The avalanche deposit consists mostly of loose material such as ash , lapilli , pumice , with only a few lithic blocks . This loose consistency may explain the lack of megablocks . Its total volume is about , less than the volume of the Mount St. Helens and Socompa deposits . It is comparable to the volume of the landslide that the Ancash earthquake triggered on Huascarán in Peru in 1970 , resulting in more than 20,000 fatalities . Evidence points to previous flank collapses at Lastarria
Ancash earthquake
1970 Ancash earthquake
Lastarria