A MORPHOMETRIC ANALYSIS USING GIS TO DEDUCE GEOMORPHOLOGICAL PROCESSES - NATURAL HAZARDS, AT ISLAND

Gournelos Th.*, Evelpidou N.**, Vassilopoulos A.**

*University of Athens – Department of Geology, Geography & Climatology Sector Panepistimiopolis, Zografou, 157-84 ***University of Athens – Department of Geology, Geography & Climatology Sector, Remote Sensing Laboratory, Panepistimiopolis, Zografou, 157-84

ABSTRACT

In order to understand the geomorphic processes on the island of Zakynthos, we made an altimetric and slope analysis in GIS environment. The spatial distribution of these variables reflects tectonic, erosional processes and vegetational distribution. The existance of environmental alteration is mainly due to natural processes and human impact. In the first factor we included mass movements, soil and coastal erosion and flood events caused by the increased erosion due to the local fires, while in the second tourism growth, wastes, mining, etc. Such analysis can be used in local and regional level to develop long term environmental policies and prevent landscape deterioration.

ΜΟΡΦΟΜΕΤΡΙΚΗ ΑΝΑΛΥΣΗ ΜΕ ΧΡΗΣΗ GIS ΓΙΑ ΤΗ ΜΕΛΕΤΗ ΓΕΩΜΟΡΦΟΛΟΓΙΚΩΝ ∆ΙΕΡΓΑΣΙΩΝ - ΦΥΣΙΚΩΝ ΚΑΤΑΣΤΡΟΦΩΝ ΣΤΗ ΝΗΣΟ ΖΑΚΥΝΘΟ

Γκουρνέλλος Θ.*, Ευελπίδου Ν.**, Βασιλόπουλος Α.**

*Πανεπιστήµιο Αθηνών – Τµήµα Γεωλογίας, Τοµέας Γεωγραφίας & Κλιµατολογίας Πανεπιστηµιόπολη, Ζωγράφου, 157-84 *** Πανεπιστήµιο Αθηνών – Τµήµα Γεωλογίας, Τοµέας Γεωγραφίας & Κλιµατολογίας, Εργαστήριο Τηλεανίχνευσης, Πανεπιστηµιόπολη, Ζωγράφου, 157-84

ΠΕΡΙΛΗΨΗ

Με στόχο την κατανόηση των γεωµορφολογικών διεργασιών στη νήσο Ζάκυνθο, πραγµατοποιήσαµε ανάλυση υψοµέτρων και κλίσεων µε τη χρήση GIS. Η χωρική κατανοµή αυτών των µεταβλητών αντανακλά τις τεκτονικές και διαβρωσιγενείς διεργασίες, καθώς και την κατανοµή της βλάστησης. Η ύπαρξη περιβαλλοντικών εναλλαγών οφείλεται κυρίως στις φυσικές διεργασίες και στις ανθρωπογενείς επιδράσεις. Τέτοιου είδους αναλύσεις µπορεί να χρησιµοποιηθούν σε τοπικό και περιφερειακό επίπεδο για την ανάπτυξη πολιτικής περιβάλλοντος. Introduction

The island of Zakynthos is characterized by two “isopic zones” the Pre-Apulian and the Ionian zone (Aubouin, J., Dercourt, J., 1962) and post Alpine deposits (Horstmann, G., 1967, Mirkou, R.M., 1974, Sorel, D., 1976, Dermitzakis, M., et al, 1977, Dermitzakis, M., 1977, Underhill, J., 1989). Muller-Miny (1965) made the first geomorphological observations of the island of Zakynthos. The structure of the island and the distribution of the different lithologies (limestones, marls, evaporitic rocks, allouvials), the climate conditions, determinate the geomorphology of this island. The main geomorphological units in the island of Zakynthos are a) the Vrachionas mountain in the western part, b) the intermediate unit from Alikes to , c) the Skopos mountain in the southeastern part of the island. The aim of this paper is to deduce geomorphological processes and natural hazards using morphometric analysis.

