The twin disasters, a 7.5-magnitude earthquake and tsunami, killed thousands of people and destroyed thousands of buildings in Palu, Central Sulawesi, on 28 September 2018. While coastal areas took heavy damage by the tsunami, three large inland flows of mud caused severe damage in densely populated areas. Intense shaking from the earthquake may have triggered liquefaction and lateral spreading, processes in which wet sand and silt takes on the characteristics of a liquid. These processes, which are especially common near streams and on reclaimed land, can produce destructive mudslides even in relatively flat areas.