Flash flooding and landslides on Indonesia’s main island of Java have killed at least 21 people and damaged villages and rice fields.
The nation is located in a busy earthquake zone and faces high levels of deforestation – factors that are linked to flooding and landslides, though it wasn't immediately clear if the areas hit are near mines or heavily logged areas.
A look at what makes landslides, why they happen with some frequency in Indonesia, and how Earth's warming climate may contribute to more in the future.
What is a landslide?
The British Geological Survey defines a landslide as a mass movement of material, such as rock, earth, or debris moving down a slope. Landslides can happen suddenly without any notice or slowly over time and can be triggered by heavy rainfall, erosion, or changes to the slope’s material that weakens its resistance to gravity. Heavy rain adds weight to the slope, making it more unstable, and can reduce the soil strength.
Where can landslides happen?
Factors that increase the likelihood of a landslide include the slope’s steepness; slopes that are being eroded at the base, which could be caused by the movement of an ocean or river; seismic activity like earthquakes; or other things that cause ground vibrations like mining and traffic. Certain rock types and soil particle sizes are also important factors that can determine how sturdy a slope is based on the amount of water the soil can absorb.
Why does Indonesia see so many landslides?
The current landslides and flooding are occurring in the middle of Indonesia’s rainy season, which typically lasts from October to March. Landslides are one of the most common natural disasters in Indonesia and their frequency is increasing due to heavy rainfall, earthquake activity and changes to the landscape such as mining, according to ReliefWeb, a humanitarian information service provided by the United Nations Office for the Coordination of Humanitarian Affairs.
Java is a mountainous island with active volcanoes and a study from 2019 reported the island sees the highest rate of landslides in Indonesia. More than 150 million people live on Java, an island smaller than New York state, which is home to roughly 20 million. That many people living in a small area that frequently sees flooding, earthquakes, and landslides heightens the risk for people and property.
Indonesia, a major mining nation and the largest producer of nickel and palm oil, has the highest amount of forest loss of all mining areas on the planet, according to the World Wildlife Foundation. Healthy forests can reduce the risk of landslides, whereas mining strips the topsoil and weakens a slope’s ability to withstand heavy rain and flooding.
World Resources Institute, a global research nonprofit, said tree loss in Pekalongan regency of Central Java — where some of the worst landslides occurred — was 50% higher in 2023 than it was the previous year, and more than double the rate in 2021.
Climate change and landslides
Studies have found that landslides may become more frequent with climate change as a warming atmosphere holds more water vapor that can fall in heavy rains.
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Isabella O'malley, The Associated Press
