<P> 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 . </P> <P> The present period began about 150,000 years ago and involved the development of the present volcanic edifice through the emplacement of lava domes made of andesite and dacite (igneous rocks) inside older calderas . During the past 11,000 years, Nevado del Ruiz passed through at least 12 eruption stages, which included multiple slope failures (rock avalanches), pyroclastic flows and lahars leading to partial destruction of the summit domes . During the past several thousand years, eruptions of the volcanoes in the Ruiz--Tolima massif have mostly been small, and the pyroclastic flow deposits have been much less voluminous than during the Pleistocene . Since the volcano's earlier eruptions are not recorded, volcanologists have used tephrochronology to date them . </P> <P> During recorded history, eruptions have consisted primarily of a central vent eruption (in the caldera) followed by an explosive eruption, then lahars . Ruiz's earliest identified Holocene eruption was about 6660 BC, and further eruptions occurred in 1245 BC ± 150 years (dated through radiocarbon dating), about 850 BC, 200 BC ± 100 years, 350 AD ± 300 years, 675 AD ± 50 years, in 1350, 1541 (perhaps), 1570, 1595, 1623, 1805, 1826, 1828 (perhaps), 1829, 1831, 1833 (perhaps), 1845, 1916, December 1984--March 1985, September 1985--July 1991, and possibly in April 1994 . Many of these eruptions involved a central vent eruption, a flank vent eruption, and a phreatic (steam) explosion . Ruiz is the second-most active volcano in Colombia after Galeras . </P> <P> On the morning of March 12, 1595, Nevado del Ruiz erupted . The episode consisted of three Plinian eruptions, which were heard up to 100 kilometers (62 mi) from the summit of the volcano . A large amount of ash was ejected, which completely darkened the surrounding area . The volcano also erupted lapilli (a form of tephra) and pumice bombs . In total, the eruption produced 0.16 km of tephra . The eruption was preceded by a large precursor earthquake three days before . The eruption caused lahars, which traveled down the valleys of the nearby Gualí and Lagunillas rivers, clogging up the water, killing fish and destroying vegetation . More than 600 people died as a result of the lahar . The 1595 eruption was the last major eruption of Nevado del Ruiz before 1985 . The 1595 and 1985 eruptions were similar in many respects, including in the chemical composition of the erupted material . </P>

When did the volcano nevado del ruiz erupt
find me the text answering this question