The steep-sided, glacier-clad Nevado del Tolima volcano contrasts with the broad profile of Nevado del Ruiz volcano to the north. The andesitic-dacitic younger Tolima volcano formed during the past 40,000 years, rising above and largely obscuring a 3-km-wide late-Pleistocenecaldera. The summit consists of a cluster of late-Pleistocene to Holocenelava domes that were associated with thick block-lava flows on the northern and eastern flanks and extensive pyroclastic-flow deposits. The summit contains a funnel-shaped crater 200–300 m deep.
Holocene activity has included explosive eruptions ranging in size from moderate to plinian. The last major eruption took place about 3600 years ago. Lava dome growth has produced block-and-ash flows that traveled primarily to the NE and SE. Minor explosive eruptions have been recorded from Tolima in the 19th and 20th centuries.