"Rock of the Month # 290, posted for August 2025" ---

PARICUTIN, a Small but Storied Volcano in western Mexico

The spectacular and minutely documented birth and development of Volcan Paricutin, in the state of Michoacan, makes it one of the most-cited volcanoes in the world, despite its relatively small size and brief history to date (Luhr and Simkin, 1993). Paricutin figures in numerous textbooks of introductory geology (e.g., Holmes, 1965; Tarbuck et al., 2015)! Across Mexico there are innumerable small volcanic features such as ash cones, and some large and historically active stratovolcanoes (Medina, 1980)

A brief history

Paricutin became the subject of detailed reporting in the 1940s and 1950s. As recorded by Foshag and Gonzalez (1956), there were ample eyewitness accounts by locals in and around the hamlet of San Juan Parangaricutiro. The initial volcanic outbreak took place on 20 February 1943 and growth was rapid that year. By the end of the first stage (Quitzocho period) of the volcano, on 19 October 1943, the cone was near its full height, at 365 m. There were periods of explosive volcanism, with a rain of volcanic bombs, through the Quitzocho and subsequent Sapichu and Taqui periods, as well as emission of lava flows, which eventually destroyed and virtually buried the village. Rainfall rapidly modified the volcanic landform in subsequent years. Ultimately, Paricutin reached a height of 460 metres, with an active life from 20 February 1943 to 04 March 1952 (Fries et al., 1993). The height of the edifice reached 550' (168 m) in 1 week and 1500' (457 m) in 8 months: the last similar event occurred at Jorullo volcano, 80 km to the southeast, in 1749: that volcano appeared and grew to 1000' (305 m) height in 5 months (James, 1948).

Ezequiel Ordoñez (1947), presented an early, detailed, trilingual review of the ongoing volcanic cycle. The early volcanism comprised ash, lava flows and volcanic bombs. An early eruption occurred six days after the inception of activity, and there was a major eruption on 22 April 1943. Lava flows soon surrounded the church of San Juan. Volcanic bombs of monzonite and granite were ejected, generally with glassy basaltic rinds. Fumaroles formed. and breadcrust bombs were hurled out. The village of San Juan itself was destroyed on 20 July 1944. The total volume of all erupted material was estimated to represent some 1.4 km³ within the magma chamber (Wilcox, 1954). The eruption of lava was quite continuous over 9 years, whereas pyroclastic material was ejected more erratically. The main eruptive sites were the northeast and southwest bases of the main cone (Wilcox, 1954).

The rocks of Paricutin

There are many volcanoes in western Mexico (Lopez Ramos, 1983). The wider region around Paricutin has some 900 cinder and lava cones, but no large active composite volcanoes, unlike other parts of Mexico. Olivine basalts and olivine andesites, generally calc-alkaline in composition, predominate. Williams (1950) provides maps of the area, and notes the distribution of lavas: basalt, andesite, olivine andesite, olivine basalt, hypersthene andesite and iddingsite-rich basalt. The lavas may display olivine phenocrysts with Cr spinel inclusions. Minerals include olivine, plagioclase, pyroxene, spinels and other oxides, and hornblende, as described by Hasenaka and Carmichael (1987). During the eruptions the lavas progressed from olivine-bearing basaltic andesite to hypersthene andesite (Housh, 1995). Glass melt inclusions hosted in olivine in tephra help to document the evolution of the cinder cone, 1943-1952 (Luhr, 2001). Samples are vesicular glass with microphenocrysts and microlites. Basaltic andesite seems to be the most abundant magma type rising from upper mantle and lower crustal depths in the region (Luhr and Lazaar, 1985). Similar volcanic fields occur elsewhere in Mexico, as in the area south of Mexico City (Martin del Pozzo, 1982; Nelson and Sanchez-Rubio, 1986).

Figs. 3-5: Two views of Paricutin on a rainy day in September 1987, showing the defiant, upstanding church tower, and the irregular forms of the surrounding lava flows. We had glimpsed the volcano Jorullo (Fig. 5, lower) the day before, in similarly cloudy conditions. Jorullo predates Paricutin by just two centuries, a geological instant!