Anisotropy of Magnetic Susceptibility and Preferred Pore Orientation in Lava Flow from the Ijen Volcanic Complex, East Java, Indonesia

Abstract

Anisotropy of magnetic susceptibility (AMS) has been used in various studies related to interpreting the direction of lava flow, some of which have shown ambiguity with regard to the data generated. In this study, we explored an alternative option to support the aforementioned application, using lava flow type igneous rock samples from the Ijen Volcanic Complex, East Java, Indonesia. We have investigated the preferred rock pore orientations from micro-computed tomography (μCT) images and quantified their directions. We then calculated their correlation with AMS data by calculating the angle between preferred pore orientation. The axis with the smallest gap to the preferred pore orientation of each sample was assumed to imply lava flow direction. Different lava flow direction preferences were obtained from different magnetic ellipsoids. Another important factor for consideration is the relative vertical position of the sampling site within a single lava flow unit. Only one out of five samples (ANY2) show good quantitative conformity between AMS data, preferred pore orientation, and topographical slope, despite these limitations. Our results point to a direction that seems to be correct and coherent on a physical basis. Additional research would likely clarify the issues involved. This encourages us to explore and work further in this field of research.

Petrology and geochemistry dataset of lava from the Ijen Crater and Mount Blau, Banyuwangi, East Java, Indonesia

“…Sampling locations were chosen based on the geological map of the Ijen Volcanic complex [2] and followed the previous studies [1,10,11]. Samples were taken from three different lava flows that are part of lava flow 3 of the Ijen Crater (Il3) and one flow from the lava flow 3 of the Mount Blau (Bl3) [2].…”

“…Samples were taken from three different lava flows that are part of lava flow 3 of the Ijen Crater (Il3) and one flow from the lava flow 3 of the Mount Blau (Bl3) [2]. Samples were taken from the unused outcrops from the previous studies [1,10,11]. These outcrops were chosen with the intention of complementing the data from the earlier studies.…”

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

“…According to the previous study (Atarita et al, 2019), the position of the sample in the outcrop of the flow may have influenced the results for the preferred pore orientations. In this study, we took six hand-sized lava flow samples at different positions from two lava outcrops.…”

“…Thus, there is a possibility that distribution of pore orientation can be correlated with AMS in determining the flow direction. As concluded by Atarita et al (2019) in their introductory study, the correlation between AMS and preferred pore orientation is evident but not thoroughly established, as the research in this regard is still insufficient (see also Wing-Fatt and Stacey, 1966;Cañón-Tapia et al, 1997;Atarita et al, 2019). In this study, a more comprehensive approach is carried out by combining AMS and preferred pore orientation (using μCT) analyses on well-dated and well-oriented lava flows from Mount Batur in Bali, Indonesia.…”

“…The use of anisotropy of magnetic susceptibility (AMS) analyses in lava flow studies has been found to have unpredictable results (Khan, 1962;Wing-Fatt and Stacey, 1966;Halvorsen, 1974;Symons, 1975;Kolofikova, 1976;Knight and Walker, 1988;Cañón-Tapia et al, 1995;Herrero-Bervera et al, 2002;Zhu et al, 2003;Panaiotu et al, 2011;Maggart, 2016;Martin et al, 2018;Atarita et al, 2019). The main difference in the conclusions from these studies was how the lava flow directions aligned with the principal magnetic susceptibility axes.…”