The October 1902 plinian eruption of Santa Maria volcano, Guatemala

Abstract

The October, 1902, eruption of Santa Maria Volcano, Guatemala, was one of the largest this century. It was preceded by a great earthquake on April 19 centered at the volcano, as well as numerous other major earthquakes. The 18–20 hour-long plinian eruption on October 25 produced a column at least 28 km high, reaching well into the stratosphere. The airfall pumice deposit covered more than 1.2 million km 2 with a trace of ash and was only two meters thick at the vent. White dacitic pumice, dark gray scoriaceous basalt (with physically and chemically mixed intermediate pumice) and loose crystals of plagioclase, hornblende, hypersthene, biotite and magnetite make up the juvenile components of the deposit. Lithic fragments are of volcanic, plutonic, and metamorphic origin. The plinian deposit is a fine-grained, crystal-rich, single pumice fall unit and shows inverse grading. Mapping of the deposit gives a volume of 8.3 km 3 within the one mm isopach. Crystal concentration studies show that the true volume erupted was at least 20 km 3 (equivalent to 8.5 km 3 of dense dacite) and that 90% of the ejecta was less than 2 mm in diameter. The plinian volume eruption rate averaged 1.2 × 10 5 m 3s −1 and the average gas muzzle velocity of the column exceeded 270 ms −1. A total of 8.3 × 10 18 J of energy were released by the eruption. A knowledge of both theoretically derived eruption parameters and contemporary information allows a detailed analysis of eruption mechanisms. This eruption was the major stratospheric aerosol injection in the 1902–1903 period. However, mid- to low- latitude northern hemisphere temperature deviation data for the years following the eruption show no significant temperature decrease. This may be explained by the sulfur-poor nature of dacite magmas, suggesting that volatile composition, rather than mass of volatiles, is the controlling parameter in climatic response to explosive eruptions.