Precipitation as a factor triggering landslide activity in the Kamień massif (Beskid Niski Mts, Western Carpathians)

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Bulletin of Geography. Physical G eo graphy Series, No. 8 (2 0 1 5 ): 5 - 1 7 h ttp ://d x.d o l.o rg /1 0.151 5/bg e o -2 01 5-000 1

Precipitation as a factor triggering landslide activity in the Kamień massif

(Beskid Niski Mts, Western Carpathians)

IS SN 20 8 0 -7 6 8 6

Tomasz Papciak1, Ireneusz M alik1, Kazim ierz Krzem ień2, M ałgorzata W istub a1, Elżbieta Gorczyca2,

Dom inika W rońska-W ałach2, M ateusz Sobucki2

1 U n iv e rsity of S ilesia in K a to w ic e , 4 1 - 2 0 0 S o s n o w ie c , Poland 2 Ja g ie llo n ia n U n iv e rsity, 3 0 - 3 8 7 K ra k ó w , Poland

Correspondence: Ireneusz Malik, Faculty of Earth Sciences. University of Silesia in Katowice, Będzińska 60, 41-200 Sosnowiec, Poland. E-mail: irekgeo@ w p.pl

Abstract. On the landslide slope in the Beskid Niski Mts (Western Carpathians) 48 silver firs were cored for dendrochronological samples. Tree-ring widths were measured for the upslope and downslope sides of each stem. Events of landslide activity were dated using the method of the eccentricity index.

The tree-ring record of landsliding w as compared with the occurrence of precipitation in the study area. The nature of the relation between precipitation and landsliding is complex. We have found a statistically significant correlation between landsliding and the number of days with 24-hour precip

itation totals above 20 mm and high 3-, 5-, and 10-day precipitation totals during winter half-years.

Thus landsliding in the Kamień massif is triggered mainly by high precipitation totals in the preced

ing winter period. No such relation w as found for annual precipitation totals and different types of precipitation totals in the summer period. Single landsliding events related to high summer precipi

tation totals were found, but the correlation is not statistically significant. In addition some landslid

ing events are 1-2 years lagged after the occurrence of high long-term precipitation totals. It seems that the strongest landsliding events resulted from sequences of w et summer, w et winter and once again w et summer seasons directly following one another.

Key words landslide, precipitation, dendrogeomorphology, Beskid Niski Mts

Introduction

Three types of precipitation have been distinguished, depending on their am ount and intensity, triggering dif

ferent geomorphological processes (Starkel 1986, 1996).

The first type is short-term local dow npours with an intensity of 1-3 m m /m in, responsible for triggering of soil ablation and down-flows. The second type is long

term dow npours (150-400 m m during 2 -5 days), resulting in the form ation of shallow landslides and transform ations of river beds. The third type is long rainy periods (100-500 m m in a period lasting up

to several m onths), responsible for the activity of deep-seated rocky and regolith landslides.

However, the course of the particular precipita

tion events is usually com plex and it is difficult to determ in e in an unam biguous m an n er th e th re sh olds of th e am o un t/in ten sity of precipitation above w hich g eom orphological processes are triggered.

The effectiveness of the given precipitation depends also on local relief, vegetation cover, soil type and its h u m id ity in the p e rio d im m ediately p re ced ing the occurrence of the process (M argielewski et al. 2008). It is especially difficult to determ ine the am o u n t o f precipitation triggering the landslides,

Bulletin of G eography. Physical G eo graphy Series 2 0 1 5 . T h is Is an Open A ccess article distributed un d er the term s of the C reative Com m ons Attribution -N oncom m ercial 4 .0 International License (http://creativecom m ons.org/licenses/by-nc/4.0/), perm itting all non-com m ercial use, distribution, and reproduction in any m edium , provided the original w o rk is properly cited.

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P recip itatio n a s a fa c to r trigg erin g la n d s lid e activity T .P a p cia k e t al.

m ainly due to the fact th at the landslide slopes are com posed of various land form s, clearly separated fro m each other, e.g. landslide niche an d tongue.

There are sm aller land form s w ithin the niche and tongue, each o f w hich can be subject to disloca

tio n during various precipitation events (M igoń et al. 2014). Yet, there is a clear correlation betw een the am ount of precipitation and the activity o f C ar

path ian landslides dated dendrochronologically, as was indicated by previous studies in the area of the Polish Flysch C arpathian M ountains (Ziętara 1968;

Gil, D ługosz 2006; Starkel 2011).

