COMPARISON OF MORPHOMETRIC ASPECTS OF DOLINES BETWEEN TWO ZONES IN BERICI HILLS (VICENZA, ITALY) PRIMERJAVA MORFOLOGIJE VRTAČ IZ DVEH DELOV GRIČEVJA BERICI (VICENZA, ITALIJA) BENEDETTA CASTIGLIONI Izvleček UDK 551.435.83(450.343) Benedetta Castiglioni: Primerjava morfologije vrtač iz dveh delov gričevja Berici (Vicenza, Italija) Gričevje Berici so skupina planotastih gričev nad benečijsko ravnino; na planoti so vrtače, zaradi katerih ima pokrajina svojstven značaj. Opisana sta dva različna dela gričevja in narejena je medsebojna primeJjava morfologije vrtač. Avtorica nekatere razlike posebej poudarja in podaja iiipotezo o vzrokih teh razlik. Ključne besede: morfometrija vrtač, nastaiiek vrtač, kraška planota, kraško površje, Italija, gričevje Berici Abstract UDC 551.435.83(450.343) Benedetta Castiglioni: Comparison of morphometric aspects of dolines between two zones in Berici Hills (Vicenza, Italy) The Berici Hills are a limestone hilly group rising with plateau features above the Venetian plane; on the top of the plateau many dolines have developed, giving peculiar characters to the landscape. Two different parts of the Berici Hills have been considered, to describe and compare morphometric aspects of their dolines. Some differences between the two zones have been identified and some hypotheses about their cause are given. Key words: morphometry of dolines, evolution of dolines, karst plateau, karst landscape, Italy, Berici Hills Address - Naslov Benedetta Castiglioni Dipartimento di Geografia dell'Universita di Padova Via del Santo 26 I - 35123 Padova Italy introduction The Berici Hills are situated in the Venetian plain, south of the town of Vicenza, in the north-east of Italy. This group is mostly formed by Eocene and Oligocene limestones (marly hmestone in the west, pure and sometime massive limestone in the east); it appears like a table-land, unitary in some parts, cut into by large valleys in others. It has very steep slopes on the eastern side, while on the western it degrades more gently to the plain. Karst morphogenesis is active on the plateau surface, and the most frequent karst form we meet is the doline. Therefore dolines represent a very important element to determine the typical characters of Berici Hills landscape; dolines are an expression both of natural environmental aspects and also of changes of human land use and impact. Since the doline bottom is always filled by sediments (terra rossa), perhaps several tens of metres deep, it is the best place of the plateau for farming. So in the landscape we can note many scattered farmhouses, each in front of one doline; in the bottom there is cultivation or meadow, while the slopes are covered by wood. The north slope, that is exposed to the south and has better microclimatic conditions, is often used for cultivation too, with terraces supported by dry stone walls. data collection The aim of this research is to compare the features of dolines in two different parts of Berici Hills with the help of statistical analysis. So I considered two zones of the plateau: the first (Fig. 1) is a lengthened and narrow ridge in the northern part (I called it "north zone"), while the second (Fig. 2) is a piece of the south-western table-land (I called it "south zone"). I observed all the dolines included in the two zones (34 in the north zone, 63 in the south zone), and I collected morphometric data with the help of the topographic map on the scale 1:5000. I considered on one hand the real doline by the isohypse that passes through the lowest rim, and on the other hand the catchment-basin pertaining to the doline. Therefore I studied in particular the following variables: - position: UTM coordinates