Attabad landslide on 4th January 2010: a pakistani disaster

Pakistan is a land of extremes where the mountains are extremely young and gravitational processes are on the agenda. On 1974 before and on 2002 after, two particularly violent earthquakes occurred in Hunza area producing tension cracks in the slope where the so called Attabad landslide happened in 2010. These tensional cracks and ruptures in a so vulnerable area remained unchanged for a long period of time until the paroxysmal moment came and the phenomena has been triggered again. The present paper focus its attention on the importance of on field monitoring technique in remote areas in order to prevent social economic disasters like the one occurred. Focus Humanitarian Assistance, Pakistan produced the first reconnaissance field assessment reports on the Active Landslide at Attabad in 2002, and subsequently in 2006 and 2007. The 1974 Hunza earthquake and the 2002 Astor valley earthquake (6.5 Richter scale) produced some tensional cracks and displacements at points of contact between a rocky and overburdened slope (scree slope) and material of colluvial nature comprised of sub-angular to sub-rounded boulders, cobbles and gravel with sand and silt matrix at Attabad. These tensional cracks and ruptures in a vulnerable area remained unchanged for a long period of time. The downward movement along the main scarp observed were about 6 to 260 cm in 2002. These cracks became wider (1- 80 cm) when the earthquake on October 8, 2005 hit the entire region. With distant aftershocks, potential amplification effects, and thunder storm rains, a slope mass began moving downward in the form of slump and debris flow two years ago. However, due to lateral movement of slope, lateral gaps in tensional cracks and wedge failure, a strong downward movement of this vulnerable, threatened area was triggered, putting locals at high potential disaster risk on 4 January 2010, at Sarat, Attabad. The Hunza river formed a landslide-dammed lake of about 10 km upstream of Sarat-Gogal Gulmit. The daily water level in this lake is continuously rising. In 1858 historically important landslides also dammed the Hunza river 35 kilometres upstream, from Salmanabad to Khabar in the Hunza region. The slide debris mass in Attabad on 4 January 2010 fell for about 1.5 kilometres (Figure 1). The movement can be divided essentially into four different phases: 1. Rock fall of large boulders from the right hydrographic side which occluded part of the riverbed, squeezing the clay deposits derived from the lake created downstream by the event of 1858. 2. The squeezed materials invested the opposite banks reaching an elevation of 2,460 m and collapsed over the previously deposited rocky material, covering it all. 3. Another rock fall, again from the right side, submerged the previous one, running through it and giving the actual shape to the deposit (Figure 1). 4. The material squeezed through a mud flow reached 0.8 km upstream and 1.2 km downstream to the dam that had been created. The colossal amount of clay deposit is due to sedimentation caused by the blockage of the Hunza river by the ancient landslide. When the dam formed, a new lake was created. The disaster affected several small settlements, mainly Sarat, Salmanabad, Attabad Bala, Payeen and Ayeenabad. Burial of villages under the debris flows and rock avalanches was followed by the lost of at least nineteen lives, with numerous persons injured or missing. Attabad, comprised of about forty-three houses, numerous cattle and thousands of fruit and timber trees, is completely buried under the landslided rubble. The Sarat and Salmanabad villages, however, had relocated due continuous landslides in the area.