Supervisors info:
Ιωάννης Αλεξόπουλος, Αναπληρωτής Καθηγητής, Τμήμα Γεωλογίας & Γεωπεριβάλλοντος, ΕΚΠΑ,(Επιβλέπων)
Νικόλαος Βούλγαρης Καθηγητής Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, ΕΚΠΑ,
Εμμανουήλ Βασιλάκης Αναπληρωτής Καθηγητής, Τμήμα Γεωλογίας & Γεωπεριβάλλοντος, ΕΚΠΑ,
Summary:
The cave of Alistrati, which is characterized as an inactive karstic conduit, is located in the Prefecture of Serres, near the foothills of Mount Menoikio, in the area of Petroto. This area is structured by crystalline limestones of the Rhodope Massif, which through fault and joint systems lead to the development of a complex and multilevel karst system.
An extensive geomorphological survey was carried out for the accurate mapping of the karst surface above the cave of Alistrati, using an Unmanned Aerial System (UAS).
For the investigation of a possible lateral extension of the existing and accessible Alistrati karstic conduit, a detailed surface geophysical investigation was planned and carried out. More specifically, three geophysical techniques were implemented: a) the electrical resistivity tomography (ERT) at 4 profiles of 940m total length and a total investigation depth of 50m, b) the GPR technique in 6 lines of 1330m total length and c) the VLF method in 3 lines of 705m total length. These 13 lines of the three geophysical techniques are fully matched at 4 locations and were join-interpreted, yielding remarkable results.
The ERT results indicated the existence of two highly resistive (>7000 Ohm.m) anomalies, which are interpreted as karstic voids and prove the existence and interconnection of the first two levels of the karstification up to the depth of 50m, and the extension of the karst system to the northeast.
The GPR survey results identified strong signal reflection surfaces and characteristic structures derived from karstic voids. Through this technique the shallow karstic system was investigated up to the depth of 15m. Subsequently, the VLF electromagnetic method was performed, the results of which, through 2D inversion, indicated the existence of highly resistive (>2500 Ohm.m) targets probably due to the presence of karstic voids.
The comparative results of the above geophysical techniques, as well as their 3D presentation highlight similar geophysical structures/anomalies, evaluated as different types of karst system structures. In conclusion, the combined geophysical survey has indicated the existence and interconnection of the first two karst levels of the area, up to a depth of 50m, as well as the possible extension of the Alistrati karstic conduit to the northeast.
