičkách 41, Prague 8 182 09, Czech Republic. Pontificia Universidad Catolica del Peru, Submit your manuscript to a Av. Universitaria 1801, Lima, Peru. journal and benefi t from: Received: 16 November 2015 Accepted: 8 April 2016 7 Convenient online submission 7 Rigorous peer review References 7 Immediate publication on acceptance Barrón G 1972. Deslizamentos de tierrasen Rampac Chico, provincia de Carhuaz. 7 Open access: articles freely available online Unpublished report Electroperu S.A., Glaciology y Seguridad Lagunas, Huarás, 7 High visibility within the fi eld Ancash, Peru. I-Geotec-007, p 3 7 Retaining the copyright to your article Carey JM, Moore R, and Petley DN 2015. Patterns of movement in the Ventnor landslide complex, Isle of Wight, southern England. Landslides 12(6): 1107–1118. Grinat M, Südekum W, Epping D, Grelle T, and Meyer R 2010. An Automated Submit your next manuscript at 7 springeropen.com Electrical Resistivity Tomography System to Monitor the freshwater/saltwater http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Reassessment of the development and hazard of the Rampac Grande landslide, Cordillera Negra, Peru

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Springer Journals
Copyright
Copyright © 2016 by Vilímek et al.
Subject
Environment; Environment, general; Earth Sciences, general; Geography, general; Geoecology/Natural Processes; Natural Hazards; Environmental Science and Engineering
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2197-8670
DOI
10.1186/s40677-016-0039-8
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Abstract

Background: The initial investigation analysed the complex Rampac Grande slope deformation from April 2009 (Landslides 8(3):309-320, 2011). The primary research in 2009 also identified an unrealistic explanation (raw mineral exploration) of the triggering of the landslide and the intention of the local authorities (from the administration centre of Carhuaz) to take measures to minimize the possible future risk to the local population. We also examined the adaptation measures introduced by the local authorities to reduce the risk for the local community. Findings: Unstable landslide material has been left after the 2009 event in the sources and transportation zone and several blocks were described as being only in a temporarily stable state. Landslide propagation could also follow the already existing lateral tension cracks identified in 2009. Areas of reactivation from 2012 were localized and triggering precipitation was evaluated. Conclusion: This study concluded that there is still a hazard of remobilization of specific parts of the landslide in Rampac Grande with potentially damaging effects on the buildings located close to the accumulation area. Keywords: Landslides, Natural hazards, Cordillera Negra, Peru Findings in Cordillera Negra after a significant rainy period dur- Introduction ing the El Niño of 1997/98 (Vilímek et al. 2000). The aim of this article is to describe the recent state of The area of Rampac Grande landslide is located within development of the catastrophic Rampac Grande com- sediments of Middle/Upper Cretaceous age (INGEM- plex landslide (Fig. 1) and to use newly available infor- MET 1995). The rocks contain argillite and schist mation to reassess the hazard level of this landslide for interlaid with sandstones, limestone and small amount the local community, because we suppose that this ex- of gypsum. Sediments are highly permeable due to perience might be useful for other landslide prone areas fracturing and their weathering (Gutierrez et al. 2004). in Calleyon de Huaylas (Department Ancash). This land- TheRampacGrandehas been classified as acomplex slide occurred on the 25th of April 2009 and was studied landslide with rotational character in the most upper by Klimeš and Vilímek (2011). Several slope deforma- part and significant translational character transform- tions were described in the close vicinity of the village of ing into flows in the middle and lower sections Rampac Grande in the past (e.g. Barrón 1972). Two (Klimeš and Vilímek 2011). The complex landslide ex- landslides were reported as having destroyed houses dir- aggeration is 383 m and maximum length and width ectly within the neighbouring Rampac Chico community are 863 and 450 m. (Zapata 1966). The surrounding area in general is land- Water infiltrates the landslide area through superficial slide prone, with several landslides also being identified sediments and deep gullies, which in