A Statistical Review of the Dates and Patterns of Volcanic Activity of Lewotolok Volcano, East Nusa Tenggara, Indonesia Triyana Muliawati (a*), Danni Gathot Harbowo (b)
a) Department of Mathematics, Institut Teknologi Sumatera
Jalan Terusan Ryacudu, Lampung Selatan 35365, Indonesia
*triyana.muliawati[at]ma.itera.ac.id
b) Department of Geology, Institut Teknologi Sumatera
Jalan Terusan Ryacudu, Lampung Selatan 35365, Indonesia
Abstract
Lewotolok is a stratovolcano located on the Lembata Island, East Nusa Tenggara (Lesser Sunda Islands), Indonesia. The first geohistory of the Lewotolok volcanic eruption was recorded in 1660 (VEI:3). Since 29/11/2020, Lewotolok has been included in the list of Indonesian volcanoes with the necessary precautions, comparable to the Anak Krakatau, Merapi, and Semeru volcanoes. We investigated Lewotolok volcanic activity by analyzing the height of the ash column data, maximum seismograph amplitude, and recorded seismic duration from 29th/11/2020 to 23th/09/2022, which are provided in magma.esdm.go.id. The results showed 191 records of eruption activity data, which formed three clusters for each variable using the Elbow Method in the Non-Hierarchical K-means clustering analysis. These data were plotted on the solar and Hijri lunar calendars. The data plot shows anomalies in the volcanic activity frequency and a significant pattern of activity at specific times. The data plot illustrates that the value of the activity frequency pattern tends to increase at Earth orbital events such as the December-January perihelion (up to 0.124) and June-July aphelion (up to 0.262) and at the new moon phases (up to 0.168). This phenomenon appears as solar and lunar tidal anomalies that commonly occur as gravitational sea tides. Along with the need for more comprehensive data, the results of this study may provide new perspectives for further research on the possible role of gravitational tide phenomena in volcanic activity, at least to explain the volcanic activity in Lewotolok.
