By 1965 fewer than a half dozen buildings had been rebuilt in the creek valley adjacent north of the city . The valley was still filled by as many as three meters of soil and debris deposited by the 1941 avalanche . Giant boulders lay about , some protruding as many as four meters above the 1965 creek bed level . Many boulders from the 1941 avalanche were strewn down to the confluence of the creek with the Santa River . Huaraz area residents who remembered the disaster of 1941 said in 1965 that the river itself was diverted by avalanche debris for some days until eroded away and carried downstream ( northward ) , and there were boulders on the west bank that had come with the avalanche . On 31 May 1970 the same reservoir dam burst during the Ancash earthquake , which had a moment magnitude of 7.9 and a maximum Mercalli intensity of VIII ( Severe ) . Down the creek valley , again came an avalanche , eerily similar to that of 1941 . In the prior four years or so , the suburb had begun to again be redeveloped : numerous residences were built atop the 1941 avalanche deposit within the at-risk creek valley . Within its duration of 45 seconds , virtually every structure of consequence in the city 's center was destroyed . A few minutes later , the north half of the city , particularly in the creek valley , was obliterated by an avalanche of icy mud carrying boulders and other debris
Ancash earthquake
1970 Ancash earthquake
Huaraz