PVMBG Explains The Cause Of Moving Land In Sianok Bukittinggi Ngarai

Residents in Bukik Cangang Ramang Village (BKCR) Bukittinggi City have temporarily evacuated due to ground activity moving in their residential area located on the lips of Ngarai Sianok. BETWEEN/AL FATAH

The Center for Volcanology and Geological Hazard Mitigation (PVMBG) conveyed an explanation regarding the incident of a moving land phenomenon that caused temporary evacuation of residents in the Ngarai Cianok area, Bukittinggi City, West Sumatra.

Head of PVMBG Hadi Wijaya said the phenomenon was influenced by steep geological conditions and valley morphology and was prone to instability when triggered by heavy rain or earthquake vibrations, especially that the Cianok Ngarai was a steep valley with cliffs reaching a slope of more than 60 percent.

"The formation of this morphology occurs due to strong erosion in volcanic rocks influenced by regional geological structures," he said as quoted by ANTARA, Monday, November 24.

According to Hadi, the lithology of the cliffs of Ngarai Cianok is composed mainly by Pirochlastic rocks in the form of angrimbrit and floating stone tufa which are fragile, porous, and easily saturated with water. On the bottom of the valley, coluvium material and rock-collapse deposits are also found that enlarge the vulnerability of soil movement.

In addition, the area is under the influence of the active segment of the Great Patan Sumatra or Sesar Semangko. Tectonic activity is considered to trigger or expand fractures on cliffs so as to reduce rock cohesiveness.

Hadi also explained that based on a potential map of PVMBG's land movement, steeply lined areas with weathered volcanic rocks are categorized as medium to high vulnerability.

Thus, he said, settlements near the cliffs of Ngarai Sianok are areas that must be watched out for, especially during intensive rain.

PVMBG recommends technical mitigation efforts in the form of handling slope stabilization, installing surface water drainage systems, and planting strong rooted vegetation to improve soil stability.

On the other hand, the community is asked to avoid activities in the cliff lip area and vulnerable zones during heavy rain or after the earthquake. Local governments are asked to regulate the use of space, prepare evacuation routes, and prepare a disaster contingency plan based on potential landslides in the tourist area.

Head of Bukik Cangang Kayu Ramang Village (BKCR) Bukittinggi, Westi Wismar previously reported that 60 residents were evacuated due to moving ground activity and landslides on the lips of Ngarai Sianok, Monday morning.

According to Westi, the residents, the majority of whom were students and students, fled using the village head office building and a safe mosque.

Kelurahan memastikan tidak ada korban dalam peristiwa tersebut. Proses evakuasi pun dilaporkan berlangsung kondusif dan dalam pendampingan tim petugas gabungan dari BPBD, TNI/Polri dan Basarnas di Bukittinggi.