of the lowest point of the doline, bottom altitude - doline dimensions: longest axis length, perpendicular axis length, area, lowest depth (the difference between the rim altitude and the bottom altitude) - basin dimensions: longest axis length, area, highest depth (the difference between the altitude of the highest point of the basin and the bottom altitude) - distance from the nearest doline (between the lowest points). I compiled two tables, one for each zone, with all the data collected (tab. 1 and tab. 2). data processing The first observation is about the distribution of dolines: while in the south zone dolines' catchment-basins cover completely the plateau, in the north zone they take up only the 33% of the surface. The remaining 67% of the north zone belongs to catchment-basins connected with the hydrographic network of the slopes; some suspended dry valleys are present too. Moreover, most of dolines of the north zone are situated at an altitude between 200m and 300m, while the south zone is at a lower altitude, between lOOm and 160m. Looking at the frequency distribution histograms it is possible to make some remarks. First of all it is possible to note that dolines are generally medium-small, but they are smaller in the north zone (Fig. 3); the average values for the variable "longest axis length" are 75m in the north, 104m in the south. It can be also noted that there are some wider dolines (perhaps uvalas), expecially in the south (Fig. 4). Regarding (Fig. 5) the depth of the doline (lowest depth), there are no big differences between south and north zone; in both zones dolines are not very deep, with values that go from 0,3m to 12,5m in the northern sample, and from 0,4m to 14,9m in the southern one. On the other side, catchment-basins are quite wide, and their dimensions are similar in the two zones; rather, there are bigger values for "highest depth" in the north zone (Fig. 6 and Fig. 7) At the end, looking at the variable "distance", we note that in the south zone dolines are closer each other than in the north one; the average values are 102m south, 158m north. The second part of the statistical anlysis consists of the correlation of the variables (with the principal components analysis), and the comparison of the results of the two zones. It can be noted that in both zones there is a strong link between the variables "dohne longest axis length" and "doline area" (correlation coeffi- cient: 0,95 north; 0,94 south) (Fig. 8) and quite a good correlation also with "perpendicular axis length". It means that the doline shape is quite regular, nearly round, and that there are not many dolines with lengthened or different shapes. On the contrary, doline depth is not strongly correlated with doline dimensions, especially in the south zone: wide dolines are not really correspondingly deep (Fig. 9). There is good correlation between doline dimensions and basin dimensions in the south zone, in particular between "doline area" and "basin area"; correlation is worse in the north zone (Fig. 10): it means that it is not always true here that a large basin pertains to a large doline and vice versa. Also the variable "distance" is differently correlated in the two zones (Fig. 11). South there is quite good correlation with doline dimensions and less good with basin dimensions; therefore smaller dolines are nearer each other. On the contrary, north there is no correlation between the distance among dolines and dimensions, and it is principally because the area is not completely covered by dolines. conclusions We have seen that there are some differences in doline shape and development between north and south zone. It is possible to try to understand