The first eruptions of Nevado del Ruiz occurred about 1.8 million years ago at the beginning of the Pleistocene epoch. Three primary eruption periods in the history of the massif have been identified: "ancestral", "older" and "present". During the "ancestral" period between one million to two million years ago, a complex of large stratovolcanoes was created. Between 1.0 million and 0.8 million years ago, they partially collapsed, forming large (5–10 km wide) calderas. During the "older" period, which lasted from 0.8 million to 0.2 million years ago, a new complex of large stratovolcanoes developed (including Older Ruiz, Tolima, Quindio, and Santa Isabel). Once again explosive summit calderas formed from 0.2 million to 0.15 million years ago.