Methodology

The first step in this work was the collection of the data concerning topography, (scale 1:50.000, Geographical Military Service), geology (1:50.000, Institute of Geology and Mineral Exploration) and information from fieldwork relative to vegetation distribution and the occurrence of natural hazards. The second step was the conversion of primary data in digital format and the creation of the corresponding databases. The third step was the analysis of these data. This step includes the slope calculation in the whole island (Fig. 1), using a 250m cellular grid. The other information layers were also used in order to complete the cell data base. Each cell was updated with information from external database concerning fields such as vegetation and lithology. The final step was the construction of different thematic maps and diagrams to present and analyse the geomorphological processes and the natural hazards of the island.

The morphometric analysis

The automation of geomorphometry using GIS techniques is a very important tool in the analysis of the landscape parameters. The island’s slope analysis (Chart 1) showed the domination of low values that range from 0 to10%. Table 1 shows the number of cells (size of 0,0625 Km2) within given % slope ranges.

Slopes %

Skinari Cape 30 to 41,3 Ormos Skinari 20 to 30 Ag.Nikolaos Isl. 10 to 20 2 to 10 Mikro Nisi Isl. 0 to 2 Kamilafka Cape

O rm os A li ko Plemonari Cape n

Gaidaros Cape Ag.Ioannis Isl. Voidi Isl. i m ro V Krioneri Cape os rm O tis ni te O S rm s o o s Zakinthos m r E O x o X o r a s Davia Cape Ormos Katevasma

Ormos Limnionas Ag.Nikolaos Cape

Kalogera Cape Ag.Sostis Isl. F UL G AS Pelouzon Isl. N GA LA u Geraki Cape rio Ke Marathonisi Isl. os rm O 0 5 10

Kilometers Keri Cape

Mizithres Isl. Marathia Cape

Fig.1

Moreover we have correlated the slope distribution with the lithological units (Fig.2, Chart 2) and it is evident that the TABLE 1 allouvial and marl formations are Slopes % present in low slopes, the allouvial Slope Range Cells cones in medium, while the limestone 0-2 2.801 formations in medium and high slopes. 2-10 2.714 Chart 2, shows the slope distribution in 10-20 1.200 the four lithological categories. The 20-30 240 category “Marly limestones” covers the 30-41 21 biggest part of the island and due to this, gives the maximum values. The vegetation distribution is also related to the lithological factor Chart 1: Slopes % in Zakynthos island (fig.3), the 3000 geomorphology 2500 (fig.4) and the local 2000 1500

climatic conditions. Cells 1000 In figure 3 we may 500 observe the relation 0 between the 0--2 2--10 10--20 20--30 30--41 lithological Slope % ranges formations and the

vegetational cover. It is obvious (Charts 3,4,5) that the categories of Pine trees and

Chart 2: Topography & Lithology

1800 Alluvials 1600 M arls/Sandstones

1400 Marly Limestones

1200 Alluvial Cones

1000

Cells 800

600

400

200

0 5 1015203050 Slope % ranges olives, grapes and lemon trees are mainly correlated low topographic slopes. The category of Bushes mainly appears in low slopes values, but it has a more normal distribution as is shown in the Chart 3: Topography & Pine trees following chart (chart 5). 1500 Figure 4 shows that all

1000 categories of vegetation are present in low topographic Cells 500 slopes, while only bushes are 0 0--8 8--16 16--24 24--32 32--42 developed in high slopes. Slope % ranges The dominant erosional process depends on the topography, the drainage development, the geology and the climate. In the island of Chart 4: Topography & Olives-Grapes-Lemon trees Zakynthos these processes are 2500 also controlled by the 2000 occurrences of fires. Figure 5 1500 shows the existence of the Cells 1000 500 main natural hazards and their 0 relation to the vegetation 0--6 6--12 12--18 18--24 24--29 distribution. In this map we Slope % ranges present the earthquake epicenters and the disasters that have occurred. Moreover, major dissaster events as landslides, rockfalls, fires and floods were added to this map. According to the Chart 5: Topography & Bushes information retrieved from the data base, the flood event in 2000 village has happened 1500 1000 slightly after the major fires in Cells 500 the surrounding area destroyed 0 most of the vegetation. 0--7 7--14 14--21 21--28 28--35 Slope % ranges

Slopes f(Allouvials)

Skinari Cape 12 to 18 (5) 6 to 12 (28) Ormos Skinari 0 to 6 (1181) Ag.Nikolaos Isl. Slopes f(Marls/Sandstones)

