 Through K @-@ Ar dating , geologist Robert Edward Drake established the age of 66 events in central Chile , and divided them into groups based on the time of their origin . In a paper published in 1976 , he described the location of each group and the west @-@ east @-@ trending movement of volcanism in the range . To the west of the Chilean Andes are an early group of eruptions , dated from the Oligocene and the Early Miocene ( 33 @.@ 3 – 20 @.@ 2 mya ) . The scale of the eruptive events that produced these features remains unclear . Further east , in the actual range , are huge numbers of eruptions . Between 15 @.@ 3 and 6 @.@ 4 mya , widespread volcanism took place , followed by extensive folding ; this process then repeated itself from 18 @.@ 4 to 13 @.@ 7 mya during the Miocene . Beginning 6 @.@ 4 mya the Chilean Andes were quiet , though whether or not this quiet period took place throughout all of the Andes remains unknown . Central Chilean volcanoes became active once again around 2 @.@ 5 mya , and have erupted almost continuously since . 