D endrochronological investigation can be of use in determ ining the activity of slight landslide m ove

m ents n o t visible in the field. Previous dendrochronological studies allowed researchers to detect a high frequency of small-scale landslide m ovem ents occur

ring alm ost every year in the C arpathians (W istuba et al. 2013). This was possible due to the fact that the trees w hich grow on landslide slopes are b en t during the events of landsliding and annually record landslide events in their rings (B ram m et al. 1987;

C orom inas, M oya 2010). A landsliding event can be recorded in the sam e calendar year (annual ring) w hen the event occurred or w ith a one-year lag, in the next calendar year (Krąpiec, M argielewski 2000;

Krąpiec et al. 2008). Application of the index of tree- grow th eccentricity allowed researchers to calculate the intensity of tree reaction to landsliding in p ar

ticular years (M alik, W istuba 2012; W istuba et al.

2013). This provides an opportunity to com pare a n nual/sem i-annual precipitation totals w ith the reac

tion o f trees to landsliding (W istuba et al. 2013).

The objective of the presented study was to exam ine the relation between the occurrence of different types of precipitation with totals calculated for vari

ous periods (annual precipitation, sum m er half-year precipitation, preceding winter half-year precipitation, m axim um daily, 3-, 5-, 10- and 30-day cumulative rolling totals, num ber of days with daily precipitation exceeding 20 m m ) and the reaction o f the trees to landsliding on the slope of the Kamień m assif (Beskid Niski Mts) expressed as an eccentricity index.

Stu d y A rea

The study was carried o u t on an eastern slope of the Kam ień m assif (714 m a.s.l.), in the Beskid N i

ski M ts (O u ter W estern C arp ath ian s in Poland) (Fig. 1A, B). We have selected tw o sam pling sites:

the study site on a landslide slope, and the reference site on a stable slope, 1 k m from the landslide slope.

B edrock o f th e Beskid Niski M ts is com posed of flysch sandstones and shales. O n the studied slope of the Kam ień m assif there is a stratigraphic b o rder betw een sandstones, shales, claystones and cherts (lower p art o f the studied slope) and series of p re do m inating sandstones in terbedd ed w ith th in lay

ers o f claystones and m udstones (upper p a rt o f the studied slope). This provides favourable conditions for developm ent o f landslides.

The m ain scarp of the studied landslide is located near the ridge of the Kam ień massif, approx. 650 m a.s.l. The m ain scarp is 2 5 -3 5 m high, the length of th e landslide is 1.4 km , the m ax im um w id th is 360 m and the area 35 ha. In the m iddle p art typi

cal landslide form s are com m on: h um m ocky relief and open landslide cracks. The accum ulation zone is com posed o f colluvial blocks and descends to ap prox. 450 m a.s.l. (Fig. 1C). A ccording to the m o d i

fied classification by Varnes (H ungr et al. 2014) the analysed landslide is probably a co m p o u n d slide w ith very low velocity o f m ovem ent an d a h ig h ly d istu rb ed flow-like lower p a rt of the landslide toe. H u m m o ck y to p o g rap h y b u t w ith o u t clear landslide scarps was observed also above the m ain scarp, up to th e top o f K am ień m o u n ta in ridge (Fig. 1).

Clim ate conditions in the study area are typical for lower m o u n tain ranges of the C arpathians w ith precipitation of c. 800-900 m m p er year. M o n th ly m ean tem peratures vary from -3°C in January to 17°C in July. Snow cover lasts 80-100 days per year.

The study area is located in M agura N ational Park.

N atural beech and fir m ixed forests cover the area of the study. There are n o large u rb an or in d u stri

al areas located less th an 20 k m from K am ień Mt.

However, the study area is located w ithin a form er C entral Industrial D istrict (CID) w hich flourished in Poland in 1920-1940. After the 2nd W orld War CID begin to decline b u t other industrial districts, located fu rth e r away from the studied landslide, de

veloped, em itted harm ful air pollution to the atm os

phere from 1960 to 1990 and affected tree grow th in so uthern Poland (M alik et al. 2012). After 1990 environm entally friendly technologies were in tro duced and air pollution decreased.

6 Citation: Bu lletin o f G e o g rap h y . P h ysical G e o g ra p h y S eries 2 0 1 5 , 8 , h ttp ://d x .d o i.o rg /1 0 .1 5 1 5 /b g e o -2 0 1 5 -0 0 0 1

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T P a p cia k et al Precip itatio n a s a facto r trig g e rin g la n d slid e activity .

Fig. 1. A - location of the studied landslide in Poland and in the Carpathians; B - relief of the Kamień massif; C - relief of the studied land

slide with the location of sampled trees and their avg. reaction to landsliding in 1957-2012 (digital terrain model of the studied land

slide with contours each 1 m in m a.s.l.)