on what these differences can depend. Probably we have to research the cause principally in the different lithology of the two zones: marly limestone south, back-reef limestone north. Moreover the different kind of relief landforms (plateau or ridge) can contribute to the doline characters in the two zones too. Actually, the results of measurements allow us to say that probably doline development is more difficult in the north zone, because on a ridge more dolines are situated on the plateau edge, opened toward the plateau escarpment. So there are smaller dolines with bigger, highest depth, on this ridge, where we found higher relief energy than in the south zone. It could be possible to study in depth the reciprocal interactions between slope and doline development, between karst and, broadly speaking, fluvial morphogenesis. Many other conditions that are involved in karst evolution are very similar in the two zones (for instance altitude, climate conditions, length of time of karst morphogenesis), so they cannot be determining factors for the identified differences. references ALBERTINI R. (1952) - Cenni geomorfologici sui Colli Berici. Rivista Geografica Italiana, 59, pp. 93-116, Firenze. LORENZONI G.G. (1988) - La natura. In AA.VV."I Colli Berici - natura e civilta", Signum Edizioni. MIETTO P. (1988) - Aspetti geologici dei Monti Berici. In AA.VV. "I Colli Berici - natura e civilta", Signum Edizioni. MIETTO P. (1988) - Carsismo e speleologia nei Monti Berici. In AA.VV. "I Colli Berici - natura e civilta", Signum Edizioni. MIETTO E, SAURO U. - Grotte del Veneto. Regione Veneto, La Grafica Editrice. BONDESAN A., MENEGHEL M., SAURO U. (1992) - Morphometric analysis of dolines. International Journal of Speleology, vol. 21 (1-4) pp. 1-55, Trieste. long. lat. bottom alt. rim alt. high. p. alt. dol.axis basin axis dol.area bas.area low.depth high.depth parp.axis distance || 1 9787 3609 319.70 320,00 368;50 45 280 1119,78 12800,00 ,30 38,80 35 165 ({ 2 9795 3623 312,50 317,50 344,40 100 180 4956,88 20690,69 5,00 31,90 65 145 3 9786 3635 311,40 317,50 327,70 75 220 3032,40 12628,96 6,10 16,30 57 145 II 4 9815 3642 291,50 30250 330,00 215 305 13086,91 40497^0 11,00 38,50 85 267 5 9603 3666 281,20 282,00 324,50 40 330 1131,06 44706,15 ,80 43,30 33 232 6 9761 3669 272,80 285,30 325,00 175 455 15289,06 90237,55 12,50 52,20 125 203 7 9776 3689 280,00 284,00 317,50 90 240 3428,45 31145,95 4,00 37,50 55 195 8 9773 3708 283,50 284,00 317,50 65 250 1397,57 40744,30 ,50 34,00 30 130 9 9782 3717 267,60 272,00 31550 62 245 2171,45 22636,50 4,40 47,60 50 130 1 10 9793 3729 254.50 257.50 315Ž0 50 1637,84 28747,40 3,00 60,70 40 ^ 11 9799 3736 246,30 247,50 270,00 50 190 1379,84 15431^5 1,20 23,70 37 95 12 9787 3737 262,00 263,00 285,00 65 180 2215,81 15216,69 1,00 23,00 42 100 13 9750 3731 284,50 287,00 31520 80 280 4095,01 31105,60 2,50 30,70 70 150 14 9753 3747 290,60 292,50 306,07 40 100 706,57 4713,90 1,90 15,47 25 120 15 9775 3745 269,20 271,50 310,00 85 320 2501,40 37418,20 2,30 40,80 37 135 16 9761 3755 280,50 281,00 302,00 50 125 1796,60 9207,07 ,50 21,50 40 83 17 9754 3759 277,20 287,50 301,00 57 130 2080,07 6586,90 10,30 23,80 45 83 18 9783 3755 253,40 257,50 280,00 50 190 1852,93 14983,66 4,10 26,60 43 95 19 9788 3764 238,20 242,50 266,00 80 190 3378,91 16199,09 4,30 27,80 55 95 20 9731 3762 265,00 277,50 300,00 115 240 5549,36 18736,76 12,50 35,00 60 165 21 9751 3769 269.60 272,50 290,00 50 125 1641,69 9969,50 2,90 20,40 43 107 22 9744 3778 253,50 257,50 285,00 75 165 2686.15 11758,12 4.00 31,50 50 90 23 9735 3776 246,20 252,50 306,70 120 465 6457,18 55738,77 6,30 60,50 65 90 24 9758 3787 249.80 252,00 285.00 85 220 3318,15 21351,93 2,20 35,20 55 170 