Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
SPATIO-TEMPORAL RECONSTRUCTION OF SNOW AVALANCHE ACTIVITY USING DENDROGEOMORPHOLOGICAL METHOD IN BUCEGI MOUNTAINS-ROMANIAN CARPATHIANS
Mircea Voiculescu, Alexandru Onaca1, Patrick Chiroiu West University of Timișoara, Department of Geography, dul B Vasile Pârvan, 4, 300223-Timișoara, Romania
Abstract. Bucegi Mountains are located on the eastern part of Southern Carpathians (Romanian Carpathians). Considering the high altitudes (over 2500 m) and massiveness and the harsh climate, there is a permanent risk of snow avalanches. Therefore, here have been recorded several casualties and also fatalities, among tourists and skiers. In 2003 was founded the Programme of Nivometeorology within the National Administration of Meteorology (PN-NAM). The PN-NAM has two laboratories in the Bucegi Mountains, one located on Vf. Omu weather station, at 2505 m altitude and the other in Sinaia weather station, at 1500 m altitude. The main purpose of PN-NAM is to study snow and its future evolution as well as snow avalanche triggering conditions and issuing bulletins on snow avalanche risk. In this study, we present the first results of regional research in some snow avalanche sectors, which were affected over time by snow avalanches. We have applied the principles of dendrogeomorphological method to reconstruct spatio-temporal patterns of snow avalanches and the dating past snow avalanches, magnitude and return period. We sampled in two characteristic sectors (Carp and Târle) and obtained 126 samples from 62 trees, respectivelly 92 samples from 46 trees. Our results were validated by meteorological and nivometeorological data, by critical snow depth, by frequency risk level and by casualties and fatalities recorded by PN-NAM confirmed or not by Sinaia Mountain Rescuers.
1. INTRODUCTION industry in particular (Höller 2007, 2009; Keiler Snow avalanches are common natural hazards 2004; Keiler et al. 2005; Stethem et al. 2003). that occur in mountains, have major impacts Our aim is to analyze the spatio-temporal about human settlements and infrastructures (Fuchs, reconstruction of snow avalanche activity in Bründl, 2005; Fuchs et al., 2005; Jamieson and Sinaia ski area in Bucegi Mountains (Southern Stethem, 2002; Stethem et al., 2003; Voiculescu, Carpathians) using the dendrogeomorphological 2009), on human life and affects the skiing method.
2. STUDY AREA erosive structure. The Sinaia ski area The Bucegi Mountains are located at the eastern (45°21’33’’N, 25°30’12’’E) is located on eastern part of the Southern Carpathians (Figure 1). The structural cliff and is Romania’s largest network highest point is the Omu Peak (altitude 2505 m), of ski pistes. We worked in two sectors: the first in the northern region, which is attached to two sector is Carp, located on the northern part of large crests that extend from it. The two crests the Sinaia ski area, between 1600 and 2013 m, peak above 2300 m and each delineates two and the second sector is Târle, located on the structural cliffs (western and eastern) structure southern part of Sinaia ski area, between 1400 consists of limestone and conglomerates with and 2013 m. The sectors are characterized by sandstone intercalations, made of simple and cuesta relief with long slopes and strong staked cuesta fronts with an erosive or tectonic- inclination, with isolated trees or clumped forest.
3. METHODOLOGY NAM) which was funded in collaboration with We follow three directions: according to McClung Météo France and the Centre d’Études de la and Schweizer (1999) and Schweizer and Neige in Grenoble, France, and finally according Jamieson (2001) we analyzed the terrain factors to several authors (Butler and Sawyer 2008; and climate variables, then we evaluated the risk Casteller et al., 2011; Decaulne et al. 2012; of snow avalanches using all data from Germain et al. 2009, 2010; Luckman 2010; Programme of Nivometeorology within the Muntán et al. 2004; 2009) we used a National Administration of Meteorology (PN- dendrogeomorphological method to evaluate avalanche activity.