M ethod s of Study

Dendrochronological analysis of landslide activity

O n the studied slope 48 silver firs (Abies alba) were sam pled (Fig. 1C). We collected samples from trees w hich grow on or near landform s such as cracks, colluvial blocks, and the m ain scarp o f the landslide.

We also sam pled trees above the m ain scarp, on the hum m o cky slope, up to the m ountain ridge. A ddi

tionally 10 firs were sam pled on a reference slope.

We to o k two cores from each tree using a Press

ler borer: one from the upslope side and the sec

ond from the dow nslope side o f a stem. Cores were glued into w ooden stands and polished in o rder to reveal the w ood structure. T ree-ring w idths were m easured w ith 0.01 m m accuracy using the LinTAB m easuring system.

Citation: Bu lletin o f G e o g ra p h y P h ysical G e o g ra p h y S eries 2 0 1 5 , 8 , h ttp ://d x.d o i.o rg /1 Q .1 5 1 5 /b g e o -2 Q 1 5 -0 0 Q 1 7

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Cores from the upslope and dow nslope side of each stem were com pared (Fig. 2). A n eccentricity index and its annual variation were calculated (M a

lik, W istuba 2012; W istuba et al. 2013). Using ref

erence thresholds obtained on the reference slope (average level of eccentricity in 10 trees sam pled on a stable slope) we dated events of landslide activity.

Comparison

of the dendrochronological record

of landsliding and the precipitation record

To determ ine the role of precipitation as a trigger of landsliding on the studied slope we have used data from the precipitation posts in B arw inek (16.8 km SE of the studied landslide, 450 m a.s.l.) and K rem p

n a (3.7 k m SW, 380 m a.s.l.). These data sets were selected because the tw o stations have the longest

A n example of the application of the eccentricity in dex m eth o d in dating landsliding is show n in Fig

ure 2. The percentage of trees showing a reaction to landsliding was calculated for each year o f the stu d ied p erio d (1957-2012) as an indicator of general landslide activity of the studied slope.

m easurem ent periods (since 1956 in Barwinek) and the closest distance to the studied landslide (K rem p

na). D ata from other precipitation posts in Nowy Żm igród (7.3 k m N, 310 m a.s.l.), D ukla (11.7 k m E, 325 m a.s.l.) and W yszowatka (12.3 k m SW, 505 m a.s.l.) were also used for the p u rp o se o f co m par

ing the precipitation data and assessing their relia

bility. For all five posts a daily precipitation record was available for different periods (Barwinek: 1956

-2012, Krempna: 1975-2012, Nowy Żm igród: 1985-

Fig. 2. Transformation of tree-ring widths into eccentricity index and its yearly variation with dated landsliding events (an example of tree grow

ing on the studied landslide)

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T. P a p cia k et al Precip itatio n a s a facto r trig g e rin g la n d slid e activity .

-1994, Dukla: 1986-2012, Wyszowatka: 1981-2012, all data from the Institute o f M eteorology and W ater M anagem ent - N ational Research Institute).

The values o f the correlation coefficients between the data from all 5 posts in 1986-1989 (the only perio d fully covered in all posts) range from 0.67 to 0.86 (Table 1) and are all statistically significant.

The data set for the B arw inek post was incom plete w ith gaps for som e single m on th s in 1990-1995.

M issing data were supplem ented using the quotient stability m eth o d (P ru ch n ick i 1987; T uom envirta 2001) based on the data from the o th er four p re

cipitation posts, w ith priority for K rem pna, showing the highest correlation coefficient w ith Barwinek.

Table 1. Correlation coefficients for examined records of precipitation in 1986-1989 in five posts surrounding the studied landslide.

Precipitation post Barw inek Krempna Nowy Żmigród W yszowatka Dukla

B arw in ek x 0 .7 3 0 .67 0 .7 0 0 .6 8

Krempna 0 .73 x 0 .8 4 0 .8 6 0 .8 6

N ow y Żmigród 0 .67 0 .8 3 x 0 .72 0 .8 6

W yszo w atka 0 .7 0 0 .8 6 0 .72 x 0 .7 0

Dukla 0 .6 8 0 .8 6 0 .8 6 0 .7 0 x

The fact th a t precipitation records from posts su rro u n d in g the studied landslide are sim ilar and correlate well one w ith an o th er suggests th at two selected data sets from B arw inek and K rem pna can be used in fu rth e r analyses o f landsliding as reliable records, representative for the w hole area and for the studied landslide. It was found th a t particu lar precipitation events recorded w ith daily resolution at five studied posts are clearly overlapping (Fig. 3).