some places cut up to 20 m into the massif enabling the water to reach dee- per layers of the bed rock. The topographic infiltration * Correspondence: vit.vilimek@natur.cuni.cz area of the complex landslide is only about 3 Km , but Department of Physical Geography and Geoecology, Faculty of Science, based on our field observations and morphology of the Charles University, Albertov St. 6, Prague 2 128 43, Czech Republic surrounding slopes, it may be more than twice as large Full list of author information is available at the end of the article © 2016 Vilímek et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 2 of 7 Fig. 1 An oblique photo of the complex landslide (after Klimeš and Vilímek, 2011). Different parts are categorized according to their prevailing character: a) scarp; b) hanging blocks in an unstable position; c) zone of depletion; d) stable part probably without any movement; e) and f) transport area; g) accumulation zone; h) stable part probably without any movement; i) detached rock block; j), k) and l) accumulation zones. Unstable blocks (1, 2, 3 and 4); partial landslides 1a, 2a as the topographic infiltration area. Observation of the geomorphological and geophysical data for the Ronco land- fissure spring at the NW border of landslide with mea- slide study (Northern Italy). They also stressed the necessity sured outflow of 0.07 l/s supports this opinion (Klimeš of diversesources in studyofcomplex landslides because of and Vilímek 2011). This water infiltration may occur the possible data uncertainty what is also true for our local- deeper into the massif. ity in the Cordillera Negra. All natural hazards in the department Ancash were There are several reasons why we returned to this area analysed (Vilímek et al. 2013) in terms of frequency of and by using field research and a comparative study of recurrence (in the period 1971-2009). The analyses re- photos we tried to reassess the landslide hazard. In gen- vealed that the most frequent type of natural hazard was eral we consider the area as being unstable because “alluvion” (a local term for debris flow), followed by some material has been left in the transportation zone; floods and extreme rainfall. If we group various forms of moreover some blocks are still in only a temporarily mass movement together, they comprise a dominant stable state. The rainy seasons following 2009 were portion among natural hazards. A major portion of nat- analysed and compared with the triggering conditions in ural hazards are generated by the direct impacts of 2008/2009. Landslide propagation could follow the extreme hydrometeorological events. already existing lateral tension cracks identified in 2009. The research carried out on landslides which maintains a state of marginal instability (e.g. Carey et al. 2015) revealed Methods the importance of the relationship between the level of We carried out field research focusing on the use of pre- groundwater and pore water pressure. With respect to the viously gathered data (Klimeš and Vilímek 2011) to fact, that our area of study does not allow us to equip the assess the processes (their type and intensity) that oc- landslide like in less remote areas, we are looking at the in- curred within the landslide since the first investigations fluence of precipitation on slope movement reactivation. and also to collect new information, which may be For instance Longoni et al. (2016) combined geological, useful in evaluating the recent hazard level that the Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 3 of 7 landslide imposes on the local community. In order to achieve this we first compared field photographs from the primary research (July 2009) with recent ones (May 2014) to identify processes ongoing within the landslide and in its close surrounding. Four pairs of pictures (Figs. 2, 3, 4 and 5) are presented here to reveal the main morphological changes; we tried to take the pictures from more or less the same distance and angle. The rainy seasons following 2009 were analysed and compared with landslide triggering conditions in 2008/ 2009. The precipitation record was analysed from the point of view of cumulative data as well as short term precipitation. Unfortunately, no station exists directly around the landslide. We had to use the Yungay (22 km to the NW, 2 530 m a.s.l.) and Huaráz (27 km to the SE, 3 050 m a.s.l.) stations, which are both available on www.senamhi.gob.pe. Electric resistivity tomography (ERT) was used to in- vestigate subsurface