Indonesia’s Semeru volcano erupted on Saturday, killing 22 people, leaving 22 missing and 56 injured. More than 5000 people were affected by the volcanic eruption, and more than 2000 took refuge in 19 evacuation points.
Saturday’s volcanic eruption produced a plume of volcanic ash that reached 15 kilometers deep into the atmosphere, accompanied by hot pyroclastic flows – dense, fast-moving solidified lava, volcanic ash and gas clouds. Volcanic mudflows, called volcanic mudflows, also roll down the steep slopes of volcanoes. Thick volcanic ash covered nearby villages and plunged some areas into temporary darkness.
Several villages were buried in volcanic material and debris up to 4 meters high, more than 3000 buildings were damaged, and the gladak Perak bridge connecting the luma River and the nearby city of Malang collapsed.
Since then, vona reported that there was further pyroclastic flow on the volcanic slope, and the volcanic ash plume was 4.5 kilometers higher than the top of the mountain. There are also reports of lava flows from the mountaintop crater.
Semeru volcano is one of the most active volcanoes in Java. It has been active in 74 of the past 80 years. The current eruption stage of the volcano began in 2014. Hundreds of meters above the crater frequently ejected volcanic ash columns, pyroclastic flows and hot lava avalanches.
Unexpected larger-scale eruption
However, unexpectedly, Saturday’s volcanic eruption was much larger than the current activity background. Eko Budi lelono, director of the Geological Bureau of the Ministry of energy and mineral resources, said that thunderstorms and continuous rainfall eroded part of the volcanic lava dome, which is the “plug” for solidifying lava at the top of the volcano. This caused the dome to collapse and triggered a volcanic eruption.
The collapse of the lava dome is a common cause of volcanic eruptions and behind some of the deadliest volcanic eruptions in history. The collapse of the unstable dome formed by solidified lava is equivalent to removing the top from a bubbling beverage bottle, depressurizing the system and triggering an eruption. Lava domes sometimes collapse under their own weight or are weakened by external weather conditions, as is clearly the case in Mount Semeru.
The fact that Saturday’s eruption was triggered by external factors rather than internal conditions makes the event more difficult to predict.
Volcano monitoring usually relies on signs of increased turbulence within volcanoes. The increase of seismicity may be a sign of magma movement underground. Another warning sign is a change in temperature or type of exhaust gas. Sometimes, small changes in the shape of volcanic or lava domes can be detected on the ground or on satellites.
In 2019, another unpredictable fatal explosive eruption occurred in whakaari (White Island), New Zealand. This event is thought to have been caused by a pressurized steam explosion rather than magma, which makes prediction challenging.
Living with active volcanoes
With the growth of the world population, more and more people live near active volcanoes. It is estimated that more than 1 billion people (14% of the earth’s population) live within 100 kilometers of active volcanoes.
In Indonesia, more than 70 per cent of the population lives within 100 kilometers of one or more of the country’s 130 active volcanoes – equivalent to a staggering 175 million people. More than 8.6 million Indonesians live within 10 kilometers of active volcanoes – completely within the range of deadly pyroclastic flows.
The fertile soil often found near volcanoes means that these communities need to balance livelihoods and risks. Paying close attention to dozens of active volcanoes poses a continuing challenge to Indonesia’s volcano monitoring and disaster management authorities.