Strombolian explosions are short blasts, separated by periods of less than a tenth of a second to several hours. Each burp probably represents the bursting of a rising bubble of gas within the magma column as it approaches the surface. The fragmented clasts propelled upwards are probably globs of the magma which formed the skin of the exploding bubble. Strombolian eruptions involve release of much larger proportions of gas to magma than other types of activity; in some cases, the magmatic material may not escape from the vent at all, and is recycled. They are usually photographed at night and are most familiar as time-exposures in which individual glowing clasts trace elegant incandescent parabolas. This daytime 1/60-second shot captures the first instants of an explosion, in which the ejected material still forms a discrete slug. Large blocks can be silhouetted against the sky on the right, and some blocks are visibly glowing against the dark central part of the column. Pacaya has been intermittently active throughout recorded history. (Fig. 6.10).

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