Severe rainfall led to flash floods on Sumatra Island in Indonesia, resulting in the deaths of at least 41 individuals with several others still unaccounted for, according to officials. The torrential rains, coupled with a significant mudslide from Mount Marapi’s cold lava flow, caused a river to overflow and devastate villages across four districts in West Sumatra province late Saturday night.

More than 100 structures were submerged, and numerous people were swept away by the floodwaters, as reported by Abdul Muhari, spokesperson for the national disaster management agency, on Sunday.

Cold lava, or lahar, refers to a blend of volcanic substances and rocks that cascades down the sides of a volcano during rainfall.

Flood Deaths Rise in Sumatra

Ilham Wahab, an official from the West Sumatra disaster mitigation agency, reported that as of Monday morning, 41 individuals had lost their lives in the flooding, while 17 others remained unaccounted for. The hardest-hit regions were Agam district, where three people were missing, and Tanah Datar, where 14 individuals were unaccounted for. These areas, inhabited by hundreds of thousands of people, suffered the most severe impacts of the flood.

On Sunday, roughly half of the deceased were discovered in Canduang village, Agam district, while nine were found in Tanah Datar and eight in the Padang Pariaman region. Flash floods on Saturday also led to the blockage of main roads in Tanah Datar district due to mud, resulting in the isolation of other cities, as stated by local police chief Kartyana Putra on Sunday. Videos released by Basarnas depicted roads submerged in murky brown waters.

This calamity occurred merely two months after heavy rainfall triggered flash floods and landslides in West Sumatra’s Pesisir Selatan and Padang Pariaman districts, resulting in the loss of at least 21 lives and leaving five others missing.

Late last year, Mount Marapi, with an elevation of 2,885 meters (9,465 feet), erupted unexpectedly, claiming the lives of 23 climbers who were caught off guard. Since 2011, the volcano has been maintained at the third-highest alert level out of four, denoting heightened volcanic activity.

Under this status, climbers and residents are advised to maintain a distance of more than 3 kilometers (approximately 2 miles) from the summit, as outlined by Indonesia’s center for volcanology and geological disaster mitigation.

Marapi is renowned for its sudden eruptions, which are challenging to forecast due to the shallow source near the summit. Unlike eruptions triggered by deep magma movements, which generate detectable tremors on seismic monitors, Marapi’s eruptions occur differently. Since a January 2023 eruption that fortunately resulted in no casualties, Marapi has remained active.

It is one of over 120 active volcanoes in Indonesia. The nation’s susceptibility to seismic activity is attributed to its location along the Pacific “Ring of Fire,” a belt of volcanoes and fault lines encircling the Pacific Basin.