A Statistical review of the dates and patterns of volcanic activity of Lewotolo Volcano, East Nusa Tenggara, Indonesia

Abstract

Lewotolo is a stratovolcano located on the Lembata Island, East Nusa Tenggara (Lesser Sunda Islands), Indonesia. The first geohistory of the Lewotolo volcanic eruption was recorded in 1660 (Volcanic Eruption Index (VEI) 3). Since November 11, 2020, Lewotolo has been included in the list of Indonesian volcanoes with the necessary precautions, comparable to the Anak Krakatau, Merapi, and Semeru volcanoes. We investigated Lewotolo volcanic activity by analyzing the height of the ash column data, maximum seismograph amplitude, and recorded seismic duration from November 29, 2020, to September 23, 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 Lewotolo.