The recent eruption of the Semeru volcano in Indonesia’s East Java province has made international headlines. This event, along with the eruptions of other volcanoes such as Merapi in Java and Sinabung in Sumatra sparked a renewed interest in the country’s seismic activity. In this context, it’s relevant to understand the specifics of the Semeru volcano, its connection to the Pacific Ring of Fire, and the geological significance of island arcs.
Understanding Semeru: The Great Mountain
Known also as “The Great Mountain”, Semeru is the highest volcano in Java and is recognised as one of the most active. It was last reported to have erupted in December 2019. Being a part of Indonesia, a country that hosts the largest number of active volcanoes in the world, Semeru plays a significant role in the country’s seismic activity. This is due to the strategic location of Indonesia on the Pacific’s Ring of Fire. Importantly, Semeru is part of the island arcs formed by the subduction of the Indo-Australian plate below the Sunda Plate, which is a part of the larger Eurasian Plate. The trench created here is known as the Sunda trench, a significant portion of which is the Java Trench.
The Pacific Ring of Fire
The Pacific Ring of Fire, sometimes referred to as the Circum-Pacific Belt, is an arcing path along the Pacific Ocean teeming with active volcanoes and prone to frequent earthquakes. It delineates boundaries between multiple tectonic plates including the Pacific, Cocos, Indian-Australian, Nazca, North American, and Philippine Plates. The interaction of these plates often leads to significant seismic activities and volcanic eruptions.
The Geological Significance of Island Arcs
Island arcs are elongated, curved chains of oceanic islands, often associated with intense volcanic and seismic activity. They are considered crucial to various orogenic, or mountain-building, processes. Characteristically, an island arc has a land mass or a partially enclosed, shallow sea on its concave side. In contrast, a long, narrow deep-sea trench almost invariably exists along the convex side of the arc. These trenches represent the deepest parts of the ocean floor. Prime examples of these geologic features include the Mariana Trench, which is considered the deepest trench worldwide, and the Tonga trenches. The Aleutian-Alaska Arc and the Kuril-Kamchatka Arc also serve as excellent examples of this form of geologic formation.
Revisiting the cause behind the eruption of Semeru and other volcanoes, it’s clear that their location within the influential Pacific Ring of Fire plays a significant role. This, along with the effects of the underlying tectonic plates and the presence of island arcs, contribute heavily to Indonesia’s high frequency of seismic upheaval.
