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),[b] 1829, 1831, 1833 (perhaps),[b] 1845, 1916, December 1984 - March 1985, September 1985 - July 1991, and possibly in April 1994.[b] 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.