Date of Award

2015

Degree Type

Thesis

Degree Name

Master of Science in Oceanography

Department

Oceanography

First Advisor

Steve Carey

Abstract

Kolumbo submarine volcano, located 7 km northeast of Santorini in the Aegean Sea, last erupted in 1650 AD resulting in significant coastal destruction from tsunamis and about 70 fatalities on nearby Thera from gas discharge. Pyroclastic materials were reported as far south as Crete and as far northeast as Turkey. Tephra from the 1650 AD submarine eruption has been correlated in sediment box cores using a combination of mineralogy and major element composition of glass shards. The biotite-bearing rhyolite of Kolumbo can be readily discriminated from other silicic pyroclastics derived from the main Santorini complex. In general, the tephra deposits are very fine-grained (silt to fine sand), medium gray in color, and covered by ~10 cm of brown hemipelagic sediment. This corresponds to an average background sedimentation rate of 29 cm/kyr in the area. The distribution of the 1650 AD Kolumbo tephra covers at least 446 km2 around the crater, nearly 5 times the approximated 97 km2 previously inferred from seismic profiles on the volcano’s slopes and in adjacent basins. Despite the expansion of the inferred deposition area, the estimated eruption volume is not enlarged significantly, and therefore remains a minimum estimate, because the box cores did not penetrate the bases of the tephra units. SEM images reveal particle morphologies attributed to multiple fragmentation mechanisms, including primary volatile degassing and phreatomagmatic activity. It is likely that phreatomagmatic activity became more important in the latter stages of the eruptive sequence when eruptions column broke the surface and a small ephemeral island was formed. We suggest that after the generation of a significant fine ash fraction during submarine and subaerial stages of explosive volcanism, the fines are efficiently removed from the vent area and transported by several mechanisms: (1) dominant local winds; (2) surges over the sea surface from subaerial eruption column collapse; (3) vertical gravity currents driven by Rayleigh-Taylor instabilities; and, (4) sediment gravity flows driven by submarine eruption column collapse. The fine-grained marine tephra deposits surrounding Kolumbo represent the complement to the very fines-poor proximal pumice sequence exposed in the crater walls.

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