Scientists warn of geological disasters after rain and floods, and how to prevent them
Every year in the rainy season, localities in mountainous areas of Vietnam suffer heavy consequences from geological natural disasters, especially landslides and flash flood. In the past few days, the circulation of storm No.3 has caused very heavy rain and heavy floods; some places exceeded the highest flood level in history; lanđslides, pipe flood, and flash flood in many localities, cause very heavy damage to people and property of the people and the State.
Assoc. Prof. Dr. Tran Tuan Anh, Vice President of Vietnam Academy of Science and Technology, Director of the Institute of Geology - Photo: VGP/Hoang Giang
Please refer to the information from the Government e-newspaper about the exchange with Assoc. Prof. Dr. Tran Tuan Anh, Vice President of Vietnam Academy of Science and Technology, Director of the Institute of Geology, on geological disasters after rain and floods and the application of science and technology as well as solutions to prevent and mitigate natural disasters.
After prolonged rain and floods, how will the geology change? Can you explain the causes of these geological accidents?
Assoc. Prof. Dr. Tran Tuan Anh: During this year's rainy season, geological disasters such as landslides and flash floods have strongly affected the Northwest mountainous provinces, especially the provinces of Lao Cai, Yen Bai, Son La, and Lai Chau. Two neighboring provinces, Bac Kan and Ha Giang, are also at risk of geological disasters. These natural disasters often hit unexpectedly, causing a lot of damage to people and property.
Geologically, most of the northern mountainous area is composed of strongly weathered ancient rocks. The weathered crust like soil reaches a depth of 15m-30m. This crust often contains clay minerals (especially montmorillonite) that change their properties very strongly, especially the huge swelling in the presence of water, which determines the characteristics of this soil that is easy to deform and disintegrate.
In particular, in the summer of 2024, the North suffers from a prolonged heat wave (from April to July), the structure of the soil has been significantly destroyed. This was followed by consecutive long-term rains in August and early September due to the influence of Typhoon No. 3, the structure of the already weakened soil was easily saturated and muddy.
The slopes in the mountains are in natural conditions that are stable. But in the above adverse conditions, the durability of the soil decreases and it will collapse, burying everything at the foot of the slope.
When the slope is high, a large volume of soil collapse, causing very serious consequences; if there are many slopes collapsing in the same locality, it is a landslide disaster.
In addition, in mountainous provinces in the rainy season, flash floods also often occur. According to statistics, flash floods usually occur in a short period of time from 40 minutes to 1 hour and 30 minutes with tremendous devastation.
Flash flood occurs when there are two factors at the same time: The existence of loose soil and rocks that are poorly cohesive in the path of the flow and the appearance of currents at a speed large enough to wash away these rocks and soils. Thus, flash floods typically occur in basins with weathered crusts and landslides formations.
After a long period of rain, the soil and rocks on the moutainside slide into the stream bed, accumulatiing to form a natural dam, forming a lake on the moutain, leaving the soil and rocks at the bottom and the walls of the lake submerged for a long time.
When there continues to be long rains, the amount of water accumulates more and more, causing the dam to burst, creating a flood flow with a mixture of water, mud, stones and tres flowing rapidly, destroying all obstacles in the path.
When encoutering flatter terrain, the conductor expands, the flow velocity decreases, and soil and rock materials will accumulate and cover the entire area.
Nu village, Phuc Khanh commune, Bao Yen district, Lao Cai province before and after the landslide
Development of disaster warning maps
Can we give early warning of flash floods, landslides and geological disasters? How can people recognize the above natural disasters?
Assoc. Prof. Dr. Tran Tuan Anh: Currently, there are many technologies and methods of early warning of flash floods, landslides and geological disasters, but they often only have a good effect on a narrow scale.
For early warning of landslides, methods such as: Installation of automatic monitoring equipment to measure the displacement of the sliding block. When this movement exceeds the limit that can cause a disaster, the system will notify the authorities and residents to evacuate the dangerous place in time.
However, the limitation of this method is that in the entire mountainous area of Vietnam, there are countless slopes and slopes at risk of landslides, we do not have enough funds and human resources to carry out this work.
On the other hand, in many places without mobile phone signals, without internet, without electricity systems, signal transmission to the warning analysis center cannot be carried out.
Therefore, we can give a simple early warning to people, that is, when we observe cracks appearing on the top of the slope, in the roof body there is turbid water flowing out, it is necessary to immediately move off the slope because the slope is about to collapse.
Regarding the early warning of flash floods, due to the characteristics of rapid and unexpected occurrence, the early warning of flash floods still faces many difficulties, scientific and technological research is still in the experimental stage.
However, there is a simpler way of early warning, that is, in the rainy season, observe that the water level of the stream is naturally normal, the water level is abnormally shallow; or the natural spring water becomes abnormally cloudy, it is a sign that flash floods are about to occur and need to be relocated immediately.
Currently, to warn of landslides, flash floods and other geological disasters, we are still using maps to warn of natural disaster risks researched and built by scientists. These maps indicate areas at risk of natural disasters at different levels, but it is not yet possible to indicate when they will occur.