conditions within and outside the 2009 landslide, searching for potential sliding planes sus- ceptible to reactivation. We constructed one profile across the main scarp (Fig. 1) in a place where we sus- pected possible future sliding activity due to the location of a spring just below the main scarp. We used a 4point Fig. 3 a from 2009, b from 2014. A new flow accumulation was placed on the body of the complex landslide from 2009 – this time it arrived from a ravine located in the close vicinity of the complex landslide light hp 10w (Grinat et al. 2010) instrument with 27 electrodes on three chains with a 3 m electrode spacing and maximum depth penetration of 12 m. Different ar- rangements of electrodes (e.g. Schlumberger, Wenner and dipole-dipole) were used and the obtained apparent resistivity values were processed in RES2DINV software using the least-squares inversion method in order to represent the true resistivity of the subsurface. We per- formed a maximum five iterations, keeping the root mean square (RMS) error below 10 %. Results Precipitation data analysis The deep-seated movement at the end of the 2008/09 rainy season was due to significant cumulative precipita- tion, reaching 950 mm, with the precipitation reaching a total of 229.6 mm during March 2009 (Klimeš and Vilímek 2011). During the periods 2011/12, 2012/13 and 2013/14 the monthly totals during the rainy season were much lower, with the highest being between 100 and 200 mm at the Yungay station (January to March). The Fig. 2 a from 2009, b from 2014. Some material in the source area level of precipitation in March 2013 reached only has been washed out down the slope since 2009 205.7 mm and January 2013 was rather dry. Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 4 of 7 Fig. 5 a from 2009, b from 2014. The erosion activity in the Fig. 4 a from 2009, b from 2014. The younger photo (b) shows direction of tensional crack in the lateral parts of the complex fresh vegetation on the surface of the flow from 2009, but also a landslide is possible to see by comparing pictures a) and b) young accumulation in the right part of the depositional area According to Mejía and Meza (2012) complex land- precipitation and that the triggering event during the 19th slide reactivation occurred on the 19th of April 2012 at of April (or the day before) was not registered at the near- 9.00. First of all we checked short term precipitation, est stations. The fact that there large differences in short because the reactivation affected only surficial part of term precipitation were registered at both stations in the the former complex landslide from 2009. Surprisingly, past can be documented in Table 1. the short term precipitation was very low at both of the nearest stations in the surrounding area (daily amount Areas of reactivation of 6.1 mm at the Yungay station and 2.3 mm at the Some areas of the Rampac Grande landslide were reacti- Huaráz station). One week precipitation totals reached vated but the activity could not be compared with the 45.1 mm in Huaráz and 35.9 mm in Yungay; 30 day to- 2009 event. We identified remobilization of the landslide tals were 142 mm in Yungay and 177.5 in Huaráz. These material in the scarp area—‘a’ (Fig. 1) which was consid- rainfall intensities were reached several times per year ered as being highly unstable by Klimeš and Vilímek during the last decade and therefore they seem unlikely (2011). In addition to Mejía and Meza (2012), local people to be responsible for this reactivation. For instance, the confirmed the sliding of this material, which probably oc- precipitation record for the 9th of March 2012 reached curred during the 2013/14 rainy season. The reactivation 48.9 mm (see Table 1) and no reactivation was reported. also involved the head scarp, which retreated by at least Also the other months during the rainy season were with- out any exception from the average—for Yungay station: Table 1 Some examples of variation in daily precipitation between February total 136.6 mm; January total 91 mm and for the 2 nearest stations to the landslide locality in Rampac Grande Huaraz station: February total 142.6 mm; January total Station 19/11/2010 9/3/2012 24/3/2012 4/1/2014 104,3 mm. To explain the reactivation during the 19th of Yungay 40.2 mm 7.5 mm 27.5 mm 0 mm April 2012 (Mejía and Meza 2012) we assume that there Huaraz 1.1 mm 48.9 mm 2 mm 27.5 mm must be a large difference in the volumes of short term Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 5 of 7 1 