The avalanche orginated at the North Peak of the Huascarán. A huge block of ice and rock fell from the mountain’s heights and accumulated ice from a glacier. This mass sped down through the valley of Rio Ranrahirca. It spilled out onto the the valley floor and followed the contours of the landscape. Some of the debris flow crashed over Shacsha hill, a natural barrier that had protected Yungay from previous glacial landslides, and onto the town that sleepy Sunday. The rest of the mass flowed into Ranrahirca and then into the Rio Santa, flowing north to Carhuaz and eventually reaching the Pacific Ocean.