Experts explain the serious landslide in the sunny weather in Da Nang

Landslides in the sunny weather: Rare phenomenon but not unusual

The particularly serious landslide that occurred at around 9:30 a.m. on November 14 in Phat village (Hung Son commune, Da Nang city) - the time when the rain stopped for 3 days and the weather was sunny - is making many people question the unusual nature of this phenomenon. The large slide has buried many areas, blocking more than 200m of DH4 road and leaving many people missing.

On November 15, speaking with Lao Dong, Prof. Dr. Do Minh Duc - University of Natural Sciences, Vietnam National University, Hanoi - who has many years of research on landslides in the Central Central region, has given initial analysis, and warned of the risk of continued appearance of new landslides in the coming days.

Experts said that the landslide phenomenon after many days without rain, although rare, occurred in Quang Nam (old) in 2017 and 2020. These cases all have one thing in common: before that, the area was subjected to prolonged heavy rain, making the land waterlogged, gradually losing its durability and continuing to deform for many days.

"The clay in this area is very flexible. After heavy rain, the pressure of the drainage water increased sharply, causing the soil to shift from a stable state to an unstable one. Although it is sunny, the soil continues to deform slowly - called luution - until it is completely destroyed, causing landslides, the expert analyzed.

Risk of continued large-scale landslides

According to Prof. Dr. Do Minh Duc, landslides in Pha village converge conditions to form a large slide: The topsoil is thick by tens of meters, highly flexible, easy to store water and slow to drain water;

Cracks develop deeply due to prolonged weather changes, planting - exploiting acacia, road construction, construction of works on steep slopes;

Heavy rainfall exceeds steep land threshold: in the surrounding area, from October 23 to 29, there will be more than 600 mm of rain; from November 1 to 3, there will continue to be over 100 mm of rain;

Water seeping from the surrounding water storage area may continue to "sink" the landslide even though it is already sunny.

Notably, landslides of this type do not create explosions, the soil is almost loose and flows as fast as water, making it difficult for people to recognize it in time.

Experts say that the Hung Son government's emergency evacuation of nearly 700 people is completely correct. If the landslide has blocked the flow, creating a reservoir to accumulate upstream as initially reported, it is necessary to promptly survey and have a plan to clear the flow or evacuate additional downstream areas if the risk of breaking the flow increases.

Relocation must be done before a new heavy rainstorm, as rainwater will continue to activate potential slides, he said.

According to experts, landslides in the old West of Quang Nam, now Da Nang, Quang Ngai and Ngoc Linh area (old Kon Tum) are a constant risk during prolonged rains. The warning work is only effective if there are detailed geological surveys and the site is regularly monitored.

The government needs to regularly review hillsides, areas along streams, rivers, and control human activities on steep land. In particular, perennial acacia forests and construction works above the slope speed up the formation of cracks. And the cracks that have formed cannot be connected without being connected, even if natural forests are replanted later.

"The landslide in Phat village was the result of a prolonged slope of water, deforming silently for many days before sliding down. The landslide "in the sunny sky" is not an unusual phenomenon but a warning about the sensitivity of the area to heavy rains" - Analyst.

In the coming days, when the weather is forecast to continue to have rain, the authorities and people need to be especially vigilant, urgently monitor the scene and not return to the dangerous area until there is a conclusion from the professional agency.