We have, however, analysed a detailed example of the daily precipitation record for the year 1987 at

all five posts and found som e differences between p a rtic u la r posts. The differences can result from the com plex spatial distribution o f precipitation in m o u n tain areas influenced by such local features as topography, elevation a.s.l., slope aspect and by the local range o f precipitation from singular storm units. Despite the above-m entioned we have found clear consistency o f precipitation records from five posts su rro un ding the studied landslide. This allows reliable com parison o f the dendrochronological re

cord o f landsliding w ith the precipitation record.

Fig. 3. Daily precipitation totals in 1987 at five precipitation posts surrounding the studied landslide

Results o f the dendrochronological analysis were com pared w ith precipitation totals for 1957-2012 in the case o f the B arw inek post and 1975-2012 in the

case o f Krem pna. We have analysed 3- 5-, 10- and 30-day cum ulative rolling totals o f precipitation and the n u m b er o f days w ith daily precipitation exceed

Citation: Bu lletin o f G e o g ra p h y P h ysical G e o g ra p h y S eries 2 0 1 5 , 8 , h ttp ://d x .d o i.o rg /1 0 .1 5 1 5 /b g e o -2 0 1 5 -0 0 0 1 9

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P recip itatio n a s a fa c to r trigg erin g la n d s lid e activity T .P a p d a k e t al.

ing 20 m m (Table 2). The analysis was conducted separately for the sum m er half-year (A pril-Septem ber: the vegetation p eriod w hen the annual tree ring is developed) and for the preceding w inter half-year (O ctober-M arch, the d o rm an t season preceding d e

velopm ent of the annual tree ring) since landsliding active at the end of the vegetation perio d and d uring the d o rm an t season can be recorded in the ring developed in the following year. To determ ine th e relatio n betw een p recip itatio n an d landsliding recorded in tree-ring eccentricity we have cal

culated the P earson correlation coefficient for the

dendrochronological record of landsliding and the following precipitation indicators for K rem pna and B arw inek posts:

• the highest daily, 3-, 5-, 10- and 30-day cu m u lated rolling precipitation totals d uring sum m er and preceding w inter half-years,

• precipitation totals for su m m er and preceding w inter half-years,

• annual precipitation totals,

• the n u m b er of days w ith daily precipitation ex

ceeding 20 m m du ring sum m er and preceding w inter half-years.

Table 2. Correlation coefficients for the activity of the studied landslide and precipitation data from Barwinek and Krempna posts: > 20 - num

ber of days with daily precipitation totals exceeding 20 mm; 3, 5, 10, 30 - maximum 3-, 5-, 10-, 30-day cumulative rolling precipita

tion totals; C - precipitation total for given period (preceding winter, summer); S - levels of statistical significance

Pearson correlation coefficients fo r particular types of precipitation data

Precipitation post Preceding w in te r half-year Sum m er half-year Year S

> 2 0 3 5 10 30 C > 2 0 3 5 10 30 C C

B arw in ek

1 9 5 7 -2 0 1 2 0.21 0 .0 6 0.11 0 .1 4 0 .0 6 0 .0 4 -0 .1 6 -0.1 2 -0 .1 4 -0 .1 3 -0 .1 8 -0.11 -0 .2 6 0 .2 6

B arw in ek

1 9 8 0 -2 0 1 2 0 .2 9 0 .1 0 0 .1 8 0 .2 3 0 .0 0 0 .0 7 -0 .0 8 -0.21 -0 .1 8 -0 .0 4 -0.1 2 -0 .1 3 -0.21 0 .3 4

Krem pna

1 9 7 5 -2 0 1 2 0.31 0 .2 4 0 .2 8 0 .2 6 0.01 0 .1 8 0 .0 4 -0 .1 7 -0 .2 3 -0.1 3 -0 .0 8 -0 .0 3 0 .2 0 0 .3 2

Krem pna

1 9 8 0 - 2 0 1 2 0.42 0.34 0.37 0.38 0 .0 9 0 .2 5 0 .1 4 -0.11 -0 .1 9 -0.0 7 -0 .0 7 0 .0 2 -0 .0 4 0 .3 4

b o ld - s t a t is t ic a lly s ig n if ic a n t c o rre la tio n s

We have checked the statistical significance for calculated correlation coefficients.

