Mount Agung, a large and active stratovolcano, is the highest point on the island of Bali, Indonesia, rising to approximately 3,031 meters. Located in the Karangasem Regency, the mountain is considered sacred by the Balinese people. Its geologic history and recent activity confirm its classification as an active volcano, meaning its magmatic system is capable of producing future eruptions. The physical characteristics of Mount Agung, including its large and deep summit crater, place it among the most closely watched volcanoes in the Indonesian archipelago. Understanding its current status requires continuous monitoring by local agencies and knowledge of the established alert systems.
Current Activity Levels and Official Alerts
The official status of Mount Agung is determined by the Center for Volcanology and Geological Hazard Mitigation (PVMBG), the Indonesian agency responsible for monitoring volcanic activity. This agency uses a four-tiered system to communicate the volcano’s condition to the public and disaster management teams. The lowest status is Level I, or Normal, indicating no immediate threat and activity levels are within baseline parameters. The highest is Level IV, known as Awas or Danger, which signifies that an eruption is imminent or already underway and carries the highest risk.
The alert level is dynamic and can change rapidly based on scientific data, but Mount Agung’s status is currently at Level I (Normal). During periods of heightened unrest, such as the 2017-2019 eruption, the status was raised to Level III, or Siaga (Alert), and even Level IV. When the volcano reaches Level III or IV, the PVMBG establishes an exclusion zone, or danger zone, around the summit crater. This zone can expand from a typical radius of four kilometers up to 12 kilometers to protect communities from dangerous phenomena like pyroclastic flows and ballistic debris. The danger zone is strictly enforced, and all activity, including trekking and tourism, is prohibited within that radius when the alert level is elevated.
Major Eruption History and Volcanic Classification
Mount Agung is a classic example of a stratovolcano, also known as a composite cone, characterized by its steep profile and a history of highly explosive eruptions. This geological structure is built up over thousands of years by alternating layers of hardened lava, volcanic ash, and other volcanic debris. Its location on the Sunda Arc, part of the Pacific Ring of Fire, places it directly above a subduction zone where the Indo-Australian Plate is sliding beneath the Eurasian Plate. This tectonic setting is responsible for generating the volatile, gas-rich magma that fuels its explosive potential.
The most catastrophic event in modern history occurred with the 1963–1964 eruption, which is regarded as one of Indonesia’s largest and most devastating volcanic events of the 20th century. This eruption sequence was multi-phased, beginning with effusive lava flows followed by a powerful explosive phase. The climactic event of March 17, 1963, reached a Volcanic Explosivity Index (VEI) of 5, a rare and enormous magnitude for an eruption. This explosion generated massive pyroclastic flows, which are fast-moving currents of hot gas and rock, that swept down the volcano’s slopes. The destructive flows and subsequent cold lahars, which are volcanic mudflows triggered by rainfall, claimed an estimated 1,100 to 1,600 lives and destroyed numerous villages.
Monitoring Techniques and Warning Signs
Scientists track Mount Agung’s subterranean movements using a suite of sophisticated instruments designed to detect subtle changes that precede an eruption. One of the primary monitoring methods is the deployment of a network of seismometers around the volcano’s flanks. These instruments record the frequency and type of earthquakes, which are usually the first clear indication of magma rising through the crust.
Increasing numbers of volcano-tectonic earthquakes suggest the magma is fracturing surrounding rock, while low-frequency volcanic earthquakes indicate fluid movement, such as gas and magma, within the volcano’s plumbing system. Ground deformation is another highly sensitive indicator of magmatic unrest, as the movement of magma and gas at depth can cause the volcano’s surface to swell or bulge.
Geodesy instruments, including Global Positioning System (GPS) receivers and tiltmeters, measure minute changes in the slope and position of the ground, detecting both inflation and deflation of the volcanic edifice. Satellite-based techniques, such as Interferometric Synthetic Aperture Radar (InSAR), provide broad-area maps of ground movement, revealing patterns of uplift that signify pressurization of a magma chamber or hydrothermal system.
The composition and output of volcanic gases are also carefully analyzed for evidence of rising magma. Scientists measure the flux of gases like sulfur dioxide (SO2) and carbon dioxide (CO2) escaping through fumaroles and vents, often using specialized sensors or airborne sampling devices. An increase in the ratio of sulfur dioxide to carbon dioxide, or a sudden rise in the total volume of gas emissions, can signal that fresh, gas-rich magma is nearing the surface.