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Survei magnetotellurik (MT) telah dilakukan di Gunung Merapi dengan menggunakan alat Phoenix Geophysics MTU5 pada Oktober 2016 dan Mei 2017. Pengukuran dilakukan dengan jarak tiap titik sekitar 1 km, durasi pengukuran untuk satu titik ±12 jam, dan lebar dipole 50 s/d 80 meter utara-selatan dan timur barat. Sebanyak 8 titik sounding digunakan untuk menyusun profil resistivitas 2-D di lereng utara dan selatan. Hasil menunjukkan bahwa resistivitas bawah permukaan Merapi terdiri dari 2 (dua) karakteristik nilai resistivitas yaitu zona resistivitas tinggi dengan nilai 183-50.000 ohm.m dan zona resistivitas rendah dengan nilai 20-175 ohm.m. Zona resistivitas tinggi dapat diinterpretasikan sebagai zona produk erupsi sebelumnya yaitu aliran lava dan material piroklastik lainnya. Sedangkan zona resistivitas rendah diinterpretasikan sebagai kantong magma terbagi menjadi dua bagian, bagian atas berada pada kedalaman 0 s/d 2.000 meter dengan diameter mencapai 1.000 meter yang mengindikasikan sebuah kantong magma dangkal, sedangkan bagian bawah terlihat menerus dari kedalaman 3.000 s/d 11.000 meter sebagai kenampakan dapur magma yang cukup besar dengan diameter rata-rata sekitar 2.000 meter yang diindikasikan sebagai kantong magma dalam. Hasil zonasi ini senada dengan posisi hiposenter dari kejadian gempa vulkanik periode tahun 2010. Selain itu, terlihat adanya struktur yang diindikasikan sebagai sesar yang memotong lintasan di sekitar puncak.Kata kunci: Gunung Merapi, kantong magma, magnetotellurik, resistivitasABSTRACTMagnetotelluric (MT) survey has been carried out on Phoenix Geophysics MTU-5 in October 2016 and May 2017. The measurement has been done with the distance between them approximately 1 km, its duration of each sounding was 12 hours, and dipole length varied from 50-80 meters on North-South and East-West direction. Here we use the result from 8 MT sounding to construct a 2-D electrical resistivity image of the northern and southern flank of Merapi. The results show that the subsurface resistivity in Merapi consists of two types of resistivity features, i.e. the high resistivity zone which having resistivity value 183-50.000 ohm.m and the low one which varied from 20-175 ohm.m. The high resistivity zone are the lava flow and another pyroclastic material, while the low resistivity zone interpreted as magma chamber divided into two parts: upper part, at a depth of 0-2,000 meters with 1,000 meters diameter which is indicated as a shallow magma chamber, lower part, continuously from the depth of 3,000-11,000 meters as the large magma chamber with an average diameter of about 2,000 meters. The zone can be correlated to the hypocenter position taken from the volcanic earthquake event of 2010 period. In addition, there is a structure which indicated as a fault that cuts the trajectory around the summit. Keywords: Merapi Volcano, magma chamber, magnetotelluric, resistivity

The Ijen volcano has Pleistocene age (294.00 ± 0.03 Ma), and this stratovolcano was very acidic crater water with a pH of 0-1. The acidic crater water seeps into the Banyupait river flow. Asembagus is a research area located on the northern slope of the Ijen volcano, and the Banyupait River drains this. The acidic river water flows from the Ijen Crater Lake, so the pH of the water river was very acidic. This study used several different analytic methodologies with some previous researchers, namely using the method of geological mapping, pH measurement, spectrophotometry, IRMS (Isotope Ratio Mass Spectrometer), and the technique of Induced Coupled Mass Spectrometry (ICP-MS). Besides, the petrographic analysis is used to determine the composition of rock minerals due to rocks interacting with acidic water. Banyupait River water in the Asembagus area has a pH of river water around 3-7.3, SO4 (220-683 ppm), and the type of water is meteoric water. Also, concentrations of Ca, K, Mg in the west Banyupait river irrigation water flow showed higher levels when compared to the eastern Banyupait River water flow. Likewise, REE elements from the Asembagus region showed lower concentrations compared to Ijen Crater water. This change in the level of chemical elements is caused by the acidity of the Banyupait River being diluted or mixed with water from other water. However, the spring was not affected by acidic water. The process of acidic water interaction with rocks can also be observed from rocks traversed by the Banyupait River flow. Chalcedony and hematite replace the primary minerals of basaltic rocks. This research is expected to improve the quality of water needed by the Asembagus community so that people can live healthily.