Previous studies have show n th at industrial air p o llu tio n strongly influenced tree grow th in P o land and the whole of Europe (e.g. Schweingruber et al. 1985; Elling et al. 2009). H igh em issions of harm fu l com pounds into the atm osphere resulted in significant reduction in tree-ring w idths (Danek 2007) (Fig. 2). Trees frequently form ed only single rows of cells instead of full grow th rings (M alik et al. 2012). Some studies suggest th at in the case of such narrow rings the reaction of trees to tilting can be supressed and grow th eccentricity m ay n o t be developed despite active landsliding (M alik et al. in press). Because in southern Poland industrial pollu

tio n resulted in particularly supressed grow th prior to the 1980s we have analysed tree rings developed after 1980 separately (Table 2).

R esu lts an d D iscu ssio n

Dendrochronological record of landsliding on the slope of the Kamień massif in 1957-2012

The highest average reaction o f trees to landsliding in 1957-2012 was observed in th e central p a rt of the studied slope, b u t sam pled trees also recorded som e landslide events in b o th the u p p er an d low er p a rt o f th e studied slope (Fig. 1C). The change in landslide activity over tim e was analysed as the percentage o f trees reacting to landsliding in the sam pled population in particular years of the stud ied period. The highest percentage o f trees show ing a reaction to landsliding was recorded in 1957, 1986 and 1987 (27% in each year). Significant lan d slide activity (> 24% of sam pled trees) was also re

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T P a p cia k et al Precip itatio n a s a facto r trig g e rin g la n d slid e activity .

corded in 1975, 1977, 1988 and 1996. Some weaker landslide events (> 15% o f sam pled trees) were also recorded in h alf o f the analysed years (Figs 4-6).

The results o btained suggest th a t the studied landslide was inactive an d stable in 1958-1959, 1964, 1967-1968, 1974, 1976, 1998, 2004, 2005 and 2011, as proven by the lack or low level o f a den-

drochro n o lo g ical reco rd o f eccen tricity in these years. The exam ined landslide shows high v aria

bility o f activity over tim e. N o longer p erio d s of active landsliding and stability were recorded. Sev

eral-year-long periods o f increased activity are sep

arated by s h o rt p erio d s w ith o u t any significant tree-ring record o f slope m ovem ent.

Fig. 4. Dendrochronological record of landsliding on the studied slope in 1957-2012 compared with various precipitation data from Barwinek and Krempna posts: A - landslide activity and maximum 10-day precipitation totals during preceding winter half-year; B - landslide ac

tivity and maximum 10-day precipitation totals during summer half-year; C - landslide activity and maximum 30-day precipitation totals during preceding winter half-year; D - landslide activity and maximum 30-day precipitation totals during summer half-year

Citation: Bu lletin o f G e o g ra p h y P h ysical G e o g ra p h y S eries 2 0 1 5 , 8 , h ttp ://d x.d o i.o rg /1 Q .1 5 1 5 /b g e o -2 Q 1 5 -0 0 Q 1 11

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P recip itatio n a s a facto r trig g e rin g la n d slid e a c tivity T P a p cia k et al

Fig. 5. Dendrochronological record of landsliding on the studied slope in 1957-2012 compared with various precipitation data from Barwinek and Krempna posts: A - landslide activity and precipitation totals during preceding winter half-year; B - landslide activity and precipi

tation totals during summer half-year

Fig. 6. Dendrochronological record of landsliding on the studied slope in 1957-2012 compared with various precipitation data from Barwinek and Krempna posts: A - landslide activity and number of days with daily precipitation totals > 20 mm during preceding winter half

year; B - landslide activity and number of days with daily precipitation totals > 20 mm during summer half-year

Comparison of tree reaction to landsliding on the studied slope of the Kamień massif and the precipitation record

M ost o f the analysed records o f precipitation do not show any statistical correlation w ith the course of the landslide process on the studied slope. There is

a slight correlation between the dendrochronological record o f landsliding and precipitation o f the preced

ing w inter half-years (O ctober-M arch) in K rem pna in 1980-2012. No correlation was found for the an

nual totals and precipitation o f sum m er half-years (Table 2, Fig. SB). Results suggest th at the activity of the landslide depends m ainly on the am o un t o f p re

cipitation d uring the previous winter. Also Ziętara

12 Citation: Bu lletin o f G eo g rap h y. P h ysical G e o g ra p h y S eries 2 0 1 5 , 8 , h ttp ://d x .d o i.o rg /1 0 .1 5 1 5 /b g e o -2 0 1 5 -0 0 0 1

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T .P a p cia k e t al P recip itatio n a s a fa c to r trig g erin g la n d s lid e a c tiv ity ,

(1968) suggests th at catastrophic landsliding is as

sociated w ith spring rather th an w ith sum m er p re

cipitation. Gorczyca (2QQ8) suggests th at factors and conditions triggering developm ent o f landslides are com plex including b o th spring thaws, spring and sum m er precipitation, long-term rainfalls and short, torrential dow npours. Also Starkel (2Q14) pointed ou t th a t landslides in 2QQ6 in the foothills o f the C arpathians and in the M oravian C arpathians m ay have been triggered by snow thaws.

