Eruptions that form lava domes are extremely common. Although the majority of the mass erupts as lava, domes often also eject ash; lava domes thus ride the line between effusive (lava) and explosive (ash and pumice) activity. I use time-lapse photogrammetry to study the Santiaguito lava dome complex at the base of Santa Maria volcano (Guatemala).
Time-lapse photogrammetry provides a method for quantifying decimeter scale motion at high frequency (as fast as synchronized image sets are acquired) from a safe distance (>2.5 km). To achieve this goal I use cameras with synchronized radio triggers built by Tim Gooding (of Mineral Sciences) and a custom photogrammetry program that I have written for MatLab.
The custom photogrammetry program tracks individual points through time and space. This means that velocity fields are (or displacement fields through time) are measured.
It's a good idea to keep a safe distance from the erupting dome. Santiaguito's Caliente Dome at 0130, 12 November 2012.