m. We were not able to distinguish the accumulation of to the left of the transportation zone (Fig. 2a,b). Pro- the slide material from the original one. cesses responsible for this remobilization are mainly The main reactivation in Rampac Grande happened water erosion starting as sheet erosion and propagating during the 19th of April 2012 (Mejía and Meza, 2012) to rill and gully forming erosion. The most prominent and is probably based on the intensive, short term pre- gully formed along the east side of the landslide (‘e’, ‘k’ in cipitation which activated only the near surface layers in Fig. 1) reaching a depth of up to 6 m in the accumula- zone ‘c’ (Fig. 1). Remobilisation of accumulation pro- tion area. This gully re-established the main drainage duced two smaller debris flows which we identified in which existed before the landslide formation (Klimeš the eastern as well as western part of the landslide and Vilímek 2011) and now drains the whole landslide area—‘k’ and ‘g’ (Fig. 1). body. A similar process is responsible for considerable Geophysical research across the main landslide scarp removal of the material from the western part of the revealed the highly variable properties of the slide mass landslide (‘b’ in Fig. 1) and in the place where the irriga- with regions of higher resistivity probably formed by tion channel crosses the landslide. A freshly looking more compact rocks and low resistivity patches which debris flow (200 m long) with a source area outside the could be related to a spring observed some 10 m to the landslide probably appeared during the 2013/14 rainy sea- east of the profile. Sharp transition of resistivity values son. It deposited a thin layer (0.4 m) of material reaching from high to low across short depth along with modelled the main landslide accumulation area (‘l’ in Fig. 1). geometry of this boundary suggest presence of water Along the incision of the ‘traditional’ stream, an saturated material which may. It may represent possible accumulation of new material was deposited in the future sliding plane of a shallow (approximately 6 m accumulation part of the landslide (Fig. 4a,b). We deep) landslide (Fig. 6). Due to the limited depth pene- assume it was deposited by reactivation in 2012. The tration, the main sliding plane could not be identified. major process involved the removal of material from A comparison of historical photographs (from 2009) the landslide area is water erosion—flows with high revealed a large remobilization of the landslide material sediment loads. Fig. 6 The ERT profile (Schlumberger electrode array) across the main landside scarp. The dashed black line shows the suggested slip surface of the shallow landslide below the main scarp where the spring is also shown Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 6 of 7 Geomorphological characteristics believes that the landslide occurred due to mineral ex- The main changes in the landscape evolution of the ploration; there are no signs informing of the danger the landslide area are connected with fluvial erosion. The landslide still possess (e.g. new material in the accumula- un-vegetated surface began to be modulated by rill ero- tion area) and only minor technical measures were taken sion and the former water drainage created just after the to try to stabilize the landslide. Unfortunately, no landslide event is specified by deep-ward erosion (up to changes have been made in the settlement and several 5 m). The identification of types and intensity of fluvial houses are directly endangered by a similar event to erosion is important because it works as a destabilising 2009 (see Fig. 1). Also, there are no signs warning the process for possible future mass movements. Many local inhabitants that the landslide area still poses a open cracks were identified on the eastern margin of danger to them and they should be ready to evacuate or the complex landslide but not in the uppermost part. should consider this hazard when using the land for Future propagation of cracks will destabilise the side agriculture or when living directly below the landslide. areas (Fig. 5). The local community begun to grow small trees over Removal of the landslide material which occurs mainly the landslide accumulation where the slope inclination is by water erosion results in steepening of the slopes lower and some small areas are covered by crops (ac- within the scarp and upper transportation area of the cording to the field visit in 2014); nevertheless, the dens- landslide