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On 3 September 2011, a large-scale deep-seated landslide was triggered by heavy rainfall produced by Typhoon Talas in the Kuridaira valley, Totsukawa village, Nara Prefecture, Japan. The landslide with 850 m in length, 600 m in width and a maximum depth of 120 m became the largest biggest landslide in the 2011 disaster. The collapsed sediment estimated to be 25 million m3. The sliding soil mass moved down and then blocked a river to form a natural landslide dam in a large basin area approximately 8.7 km2. The dam had a water storage capacity of 7.5 million cubic meters.

On October 8, 2005, a huge landslide triggered by Kashmir earthquake (M 7.6) at Hattian Bala Town in the state of Azad Jammu Kashmir of Pakistan. The Hattian Bala landslide dam had a maximum depth estimated up to 500 m. The debris mass of 65 million m3 blocked two tributaries of the Karli branch of the Jhelum River and formed Karli Lake and Tang Lake. The disaster posed secondary hazards to the people living downstream of both the Karli and the Jhelum Rivers, such as the potential risk of flooding, landslide dam breaching, slope deformations/erosions. After the event, structural countermeasures were carried out to strengthen the dam. However, after a period of about four years and four months, Karli Lake breached the northwestern part of the dam on 9th February 2010 due to a continuous 5-day rainfall. Later on, Tang Lake also breached the northeastern lobe of the dam due to monsoon rains during the period from July to August of 2010. Post-formation behaviors of the landslide and breaching-inflicted changes were analysed by Konagai et al. (2011). Source: Kazuo Konagai, Ahsan Sattar (2011) “Partial breaching of Hattian Bala Landslide Dam formed in the 8th October 2005 Kashmir Earthquake, Pakistan”, Landslides Vol.9 (1), 11 pages.

The Macesnik landslide in N Slovenia was triggered in 1989 above the Solčava village, but it enlarged with time. In 2005, the landslide has been threatening a few residential and farm houses, as well as the panoramic road, and it is only 1000m away from the Savinja River and the village of Solčava. It is 2500m long and up to more than 100m wide with an estimated volume in excess of 2million m3. Its depth is not constant: on average it is 10 to 15m deep, but in the area of the toe, which is retained by a rock outcrop, it reaches the depth of 30 m. The unstable mass consists of water-saturated highly-weathered carboniferous formations. The presently active landslide lies within the fossil landslide which is up to 350m wide and 50m deep with the total volume estimated at 8 to 10 million m3. Since 2000, the landslide has been investigated by 36 boreholes, and 28 of them were equipped with inclinometer casings, which also serve as piezometers. Surface movements have been monitored geodetically in 20 cross sections. This helped to understand the causes and mechanics of the landslide. Therefore, landslide mitigation works were planned rather to reduce the landslide movement so that the resulting damages could be minimized. The construction of mitigation works was made difficult in the 1990s due to intensive landslide movements that could reach up to 50 cm/day with an average of 25 cm/day. Since 2001, surface drainage works in the form of open surface drains have mainly been completed around the circumference of the landslide as the first phase of the mitigation works and they are regularly maintained. As a final mitigation solution, plans have been made to build a combination of subsurface drainage works in the form of deep drains with retaining works in the form of concrete vertical shafts functioning as deep water wells to drain the landslide, and as dowels to stop the landslide movement starting from the slide plane towards its surface. Due to the length of the landslide and its longitudinal geometry it will be divided into several sections, and the mitigation works will be executed consecutively in phases. Such an approach proved effective in the 800m long uppermost section of the landslide, where 3 parallel deep drain trenches (250m long, 8 to 12m deep) were executed in the autumn of 2003. The reduction of the movements in 2004 enabled the construction of two 5m wide and 22m deep reinforced concrete shafts, finished in early 2005. In Slovenia, this sort of support construction, known from road construction, was used for the first time for

Karanganyar and the surrounding area are situated in a dynamic volcanic arc region, where landslide frequently occurs during the rainy season. Indeed, the rain-induced landslide disasters have been resulting in 65 fatalities and a substantial socio-economical loss in last December 2007. Again, in early February 2009, 6 more people died, hundreds of people temporary evacuated and tens of houses damaged due to the rain-induced landslide. It was found that weathered andesitic-steep slope (steeper than 30o) was identified as the highest susceptible slope for rapid landslide, whilst the gentle colluvial slope with inter-stratification of tuffaceous clay-silt was found to be the susceptible slope for creeping. Finally, a programme for landslide risk reduction and control were developed with special emphasize on community-based landslide prevention and early warning system. It should be highlighted that the social approach needs to be properly addressed in order to guarantee the effectiveness of landslide risk reduction. Source: Karnawati, D., Fathani, T.F., Ignatius, S. et al. J. Mt. Sci. (2011) 8: 149. doi:10.1007/s11629-011-2107-6

A pilot area for landslide monitoring, prediction and early warning program has been established in Banjarnegara Regency, Central Java Province, since year 2007. Based on the site investigation, it is clarified that not only the rain intensity but also the morphology and geological conditions of study area significantly control the occurrence of landslides. The unstable zone in the study area is situated at lower slope of mountains with the slope inclination of 20 degrees to 60 degrees. The moving materials consist of colluvial deposits of silty clay overlying the inclined impermeable layer of clay, which is situated at the lower part of the andesitic breccias mountain. The clay layers are inclined at the same direction of the slope (i.e. 85 degrees) and this becomes the sliding failure for the above colluvial soils. The moving zone is saturated at most of the rainy season due to the lower position of the zone comparing to the surrounding mountainous slopes. The existence of impermeable clay layer underneath the colluvial soils creates the saturation condition within colluvial soil gradually increased and maintained during the rainy season, until then the rise of pore water pressure within this soil induces the movement. Therefore, monitoring of the pore water pressure (groundwater table) in response to the rain infiltration should be the main concern in establishing early warning for the slope movement. The Asian Joint Research Project for Early Warning of Landslides consisting of International Consortium of Landslide (ICL), Gadjah Mada University (GMU), and Disaster Prevention Research Institute of Kyoto University (DPRI/KU) has conducted a preliminary investigation and established a real-time monitoring and early warning system at that pilot area. The outdoor unit of fieldserver gathers the data from multiple sensors (two long-span extensometers, raingauge, IP camera and water pressure sensor), whereas indoor processing unit will store data on the monitor, and send the data through GPRS modem to be displayed in a webserver. Source: Teuku Faisal Fathani, Dwikorita Karnawati, Kyoji Sassa, Hiroshi Fukuoka, Kiyoshi Honda. Development of Landslide Monitoring and Early Warning System in Indonesia.