Preferred Pore Orientation as a Complement to Anisotropy of Magnetic Susceptibility: A Case Study of Lava Flows From Batur Volcano, Bali, Indonesia

Anisotropy of magnetic susceptibility (AMS) analyses have been used widely in many applications that include studying lava flows. In this paper, we introduce an auxiliary parameter, i.e., preferred pore orientation, on the use of AMS for lava flow studies on the basaltic lava samples from Batur Volcano in Bali Indonesia. We also examine the effect of sample position in lava flow outcrop to the relationship between preferred pore orientation and AMS. The samples are subjected to petrographic analyses as well as to magnetic measurements and micro-computed tomography (μCT) imaging. Preferred pore orientations were obtained by quantified the long-axis of the vesicles from the images. The correlation was evaluated by measuring the angle between the maximum susceptibility axes and the preferred pore orientations. All samples show that the maximum susceptibility axes are parallel with the flow direction. Three out of six samples of two lava flows from the same eruption show a positive correlation between AMS and preferred pore orientation, where both parameters point to the northeast direction. A difference of sample position in the outcrop of lava flow was observed as a possible factor that influenced the results for the preferred pore orientations. Samples which were taken from the summit of the lava flow have pore orientation parallel to the lava flow direction. While samples which were taken from the foot slope of the lava flow have pore orientation perpendicular to the lava flow direction. This study provides further evidence that pore orientation might be positively correlated with the AMS.

Memadukan Pendakian dan Wisata Edukasi: Persoalan Gunung Api dan Geopark Batur di Kawasan Kintamani, Bali

The Batur volcano in Kintamani tourist resort has enhanced its existence through the establishment of Batur UNESCO Global Geopark since 1st April 2016. However, the two tourist attrac- tions have not been mutually utilized each other. This study is conducted to determine the level of relationship and integra- tion between the two tourist attractions in order to find out beneficial solution for the two tourism industries. The results revealed that not all tourists’ climbers of Mount Batur visited the Geopark as an artificial-tourist attraction, whereas, not all the first tourists who visited the geopark was climbing the sa- cred mountain. Therefore, it is required more intensive efforts in tourism business in order to create a mutual synergy be- tween the two tourist attractions by all stakeholders including government, tourism industry, and the society. This is for the benefit of tourism business and of carrying out the natural con- servation and the preservation of local cultural values.

ANALISIS DEFORMASI GUNUNG API BATUR BERDASARKAN DATA PENGAMATAN GPS BERKALA TAHUN 2008, 2009, 2013, DAN 2015 DEFORMATION ANALYSIS OF BATUR VOLCANO BASED ON PERIODIC GPS OBSERVATIONS DATA IN 2008, 2009, 2013, AND 2015

ABSTRAKGunung Batur yang terletak di Kabupaten Bangli, Bali, terakhir meletus pada tahun 2000. Pada 2009 terjadi peningkatan aktivitas vulkanis di Gunug Batur walaupun tidak terjadi letusan. Penelitian ini bertujuan untuk mengetahui pola deformasi pada Gunung Batur serta keterkaitannya dengan peningkatan vulkanis pada tahun 2009. Analisis didasarkan pada pola vektor pergeseran dan pola regangan masing-masing titik pengamatan GPS berkala pada area Gunung Batur tahun 2008, 2009, 2013, dan 2015. Berdasarkan pengamatan GPS Oktober 2008-November 2009 pola deformasi menunjukkan adanya inflasi dengan pola vektor pergeseran titik pengamatan GPS dominan ke arah luar dari Gunung Batur, selain itu pola regangan memperlihatkan bahwa pada area bagian utara dan timurlaut Gunung Batur dominan terjadi ekstensi. Pada pengamatan GPS untuk periode November 2009-Februari 2013 pola deformasi menunjukkan adanya deflasi pada Gunung Batur dengan pola vektor pergeseran titik pengamatan GPS berarah menuju Gunung Batur dan pola regangan memperlihatkan bahwa pada area Gunung Batur terjadi kompresi. Kata Kunci: Gunung Batur, deflasi, deformasi, pergeseran, GPS, inflasi, regangan. ABSTRACTBatur volcano located in Bangli, Bali, last erupted in 2000. Increased in the volcanic activity occurred in 2009 but did not followed by eruption. This study aims to determine ground deformation pattern in Batur volcano and its association with the increased in volcanic activity in 2009 based on the pattern of displacement vector and strain using 2008-2015 campaign GPS data. During period of October 2008-November 2009, Batur Volcano experience inflation and strain pattern shows that the area of the north and northeast of Batur Volcano experienced extension. During November 2009-February 2013, Batur Volcano experienced deflation with GPS displacement directed towards Batur Volcano and a strain pattern of compression around Batur Volcano. Keywords: Batur Volcano, deflation, deformation, displacement, GPS, inflation, strain.

DEFORMATION OF BATUR VOLCANO INFERRED FROM GPS MEASUREMENTS

In the period of 1994 and 1999, the volcano erupted, resulting in three new craters. GPS surveys for monitoring the deformation of Batur volcano has been carried out in May 1999 and February 2001. Nine existing EDM benchmarks in the vicinity of the outer caldera rim and the crater of the volcano were occupied by employing five geodetic double-frequency GPS receivers. The pattern of the horizontal displacement is mostly characterized by radially directing direction toward to the volcano. It seems the volcano was experiencing a deflation process with the magnitudes of about 0.8 to 6 cm. The estimated pressure source based on Mogi model is located around the first crater with the depth of about 8 km beneath the caldera base.

CALDERA ACTIVITIES IN NORTH BALI, INDONESIA

One of the most serious natural hazards is largescaled Plinian eruption that forms caldera. Although the probability to have such large-scaled eruption is very low, the result will be catastrophic if it happens. Thus, it is important to clarify features of caldera system including eruption timing, scale of eruption, precursor activity, etc. With enough scientific information, we may be able to mitigate such very rare but extremely large-scaled geohazard. In Bali Island, Indonesia, there are two caldera systems; Batur caldera and Buyan-Bratan caldera. Batur caldera was previously well studied (e.g. Sutawijaya, 2009), whilst Buyan-Bratan caldera’s geological and volcanological features have not been examined at all. The Buyan-Bratan caldera is about 6 km × 11 km in size and contains three caldera lakes. Wellformed several post-caldera cones are covered by thick soil and vegetation and developed from central to southern part of the caldera. BuyanBratan caldera and post-caldera cones are thought to be older than Batur caldera activities. Geothermal manifestation is confirmed within the caldera. Geological features of the Buyan-Bratan caldera and post-caldera cones were clarified by petrographic and petrochemical analyses. Also, KAr ages were obtained for each volcanic edifice in Buyan-Bratan caldera system. Keywords: Caldera, Plinian eruption, Buyan, Batur, volcano hazards