Why landslides occur in Lao Cai, Cao Bang, Yen Bai?

This is the first time I witness such fatal landslides that killed so many people since 1989, said Vu Trong Hong, former Deputy Minister of Agriculture and Rural Development.

Yagi, the strongest storm recorded over the last 30 years, hit Viet Nam's northern coastline on September 7 and brought heavy rain, prompting the Viet Nam Meteorological and Hydrological Administration to issue the pink warning – the highest level of the five-tier warning system for landslides and flash floods over the subsequent three days.

Based on the warning level, several northern localities evacuated citizens from areas with high risk of flash floods and landslides but it was not enough as all 14 northern mountainous provinces experienced flash floods and landslides, with seven of them documenting deaths.

The massive landslide in Lang Nu village in Lao Cao province on September 10 was the most deadly horror as it left 52 people dead and 14 others still missing.

The same day, two more deadly landslides occurred in Lao Cai, killing 12 people and other 11 persons are still missing.

Lao Cai become the hardest-hit locality with 172 deaths and missing people, accounting for 49 percent of the death toll from the aftermath of the typhoon, followed by Cao Bang with 58 dead and missing or 16 percent, and Yen Bai with 54 dead and missing or 15 percent, as of September 15.

With 40-year experience in geology studies, Tran Tan Van, former Director of the Institute for Geology and Minerals under the Ministry of Natural Resources and Environment said the expansion of flash floods and landslides to 14 localities in the northeastern region to Nghe An and Thanh Hoa is an abnormal phenomenon.

Even localities with low risk of landslides such as Cao Bang and Ha Giang reported massive landslides.

A survey, carried out by the Institute for Geology and Minerals in 2012-2020, showed that northweast part (Hoa Binh, Lai Chau, Son La, Dien Bien, Lao Cai and Yen Bai) accounts for 61 percent of landslides of north Viet Nam while the eastern part (Tuyen Quang, Ha Giang, Bac Kan, Cao Bang, Lang Son, and Bac Giang) only makes up 39 percent.

Despite its low risk, Cao Bang still experienced great damages, ranking second in terms of human loss.

Ten days before the typhoon, Lao Cai, Yen Bai, and Cao Bang recorded the average daily rainfall of over 10mm. One week before the storm, Yen Bai experienced a daily rainfall of 270mm.

Two days after the storm, the daily rainfall in 14 northern mountainous localities averaged around 130mm. In the following four days, the region reported a rainfall of 470mm each day.

The above situation prompts the need to build landslide and flash flood risk maps that are most detailed possible, said Trinh Hai Son, Director of the Viet Nam Institute of Geosciences and Mineral Resources.

Such maps should provide real-time warnings, he added./.