Observations of eruptive activity at Santiaguito volcano, Guatemala

The study of active vent dynamics is hindered by the difficulty of directly observing features and processes during eruptive periods. Here, we describe some recent observations of the summit dome activity of Santiaguito volcano, Guatemala, from the vantage point of its parent, Santa Marı́a. We have taken 12 h of digital video of activity over a 3-year period, which includes 28 eruptions and numerous smaller gas exhalations. Santiaguito persistently extrudes a dacitic lava flow, and produces strombolian eruptions on the order of every 0.5 to 2 h; we have documented many of these eruptions as emitting from a ring-shaped set of fractures in the dome surface. The ring has apparently grown from 70 m diameter in 2002 to 120 m in 2004, which could reflect an increasing conduit opening. Eruptions typically consist of 30–60 s of vigorous emissions; measurements of emission exit velocities have ranged from 5 to 30 m/s. The observed ash bursts, correlated with measured extrusion rates, suggest an incremental plug flow through the conduit. Bubble generation and shearing at the conduit boundaries produce the ring-shaped ash and gas pulses. Continued field studies from this unique observation site may help relate summit emission characteristics to conduit geometry and eruption processes.