The results obtained, w hich suggest the im p o r

tance of w inter precipitation in triggering landslide activity, are also com pliant w ith investigations by Gil et al. (2QQ9), w ho com pared data from incli

nom eters w ith am ounts of precipitation of sum m er and w inter in 2QQ7-2QQ9. Studies were conducted in the Beskid Niski Mts, w here the Kam ień m assif is also located. Gil et al. (2QQ9) found th at colluvial bodies of landslides were m oving m ainly during w inter half-years due to high rates o f precipitation in w inter and m elting of the snow cover.

Excluding data from before 198Q from the co rre

lation increased the values of correlation coefficients obtained, in the case of the 3-, 5- and 1Q-day p re

cipitation totals during preceding w inters in K rem p

n a even above the level of statistical significance (Table 2). Thus it seems th a t grow th suppression in the perio d of air pollution (Fig. 2) concealed the reaction of trees to landsliding - tree-rin g eccen

tricity was n o t as clear as later. A sim ilar p h en o m enon was observed by O pała and M endecki (2Q14) in a dendroclim atic study conducted for the Silesian Upland. They have also excluded the 196Q-198Q p e rio d from the analyses since the dendrochronological signal was m ainly a reflection of the atm osphere pollution changes and n o t clim atic changes (Opała, M endecki 2Q14).

The strongest events of landsliding and events of slope stability recorded in tree rings in the Kamień massif compared with precipitation data

Because of th e com plex n atu re of landslide trig gers and the lack of an unam biguous relation b e tw een landsliding events on the studied slope of the Kam ień m assif and the precipitation record we have analysed p recipitatio n con ditions in single years

w ith a particularly strong dendrochronological re cord of landslide activity.

In 1957 w hen 27% of sam pled trees recorded landsliding there were two relatively strong precipita

tion events (data from Barwinek post): at the begin

ning of M ay (c. 150 m m in 10 days) and in mid-July (c. 200 m m in 20 days). The sum m er half-year was hum id (90 m m above the 1957-2012 average), w here

as the precipitation o f the preceding w inter was aver

age (341 m m , 31 m m above the average). However on M ay 13th 1957 an earthquake occurred (Rączkowski 2007). The role of the 1957 earthquake in trigger

ing the landslide in Lipownica near Dukla (11 km E of the Kamień m assif) was described by Gerlach et al. (1958). By contrast, Gil and Długosz (2006) indi

cated that landsliding in 1957 w hen an earthquake took place could have been triggered by rainfall and snowfall exceeding average values and by an in ten sive thaw at the tu rn of April and May.

In 1977 landsliding was recorded by 26% of sam pled trees. A ccording to p recip itatio n d ata from B arw inek and K rem pna it was quite a d ry year.

P recipitation d u rin g th e su m m er half-year term did n o t exceed th e average values at b o th posts.

The previous w inter was, however, wet, w ith p re cipitation exceeding average values. The m axim um 30-day precipitation total was 143 m m in Barw inek and 149 m m in K rem pna (Fig. 4C), com pared to average values: 121 m m and 111 m m , respective

ly. Precipitation totals o f the preceding w inter half

year in 1977 were 442 m m (average 311 m m in the Barw inek post) and 366 m m (average 275 m m in th e K rem pna post) (Fig. 5A). H igh p recip ita

tion am ounts were also recorded in previous years.

In 1975, w h en landslide activity was slightly low er (reaction of 24% o f sam pled trees) precipitation rates were the highest d urin g the whole perio d of 1957-2012 (Figs 4 -6 ). Total precipitation one year earlier, in 1974, reached 1382.7 m m , 296.2 m m of w hich occurred during 30 consecutive days in su m m er (rainfall total of July: 282.2 m m ). There were 11 days w ith daily precipitation exceeding 20 m m (com pare w ith 6.6 on avg.) d u ring the 1974 su m m er half year and 7 such days d urin g the 1974/75 w inter h alf year (1.1 on avg.) (Fig. 6). The precipi

tation total of the 1974/75 w inter half-year was 555 m m (with 310 m m on avg.) w ith m axim um 10- and 30-day precipitation totals also twice as high as av

erage values (Fig. 4). The landslide activity dated to

Citation: B u lletin o f G e o g rap h y . P h ysical G e o g ra p h y S eries 2 0 1 5 , 8 , h ttp ://d x .d o i.o rg /1 0 .1 5 1 5 /b g e o -2 0 1 5 -0 0 0 1 13

