A Ma­jor Change in the Stratigraphy of the San­torini Vol­cano in Greece

(part IV)

Santorini Traveler - - EDITORIAL -

14. Dis­cus­sion

One could ar­gue that the LPS was lo­cally eroded away prior to the LBA erup­tion, but it has not been found in drillings or at ex­cava- tion sites. Fur­ther­more, the so-called LPS de­posits in deep-sea drillings are not from San­torini. Ar­chae­o­log­i­cal ev­i­dence of Cy­cladic ob­jects at sev­eral lo­cal­i­ties un­der the so­called LPS proves that these ob­jects were buried by the LBA erup­tion and not by an older layer of pumice some 200,000 years ago. Its prod­ucts were partly de­posited on the in­ner side of the com­monly steeply slop­ing caldera wall. The to­pog­ra­phy, slump­ing and later ero­sion led to dif­fi­cul­ties in in­ter­pret­ing the lo­cal stratigraphy.

15. Con­clu­sions

A wa­ter-filled caldera ex­isted at San­torini be­fore the LBA erup­tion. The LBA pumice draped the en­tire land­scape and was thick­est on ter­races on the caldera wall (Fig­ure 2(d)). Af­ter ero­sion, pumice re­mained on ter­races at dis­tinct lev­els ( Fig­ure 7). Pumice on two ma­jor ter­races was in­ter­preted as be­ing formed by sep­a­rate ex­plo­sive vol­canic erup­tions 200,000 years apart, but in fact were both part of the same LBA erup­tive event. Study of the caldera wall and lo­cal­i­ties on Thera sug­gests that the LPS does not ex­ist and the mag­matic cy­cle the­ory is con­se­quently in­valid. The pumice be­low Fira was de­posited on the in­ner side of an ex­ist­ing caldera dur­ing the LBA erup­tion. The caldera wall, con­sist­ing of lavas and py­ro­clas­tic lay­ers, was in­ter­sected by ra­dial and con­cen­tric faults. We de­duce this from small erup­tion points ar­ranged in curved tec­tonic lines which pre­date the LBA erup­tion. Tec­tonic events gave rise to curved ter­races and niches on the caldera wall upon which the prod­ucts of the LBA erup­tion were de­posited.

These de­posits have been partly re­worked by down-slid­ing since they con­tain xeno­liths of older py­ro­clas­tic ma­te­rial, such as dark lapilli from the older Up­per Sco­ria Se­ries. This can pos­si­bly also ex­plain the old ra­dio­met­ric data ob­tained for the LPS and its slightly darker colour. The lo­cal­ity be­low Oia where Druitt [21] sam­pled is an iso­lated oc­cur­rence of welded pumice which could be a relic of an old in­tra-caldera vol­cano.

One could ar­gue that the LPS was lo­cally eroded away prior to de­po­si­tion of the LBA erup­tion, but it has not been found in drillings or at ex­ca­va­tion sites. Fur­ther­more, the so-called LPS de­posits in deep sea drillings are not from San­torini. Ar­chae­o­log­i­cal ev­i­dence of Cy­cladic ob­jects at sev­eral lo­cal­i­ties un­der the so-called LPS proves that these ob­jects were buried by the LBA erup­tion and not by an older layer of pumice. Redis­cov­ery of an old ex­ca­va­tion site at Ba­los helped us to solve a 150 years old enigma: both the so-called LPS and the UPS were de­posited by the same LBA erup­tion around 1613 BC. Its prod­ucts were partly de­posited on the in­ner side of the com­monly steeply slop­ing caldera wall. The to­pog­ra­phy, slump­ing and later ero­sion led to dif­fi­cul­ties in in­ter­pret­ing the lo­cal stratigraphy.

FIG­URE 2 Satel­lite im­age, ESA (( d), right) of Thera, the main is­land of the San­torini vol­canic group. ( a) Fira Quarry; ( b) North of Cape Alon­aki; ( c) North of Kara­georghis quarry where the UPS has been ra­dio­car­bon dated by an olive tree found in...

FIG­URE 7 The pumice and ash of the LBA erup­tion had man­tled the en­tire vol­canic ed­i­fice in­clud­ing the in­ner side of the caldera. Ero­sion has re­moved most of it but rem­nants are still vis­i­ble where con­cen­tric ter­races ex­isted on the wall. The caves of...

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