The eroded volcano has had at least four major eruptive periods during the past 15,000 years.
Nevado del Ruiz has undergone three distinct eruptive periods, the first beginning 1.8 million years ago.
At least one eruptive period lasted for 18 hours, creating an "exceptionally uniform" deposit.
The second eruptive period, the Cougar Stage, started 20,000 years ago and lasted for 2,000 years.
This eruptive period built a broad composite cone made of dacite and breccia.
A series of pillow lavas were also deposited during this eruptive period.
It has since alternated between eruptive and calm periods.
The most recent eruptive period of Lassen Peak began in 1914, and lasted for about seven years (see below).
The current volcanic cone formed during the present eruptive period, which began 150 thousand years ago.
During its eruptive periods, population numbers can reach hundreds of individuals per square hectare.