1Corresponding author address: Onaca Alex. West University of Timișoara, Department of Geography, Bdul V. Pârvan, 4, 300223-Timișoara, Romania; tel: +40256592117; email: [email protected]
729 Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
4. SAMPLING STRATEGY AND SAMPLE Bollschweiler (2008). In this respect the counting ANALYSIS of the tree rings and the measuring of tree-ring We sampled trees and we collected with a widhts were performed with a digital LINTAB Haglöf increment borer 124 samples (with Ø measuring device connected to a Leica 5.15 mm and various heights) from 62 trees (59 stereomicroscope and to TSAP WIN software larches - Larix decidua and 3 spruces - Picea (Rinntech, 2006). All the samples were then alba) in Carp sector and 92 samples from 46 analyzed visually in order to capture growth trees (2 larches - Larix decidua and 44 spruces - disturbances (GD) such as: reaction wood (RW), Picea alba) in Târle sector, respecting callus tissue (CT), tangential rows of traumatic recommended minimum 20 trees/snow resign ducts (TRD) and abrupt growth decrease avalanche path (Decaulne et al. 2012; Hebertson (AGD). For TRD and CT we determined the and Jenkins 2003). Using a GarminGPS76CSx precise location of the damage within the annual we obtained the coordinates (longitude, latitude tree ring to distinguish between snow avalanche and altitude) of the sampled trees. The and other geomorphologic processes (e.g. increment cores were analyzed following the rockfalls). Therefore we considered only the TRD standard dendrogeomorphological procedures located at the beginning of the earlywood. described by Bräker (2002) and Stoffel and
Figure 1: Location of the Sinaia ski area and of our study area
730 Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
5. RECONSTRUCTION OF SNOW AVALANCHE CHRONOLOGY All the GD’s assigned to snow avalanches were where Rt is the response of a tree to an event in used to build the event response histogram and year t and Nt is number of living trees in that to calculate the avalanche activity index (AAI year. According to several studies (Corona et al., with values from 0 to 100%), for each year t, 2010, 2012; Decaulne et al., 2012; Germain et based on the percentage of tree responses (R) al., 2009, 2010; Reardon et al., 2008), we in relation with trees alive in year t (Shroder considered that an event with I > 10% and with a 1978, Germain et al. 2009, Corona et al. 2010, minimum number of ten impacted trees 2012): respresents a major snow avalanche.
n n AAIt = Rt ∑∑ Nt*100 i=1 i=1
6. FREQUENCY AND RETURN PERIOD the individual return period for each tree CALCULATION (1/frequency). Return periods of snow According to Corona et al. (2010, 2012), avalanches were spatially visualized with the Reardon et al. (2008) and Decaulne et al. ArcGIS 9.3 Geostatistical Analyst. (2012), individual GD frequency (f) is calculated for each tree (T) with the formula: 7. RESULTS 7.1 Climate variables n n We used the climatic analysis based on fT = GD /∑∑ yr processed meteorological data from weather =Ti =Ti stations in the observation area (Vf. Omu and Sinaia 1500). The relevant climatic parameters where GD represents the number of growth recorded between 1961 and 2011 are shown in disturbances for each tree while yr the total Table 1: number of years tree T was alive. We calculated
Table 1 Weather parameters in the Bucegi Mountains between 1961 and 2007 Weather station Geographical coordinates Air temperature Rain Number the Number the Average snow depth (alt) Latitude Longitude (annual mean) (annual days with days with heavy annual selected period time 01 mean total) snowfall snowfall November-31 April Vf. Omu (2505 m) 45o27’ 25o27’ -2.5o 1065.9 mm 133.7 92.4 36.7 cm 54.3 cm Sinaia (1500 m) 45o23’ 25o30’ 3.7o 1226.9 mm 90.6 23 14.5 cm 28.4 cm
7.2 Snow avalanche risk incidence of snow avalanches in March, April The likelihood of a snow avalanche depends on and even May. Avalanches occurred on 10-13 the snow depth. A depth of 30-50 cm is days in March, 6-10 days in April and 1-5 days in necessary to produce an avalanche and May. The frequency risk level in the our sectors represents a moderate risk (Birkeland and Mock increased steadily from the winter season of 1996; Esteban et al. 2005) and a snow depth of 2004-2005 to the same period in 2009-2010, 100 cm is necessary to trigger an extreme snow with a resulting impact on winter sports. In this avalanche (Schweizer et al. 2003). To highlight context, in our sectors were recorded the the risk of a snow avalanche, we analysed the following cases of buried and dead skiers (Table relationship between snow depth and the 2). We must mention that Sinaia Mountain number of days with snow avalanches in the Rescue Statistics are unfortunately incomplete, selected time period between October 1st and inaccurate and discontinued. Currently, the only May 31st when snow avalanches are most likely credible source is PN-NAM and our field according to Laternser and Schneebeli (2002). In observations. our sectors, the PN-NAM recorded the greatest
7.3 Growth disturbances in trees and event formation of TRD, followed by an AGD. There years were notably nine observations of scars in the In our sector, the most common snow avalanche wood. The scars result from the impact of snow impact is the formation of RW generated by tree avalanches, which carry eroded aggregated tilting. The next most significant sign is the debris from the top of the cuesta relief. The
731 Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska analysis of all samples enabled reconstruction: in representing the oldest and 2010 the most Carp sector of 34 event years between 1954 and recent year with internal disturbances. We 2011, with 1954 representing the oldest and identify the number of snow avalanche events, 2011 the most recent year with internal using an index numbers (Table 3) and event- disturbances and in Târle sector of 32 event response avalanche induced growth response years between 1964 and 2010, with 1964 (Figure 2).
