2:15 PM - 2:30 PM
[HDS10-03] Landslides in humid-temperate mountainous areas in northwestern Vietnam perceived by satellite images
Keywords:Landslide, Northwestern Vietnam, Satellite image, Geology, Land-use, Heavy rainfall
Introduction
Landscape in northern Vietnam is characterized by intensive land-use on relatively steep mountain slopes, on which landslides often occur, induced by heavy rainfall brought by typhoons (or tropical storms) and convergence zones. Landslides are a major process of the geomorphic evolution in northern Vietnam and various studies for better understanding of landslides along the biophysical contexts in northern Vietnam have been progressing. We report here initial reconnaissance, which was only remotely possible due to COVID-19, on recent landslides in northewestern Vietnam, i.e. the region to the west of the Hong River (Red River).
Topography, Geology and Land-use
Three major rivers in northwestern Vietnam, namely the Hong River, Da River and Ma River, parallelly flow in the direction of NW-SE, which are aligned parallel to the Red River Fault Zone that represents the regional tectonic structure. The Con Voi Mountains have built between the Hong and Da Rivers up to the elevation higher than 2500 m. Paleozoic and Mesozoic sedimentary rocks that commonly include limestone units extensively occur in the area, while Mesozoic volcanic and pyroclastic rocks and metamorphic rocks predominantly underlie specific areas. Mountain slopes are extensively used for cultivation and forestry and are often terraced up to the ridge. Bare lands are occasionally distributed due to deforestation or intensive land-use.
Rainfall
Northwestern Vietnam is under a humid-temperate climate and experiences heavy rainfall mostly during the rainy season from April to September, which is either brought by typhoons (or tropical storms) or due to a strong wind convergence developed by the tropical disturbance together with the persistent Asian monsoon. A statistical analysis indicated an increase of heavy rainfall in northern Vietnam during both La Nina and El Nino events, suggesting an effect of the ENSO cycles on heavy rainfall in northern Vietnam. A GSM-based simulation projected an increase of heavy rainfall in the middle and late 21st century compared to the late 20th century in northern Vietnam.
Areas, characteristics and occurrence of landslides
We used multiple-year satellite images available on Google Earth as well as multiple-year images taken by the Worldview-2 and Pleiades satellites. Landslide features have been identified in various areas in northwestern Vietnam and most critical ones can be picked up in Yen Bai and Lai Chau provinces. Landslides in those areas likely occurred during the 2018 rainy season when three tropical storms, namely Ewiniar in June, Son-Tinh in July and Bebinca in August, brought heavy rainfall in northwestern Vietnam. In the Yen Bai site, numerous shallow landslides appear on deforested mountain slopes underlain by plutonic rocks at the altitudes of 1500-2000 m. In the Lai Chau site, a massive, deep-seated landslide with a dimension of 100 m in width and 650 m in length is found on broadly deforested mountain slopes underlain by on basaltic bedrocks at the altitude approximately 600 m. A village located immediately above the landslide body was disappeared after the devastating landslide. Landslide debris were deposited along an approximately 4-km section of the valley, which also caused damage.
Working progress
Geomorphic attributes, such as topography, bedrocks, soil layers, hydrology and land-use, will be investigated in the Yen Bai and Lai Chau sites to uncover conditions and mechanisms of the 2018 landslides. Results should provide key features for creating landslide risk maps in the areas and proposing a concept of disaster-preventive land-use planning that accords with regional or local biophysical (and social) contexts. Importantly, climate change adaptation should be considered in the map and concept as heavy rainfall is projected to increase through the 21st century in northern Vietnam.
Landscape in northern Vietnam is characterized by intensive land-use on relatively steep mountain slopes, on which landslides often occur, induced by heavy rainfall brought by typhoons (or tropical storms) and convergence zones. Landslides are a major process of the geomorphic evolution in northern Vietnam and various studies for better understanding of landslides along the biophysical contexts in northern Vietnam have been progressing. We report here initial reconnaissance, which was only remotely possible due to COVID-19, on recent landslides in northewestern Vietnam, i.e. the region to the west of the Hong River (Red River).
Topography, Geology and Land-use
Three major rivers in northwestern Vietnam, namely the Hong River, Da River and Ma River, parallelly flow in the direction of NW-SE, which are aligned parallel to the Red River Fault Zone that represents the regional tectonic structure. The Con Voi Mountains have built between the Hong and Da Rivers up to the elevation higher than 2500 m. Paleozoic and Mesozoic sedimentary rocks that commonly include limestone units extensively occur in the area, while Mesozoic volcanic and pyroclastic rocks and metamorphic rocks predominantly underlie specific areas. Mountain slopes are extensively used for cultivation and forestry and are often terraced up to the ridge. Bare lands are occasionally distributed due to deforestation or intensive land-use.
Rainfall
Northwestern Vietnam is under a humid-temperate climate and experiences heavy rainfall mostly during the rainy season from April to September, which is either brought by typhoons (or tropical storms) or due to a strong wind convergence developed by the tropical disturbance together with the persistent Asian monsoon. A statistical analysis indicated an increase of heavy rainfall in northern Vietnam during both La Nina and El Nino events, suggesting an effect of the ENSO cycles on heavy rainfall in northern Vietnam. A GSM-based simulation projected an increase of heavy rainfall in the middle and late 21st century compared to the late 20th century in northern Vietnam.
Areas, characteristics and occurrence of landslides
We used multiple-year satellite images available on Google Earth as well as multiple-year images taken by the Worldview-2 and Pleiades satellites. Landslide features have been identified in various areas in northwestern Vietnam and most critical ones can be picked up in Yen Bai and Lai Chau provinces. Landslides in those areas likely occurred during the 2018 rainy season when three tropical storms, namely Ewiniar in June, Son-Tinh in July and Bebinca in August, brought heavy rainfall in northwestern Vietnam. In the Yen Bai site, numerous shallow landslides appear on deforested mountain slopes underlain by plutonic rocks at the altitudes of 1500-2000 m. In the Lai Chau site, a massive, deep-seated landslide with a dimension of 100 m in width and 650 m in length is found on broadly deforested mountain slopes underlain by on basaltic bedrocks at the altitude approximately 600 m. A village located immediately above the landslide body was disappeared after the devastating landslide. Landslide debris were deposited along an approximately 4-km section of the valley, which also caused damage.
Working progress
Geomorphic attributes, such as topography, bedrocks, soil layers, hydrology and land-use, will be investigated in the Yen Bai and Lai Chau sites to uncover conditions and mechanisms of the 2018 landslides. Results should provide key features for creating landslide risk maps in the areas and proposing a concept of disaster-preventive land-use planning that accords with regional or local biophysical (and social) contexts. Importantly, climate change adaptation should be considered in the map and concept as heavy rainfall is projected to increase through the 21st century in northern Vietnam.