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1975 has, therefore, a substantiated background of extrem e precipitation in July 1974 an d a very h u m id preceding w inter term . We assum e th at the de

bris m antle and b ed ro ck were oversaturated w ith water for m any m onths, w hich resulted in intensi

fied landsliding in 1975. The long-lasting increased precipitation rates in the subsequent years explain landslide activity recorded in 1977. Also som e p re vious studies indicate the com plicated n atu re of precipitation as a factor triggering landslide activi

ty, due to its tem poral and spatial variability and its com plex effect on g ro u n d w ater level (Gil, Slupik 1972; Starkel 1976, 2011).

A sim ilar longer landslide event to o k place in the years 1986-1988 w hen 26-27% o f trees showed a reaction to landsliding. This perio d was charac

terised by average annual precipitation totals, low precipitation totals o f sum m er half years in relation to the average value as well as increased precipita

tio n d urin g previous w inter half-years. Landsliding was also preceded by high am ounts of precipitation in the sum m er of 1985. Thus, probably sim ilarly to 1975, the w et p eriod started d uring the preceding sum m er. Since 1980 the correlation coefficient b e

tw een dendrochronologically recorded landsliding and m axim um 3-, 5-, 10-day precipitation totals in K rem pna is statistically im p o rtan t (Table 2). There

fore, it seems th a t in the discussed years 1986-88 th e precipitation from the preceding w inter could have been the m ain triggering factor for landslide activity. The 10-day precipitation totals of preceding w inters were increased for the w hole 1986-88 p e

riod, reaching 82.6 m m in 1986 in K rem pna, and 91.9 m m in 1988 in Barw inek. W in ter half-year precipitation totals reached 302.6 m m in 1987 and 396.4 m m in 1988 in Krem pna.

In 1996 w hen 24% of sampled trees recorded landsliding high precipitation occurred in July (m onthly total: > 150 m m ) and Septem ber (> 200 m m ), and the m axim um daily rainfall total reached 78 m m . There is no p roof th at the landslide event can be connect

ed to precipitation of the preceding winter, which, according to gathered data from K rem pna and Bar

winek, was at the average level or below it (Fig. 5A).

It seems th at landslide activity in 1996 resulted m ain ly from increased sum m er precipitation.

The year 2010 was ex traordinarily w et in the w hole of the W estern C arpathians. The tree-rin g record of landsliding on the studied slope in 2010

is strong. 26% o f sam pled trees showed a reaction to slope m ovem ents then. A very high am o u n t of precipitation during the sum m er half-year occurred along w ith som e events o f long-term dow npours in M ay-June (100-150 m m each). Heavy precipitation occurred also in the second half o f June. The preced

ing 2009-2010 w inter was also distinctly wet. Very high sh o rt-term precipitation totals and num erous days w ith daily precipitation exceeding 20 m m were recorded b o th during the sum m er in 2010 and the previous w inter season (Fig. 6); also the m axim um 10-day precipitation totals significantly exceeded the average value (Fig. 4A, B).

Also the periods of slope stability dated by means of dendrochronology were com pared with the precip

itation record. After the landsliding event in 1957, in 1958-1959 the tree-ring data obtained suggest that the studied slope was stable (only 6-9% of sampled trees recorded slope instability). The period was character

ised by average precipitation, both during the sum m er and the preceding w inter half-years. Analysed indicators of precipitation were lower th an the aver

age; only the longer-term totals were slightly higher (Figs 4 -6). The lack of strong precipitation probably resulted in stabilisation of the studied landslide.

The studied slope of the Kam ień m assif was also stable in 1967-68 (only 3-8% of sam pled trees re corded landsliding) and 1973-1974 (0-5% ). The first of th e above-m entioned periods was relatively wet, b o th in term s o f the w inter and sum m er half-year precipitation. Still, the preceding years w hen the landslide was highly active were even m ore h u m id. In 1974 extrem ely high precipitation occurred in the su m m er (Fig. 4B, D). Precipitation of the su m m er half-year reached 813 m m (com pared to 562 m m on avg.) (Fig. 5B). Despite such high p re

cipitation am ounts in su m m er the d en dro chrono - logical record of landsliding in 1974 is p o o r (5% of sam pled trees show a reaction to slope instability).