25 9744 3798 238,80 241,50 280,00 65 265 3035.54 22837,84 2,70 41,20 55 180 26 9698 3803 219,90 221,50 263,10 60 285 2266,51 18674,15 1,60 43,20 50 110 27 9710 3802 224.00 227,50 263.10 75 265 3504,63 17231,68 3,50 39,10 65 80 28 9716 3808 218,50 221,10 250,00 75 210 3368,83 9088,12 2,60 31,50 65 80 29 9763 3814 222,80 224,00 266,20 42 315 1267,56 48110,02 1,20 43,40 35 90 30 9766 3823 213,50 217,50 254,00 70 300 2279,95 2698630 4,00 40,50 40 90 31 9752 3833 202,00 207,00 225,50 65 150 2443,35 12432,82 5,00 23,50 40 170 "32 9758 3876 156,00 159,00 207,60 57 375 1709,48 46386^0 3,00 51,60 40 435 33 9828 3899 144,20 144,50 164,20 80 185 3314,88 16700,07 ,30 20,00 50 435 34 9816 3941 105,90 106,50 111,60 40 115 996,84 6452,57 ,60 5,70 30 435 Tab. 1 - Collected data for north zone long. lat. bollom all. j rim alt. high.p.alt. dot.axis basin axis dol.area bas.area !ow.dei3lh high.depth peip.axis distance 1 9129 2710 129,8 136,5 164,1 93 270 4967 17986 6,7 34,3 70 92 2 9133 2713 137.0 139,0 148.8 60 160 2069 10274 2,0 11,8 47 85 3 9141 2714 136,2 143,0 164,1 95 275 5869 20409 6,8 27,9 80 85 4 9150 2704 147,3 147,9 164.1 50 225 1251 14877 ,6 16,8 33 95 5 9159 2703 146,5 146,9 164.1 55 300 1286 15704 ,4 17,6 30 70 6 9160 2696 142.3 146,9 164.1 90 350 4946 36936 4,6 21.8 75 70 7 9180 2664 125,8 132,5 172,0 135 530 9890 78744 6,7 46.2 105 140 8 9109 2800 140,5 146,5 166,0 170 410 12390 39578 6,0 2S.5 100 100 9 9100 2798 144,0 146,5 159,4 72 350 3119 14706 2,5 15.4 55 100 10 9083 2798 137,7 142,0 159,4 95 260 5976 24780 4.3 21,7 80 120 11 9075 2792 134,6 138,0 152,1 85 280 4252 14591 3,4 17.5 65 85 12 9067 2791 134,1 138,0 151,0 70 200 3640 11186 3,9 16.9 65 85 13 9067 2776 125.4 132,5 141,0 92 205 6128 18838 7,1 15,6 85 65 14 9056 2775 130.0 132,5 136,7 60 130 1997 7160 2,5 6.7 45 65 15 9077 2782 132.0 133,0 141,0 50 225 1452 9779 1.0 9.0 40 90 16 9183 2776 153.2 162,0 170,0 160 260 12800 28172 8.8 16.8 100 90 17 9196 2762 157,0 164,0 172.0 85 200 5359 17203 7,0 15.0 80 115 IB 9204 2752 162,8 168,0 175,9 67 135 3145 10023 5,2 13.1 62 65 19 9192 2750 151,6 162,5 170,0 125 165 9111 14023 10,9 18,4 95 95 20 9177 2754 151.0 158,5 170,0 165 240 12460 28751 7,5 19,0 110 152 21 9175 2769 156,9 159,5 170,0 90 200 3106 9621 2,6 13,1 40 85 22 9170 2776 160,7 162,5 171,0 70 150 2699 12072 1,8 10,3 50 85 23 9160 2762 147.0 155,1 174,2 150 420 10980 46168 8,1 27,2 115 162 24 9146 2755 139,0 143,0 174,2 240 430 9062 64571 4,0 35,2 57 162 25 9132 2764 140,4 143,0 174,2 140 380 7398 45475 2,6 33,8 68 105 26 9124 2782 146,4 151.0 171,3 175 300 12950 45233 4,6 24,9 110 115 27 9121 2766 143,5 147.0 155,5 60 140 2011 7648 3,5 12,0 45 105 28 9104 2755 127,8 138.0 155,5 160 350 12810 45421 10,2 27,7 110 130 29 9093 2763 124,4 135,3 150,0 125 270 11190 28633 10,9 25,6 115 130 30 9091 2780 128,7 129,5 157,1 110 280 4421 42114 ,6 28,4 50 62 31 9085 2784 124,7 129,5 152,0 80 270 4404 25029 4,8 27,3 70 62 32 9075 2765 124,5 128.0 142,5 55 250 1960 19554 3,5 18,0 40 90 33 9067 2767 124,5 128.0 140.0 50 160 1804 8308 3,5 15,5 45 90 34 9064 2759 122,3 127.4 140,0 240 340 18350 46939 5,1 17,7 95 92 36 9045 2756 116,6 119.0 136,7 80 250 3669 26036 2,4 20,1 62 58 36 9039 2755 117,0 119,0 126,5 60 210 1942 13517 2,0 9,5 43 58 37 9041 2769 122,8 128,0 136,7 65 180 3086 14877 5,2 13,9 60 112 38 9035 2764 116,1 122,5 135,6 105 230 7297 17343 6,4 19,5 92 100 39 9036 2776 129,3 132,0 136,0 60 120 2143 6800 2,7 6,7 50 73 40 9028 2776 124,9 127,0 145,8 75 285 3436 20640 2,1 20,9 60 73 41 9024 2762 116,9 117.8 145,8 50 370 1075 18797 ,9 28,9 30 95 42 9020 2753 111,1 114.5 124,3 70 225 2676 13733 3.4 13,2 55 100 43 9012 2759 109,7 111.5 145,8 80 470 3412 33091 1.8 36,1 63 100 44 9001 2760 105,4 