Geochemical Indication of Formation Water Influx to The Volcanic Hosted Hot Springs of Slamet Volcano, Indonesia

Abstract

DOI:10.17014/ijog.7.1.1-14The Slamet Volcano is an active volcano lying above a sedimentary rock substratum with three complexes of geothermal manifestations: Baturaden, Guci, and Paguyangan. In order to understand the characteristic and origin of the geothermal fluid related to the Slamet volcanic system emphasizing the identification of formation water influx represented by sea water signature in the thermal fluid, the water chemistry has been analyzed including stable isotopes of the hot springs, cold springs, shallow groundwater, rainwater, and river water surrounding the Slamet Volcano. The temperature of manifestations is in the range of 42 - 72°C, while the chloride concentration of the geothermal water is ranging from 17 to 754 mg/L. Specifically, the manifestations in Baturaden are distinctively featured by a huge travertine deposit. The values of Cl/B ratio and non-equilibrium state of the reactive elements indicate the existence of two main geothermal fluid flows discharging as hot springs at Baturaden, Paguyangan, and Guci complexes. Guci hot spring complex shows a similar characteristic as fumarole condensate water from the summit of Slamet Volcano which has been diluted by meteoric water. On the other hand, Baturaden hot spring complex appears to be affected not only by fumarole condensate, but also by the contribution of formation water from marine sedimentary rock. Meanwhile, Paguyangan hot spring is more likely as the outflow of a geothermal reservoir which has also been interacting with marine sedimentary rock. Furthermore, the signature of stable isotope of δ18O and δ2Η shows a significant portion of meteoric water contributing in the dilution of thermal waters.

Origin of Groundwater in Kawung Carang Cold Spring, Sumbang District, Banyumas Regency, Central Java

“…This sequence is dominantly composed of andesitic lava and pyroclastic deposit. While, Lava of Mount Slamet unit was product of the Young Slamet sequence that comprises dominantly basaltic lava flow [10].…”

“…Slamet Volcano is located in the northern part of Banyumas Regency, Central Java. There are several springs appearing around the Slamet Volcano, such as Guci hot spring on northern flank, Baturaden cold and hot spring on southern flank, and Paguyangan hot spring on western flank [10]. Several hydrochemical studies of Slamet Volcano's hot spring water has been conducted to identify their origin.…”

“…Slamet formation. Cold spring water discharging on lahar sedimentary deposits consisting of andesitic-basaltic volcanic boulders product of Slamet Volcano [5] [10].…”

Kajian Pemetaan Potensi Mata Air Di Kota Semarang

“…Seperti sesar Kaligarang yang memotong batuan muda di wilayah selatan Kota Semarang dan diperkirakan menerus hingga Laut Jawa, di mana sesar Kaligarang sendiri memiliki laju pergeseran batuan sebesar 4,5mm per tahun sehingga dari pergeseran batuan tersebut berpotensi memunculkan atau menghilangkan mata air di wilayah Kota Semarang (Poedjoprajitno et al, 2008). Sebagaimana disampaikan oleh Harijoko (2020), mata air merupakan sumber air yang muncul dengan sendirinya ke permukaan dari dalam tanah, di mana untuk sumber dari aliran airnya berasal dari air tanah yang mengalami patahan atau retakan sehingga muncul ke permukaan. Terdapatnya perubahan struktur geologi yang diakibatkan oleh proses patahan, pengelupasan kulit dan lipatan menjadi faktor pendorong terbentuknya mata air, sehingga air tanah muncul di atas permukaan.…”