The Citarum River has a volcanic catchment area in West Java Province, and is one of the nationally strategic rivers in tropical Indonesia due to its roles in water supply and in power generation. The river is economically important, but it is also polluted by industrial, agricultural, and residential wastes. Suspended sediment samples were collected along a certain section of the Citarum River, starting in Balekambang through the area of Bandung Regency to the downstream village of Nanjung, where the river is dammed. Similar samples were also collected from seven tributaries of the Citarum River. Magnetic and heavy metal analyses show that unlike river sediments from a non-volcanic catchment area in temperate climates, magnetic susceptibility values tend to decrease downstream, showing that the magnetic minerals in the upstream area are mostly lithogenic in origin, containing more Fe-bearing minerals compared to those in tributary samples which are anthropogenic in origin. Anthropogenic pollution is also represented by the increase of Zn content along the river. The results suggest that applying magnetic methods for monitoring river pollution in the tropics or in the volcanic areas should be carefully analyzed and interpreted.

Lava has complex geochemical characteristics based on differences in eruption centers, eruptive events, and flow emplacement. Characterization of lava is useful for understanding the geological conditions of a volcanic region. To complement geochemical methods, rock magnetic methods are being used to analyze lava. To explore the potential uses of rock magnetic methods for lava characterization, a series of magnetic measurements were completed in lava samples from eight locations in the Ijen Volcanic Complex (IVC) in Banyuwangi, East Java, Indonesia. These locations were grouped into two eruption centers: Ijen Crater and Mount Anyar. The magnetic measurements included frequency-dependent magnetic susceptibility, thermomagnetic, anhysteretic remanent magnetization (ARM), isothermal remanent magnetization (IRM), and hysteresis curve analyses. These measurements were supplemented using X-ray fluorescence, petrography analyses, and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS). Based on their lithology, lava samples were categorized into basalt, basaltic andesite, and basaltic trachyandesite. The dominant magnetic mineral contained in the sample was iron-rich titanomagnetite and titanium-rich titanomagnetite with a magnetic pseudo-single-domain and small amounts of superparamagnetic grain minerals in some samples. The significant difference in mass specific susceptibility (χ_LF) is caused by differences in the crystallization process. The differences in susceptibility frequency dependence (χ_FD) highlighted the differences in the magma cooling rate, demonstrated by the differences in the percentage of opaque mineral groundmass. The rock magnetic method was proven to support the geochemistry and petrography methods used to characterize lava and identify the causes of differences in lava characteristics.

Volcanic ash is a volcanic product with a wide distribution that can be used as a geological marker. In volcanic regions such as Indonesia, the identification of the sources of volcanic ash and tuff layers from different volcanoes or eruptive events is a challenging task. In this study, samples of volcanic ash from the 2010 eruption of Bromo—a relatively young and active tuff cone volcano within the Sandsea caldera in the Tengger volcanic complex in East Java, Indonesia—along with two older tuff layers from the same caldera (Widodaren tuff: 1.8 kyr and Segarawedi tuff: 33 kyr) were subjected to magnetic measurements, geochemical analyses, and petrographic analyses. The aim is to attempt to use magnetic characters as a fingerprint for volcanic ash and tuff layers. The results show that the samples had variations in grain size and magnetic domain as indicated by the hysteresis parameters. These magnetic characters correlated with the results of geochemical and petrographic analyses, suggesting that magnetic properties may potentially be used as fingerprints to identify volcanic ashes and tuff layers.

As an agricultural country, the study of agricultural soil in Indonesia is very important. Fertile agricultural soil has a good impact on agricultural products. Lampung is one of the provinces that have extensive agricultural land in Indonesia. The purpose of this research is to know the correlation between pH and magnetic susceptibility to soil fertility level around Institut Teknologi Sumatera. The sample consists of soil from Way Hui (NN 2.1, NN 2.4 and NN 2.5), Harapan Jaya (NN 2.2), and Korpri Jaya (NN 2.3). The method used is rock magnetism method combined with pH analysis. The results of this research are soil pH between 5 to 6.5 and magnetic susceptibility value of the soil around 27.3 to 115.3 (×10⁻⁸ m³/kg). Based on the pH classified by Badan Penelitian Tanah, the level of fertility of agricultural soil around Institut Teknologi Sumatera consists of two groups, namely low (NN 2.1, NN 2.2 and NN 2.5) and medium (NN 2.3 and NN 2.4). Low samples have magnetic susceptibility value around 27.3 to 50 (×10⁻⁸ m³/kg). While, medium samples have magnetic susceptibility value around 80.5 to 115.3 (×10⁻⁸ m³/kg). Generally, magnetic susceptibility is increase by increasing pH value. This preliminary study still needs further research.

Some volcanoes erupt quite frequently on roughly predicted time interval so that the populations in their vicinities are used to volcanic hazards and are prepared mentally to deal with them. However, some volcanoes like Mount Sinabung erupt infrequently so that the previous eruptions were not recorded in the collective memories of the population living in their vicinities. Studying volcanic ashes from Tengger Volcanic Complex, Santoso et al. reported that each eruptive event has unique set of magnetic parameters inferring that magnetic parameters could be used as finger prints for volcanic ash. In this study, volcanic ash samples from Mount Sinabung, Mount Soputan, and Mount Kelud were subjected to magnetic measurements as well as to X-Ray Fluorescence (XRF) analyses to establish their magnetic characteristics. The results were then also compared with that of Tengger volcanic complex. The most obvious characteristic was found to be the plot of mass-specific magnetic susceptibility and frequency-dependent magnetic susceptibility. Each volcanic sample has a distinct position in the plot. This finding implies that the eruptive history of volcanoes such as Mount Sinabung can be studied through studies of volcanic ash layers in outcrops, lake sediments as well as in marine sediments in the vicinity of these volcanoes. For instance, magnetic measurements could be used to differentiate which of the volcanic ash layers found in North Sumatera belongs to Mount Sinabung.

The development of coffee productivity in Lampung province has increased from 2018 to 2022 by 0.54%. Based on data from the Central Statistics Agency of Lampung Province in 2018, the production of Robusta coffee plants was 33,482 tons in the Tanggamus area. To maintain the stability of coffee productivity, it is necessary to conduct subsurface studies and the suitability of Robusta coffee land. The purpose of this study was to create a subsurface model and a map of the suitability of the coffee land. The methods used are magnetic, pH, and soil temperature. Research using a combination of these 3 methods has never been conducted for the identification of coffee fields. Based on the results of magnetic data processing, it is suspected that the coffee garden soil is latosol soil. This soil is very fertile because it comes from weathering Brexit and Andesite rocks. Based on the distribution of pH and soil temperature, the study area was dominated by land suitability class of S1 (very suitable) which is categorized as land suitable for robusta coffee cultivation, class S2 (quite appropriate) needs to be fertilized by farmers, and class S3 (according to marginal) needs intervention from the government in improving plantation land. The pH and temperature methods can be used as a simple method to monitor the suitability of coffee fields in Indonesia.