Santiaguito Dome, Guatemala, continuously extruded dacite lava and underwent daily, vertical, phreatomagmatic eruptions during 1986 to 1988. Three Landsat satellite Thematic Mapper (TM) subscenes recorded this activity over a two-year period. The subscenes show a stationary, high-temperature thermal amomaly around the active vent, Caliente. Two of the subscenes depict vertical ash eruptions, one of which reached 4.5 to 5 km above the dome. The subscenes provide evidence that a recently detected deep erosional episode on the dome did not begin significantly before February 1988.

At Pacaya Volcano, Guatemala, a basaltic cone in nearly continuous eruption since 1967, a single subscene shows a large, high-temperature thermal anomaly with the characteristics of a basaltic lava flow. Periodic processing of TM images can provide a valuable, supplemental monitoring tool for active volcanoes, particularly when on-site monitoring is limited by economic or personnel resources.