This thesis describes the volcanic deposits on Nisyros, Aegean sea, Greece and uses them to understand volcanic processes and the evolution of the island. Nisyros is a small (42 km<SUP>2</SUP> in area) symmetric stratovolcano which has evolved on the eastern end of the Aegean volcanic arc over the last 200 ka of the Quaternary. The first volcanic activity was submarine. This left a layer of pillow larvas of basaltic-andesite composition overlying the Tertiary sedimentary basement of the Aegean. Subsequent volcanic activity was subaerial, and over 20 lava and pyroclastic eruptions of basaltic-andesite to rhyolite composition led to the formation of a stratovolcano. The younger eruptions were rhyolitic and the magma emitted is estimated to be of the order of a few km<SUP>3</SUP> in volume. These eruptions led to the formation of a 10 km<SUP>2</SUP> in area caldera which now dominates the centre of the island. A suite of domes were extruded progressively on western side of the caldera floor with field appearances suggesting activity continuing into the Holocene. The activity documented in historical records and seen at the present day is entirely phreatic and is the expression of a geothermal reservoir at a shallow depth below the caldera floor. The aims of this project were to describe the volcanic stratigraphy, to use the xenolith suite to understand magmatic and vent erosion processes, and to use the deposits from the three rhyolite eruptions to understand the youngest volcanic history of the island and timing of the caldera formation. Fieldwork was used to deduce the stratigraphy of the island. The stratocone succession consists of 3 cycles that start with basaltic-andesite to andesite lavas (BA&AI, BA&AII. BA&AIII) and pyroclastic deposits (SPI, SPII, SPIII) and proceed to dacite to rhyolite lava extrusions (DI, DII and RI, DIII) and pyroclastics (MSP, PK, LP).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:603684 |
| Date | January 1997 |
| Creators | Hardiman, J. C. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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