Vietnam Natural Disaster Atlas (land part) - Photo: VGP/Hoang Giang
Currently, how is science and technology applied in natural disaster damage prevention and mitigation? What is the effectiveness of research topics in this field?
Assoc. Prof. Dr. Tran Tuan Anh: As I shared above, scientists are conducting a lot of research in many different directions to serve natural disaster prevention, from developing methods and technologies to forecast, early warning, and immediate warning of natural disasters occurring in the territory at different scales, from the national level, to each region and location at risk of natural disasters.
Many state-level science and technology programs have been approved by the Ministry of Science and Technology, Ministry of Natural Resources and Environment, Ministry of Agriculture and Rural Development implemented through many stages, with the participation of a large number of scientists from research institutes and universities.
One of the basic solutions with long-term impacts, serving sustainable territorial planning, developing natural disaster prevention and control strategies, and response scenarios when natural disasters occur is the development of natural disaster warning maps.
So far, we have made progress in developing disaster risk warning maps at the small (nationwide) and medium (province) rates. These maps indicate areas that are likely to experience natural disasters at different levels.
The Institute of Geology (Vietnam Academy of Science and Technology) is one of the leading units in the field of natural disaster research.
For solutions to early warning of natural disasters, since the 90s, the Institute has soon applied advanced technologies to build automatic monitoring stations for landslides in many areas such as Hoa Binh, Ha Giang and some Central Highlands provinces.
The Institute has successfully developed a research methodology and developed disaster warning maps.
Especially in 2015, Institute of Geology edited and published natural disaster warning maps and the Vietnam Natural Disaster Atlas (land part) showing the results of research and assessment of the 12 most severe types of natural disasters, which have been, are and will certainly cause a lot of damage in our country: storms, droughts, floods, landslides, flash floods, mud floods, erosion ditches, karst, riverbank erosion, saltwater intrusion, coastal erosion, earthquakes and soil cracks. This project has been actively contributing to natural disaster prevention in Vietnam.
Functional forces carry out search and rescue work in Nu village, Phuc Khanh commnune, Bao Yen district, Lao Cai province, where a serious lansilde occured that left nearly 100 people dead or missing - Photo: VGP
It is necessary to plan residential areas to avoid landslides and flash floods
The recent serious landslide points are all on the list of forecast and warning areas, including sensitive key communes that need to focus on detailed investigation and assessment. So why is there still human damage? How can disaster prevention and mitigation solutions be made more effective?
Assoc. Prof. Dr. Tran Tuan Anh: There are many reasons. In which, the maps to assess the risk of natural disasters that we have built are at a scale of 1:1,000. 000, or 1:500,000, or 1:250,000, means that 1cm on the map is equivalent to 10km, or 5km, or 2.5km in the field.
Therefore, on theese maps, slopes, streams at risk of landslides of flash floods when it rains cannot be shown so that the locality is vigilant. We do not have detailed statistics and assessments of specific locations at risk of landslides and flash floods.
The long-term forecast of storm level and rainfall in the storm is and where it will occur, the timing of long-term heavy rains is also quite good, but the accuracy and detail also need to continue to be improved.
In addition, the time of rain and the amount of rainfall that causes landslides and flash floods in each specific area cannot be measured, so when natural disasters occur, they are surprising for the locality. Moreover, because natural disaster risk scenarios have not been developed to serve the response, search and rescue work, when natural disasters occur, localities are also somewhat passive.
In order to minimize damage caused by landslides and flash floods in mountainous areas, localities need to have statistics at the village level on the number of slopes and streams at risk of causing landslides and flash floods.
This work was done by researching and developing maps to assess the risk of landslides and flash floods occurring in the locality at a scale of 1:5,000 or 1:10,000. On this map, each slope and stream at risk of natural disasters will be indicated, the risks of each house when natural disasters strike.
Localities, especially mountainous localities, need to develop natural disaster risk scenarios to the village level, which indicate the direction of natural disaster risk coming, the direction of escape, and the search and rescue plan when a natural disaster occurs.
At the same time, it is necessary to plan residential areas to avoid landslides and flash floods, specifically such as: For natural disasters such as landslides, it is recommended to choose to build residential areas far from the influence of slopes. If residential areas must be near slopes, the slopes need to be reinforced with solid retaining walls and landslide disaster early warning systems installed.
An effective and economical solution in preventing flash floods is to plan safe living spaces, not in places where the flow is directed (residential area planning on the small curved bank of the stream); residential area planning only on one side of the stream (high bank is better).
There, it is possible to build shore protection works, the strip of land on the low bank is not built, is the land fund used for agricultural production and flood drainage space to reduce flood energy when natural disasters occur.
In recent years, landslides and flash floods have caused more damage to people and property than the current perception of society. In addition to the objective factor of nature, we must also pay attention to economic activities for sustainable development. We must balance economic benefits and the stability of the natural environment.
Thank you very much!
Translated by Phuong Ha
Link to Vietnamese version
