Landslide Susceptibility Mapping and Their Rainfall Thresholds Model in Tinalah Watershed, Kulon Progo District, Yogyakarta Special Region, Indonesia

Landslide often occurred in Tinalah watershed, Kulon Progo District, every year. The frequency of landslide events is increasing after high rainfall intensity. Some factors control landslides such as slope gradient, land use, geological structure, slope hydrology, and geological condition. This research has an objective to develop the susceptibility map of Tinalah watershed and to identify the rainfall threshold to trigger a landslide. The development of the susceptibility map using frequency ratio method with four parameters including slope, type of rock, land use, and lineament density. The landslide data were collected during the field survey and from regional disaster management authority (BPBD) Kulon Progo. Rainfall data were collected from BMKG and GSMap. Soil analysis also was conducted to develop a numerical model to verify the rainfall threshold value. The result shows a high susceptibility of the landslide area is dominated in Tinalah watershed. The rainfall threshold for the low susceptibility of the landslide zone is I=490.14 D-1.404with 5-7 days antecedent rain. The rainfall threshold for medium susceptibility map is I=164.32D-0,689 3-7 days antecedent rain. Moreover, the rainfall threshold for the high susceptibility of the landslide zone is 111.62 D-0.779, with 2-7 days antecedent rain.

The Promotion Mechanism of Frozen Stagnant Water on the Sliding in the Loess Landslide Zone of Heifangtai

Freeze-thaw cycles can significantly change the hydrologic and thermal state of slopes in cold regions and affect their stability. Landslides occur continuously in the slip area of seasonally frozen soil area during the freezing period. The freeze-thaw action and the difference in the characteristics of the underlying surface of the slope are important factors inducing landslides. Taking Heifangtai slope in Gansu Province as an example, the freezing-thawing characteristics of the slope surfaces under different underlying surface conditions were analyzed by field monitoring. A thermohydromechanical coupling model was established to reconstruct the frozen stagnant water process of the Heifangtai landslide zone, and the impact of freeze-thaw action on the loess landslide zone was studied. The results show that differences in the underlying surface led to different freezing-thawing characteristics between the unsaturated area and the groundwater overflow zone. During the freezing period, the soil freezing depth was greater, and the freezing duration was longer in the unsaturated area. The frozen stagnant water effect of the Heifangtai loess landslide zone is obvious. The maximum difference in the groundwater level between February and August could reach nearly 1 m. Meanwhile, the frozen stagnant water process of the Heifangtai landslide zone has a slip-promoting action on the slope. The factor of safety declined during the freezing period and increased during the thawing period. It reached a minimum of 1.42 in February.

Landslide variation with morphometric factors using the GIS techniques: The case of Shaqlawa Forest

This study deals with the application of geographical information system (GIS) datasets and methods to assess the landslide susceptibility in Wadi Hujran. The area has a rocky terrain and belongs to the Shaqlawa district of the Kurdistan Region of Iraq. The region is placed towards the Northeast side of Erbil city. The region covers an area of 18.56 Km2 (1856.1 ha) and consists of rough broken and stones. The watershed area is surrounded by North latitudes 36° 21' 53.514" to 36° 17' 49.7796" and East longitudes 44° 17' 5.658" to 44° 20' 9.06". Three factors, namely the morphometric, geological, and environmental, were used to prepare the landslide susceptibility index. The study made use of AHP method and prepared a landslide susceptibility map. Data related to geology, topography, hydrology, rainfall, and land use were used to prepare the map. Physical and statistical methods were used to validate the map. A heuristic approach was incorporated to produce the final susceptibility map. ArcGIS software was used to generate the landslide zones. A total of five landslide zones were generated, which varied from very low landslide zones (80.5) to very high landslide zone (84.5). The zones also included low landslide zone (1262.2), moderate landslide zone (1505.9), and high landslide zone (566.8), and the ratio of consistency in the present study was 0.06 AHP less than 1, and all the five zones in the study were compiled landslide zonation estimated.

Landslide Zone Investigation by Determining Cracks and Cracks Compressive Strength Test in Waru District, Pamekasan Regency

Landslide zone investigation has been conducted using geoelectricity to determine the number of cracks and using a compressive strength test to determine compressive strength cracks. The result of this research is that the rock layers of Waru District consist of soil layers resulting from the weathering of quartz rock into quartz sandstone. This quartz sandstone lies on top of a more solid rock layer. The type of landslide that is formed in the Waru sub-district is translational. This type of landslide is caused by water entering the lower layer, causing landslides and the number of cracks that trigger landslides. The results of the low compressive strength test resulted in landslides. This result was due to a decrease in the number of pores filled with water and an increase in the pores that were not filled with water. This occurs due to the presence of water in the cracks, the number of cracks cavities, and the density of the cracks which results in reduced adhesion between the cracks holding layers.

A case study on causation of the landslide on 26 October 2016 in the northern Colombian Andes

This paper presents the results of a technical investigation on the causation of the landslide that occurred in Las Nieves quarry on October 26, 2016 in the municipality of Copacabana, located in the northern part of the Colombian Andes. This landslide caused the highest number of fatalities in Colombia in 2016, totalling 16 deaths. The study included field visits, soil sampling, study of the geology and geomorphology, as well as analysis of rainfall and groundwater flows presented in the area. The information collected in this study is consistent with the hypothesis that the regional groundwater flow which comes from recharge zones, generated an increase in water levels in the landslide zone thus triggering the landslide. Finally, a stability analysis (statistical analysis and sensitivity analysis) was performed using the limit equilibrium method, where the effect of the rise in the ground water table was modelled as the trigger. The results of the stability analysis showed a low safety factor for the slope, even when low water levels were considered.