This m ay result from very po o r precipitation of the w inter half-years d uring the p erio d (265.4 m m for the w inter preceding 1973 and 243.5 m m for 1974).

In the 1980s and 1990s there was a significant in crease in the activity of the studied landslide. In the p eriod n o long-term , distinct stability o f the slope was recorded. O nly in 1998 was the reaction of the trees p oor (4% of sam pled trees recorded landsliding). In this year precipitation b o th in sum m er and preceding w inter half-years was average (Figs 4

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T .P a p cia k e t al P recip itatio n a s a fa c to r trig g erin g la n d s lid e a c tiv ity ,

and 5). In the Beskid Niski Mts, opposite to areas of the C arpathian m o untain belt located m ore to the west, the year 1997 was also d ry (annual precipita

tion total lower th an avg. by 170 m m in Barwinek and 80 m m in K rem pna). In 1997 landsliding on the studied slope was recorded only by 4 trees (9%

o f th e sam pled population). Similarly in 2004 and 2005 landslide activity was low (6% of trees recorded landslides). These were hum id years, w ith a p articu larly high share of the sum m er term precipitation, b u t also w ith particularly low 10-day precipitation totals during w inter half-years (Fig. 4A). Also tree- ring data obtained for the year 2011 indicate slope stability in the period (7% of sam pled trees showing a reaction to landsliding). The reason is probably the fact that the 2010/2011 w inter season was particular

ly d ry (Fig. 5). The analysis suggests that the stability periods of the exam ined landslide body are related to the relatively low precipitation, especially during the preceding w inter term . Still, we cannot exclude that, for example in 2011, the studied landslide was inactive since all the available m aterial had already been dislocated during the strong event in 2010.

C o n clu sio n s

a) The studied landslide in the K am ień m assif is contem porarily active show ing high frequency of small-scale m ovem ents of colluvia. In 1957

-2012 m ovem ents of the landslide bo dy occurred alm ost every year b u t w ith different strength. In particular years landsliding occurred in different parts of the studied slope. Increased landslide ac

tivity was recorded in tree rings in 1957, 1975, 1977, 1986-1988 and 1996.

b) N either the im portance of high precipitation to tals during the whole sum m er half-year n o r in tensive short term precipitation occurring during the sum m er appeared to be significant as factors triggering slope instability in the K am ień m as

sif. Still, in the case of several landslide events th ey have probably played some role (e.g. 1957, 1996, 2010). Precipitation o f the preceding w in ter half-year seems to be the m ost im p o rtan t fac

to r in triggering landslide activity on the study slope, despite the fact th a t the precipitation to tals of w inter seasons are generally lower th an

during sum m er. D uring w inter seasons reduced evaporation, w ater reten tion in snow cover and m id-w inter and spring thaw s cause saturation of bedro ck w ith water, w hich becom es m ore su s

ceptible to landsliding.

c) The n atu re of th e relatio n betw een p recip ita

tio n and landsliding is com plex. The strongest landsliding on the studied slope resulted from sequences of w et sum m er, w et w inter and once again w et su m m er half-years directly follow ing one another. L o ng -term satu ratio n of the g ro un d w ith w ater (lasting several m onths) can decrease the threshold of precipitation necessary for finally triggering landslide activity. Therefore long-term rainfalls are im p o rtan t as factors p re

paring a slope for landslide events. The analysis additionally suggests th at also earthquakes m ay have b een a factor triggering the instability of the studied slope.

d) Analysis of th e relations betw een the d end ro - chronological record of landsliding and precipi

tatio n occurrence have revealed som e difficulties associated w ith the annual record of eccentricity.

We have found large reductions in rin g w idths caused by h arm fu l air p ollution in 1960-1985.

Strong re d u c tio n s overlap eccen tric gro w th caused by landsliding. This m ay lim it th e p o s

sibility of dating landslide activity from dendrochronological records.

Acknowledgem ents. Studies c o n d u c te d in the K am ień m assif in the Beskid Niski M ts were sup p o rte d by th e P olish N atio n al Science C en tre th ro u g h grant no. 2011/01/B/ST10/07096.

D ata for the digital terrain m odel for the area of the M agura N ational Park were gathered in the p ro je c t no. P 0 IS .05 .03 .0 0.0 0-27 6/10 “D e v elo p ing a plan of conservation for the M agura Refuge 180001 and the plan o f conservation of the M agura N ational Park” co-funded by th e European U nion th ro u g h the European Regional D evelopm ent Fund.

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Manuscript received 2 February 2015, revised and accepted 16 April 2015