and also creates longer slopes below landslide ity of the vegetation cover is still low. Moreover, the parts that were described as unstable in 2009 (numbers local community has begun to utilize the landslide area 1, 2, 3 and 4 in Fig. 1). We consider this process to be (e.g. establishing fields, planting fruits, and crossing it especially dangerous in the case of three individual land- with cattle) for everyday use, which may strengthen their slides (numbers 1, 2, 3 and 4 in Fig. 1) as landslides 1 understanding of the landslide as an integral part of their and 2 are exposed to continuous and quite intensive environment. Such a mental image does not contribute unloading at their toes. They have clear scarps with towards vulnerability reduction. evidence of vertical movements of 5 m (landslide 1) and To change these unfavourable conditions with respect 7 m (landslide 2), which occurred during 2009. There to possible future landslide risk mitigation, development are also two temporarily stable landslides (1a, 2a on project of the Czech Development Agency will be conduct Fig. 1) just next to them. Along with the toe unloading, during 2016. It aims on landslide hazard dissemination we assume that weathering of the loosened landslide among the local inhabitants, identification hazardous and material mainly along the shear planes further dimin- safe areas around the landslide placing evacuation signs to ishes their stability. Considering these recent processes show the proper evacuation rotes in case of the landslide and the long history of landsliding in this area, we con- reactivation. Simple but reliable manual tape extensom- sider it highly probable that landslide 1 or 2 (Fig. 1) will eter monitoring of the most dangerous landslide parts undergo major movement in the next 50 years. will be also established involving also placement of rain Mapping of tension cracks (4 on Fig. 1) suggests a gauge station on convenient site near the landslide. The deep discontinuity crossing the narrow ridge to the east provincial government of Carhuaz is involved and sup- of the Rampac Grande landslide. Possible future propa- ports these activities. gation of these cracks may result in mobilization of approximately 25,000 m of the estimated volume of the Discussion rocks causing a smaller scale disaster than the landslide The uncertainty of the precipitation analysis is not only in 2009. Recent knowledge does not allow us to estimate due to the small differences of the positions between the the hazard degree of such a scenario. Nevertheless, the landslide head scarp and the rain gauge stations (eleva- 2009 landslide proves it is feasible; therefore, we recom- tion and position inside the valley) but also the local mend establishing a long term project of monitoring of differences in the precipitation records even within short this part of the landslide, whose main requirement is a distances because of the high mountains in the sur- positive approach of the local community and their roundings. During the time when the Yungay station active involvement in the monitoring. registered very high short-term precipitation (see Table 1) the Huaráz station which is 48 km away from Yungay Interaction of the community and natural hazards showed only low amounts per day (and also no signifi- Despite the large attention the event attracted in the cant rains occurred a few days before or after). This days following its occurrence and the largely proper res- means that the local differences in precipitation in such cue action of the local authorities, all of the governmen- a high mountain area are very significant, and we cannot tal organizations on various different levels failed to take be completely sure of the exact triggering totals of pre- any effective action to lower the possible future risk cipitation. Similar situation we already described in an- caused by the event. The local community still largely other part of Peruvian Andes (Vilímek et al. 2006). Vilímek et al. Geoenvironmental Disasters (2016) 3:5 Page 7 of 7 Conclusion Zone on a North Sea Island, Extended abstracts. Zurich: 16th European Meeting of Environmental and Engineering Geophysics. Five years on from the main Rampac Grande landslide Gutierrez FM et al 2004. Mapa de peligro, plan de usos del suelo y medidas de only small reactivations have been identified; neverthe- mitigacion ante desastres, ciudad de Carhuaz. Unpublished report Proyecto less, several parts of the complex landslide were unstable INDECI