106.5 137,0 48 300 704 16982 1.1 31,6 20 80 45 9072 2740 124,6 133,5 140,0 110 240 8662 19887 8.9 15,4 110 155 46 SOQO 2736 117.0 131,9 144.7 190 290 19218 43446 14,9 27,7 130 170 47 9113 2742 134,0 141,0 146,0 115 190 8173 14962 7,0 12,0 95 155 48 9130 2745 132,1 140,8 158,6 220 330 20366 58508 8,7 26,5 120 170 49 9086 2740 156,6 163,9 173,9 140 260 7028 24169 7,3 17,3 70 105 50 9201 2747 157,9 163,0 183,2 90 310 2742 17182 5.1 25,3 45 65 51 9196 2731 162,2 164,5 181,1 65 170 2497 13711 2.3 18,9 55 70 52 9200 2726 164,0 166,5 183,2 65 200 2942 15231 2.5 19,2 57 70 63 9193 2711 157.0 164,8 173,9 85 200 4189 17618 7.8 16,9 67 145 54 9177 2714 150.6 155,5 173,9 100 275 5833 33311 4.9 23,3 85 97 55 9176 2705 156.3 160,5 173,4 70 150 3637 13531 4.2 17,1 65 97 56 9166 2717 141.1 144,5 170,0 65 270 2868 17862 3.4 28,9 60 65 5/ 9161 2722 139.2 144,5 160,0 80 200 4259 17455 5.3 20,8 65 65 58 9165 2730 144,3 148,0 171,0 95 230 3947 24817 3.7 26,7 55 95 59 9154 2736 145,3 148.0 159,8 60 160 1635 13189 2.7 14,5 35 125 60 9139 2727 135,2 140,8 159,8 160 320 9035 35635 5,6 24,6 80 102 61 9111 2721 119,8 131,9 164,1 340 650 27540 104375 12,1 44,3 130 195 62 9092 2717 123,5 132,5 141,2 90 170 5076 17357 9,0 17,7 75 140 63 9072 2723 116,5 127,0 138,2 140 260 11720 27429 10,5 21,7 105 140 Tab. 2 - Collected data for south zone 30 - 25 - 20 - T-1 25 50 75 100 125 150 175 200 225 250 275 doline longest axis NORTH 30 - 25 - 20 -t 15 H v FM 10 H 5 - O 1-'T—'---T-T—--—r--T—---1 25 50 75 100 125 150 175 200 225 250 275 doline longest axis SOUTH l; 16 -14 1 12 - I 10- £ V p. J 6 -4 -2 - 0 I ■ .......... 2000 4000 6000 8000 10000 12000 14000 16000 doline area NORTH 10 - 9 •: 8 -7 6 ^ 5 : 4 - 3 -2 1 -0 I ■ ■ ' I 0 2000 4000 6000 8000 10000 12000 14000 16000 doline area SOUTH 20 1 18 -16 -14 -12 - I I 10 H fi 8 H 6 -4 -2 -0 -2 4 6 g 10 lowest depth NORTH 16 / / \ \ 4 6 8 10 12 14 16 lowest depth SOUTH \ \ \ \ 200 300 400 500 600 basin longest axis NORTH ■ I 700 800 \ Nl 200 300 400 500 600 basin longest axis SOUTH I ' ■■■' I 700 800 20 18 16 14 12 1 10 8 6 4 2 0 10 20 30 40 50 60 70 highest depth NORTH I / \ 10 20 30 40 50 60 70 highest depth SOUTH I ^ 10000 o ^ 8000 £ TO 0) 6000 C 2000 - 40 60 80 doline longest axis NORTH 1——1—I—r 100 120 140 160 180 200 220 30000 - 25000 - 100 150 200 doline longest axis SOUTH 300 350 100 120 doline longest axis NORTH 50 100 150 200 doline longest axis SOUTH 350 X H cc o z CO £ (D C "to (C 2000 4000 6000 8000 10000 12000 14000 16000 doline area NORTH ID O W P ro c 120000 100000 80000 60000 40000 20000 -r ' ■ ■ ' I ■ ' ' ' I.....• 5000 10000 15000 20000 25000 30000 doline area SOUTH 60 80 100 doline longest axis NORTH doline longest axis SOUTH primerjava morfologije vrtač iz dveh delov gričevja berici (vicenza, italija) Povzetek Oblika vrtač kaže določene razlike med severnim in južnim delom gričevja Berici. Glavni vzrok je najbrž v različni litološki sestavi: lapornati apnenci na jugu, grebenski apnenci na severu. Razen tega so tudi različne reliefne oblike (planota ali sleme) tiste, ki so prispevale k različnemu značaju vrtač. Rezultati meritev opravičujejo domnevo, da je severna cona bolj neugodna za nastanek vrtač, saj je na območju slemena več vrtač na robu planote odprtih proti pobočjem. Na slemenu je tako več manjših, a globokih vrtač, saj je tod večja reliefna energija, kot v južni coni. Dobro bi bilo poglobljeno preučiti medsebojni vpliv med razvojem pobočij in razvojem vrtač, med kraško in rečno morfogenezo v širšem smislu. Več drugih okoliščin, pomembnih za razvoj krasa, je v obeh conah zelo podobnih (nadmorska višina, klimatske razmere, trajanje kraške morfogeneze), tako da ne morejo biti odločilni dejavniki za navedene razlike.