Hasandağı Stratovolkanı’nın (Aksaray, Türkiye) Hidrotermal Aktivitesinin Uzaktan Algılama ve Jeofiziksel Yöntemlerle İncelenmesi

Abstract

Hasandağ is one of the largest volcanic centers in Central Anatolia with a double summit consisting of Greater Hasandağ (3268 m) and Lower Hasandağ (3060 m). The volcanic cone rises about 2250 m from the surrounding basin. Remains of the caldera structure, referred to as Meso-volcano, are still observable and a large part of this caldera is covered by block and ash flows, lava flows and the debris avalanches of the Neo-volcano. During the Holocene, effusive activities were also recorded after the most recent explosive eruption.

On the western summit flank of Hasandağ, more than one fumerol vents and hydrothermally altered rocks were detected between 3000-3100 meters. Within the scope of this study, it was aimed to reveal the hydrothermal activity of Hasandağı and obtain information about the activity of the volcano. Self-potential (SP), surface temperature (ST), and CO2 gas measurements were carried out on Hasandağ to reveal the hydrothermal fluid circulation. In addition, rock samples were collected on the hydrothermally altered zone in order to determine the contents of hydrothermal fluids and alteration minerals. FT-IR, XRD, and SEM-EDS analyses were used to analyze collected samples. Surface temperature anomalies and intense hydrothermal alteration according to the correlation of geochemical/mineralogical analyzes were mapped using remote sensing studies. ASTER night thermal infrared satellite (TIR) and MODIS night-time land surface temperature images were used in order to detect the surface temperature anomalies.

A total of 154 km long SP measurements were made along the 9 radial profiles from the summit and a wide encircling profile surrounding the base of the volcano. The typical “W” shaped anomaly observed in active volcanoes appeared in Hasandağ Self-Potential measurements and the maximum potential difference was measured 3,8 V on the volcano. The Ce-gradient map was calculated, the hydrogeological/hydrothermal zones were differentiated and the half-buried meso-caldera in the hydrogeological zone were structurally observed on Ce-gradient map. The highest fumerol gas temperature and CO2 gas values were measured 71,2 ° C and >100.000 ppm, respectively. The hydrothermal alteration minerals found in the area were determined as halloysite, alunite and opal-AN. Using remote sensing, enhanced derivative images were created by using band ratios in ASTER and Sentinal-2B images in order to map alteration minerals. On the scope of the remote sensing studies, surface temperature anomalies were detected using different techniques.

On a double-peaked stratovolcano system, Self-Potential measurements covering both of the summit peaks were carried out for the first time in the world, and hydrothermally active regions were geophysically revealed on the volcano. In addition, new information about the fault systems on Hasandağ was documented by the analysis of structural elements. Monitoring and recording the hydrothermal activity of Hasandağı volcano will allow us to determine and manage the volcanic risk.