PNUD PER/02/051, Carhuaz, Ancash, Peru, p. 222 INGEMMET: Carta Geologica del Peru, Map 19-h Carhuaz, M 1:100 000, 1995, Lima in 2009 and continuing fluvial erosion enhanced this Klimeš J, and Vilímek V 2011. A catastrophic landslide near Rampac Grande in the hazard. The comparison of precipitation revealed that Cordillera Negra, northern Peru. Landslides 8(3): 309–320. the reactivation identified by local people as taking place Longoni L, Papini M, Brambilla D, Arosio D, and Zanzi L 2016. The role of the special scale and data accuracy on deep-seated gravitational slope deformation on the 19th of April 2012 did not match any enormous modeling: The Ronco landslide, Italy. Geomorphology 253: 74–82. precipitation event at the nearest stations. Mejía JMS, Meza LR. Informe No. 102 – PMS/DATYDC. Informe Tecnico de Defensa The anthropogenic measures are both positive and Civil, Unpublished report,2012,p.6 Vilímek V, Zapata ML, and Stemberk J 2000. Slope movements in Callejón de negative. The revegetation could be considered as posi- Huaylas, Peru. Acta Univ Carol Geogr 35(Supplementum): 39–51. tive measure even if it is not sufficient. The negative Vilímek V, Klimeš J, Vlčko V, and Carreño R 2006. Catastrophic debris flows near influences unfortunately prevail e.g. a simple water pipe- Machu Picchu village (Aguas Calientes), Peru. Environ Geol 50(7): 1041–1052. Vilimek V, Hanzlík J, Sládek I, Šandová M, Santillán N 2013 . The Share of Landslides in line is crossing the landslide body and in the case of any the Occurrence of Natural Hazards and the Significance of El Niño in the Cordillera rupture the concentration of water into the landslide Blanca and Cordillera Negra Mountains, Peru. – In Sassa K, Rouhban B, area will be a problem, and on the other hand the local Briceno S, McSaveney M, He B (eds.): Landslides: Global Risk Preparedness, 133-148, Springer, 385 p. people avoid the possibility of concentrating the water Zapata ML 1966. Deslizamento de tierras en Rampac Chico (Carhuaz). Unpublished flow out from the landslide area (western margin). They report Electroperu S.A., Glaciology y Seguridad Lagunas, Huarás, Ancash, Peru. I- have also not refused any directly endangered houses Geotec-002, p 4 (Fig. 1) and have even not informed the local residents about the hazard. The wrong idea about the triggering factor in the village is still evident—they are afraid of mining, the effects of which have not been confirmed and are not too worried about high precipitation, which will be of greater importance in the future (especially during El Niňo). It seems that the local population are not sufficiently educated about the landslide hazard and do not reflect it in their everyday lives, which creates negative conditions for future disasters. Competing interests The authors declare that they have no competing interests. Authors’ contributions All of authors performed the field research. Vít Vilímek analysed the precipitation and Jan Klimeš with Marco Zapata Torres carried out the geophysical investigation. All of the authors drafted, read and approved the final manuscript. Acknowledgements This work was carried out thanks to the support of the long-term conceptual development research organisation RVO: 67985891. Author details Department of Physical Geography and Geoecology, Faculty of Science, Charles University, Albertov St. 6, Prague 2 128 43, Czech Republic. Institute of Rock Structure and Mechanics, Academy of Sciences, V Holešovičkách 41, Prague 8 182 09, Czech Republic. Pontificia Universidad Catolica del Peru, Submit your manuscript to a Av. Universitaria 1801, Lima, Peru. journal and benefi t from: Received: 16 November 2015 Accepted: 8 April 2016 7 Convenient online submission 7 Rigorous peer review References 7 Immediate publication on acceptance Barrón G 1972. Deslizamentos de tierrasen Rampac Chico, provincia de Carhuaz. 7 Open access: articles freely available online Unpublished report Electroperu S.A., Glaciology y Seguridad Lagunas, Huarás, 7 High visibility within the fi eld Ancash, Peru. I-Geotec-007, p 3 7 Retaining the copyright to your article Carey JM, Moore R, and Petley DN 2015. Patterns of movement in the Ventnor landslide complex, Isle of Wight, southern England. Landslides 12(6): 1107–1118. Grinat M, Südekum W, Epping D, Grelle T, and Meyer R 2010. An Automated Submit your next manuscript at 7 springeropen.com Electrical Resistivity Tomography System to Monitor the freshwater/saltwater

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