About 50 different volcanoes and geothermal features have been active in the Central Andes during the Holocene, with earthquakes observed at Guallatiri, Irruputuncu, Isluga, Lascar, Olca, Parinacota and Putana. Most volcanoes of the Central Volcanic Zone (CVZ) are relatively poorly researched and many exceed of elevation. Some of these volcanoes were active during historical time; these include El Misti, Lascar, San Pedro and Ubinas; the largest historical eruption of the CVZ occurred in 1600 at Huaynaputina. Other volcanoes in the CVZ that have been the subject of research are Galan and the Purico complex. The CVZ has a characteristically thick crust () and the volcanic rocks have peculiar oxygen and strontium isotope ratios in comparison to the Southern Volcanic Zone (SVZ) and the Northern Volcanic Zone (NVZ).