Debris flow of the latest catastrophic landslide at Mundakkai in Wayanad travelled five times farther than the 1984 incident and covered almost 21 acres of land, shows a comparison of findings of the study report on Mundakkai landslide dated 1985 and the landslide impact map released by the National Remote Sensing Centre (NRSC).
A study report prepared by the Centre for Water Resources Development and Management, Kozhikode did a case study on Mundakkai landslide which happened on July 1, 1984. The report showed that the landslide originated at an elevation of 1,240 metres above mean sea level ( MSL) and the debris followed the path of Arunapuzha stream, destroying everything on it's way and travelled 1.5 km downstream of the origin area.
Interpretation of satellite images of ISRO released on July 31 notes that the debris flow of the landslide which happened on July 30 ran for approximately 8 km. The state emergency operations centre (SEOC) initially estimated it to be around 6 km. The ISRO note also says that the debris flow widened the course of the Iruvanjipuzha river causing breach of its banks and houses and other infrastructure along the banks were damaged by the debris flow. It originated at an elevation of 1550 m above MSL.
In 1984, the aerial extent of the landslide was 80 acres , this time it was lesser - 21 acres, however the devastation was manifold. 14 deaths were reported in 1984 and this time the death toll is far worse. The 1985 report says that the actual death would have been much more but for the fact that the landslide area was in the reserved forest and majority of the field estate workers were away to attend a festival.
Extreme rainfall was the trigger in 1984 as well. The downpour was 340 mm in 24 hours on the day of landslide. Monthly rainfall during June-July of 1984 in this region was as high as 1400 mm, the report noted. Areas around Mundakkai received 372 mm rainfall in 24 hours triggering a massive landslide in the early morning hours on July 30.
The case study done by two scientists P Basak and N B Narasimha Prasad made some crucial observations regarding Mundakkai. Unfavourable geologic environment and extreme climatological response were cited as two key reasons for the landslide.
“The landslide at Mundakkai is one of the largest of its kind not only in the Western Ghats but also in the country. Unfavourable geological formations like lateritic deposit, presence of viscous plastic clay, highly weathered rock basement, steep slope, presence of tension cracks, unusually heavy rainfall on the fateful day, extreme saturation coupled with possible tampering of natural drainage combined at various proportions and triggered this catastrope at Mundakkai,” the authors noted in the report.
The final remarks were telling. “The best way to get least affected by the natural disasters will lie in planning township and other concentrated human activities outside the periphery of the pre-calculated origin and influence zone of landslide prone areas.This has to be coupled with following the basic dictum of not doing anything that will add to the destablising forces in an already unstable system.”
Four decades later, nearly 550 houses were permitted to be built in an area which was long deemed as unstable due to unfavourable geological conditions. As per the latest estimates of the panchayat barely 20 houses remain in the landslide-hit zone.
