High on the Alti Plano at the head of Colca Canyon in the town of Chivay the Sabancayo volcano can be seen erupting every 20 minutes or so in the distance:
An eruptive phase accompanied by an earthquake severely damaged Chivay's church the previous year.
The drive to the base of Sababcayo is convoluted and takes a couple of hours and is best undertaken using a 4by4.
It is well worth the trip, however if there was a next time, time permitting I would perhaps not try to get Puno in the same day, perhaps visit the source of the Amazon, just to the west with another night in Chivay.
The Alti Plano and its volcanics owe their existence to the low angle subduction of the Pacific Plate.