The 26 October-23 November 2010, eruption is Merapi's largest event (VEI 4) over the past 140 years. We tracked and identified the 2010 Merapi's PDC deposits in the most impacted catchment (South) using high-resolution optical (from GeoEye and SPOT-5 satellites as well as low altitude photograph) imagery. We show that high-resolution imagery enables mapping with unprecedented detail the effects of the 2010 eruption in the summit area and across the most devastated catchment on Merapi. We investigated the relationships between the morphology of the river channel, and the apparent behavior of the PDCs and lahars, as deduced from over-banking processes. The 2010 pyroclastic deposits cover an area of ∼27 km2 in the Gendol-Opak catchment, i.e. 35% of the total deposit area. We analyze how unconfined PDCs with over-bank and veneer facies, as well as two types of surges have mantled widespread areas on both sides of the Gendol valley which contain the confined PDC deposits. Geometric and geomorphic characteristics that allow over bank and veneer deposits beyond the main valley are: limited cross-sectional areas under 1500 m2 and the decreasing longitudinal rate of channel confinement. Subsequent lahars six months after the eruption have devastated several villages along the Gendol River 20km from the summit on the ring plain. Small areas down-valley was affected by over-bank lahars once pyroclastic deposits were remobilized 3.8km farther than the PDC front. The over-bank and avulsed lahars can be attributed to the limited capacity (200-250 m2) of river channels and meandering river (sinuosity index of 1.25) across the lowest-angle (

In the last part of the 20th century and the beginning of the 21st century, Mt. Merapi in Central-Java Indonesia erupted about every 2–5 years. Most of the eruptions were low in explosivity, with VEI-3 or less. Eruptions usually involve the formation of a lava dome, either in the beginning or in the end of the eruptive episode. For the 2006 eruption, the precursory signal was first observed in the middle of the year 2005 with a decrease in EDM slope distances to points on the rim, an increase of seismicity and a possible increase of SO 2 emissions. Those early events marked the beginning of a more continuous period of inflation, which led to the eruption. In total, the pre-eruption displacement of the southern rim reached at least 2.4 m toward the measuring station in Kaliurang (KAL). From late April until June 2006, a lava dome grew on the summit with a volume that gradually increased until it reached about 4.1 million m 3 in 38 days. The total of erupted magma was about 5.3 million m 3 dense-rock-equivalent (DRE). The dome subsequently collapsed in three steps from June 4 to June 14, leaving an open scar on its southeast side. In this paper we detail the changes of dome morphology that were monitored by taking successive photographs from similar positions. The eruption in 2006 marked a significant change in summit morphology, from west-southwestward opening during the 20th century to the currently southeast orientation. Also, an Mw 6.4 earthquake occurred on 26 May, midway through the eruption, which adds interesting questions about the relationship of the eruption and the earthquake. EDM data from 2006 and previous eruptions show that the summit remains inflated after each eruption, i.e., no significant deflation occurs following eruptions. The lack of post-eruption deflation suggests that magma remains in the shallow parts of the edifice after the eruption. As a result, the complex of summit lava domes and their intrusive roots grow with time and Merapi's rim and summit become progressively more unstable and prone to collapse.

Pyroclastic density current deposits remobilized by water during periods of heavy rainfall trigger lahars (volcanic mudflows) that affect inhabited areas at considerable distance from volcanoes, even years after an eruption. Here we present an innovative approach to detect and estimate the thickness and volume of pyroclastic density current (PDC) deposits as well as erosional versus depositional environments. We use SAR interferometry to compare an airborne digital surface model (DSM) acquired in 2004 to a post eruption 2010 DSM created using COSMO-SkyMed satellite data to estimate the volume of 2010 Merapi eruption PDC deposits along the Gendol river (Kali Gendol, KG). Results show PDC thicknesses of up to 75 m in canyons and a volume of about 40 × 106 m3, mainly along KG, and at distances of up to 16 km from the volcano summit. This volume estimate corresponds mainly to the 2010 pyroclastic deposits along the KG — material that is potentially available to produce lahars. Our volume estimate is approximately twice that estimated by field studies, a difference we consider acceptable given the uncertainties involved in both satellite- and field-based methods. Our technique can be used to rapidly evaluate volumes of PDC deposits at active volcanoes, in remote settings and where continuous activity may prevent field observations.

The research area was an area of hydrothermal alteration resulted of Tertiary volcanoes activity. Stratigraphically this region was composed of volcanic breccia, andesite lava intruded by andesite and then undergoes hydrothermal alteration. The result of the interaction between hydrothermal fluids and rocks produce some heavy metals. The elements will be contained also on the soil which was the result of its weathering and then the heavy metal elements were absorbed by the plant. The elements with certain level were very dangerous for human health. This phytoremediation process can also occur in alteration rocks of Quaternary volcanoes. Then some plants will have different capabilities in absorbing certain heavy metals. This research was conducted to know the characterization of vegetable plants that absorb heavy metals and this research using methodology are: petrography, X-ray diffraction (XRD), X-Ray Fluorences (XRF) and mercury analysis using Mercury Survey meter. This methods were done to know the rocks type, alterations type and heavy metals content. The analysis yields andesitic rock type which is hydrothermally altered to argillic. These argillic rocks become soils containing heavy metals including Mn, Fe, Co, Cu, As, Hg and Pb. With the process of phytoremediation then heavy metals can be contained in plants. The results showed that vegetable plants have the character of absorbing certain heavy metals, such as: chilli (Capsium fruteceus) absorb Hg. Kale (Ipomoea aquatica), chilli, bay (Eugenia aperculata) leaf, papaya (Carica papaya) and taro (Colocasia esculenta) leaf are absorbed Fe element. It proves that the metallic minerals as result of hydrothermal alteration process are absorbed by plants or vegetables.

