The following is a report from W.I. Rose, Jr., based on air and ground observations 22 January-10 February.

"Activity was similar to that of the past 5 years, characterized by steady weak gas emission from Caliente vent, punctuated by ash explosions at intervals of 1/2-6 hours. Ash from some of the explosions reached heights of more than 2.5 km above the crater. Particularly large blasts were observed on 22 January at 0945, 26 January at 1500, and 6 February at 1110. On 26 January, a dusting of ash fell on Quetzaltenango.

"Caliente vent was surrounded by a cone of debris that by 28 January had reached the height of the highest spines (2,500 m above sea level) on the dome. The cone was breached on the S side, and a 400-m-long blocky lava flow descended from the mouth of the vent down the talus slope to the S, where it broke up into hot, dusty avalanches. These avalanches occurred almost continuously and larger ones resembled small nuées ardentes. No activity (other than fumarolic) was observed anywhere else on the dome. The combination of lava flow activity and ash explosions at Caliente vent is similar to activity described by Von Türkheim in the 1930's. At that time, nuées ardentes became quite prominent."

Geological Summary. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing E towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: W. Rose, Jr., Michigan Tech. Univ.