Table 2 Cases of buried and dead skiers in snow avalanches Winter season Event day Human casualties buried/fatalities) Altitude (m) Exposition Sector 01.28.2006* 2 buried skiers 2000-1800 SE Carp 02.16.2006* 2 buried skiers 1900-1700 SE Carp 2005-2006 02.17.2006* 1 buried skier 1800-1600 SE Carp 02.18.2006* 3 buried skiers 1800-1600 SE Carp 2008-2009 02.21.2009* 1 dead skier 1800-1600 SE Târle 1980-1981 01.21.1981** 2 dead skiers 1600-1700 SE Târle * according to Administraţia Naţională de Meteorologie - National Administration of Meteorology (2005-2006, 2008-2009) ** according to our observations observations in the field and to confirmation of Sinaia Mountain Rescuers
Table 3 Use an index number of 10%, 20 and 30% or 40% AAI > 10% AAI > 20% AAI > 30% or AAI > 40% (Germain et al. 2010, Reardon et al. 2008) Mundo et al. 2007 (Bryant et al. 1989; Butler Malanson 1985; Butler et al. 1987) Carp sector 1974, 1977, 1982, 1989, 2006 1985 and 1998 1970, 2003 Târle sector 1972, 1974, 1975, 1984, 1992, 1993, 1995, 1967, 1981, 1998, 2003 1998 1997, 2005
Figure 2: Event-response histogram showing avalanche induced growth response (a.) and calculated snow avalanche return period for each the trees sampled (b.)
We calculated also the return period (see years with an average of 16.6 years) and for 43 Figure 2): in Carp sector for 19 trees that trees that experienced more than one event experienced a single event (ranged from 9 - 38 (ranged from 5.50 - 20 years with an average of
732 Proceedings, 2012 International Snow Science Workshop, Anchorage, Alaska
9.7 years) and in Târle sector for 17 trees that trees that experienced more than one event experienced a single event (ranged from 11 - 50 (ranged from 4.3 - 22 years with an average of years with an average of 24 years) and for 26 11 years).
7.4 Spatial extent of past events these involve a limited amount of snow; large The spatial extent of past events within the snow avalanches with a 10-26 years return period avalanche tracking zone suggests the activity of cover 50% of the investigated tracking zone, three major types of snow avalanches: small during these events a considerable number of avalanches with sub-decadal return period trees would have been affected (with AAI > 20%) restricted generally to the uppermost central part and very large avalanches overlapping most of of the stand, these avalanches obstructed the the tree cover (with AAI > 30o% and 40%) with a growth of the trees (with AAI > 10%) although return period ranging from 26 - 38 years.
8. CONCLUSIONS sector and one in Târle sector. It should be noted In this study, we test for the first time in Bucegi that some avalanche with AAI> 10% occurred in Mountains the dendrogeomorphogical methods the same year in both sectors. Large avalanches to identify the spatial distribution of snow or very large avalanches with AAI> 20% or even avalanche activity. It is the only method capable AAI> 40% occurred in some year in both sectors of reliably identifying such events where (in 1998 winter season and in 2003 winter historical records are lacking. The analysis of season). Very important snow avalanche events 124 samples, respectivily 92 samples allowed for were validated by meteorological and a reconstruction of small avalanches (with AAI > nivometeorological data (Corona et al. 2010; 10%), 6 in Carp sector and 9 in Târle sector, 2 Muntan et al. 2009), by critical snow depth, by large avalanches (with AAI > 20%) 2 in Carp frequency risk level and by casualties and sector and 4 in Târle sector and very large fatalities recorded by PN-NAM confirmed or not avalanches (with AAI > 30% or 40%) 2 in Carp by Sinaia Mountain Rescuers.
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