ANALISIS MORFOTEKTONIK DAS GRINDULU DI DAERAH PACITAN DAN SEKITARNYA, KABUPATEN PACITAN, JAWA TIMUR

ANALISIS MORFOTEKTONIK DAS GRINDULU DI DAERAH PACITAN DAN SEKITARNYA, KABUPATEN PACITAN, JAWA TIMUR

  • arif hanif hidayat FITB

Abstract

MORPHOTECTONIC ANALYSIS OF GRINDULU WATERSHED IN PACITAN AND SURROUNDINGS,


PACITAN DISTRICT, EAST JAVA.


Tectonic geomorphology is the main factor that controls the development of land forms in active tectonic areas and has a significant influence on river systems and mountainous landforms. This tectonic geomorphological research focuses on the Grindulu River Basin (DAS) in Pacitan and its surroundings, dividing it into 10 sub-watersheds. The Grindulu watershed is administratively located in three regions, namely Pacitan Regency, Ponorogo Regency and Wonogiri Regency with an area of ​​674.90 km². Covering an area of ​​612.36 Km² or 90.6% of this watershed, it is included in the administrative area of ​​Pacitan Regency, which is spread across several districts. In the Grindulu watershed there are several large faults including the Grindulu Fault, the Kayuwayang Fault, the Karangrejo Fault and the Tegalombo Fault.


The Grindulu fault is a fault that is thought to be active so that it is the basis of this study. The movement of faults in the Grindulu watershed is dominated by faults trending southwest-northeast. The purpose of this study is to determine and analyze the tectonic geomorphology of the Grindulu watershed, in the form of geomorphological, morphometric, and seismic history analyzes. The study area and its surroundings are part of the eastern Southern Mountain Zone which lies in the transitional zone between Cretaceous subduction and Tertiary period subduction. Geographically, the research area is located between 07˚ 55 '10' 'LS - 08˚ 17' 30 '' LS and 110˚ 55 '10' 'BT - 111˚ 25 "10" BT.


One method to identify the level of activity of the Grindulu watershed is to use a tectonic geomorphological approach through quantitative morphometric parameters. Quantitative morphometric analysis is used to identify the Relative Tectonic Activity Index (IATR), namely, knickpoint, river length gradient index (SL), watershed asymmetry (AF), integral hipsometry and curve hipsometry (HI), valley-to-valley floor width ratio (Vf ), and the form of the watershed (Bs). All parameters are combined with geological data including rock distribution, topography, and geological structures in the study area, as well as historical seismic data to produce a quantitative map of relative tectonic activity in the Grindulu watershed.


Based on the results of the relative tectonic activity in the Grindulu watershed, the research area can be divided into three classes; high tectonic activity class, medium tectonic activity class, and low tectonic activity class. Based on the results of the IATR value analysis, the Grindulu watershed which has high tectonic activity are Sub-DAS 2, 7, and 10, occupying 33.57% of the research area, for moderate tectonic activity are Sub-DAS 1, 3, 5, 8, and 9 occupied 49.28% in the study area, while for low tectonic activity were Sub-DAS 4 and 6, occupying 17.16% in the study area.


Based on the results of this study in general, it can be concluded that the Grindulu watershed has a relatively medium-high tectonic activity index, so it is hoped that this result can be a basis for consideration of the development of the Pacitan and surrounding areas.


 


Keywords: Watershed, Grindulu, tectonic geomorphology, morphometry, Pacitan.

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Published
2021-07-21
How to Cite
HIDAYAT, arif hanif. ANALISIS MORFOTEKTONIK DAS GRINDULU DI DAERAH PACITAN DAN SEKITARNYA, KABUPATEN PACITAN, JAWA TIMUR. Bulletin of Geology, [S.l.], v. 5, n. 3, p. 708-717, july 2021. ISSN 2580-0752. Available at: <https://buletingeologi.com/index.php/buletin-geologi/article/view/122>. Date accessed: 15 oct. 2021.