Volcanologic and petrologic analysis of the 1650 AD submarine eruption of Kolumbo Volcano, Greece

Kathleen Cantner, University of Rhode Island

Abstract

The mechanisms of submarine explosive eruptions have previously been investigated by examination of uplifted deposits on land or subaerial observations of shallow water eruptions which present significant uncertainties in the paleodepth and nature of the source activity. The 1650 AD submarine eruption of Kolumbo volcano provides a unique opportunity to study shallow water explosive volcanism by combining eyewitness observations of the eruption with direct geochemical analysis and stratigraphic reconstruction of the in situ deposits. The submarine volcano Kolumbo has a 1700 m wide, 500 m deep crater located 7 km northeast of Santorini, Greece in the central Hellenic volcanic arc. It erupted explosively in 1650 AD, which led to the formation of thick sequences of stratified pumice deposits on the upper crater walls as well as extensive pumice rafts that were dispersed throughout the southern Aegean Sea and subaerial tephra fallout as far east as Turkey.^ In 2006, Kolumbo was explored by remotely operated vehicles (ROVs) in an expedition led by the University of Rhode Island, the Hellenic Center for Marine Research (HCMR), and the Institute of Geology and Mineral Exploration (IGME) in Athens. ROV video footage from the northern and southwestern transects of the crater wall has been used to create stratigraphic sequences of the 1650 AD deposits. Petrographic and geochemical analyses of samples by X-ray fluorescence and electron microprobe reveal that the bulk of the deposit consists of white, highly vesicular, sparsely porphyritic, biotite-bearing rhyolite pumice. Pre-eruption volatile contents determined using the volatile-by-difference method on plagioclase-hosted melt inclusions yield an average value of 5.8 wt.%. Assuming a H2O-saturated magma, this corresponds to a pre-eruption storage pressure of 180 MPa, or a depth of 5 km. 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. Preeruption temperature was estimated at 750°C based on the plagioclase-melt geothermometer of Putirka (2008).^ 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, which is the maximum vent depth. The high volatile content of the Kolumbo magma and historical accounts of substantial subaerial eruption plumes suggests that the explosive eruptions were driven by primary volatile degassing and that there were periods of sustained magma discharge. Although the thinly bedded lapilli and pumice breccia deposits at Kolumbo strongly resemble similar stratified deposits at Yali in the eastern Aegean, the Kolumbo eruption was not caused by the disruption of a pumiceous dome carapace as is proposed for Yali. The 1650 AD Kolumbo eruption was likely initiated by injection of mafic magma into the magma reservoir and was driven by primary degassing. The eruption was characterized by two phases; an initial submarine eruption during which the vent became shallower as pyroclastic material accumulated, and a dominantly subaerial phase with substantial fallout from a subaerial eruption plume.^

Subject Area

Marine Geology|Geochemistry

Recommended Citation

Kathleen Cantner, "Volcanologic and petrologic analysis of the 1650 AD submarine eruption of Kolumbo Volcano, Greece" (2011). Dissertations and Master's Theses (Campus Access). Paper AAI1489586.
http://digitalcommons.uri.edu/dissertations/AAI1489586

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