Mikro Nisi Isl. 10 to 15 (24) Kamilafka Cape 5 to 10 (110) 0 to 5 (1373) O rm os A Slopes f(Marly Limestones) lik Plemonari Cape on 16 to 24 (37) 8 to 16 (686) Gaidaros Cape 0 to 8 (3499) Ag.Ioannis Isl. Voidi Isl. i m ro V Krioneri Cape os rm O tis ni te O S r s m o o m s Zakinthos r E O x o X o ra s Davia Cape

Ormos Katevasma

Ormos Limnionas Ag.Nikolaos Cape

Kalogera Cape Ag.Sostis Isl. F UL G S NA Pelouzon Isl. GA LA u rio Geraki Cape Ke s Marathonisi Isl. o rm O 0 5 10

Kilometers Keri Cape

Mizithres Isl. Marathia Cape

Fig.2

Conclusions

The island’s morphology is strongly affected by the tectonic activity. The slope distibution shows that areas with high slopes are associated with the main large faults of the island. A characteristic example is the slope category 10-20% that appears as a linear stucture in figure 1. Eastern of this linear stucture, topographic slopes are very

Skinari Cape Slope Ranges % Slopes f(PineTrees) Ormos Skinari 16 to 24 (93) Ag.Nikolaos Isl. 8 to 16 (294) 0 to 8 (1269) Slopes f(Olives/Grapes/Lemon trees Mikro Nisi Isl. Kamilafka Cape 12 to 18 (26) 6 to 12 (202) 0 to 6 (2293) O rm os A Slopes f(Bushes) li ko Plemonari Cape n 14 to 21 (142) 7 to 14 (702) 0 to 7 (1949) Gaidaros Cape Ag.Ioannis Isl. Voidi Isl.

i m ro V Krioneri Cape os rm O tis ni te O S rm os o Zakinthos m s r E O x o X o ra s Davia Cape

Ormos Katevasma

Ormos Limnionas Ag.Nikolaos Cape

Kalogera Cape Ag.Sostis Isl. F UL G S NA Pelouzon Isl. GA LA u io Geraki Cape er K os Marathonisi Isl. rm O 0 5 10

Kilometers Keri Cape

Mizithres Isl. Marathia Cape

Fig.4 low (0-2%). Natural hazards in Zakynthos island are stongly associated to other hazard events. It is obvious that both earthquakes and general tectonic activity in combination with the morphology of the area (high slopes), produce other hazards, such as rockfalls and land-slides. Moreover, fire events result to floods and erosion problems. Finally vegetation distribution is related to slope, lithology and natural hazard distribution (Fig. 3, 4, 5).

Natural Hazard Map of Zakynthos Town & Villages +Skinari Cape T .Town Ormos Skinari . Village Ag.Nikolaos Isl. T v T v.Ag.Nikolaos ((( TT 66Earthquakes Epicenters T Ano Mikro Nisi Isl. & Magnitudes T v.v Kamilafka Cape T v. vVolimes O ( rm Earthquake Epicenters os A lik v on Plemonari Cape v Earthquake Disasters

v +Earthquake Disasters . Gaidaros Cape Ag.Ioannis Isl. . v v Ano Gerakario Voidi Isl. RockFalls & LandSlides i m ro v V v Krioneri Cape os (rm . TLandSlides O Skoulikadon Ag.Kirikos T ( 6 tis + + ni v . . +Mpoxali te O . +. 6 S r + T s m T Ag.Dimitris . .+vZakinthos RockFalls o o + Zakinthos m s v v r E O x Gaitanio o T X T o T v rTa Fire Disasters s Ampelokipi v Maheradon v Davia Cape . . T v Ormos Katevasma v v Fire Disasters Mouzaki . Ormos Limnionas .v. Flood Disasters Pantokratoras Ag.Nikolaos Cape + vv vv Kalogera Cape v+ Flood v.v + Ag.Sostis Isl. F + UL G vv S v+v NA Pelouzon Isl. GA (6 LA TT(6 u Vegetation io Geraki Cape er T K os Marathonisi Isl. m r O Bushes 0 5 10 Olives-Grapes-Lemon trees T v+ Pine Trees Kilometers .Keri Keri CapeT Mizithres Isl. Marathia Cape

(6 (6 (6 Fig.5

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