PEMETAAN GEOHAZARD BANJIR LAHAR DINGIN STUDI KASUS: DAERAH ALIRAN SUNGAI BATANG MALANO, GUNUNG MARAPI, SUMATERA BARAT

NARDI, RAJHI FEBRI and Setiawan, Budhi (2025) PEMETAAN GEOHAZARD BANJIR LAHAR DINGIN STUDI KASUS: DAERAH ALIRAN SUNGAI BATANG MALANO, GUNUNG MARAPI, SUMATERA BARAT. Undergraduate thesis, Sriwijaya University.

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Abstract

The increase in volcanic activity at Mount Marapi, which occurs periodically from January to March 2024, causes a buildup of volcanic material around the crater and on the mountain slopes. Recorded until June 2025 volcanic activity on this mountain occurred several times and experienced eruptions that spewed volcanic material at a radius of 2 - 3 km from the crater of Mount Marapi. This accumulation of volcanic material is certainly very dangerous which can cause new disasters in the future. The increase in rainfall that occurred in the Mount Marapi area caused the accumulated volcanic material to slide and be carried by the river flow, resulting in flash floods that carried rocks of various sizes, ranging from large to fine, known as cold lava floods. A cold lava flood occurred in May 2024, affecting several watersheds in Tanah Datar Regency and Agam Regency, West Sumatra Province. One of the affected watersheds is the Batang Malano watershed that flows from Nagari Pariangan to Nagari Rambatan, Tanah Datar Regency, which is the research area. This research employs the Normalized Morphometric Flood Index (NMFI) method, which aims to normalize the values of morphometric parameters on a scale of 0 to 1. Each parameter is normalized and overlaid, and then grouped into three classifications: low (0.00 - 0.33), medium (0.33 - 0.66), and high (0.66 - 1.00). Normalization is done to reduce the error rate and increase the accuracy of values in analyzing the potential of cold lava floods in a river basin. Meanwhile, the overlay technique aims to combine data - morphometric parameter data that has been normalized earlier in the intersect tools in the ArcMap 10.8 application. There are seven parameters used in the study of lava floods, namely drainage density with the function to determine the drainage density or a river flow that reflects the ability to channel water, bifurcation ratio with the function to show the level of branching in the river with the influence of geological aspects, ruggedness number with the function to determine the roughness index on a relief or topographic condition of an area, slope with a function to determine how much the value of the slope of an area, dissection index with a function to determine the erosion zone based on the calculation of the relief division of an area, basin relief with a function to show the difference in relief at the highest point and the lowest point in an area, and relief ratio with a function to show the ratio between the basin relief index and the length of the main river from upstream to downstream. In addition to morphometric parameters, there are also several supporting aspects related to the process and impact caused by the cold lava flood. There are three supporting parameters studied in the research area, namely the local geology parameter and the type of rock formation which aims to determine the type of rock formation and lithology around Mount Marapi, the land cover parameter which aims to determine how land use is in the area around the Batang Malano watershed, and the rainfall parameter which aims to measure a certain area in a certain period that shows the height of rainwater collected on the surface without experiencing evaporation, infiltration, and run off. After that, the final result of the Lava Flood Vulnerability map of Batang Malano watershed was obtained with a percentage of low hazard class 36.89% with a total of 86,766 polygons, then medium hazard class 60.59% with a total of 142,545 polygons, and high hazard class 2.52% with a total of 5,897 polygons. Along the Batang Malano watershed, the hazard index is high in the upstream part of the river and gradually decreases to a moderate hazard index as one heads downstream. With these results, the potential for lava floods to occur again is quite high, as Mount Marapi is still experiencing several eruptions as of 2025. This is reinforced by the supporting parameters of lithology types such as andesite, tuff, and breccia which tend to be loose and not solid so that they are easily carried by the lava flood flow, then the land cover parameter which is mostly in the form of plantations, rice fields, and settlements which tend to change the characteristics of the land surface and accelerate the flow of surface water, and finally the high - very high rainfall parameter calculated until May 2025 is certainly an important factor in the danger of this cold lava flood happening again. There is a need for careful mitigation planning, evacuation routes, and good infrastructure planning around the Batang Malano watershed.

Item Type:	Thesis (Undergraduate)
Uncontrolled Keywords:	Banjir Lahar Dingin, Batang Malano, DAS, Morfometri, NMFI
Subjects:	Q Science > QE Geology > QE1-996.5 Geology Q Science > QE Geology > QE521-545 Volcanoes and earthquakes
Divisions:	03-Faculty of Engineering > 34201-Geological Engineering (S1)
Depositing User:	Rajhi Febri Nardi
Date Deposited:	24 Jul 2025 02:45
Last Modified:	24 Jul 2025 02:45
URI:	http://repository.unsri.ac.id/id/eprint/180154

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