In a special report from 15 April INSIVUMEH stated that activity at Caliente cone, part of Santa María's Santiaguito lava-dome complex, continued at a high level. A loud explosion at 0825 was followed by a pyroclastic flow that descended the SE and W flanks of Caliente cone. Collapses of the E and W edges of the crater generated a mushroom-shaped ash cloud that rose 4 km and then drifted 25 km W and SW. Ash fell in areas downwind including Monte Bello, Loma Linda, Las Marías, San Marcos (10 km SW), and Palajunoj (18 km SSW). Cloud cover obscured views during 16-18 April, though during 17-18 April an ash plume from an explosion rose 700 m and drifted SW, causing ashfall in San Marcos Palajunoj. An explosion at 0800 on 19 April generated pyroclastic flows down the SE and W flanks of Caliente cone. Collapses of the E and W edges of the crater generated a mushroom-shaped ash cloud that rose 4.5 km and then drifted 25 km W and SW. Abundant ash fell in the same areas that were affected by the 15 April explosion. Strong explosions continued during 21-22 April, along with pyroclastic flows and block avalanches on the SE flank of the cone.

In another special bulletin from 23 April, INSIVUMEH stated that a very high level of activity continued, and was the highest recorded in the previous two years. Explosions generated ash plumes that rose 4-5 km above the cone and drifted 60 km downwind, causing ashfall in the departments of Quetzaltenango, Retalhuleu, and Mazatenango. Abundant amounts of ash fell in communities closer to the volcano including San Marcos, Loma Linda, Palajunoj, Las Marías, El Palmar, and San Felipe Retalhuleu, as well as in the Monte Bello, Monte Claro, El Faro, Patzulin, and La Florida farms. Pyroclastic flows traveled 3 km E and W down the Cabello de Ángel and San Isidro drainages. The report noted that during the previous four days explosions had ejected ballistics 2-3 m in diameter as far as 3 km. On 24 April explosions produced ash plumes that rose 3.3-3.5 km. During 25-26 April a few weak explosions were observed along with avalanches from the E crater rim.

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.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)