Biotite-bearing, crystal-poor rhyolite magma was the predominant magma type discharged during the 1650 AD explosive eruption of Kolumbo submarine volcano, Greece. The eruption produced thick sequences of pumice deposits (~100 m) in the upper crater walls of the volcano, but also led to the formation of extensive pumice rafts that were dispersed throughout the southern Aegean Sea, and subaerial tephra fallout as far east as Turkey. Preliminary estimates of pre-eruption volatile contents have been determined using the volatile-by-difference method on plagioclase-hosted melt inclusions and yield an average value of 6.0 wt.%. This corresponds to a pre-eruption storage pressure of 180 MPa, assuming a H2O-saturated magma. Comparison of the natural glass compositions and mineral assemblage of the Kolumbo samples with experimental results on other rhyolite magmas of similar composition in the modified haplogranite system of Blundy and Cashman (2001) supports the pressure and total volatile estimates. Pre-eruption temperature was estimated at 750° C based on the plagioclase-melt geothermometer of Putika (2008). Preliminary modeling of volatile degassing based on the pre-eruption P,T and volatile contents indicates that a fragmentation threshold of 75% can be easily obtained at water depths of 500 m (existing crater depth). The high volatile content of the Kolumbo magma and historical accounts of substantial subaerial eruption plumes suggests that the explosive eruption was driven by primary volatile degassing and that there were periods of sustained magma discharge. Initiation of the eruption may have been caused by injection of more mafic magma into the Kolumbo magma reservoir as evidenced by the abundance of mafic enclaves present in many of the pumice samples.

AGU session number V23B-2442.