A series of strong explosions that began at about 1030 on 13 July sent eruption clouds to 7.5 km. Vigorous explosive activity continued until the next morning, depositing as much as 4 cm of ash, mostly S-SW of the vent. Geologists calculated a preliminary ash volume of 2.6 x 10⁵ m³. Damage from ashfall was minimal. A pyroclastic flow extended 6.5 km down the Nimá II valley, generating a large vapor cloud where it encountered river water. An overflight on 17 July revealed that the pyroclastic flow deposit had not dammed the river, a possibility that had concerned hazard officials. Smaller explosions typical of Santiaguito's long-term eruption continued after the end of the vigorous activity. Eight explosions were recorded on 14 July, the largest producing a cloud that reached about 3,000 m above sea level (roughly 500 m above the dome's summit); the other 7 were of relatively low energy. Four low-energy explosions were recorded on the 17th.

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: E. Sánchez and Otoniel Matías, INSIVUMEH.