Children in the Indonesian city of Palu began returning to school on Monday to tidy up their classrooms and hopefully see their friends 10 days after a major earthquake and tsunami struck.

The 7.5 magnitude quake on Sept. 28 brought down many buildings in the small city on Sulawesi island, 1,500 km northeast of Jakarta, while tsunami smashed into its beachfront.

But the biggest killer was probably soil liquefaction, which happens when a powerful quake turns the ground into a liquid mire and which obliterated several Palu neighborhoods.