Landslide-prone Areas Recognised: Sumatra, Indonesia

By Barrie | December 27th, 2006 | No Comments

Unfortunately, lives are lost in landslides and property damaged. It seems to be a fact of life in Indonesia but, farmers never listen and continue clearing land for crops or structures.

Geologists in Sumatra have recognised four landslide-prone areas on the island but their scientific assessment will only fall on deaf ears, so to speak.

Geologist urges closure of landslide-prone areas
Syofiardi Bachyul Jb, Padang

Following the Dec. 15 landslide in Solok regency, West Sumatra, that killed 18 people, a geologist has urged the provincial and regency administrations to bar all human settlement in landslide-prone areas.

Ade Edward said several areas in the province were at great risk of landslides, most along the Semangko fault and other minor fault lines in Sumatra.

“The movement of the Earth’s crust in the fracture zones creates an unstable soil structure that is prone to landslides. The rock formations are not strong and are unable to bind the soil like formations in mountainous areas far from fracture zones,” said Ade, who is chairman of the West Sumatra chapter of the Indonesian Geologists Association.

Ade, who works at the West Sumatra Mining and Energy Office, has mapped out four landslide risk zones in the province. These range from a very mild earth movement zone, called the green zone, to a severe movement zone, or red zone.

According to Ade’s mapping, 60.42 percent of West Sumatra’s land area is located in landslide-risk zones. Of this figure, 31.91 percent is in the red zone, or the most at risk, and 28.51 percent is in the yellow zone, or the average earth movement zone.

A large section of the red zone is located in Solok, South Solok, Pesisir Selatan, Agam, Pasaman, Limapuluh Koto and Padang regencies.

The Dec. 15 landslide occurred in Air Dingin subdistrict, which is located in the red zone.

The red and yellow zones, located near the top of the Semangko fracture, which intersects Sumatra island through Air Dingin subdistrict, and in other minor fracture zones, are in constant motion.

“The Semangko fault shifts 12 centimeters annually due to the Indian Ocean plate pressing up against the Eurasian plate. As a result, the western part of Sumatra shifts northward while the southern part of the island moves southward, causing the soil in the fracture zone to become unstable,” he said.

A lack of government control has resulted in people building houses below cliffs and on mountain slopes in the red zone.

There also has been forest clearance activities in the red zone as people have moved in and planted crops.

“Whatever is being done to expedite human settlement in the red zone will not be fruitful. Whether they are growing crops like rice or passion fruit, which are abundant in Solok, landslides will still happen, usually triggered by heavy rain, like the landslide in Air Dingin,” Ade said.

He recommends the West Sumatra provincial administration declare areas at great risk of landslides permanently off-limits for human settlement, and resettle those people already living in high-risk zones.

The Warsi Indonesian Conservation Community, an environmental group based in Jambi, said deforestation in delta areas of the Batanghari River has contributed to landslides.

Air Dingin is located along the Sarasah River, the upstream area of the Batanghari River, which empties into the Malacca Strait in Jambi.

“Forested areas only cover 20 percent of the Batanghari River’s delta areas, far below the 30 percent stipulated in the Forestry Law. Deforestation is usually caused by the conversion of forest areas into farmland. These areas will remain vulnerable to landslides and floods that threaten residents unless they are reforested and turned into conservation areas,” Ade said.

Solok Regent Gusmal said his office would resettle as many as 60 families affected by the recent landslide in Air Dingin, and would bar new settlements in the area.

“We have prepared a plot of land in Bukit Sagi, around two kilometers from the disaster site, which has been recommended by geologists. This effort will cost around Rp 1.5 billion (about US$167,000) from the regency budget,” Gusmal said Monday.