Analysis of Galileo Near Infrared Mapping Spectrometer (NIMS) observations of Marduk Fluctus, a volcano on the jovian moon Io, reveals a style of volcanic activity not previously seen there – a powerful thermal event lasting only a few minutes in 1997. The thermal emission rapidly fades, suggesting extremely rapid cooling of small clasts. The duration and evolution of the explosive eruption is akin to what might be expected from a strombolian or vulcanian explosion. The presence of such events provides an additional volcanic process that can be imaged by future missions with the intent of determining lava composition from eruption temperature, an important constraint on the internal composition of Io. These data promise to be of particular use in understanding the mechanics of explosive volcanic processes on Io.