The processing of gold by means of amalgamation produces mercury wastes. Mercury wastes can pollute the environment. This study aims to determine the diversity of fruit crops and mercury content in the gold mining area of Dusun Mesu. The research method used is survey method, measurement, field observation, and laboratory analysis. The types of plants found are recorded, the number and the diameter. Samples of roots, stems, and leaves of plants were analyzed mercury contents in the laboratory. Based on the results of the analysis, there were 7 types of fruit plants, as many as 32 individuals with the type of vegetation seedling, stake, poles, and trees. The results of calculation of diversity index (H¹), uniformity index (E), and dominance index (C) at all growth rates show low diversity (H = 0.02222 - 0.86648), low uniformity (E = 0.00403-0) , 27959), low dominance (C = 0,0000162 - 0,08). The content of mercury in the soil ranges from 0.001 to 0.044 mg/m³. The content of mercury in fruit crops ranges from

The research area is one of the Wonogiri gold producer. In this region there are nearly 30 gold processing locations. This area has a steep morphology which is part of Mt. Mas. The work of the gold processing is a part time job besides for the local farmer population. To get the gold bearing rocks, are by digging holes manually around Mt. Mas, while gold processing is carried out in their homes. As a result of these activities, then identified the distribution of mercury in the surrounding settlements. Analytical methods used in this study is the measurement mercury content using Hg meter on altered rocks, soil and using XRF (X-Ray Fluorescence) for plant samples. This results of research shows that there are conducted on mercury contents in the altered rocks, soil and plants showed significant mercury contents in altered rocks, soil and plants. This proves that mercury has polluted the environment surrounding residents, both of people living in the hill down on the lower plain areas. The results of this study are expected to be used as reference to help overcome the pollution of the area.

Following the eruption of January 1992, episodes of lava dome growth accompanied by generation of dome-collapse nuees ardentes occurred in 1994–1998. In addition, nuees ardentes were generated by fountain-collapse in January 1997, and the 1998 events also suggest an explosive component. Significant tilt and seismic precursors on varying time scales preceded these events. Deformation about the summit has been detected by electronic tiltmeters since November 1992, with inflation corresponding generally to lava dome growth, and deflation (or decreased inflation) corresponding to loss of dome mass. Strong short-term (days to weeks) accelerations in tilt rate and seismicity occurred prior to the major nuees ardentes episodes, apart from those of 22 November 1994 which were preceded by steadily increasing tilt for over 200 days but lacked short-term precursors. Because of the combination of populated hazardous areas and the lack of an issued warning, about 100 casualties occurred in 1994. In contrast, the strong precursors in 1997 and 1998 provided advance warning to observatory scientists, enabled the stepped raising of alert levels, and aided hazard management. As a result of these factors, but also the fortunate fact that the large nuees ardentes did not quite descend into populated areas, no casualties occurred. The nuee ardente episode of 1994 is interpreted as purely due to gravitational collapse, whereas those of 1997 and 1998 were influenced by gas-pressurization of the lava dome.

More than 50 volcanic debris flows or lahars were generated around Mt Merapi during the first rainy season following the nuees ardentes of 22 November 1994. The rainfalls that triggered the lahars were analyzed, using such instruments as weather radar and telemetered rain gauges. Lahar dynamics were also monitored, using new non-contact detection instrumentation installed on the slopes of the volcano. These devices include real-time seismic amplitude measurement (RSAM), seismic spectral amplitude measurement (SSAM) and acoustic flow monitoring (AFM) systems. Calibration of the various systems was accomplished by field measurements of flow velocities and discharge, contemporaneously with instrumental monitoring. The 1994–1995 lahars were relatively short events, their duration in the Boyong river commonly ranging between 30 min and 1 h 30 min. The great majority (90%) of the lahars was recognized at Kaliurang village between 13:00 and 17:30 h, due to the predominance of afternoon rainfalls. The observed mean velocity of lahar fronts ranged between 1.1 and 3.4 m/s, whereas the peak velocity of the flows varied from 11 to 15 m/s, under the Gardu Pandang viewpoint location at Kaliurang, to 8–10 m/s at a section 500 m downstream from this site. River slopes vary from 28 to 22 m/km at the two sites. Peak discharges recorded in various events ranged from 33 to 360 m3/s, with the maximum value of peak discharge 360 m3/s, on 20 May 1995. To improve the lahar warning system along Boyong river, some instrumental thresholds were proposed: large and potentially hazardous lahars may be detected by RSAM units exceeding 400, SSAM units exceeding 80 on the highest frequency band, or AFM values greater than 1500 mV on the low-gain, broad-band setting.