Landslides in Indonesia (2025)
12/04/2025
Samuel Clifford
Overview of Sumatra
Sumatra, the sixth-largest island in the world and is one of Indonesia’s most diverse and dynamic regions. Stretching across 482,000 km² (186,000 sq mi), it makes up nearly a quarter of Indonesia’s land area. The island is home to approximately 60.8 million people (2023 estimate) and is renowned for its dramatic landscapes, cultural variety, and rich biodiversity. The Barisan Mountains run along its western spine, while vast lowlands and river systems dominate the east. Despite decades of deforestation, Sumatra still retains significant rainforest cover, particularly in its highlands, which shelter endangered species such as orangutans, tigers, and elephants.
Cyclone Senyar
In late November 2025, Sumatra faced one of its most destructive natural disasters in recent history. Cyclone Senyar, also known as Tropical Depression 34W in the northwest Pacific, formed on the 25th of November 2025 over the Strait of Malacca. The cyclone struck Sumatra on November 26th, bringing torrential rains and violent winds. After battering northern Sumatra, it moved into Peninsular Malaysia and southern Thailand, before weakening and dissipating by November 30th. Meteorologists noted that Senyar was Indonesia’s first recorded November cyclone and only the second cyclone ever documented in the Malacca Strait, the last being Cyclone Vamei in 2001. Its formation was highly unusual, given the region’s proximity to the equator, where cyclones rarely develop.
Image Credit: Zoom Earth – Satellite HD Map, November 26, 2025. Retrieved from 26 Nov AM | 4.6°N 98.1°E | Zoom Earth
Impact
The impact of Senyar was catastrophic. Over 1,100 people were reported dead, more than 2,700 injured, and at least 518 remain unaccounted for. Losses are estimated at $19.8 billion USD or more. The cyclone’s torrential rains triggered widespread floods and landslides, wiping out villages and destroying infrastructure. In Aceh Province, rainfall reached 16 inches in a single day, submerging communities and sweeping away four villages. In North Sumatra, torrents of timber and debris crashed into residential areas, turning logs into deadly projectiles. Rescue workers described roads lined with piles of timber that had smashed into homes. More than 570,000 residents were displaced, with roads and bridges destroyed, isolating communities and complicating rescue efforts.
After devastating Sumatra, Senyar continued westward, striking Malaysia and Thailand. Heavy rains unleashed flash floods and landslides across the region, though the vast majority of casualties occurred in Indonesia. Hundreds of thousands remain displaced, with relief operations struggling to reach affected areas.
Satellite Image on November 1, 2025
Satellite Image on November 29, 2025, After Cyclone Senyar
Causes
While the cyclone itself was the immediate trigger, experts point to deeper causes that worsened the disaster. Large sections of Sumatra’s forests have been cleared for palm oil plantations, pulpwood farms, and mining. Logs from these operations became floating battering rams during the storm, intensifying destruction. North Sumatra alone lost 28% of its tree cover between 2001 and 2024, according to monitoring groups. Environment Minister Hanif Faisol Nurofiq acknowledged that the disaster “cannot be attributed solely to natural causes.” He pledged to review environmental approvals and summon companies responsible for illegal logging and mining. The Meteorology, Climatology, and Geophysics Agency reported that warnings were issued eight days before Senyar fully formed, but not all regional leaders acted on them.
Volcanologist Tim Catron argues that deforestation was not the primary cause of the landslides, noting that the worst-hit areas were pristine rainforests on rugged mountains. He emphasized that rising atmospheric temperatures intensified the cyclone, making it stronger and more destructive.
Cyclone Senyar was both a rare meteorological event and a devastating humanitarian crisis. Its torrential rains and winds wreaked havoc across Sumatra, leaving thousands dead and hundreds of thousands displaced. While the cyclone itself was the direct cause, illegal deforestation may have made the storm more severe. However, the deforestation, while still needing to be addressed, may have not worsened the impact and disaster as much as some media outlets state.. The tragedy has reignited debates over deforestation, climate change, and governance in Indonesia, raising urgent questions about how the island can protect its people and ecosystems from future storms.
Sources
GeologyHub. “Indonesia Floods and Landslides Update.” YouTube, uploaded by GeologyHub, 2 Dec. 2025, https://youtu.be/nhywye_NcdU?si=tEu0C5_DX7ez2EiL.
Reuters. “Death Toll in Indonesia’s Floods, Landslide Hits 753, Disaster Agency Says.” Reuters, 2 Dec. 2025, https://www.reuters.com/business/environment/death-toll-indonesias-floods-landslide-hits-753-disaster-agency-says-2025-12-02/.
Paddock, Richard C., and Muktita Suhartono. “Indonesia Floods Leave Timber and Tragedy in Sumatra.” The New York Times, 3 Dec. 2025, https://www.nytimes.com/2025/12/03/world/asia/indonesia-sumatra-floods-timber-logs.html.