An M7.9 earthquake on the Pacific sea floor only 15nm offshore from Chimbote struck on 31 May 1970. In additon to the tsunami generated, the quake affected Nevado Huascaran, dislodging ice from its glaciers and picking up mud and water as a large avalanche developed. It swept down the Callejón de Huaylas valley breaking roads, railways and bridges, burst dams (releasing more water) and buried parts of Yungay and Huras, killing tens of thousands in its wake. One estimate put 800,000 people left homeless.
An international relief effort began with the USA in the lead. The US Air Force responded with:
2x UH-1 from Canal Zone units were flown into Lima
2x CH-47 with high altitude modifications were flown in from Harrisburg to Lima
Offshore from Chimbote, USS Guam
with CH-46 157668 / YM, along with 13 others aboard and embarked US Marines provided medical transport services and acted as a hospital ship for 10 days during June.