A modelling approach to the investigation of the effects of the Minoan supervolcanic eruption on Aegian sand fly diversity

The late Bronze Age eruption of the Thera volcano was among the largest eruptions of the Holocene era. This catastrophic event might perish all organisms from the ancient Santorini and could seriously impact the sand fly fauna of the Aegean islands. To investigate these effects, the survival possibility of the sand fly fauna in the Santorini islands and the biogeographic investigation of the sand fly fauna of eleven Aegean islands were conducted. It was found that only the south and east slopes of the massifs of Thira could provide refuge for sand fly populations. The expression-based heat map of the Jaccard coefficient matrix data showed that the Santorini islands and their neighbouring Anafi, Folegandros had clearly different z-score patterns compared to the other islands. It could be a late sign of the devastating effect of the Minoan eruption and/or the consequence of the distance of these islands from the mainland. Neither the glacial seashore patterns nor the geographic-climatic conditions can explain the present sand fly fauna of the Aegean Archipelago. If the sand fly populations of ancient Santorini survived the Minoan cataclysm, it could indicate that the environmental tolerance and the resilience of the sand fly populations can be high, and local geological and geomorphological conditions can play a greater role in the survival of sand fly species than previously assumed.

Gravity observations on Santorini island (Greece): Historical and recent campaigns

Santorini is located in the central part of the Hellenic Volcanic Arc (South Aegean Sea) and is well known for the Late-Bronze-Age “Minoan” eruption that may have been responsible for the decline of the great Minoan civilization on the island of Crete. To use gravity to probe the internal structure of the volcano and to determine whether there are temporal variations in gravity due to near surface changes, we construct two gravity maps. Dionysos Satellite Observatory (DSO) of the National Technical University of Athens (NTUA) carried out terrestrial gravity measurements in December 2012 and in September 2014 at selected locations on Thera, Nea Kameni, Palea Kameni, Therasia, Aspronisi and Christiana islands. Absolute gravity values were calculated using raw gravity data at every station for all datasets. The results were compared with gravity measurements performed in July 1976 by DSO/NTUA and absolute gravity values derived from the Hellenic Military Geographical Service (HMGS) and other sources. Marine gravity data that were collected during the PROTEUS project in November and December 2015 fill between the land gravity datasets. An appropriate Digital Elevation Model (DEM) with topographic and bathymetric data was also produced. Finally, based on the two combined datasets (one for 2012–2014 and one for the 1970s), Free air and complete Bouguer gravity anomaly maps were produced following the appropriate data corrections and reductions. The pattern of complete Bouguer gravity anomaly maps was consistent with seismological results within the caldera. Finally from the comparison of the measurements made at the same place, we found that, within the caldera, the inner process of the volcano is ongoing both before, and after, the unrest period of 2011–2012.

Using “Selfie drones” for 3D mapping of volcano-tectonic features in Santorini, Greece

<p>Generally, key geological outcrops are inaccessible for classical mapping due to the hard-logistic conditions of their location in remote or dangerous areas like active volcanoes or fault zones. The UAV-based photogrammetry is a helpful technique to overcome such difficulties in site investigation. It allows a very high-detailed 3D model reconstruction of relevant outcrops, providing also the possibility to cover wider areas.</p><p>In this study, we tested the use of a “Selfie drone” aimed at outcrops reconstruction for 3D mapping of volcano-tectonic features. Two different sites in Santorini volcanic complex with different characteristics have been chosen: i) the Vlychada Beach, located in the southern part of the island, characterized by vertical cliffs that offer great exposure of the pumice layers from the well-known Late Bronze Age (LBA) (Minoan) eruption and ii) a historical volcanic crater located in the northern part of Nea Kameni island, related to the 1570 A.D. eruption, with a diameter of about 85 m, which is mostly inaccessible within its internal part and cannot be studied by classical field methods. </p><p>The “Selfie drone” which was used for the photo collection, is a 0.300-kg quadcopter equipped with a 12 Megapixel camera, EXIF information (Exchangeable Image File Format) and GPS coordinates. This drone has a flight time of approximately 16 minutes. A total of about 1900 photos has been collected, considering both sites, that have been reconstructed using photogrammetry techniques.</p><p>The resulting 3D models are characterized by a sub-centimetric texture resolution, allowing detailed mapping of the Minoan pumice layers, fractures, crater geometry, and related volcanic deposits, proving the usefulness of “Selfie drones” for geological – tectonic mapping.</p>

The Minoan Santorini Eruption and its14C Position in Archaeological Strata: Preliminary Comparison Between Ashkelon and Tell El-Dabca

ABSTRACTThe volcanic mega event of the Minoan Santorini eruption constitutes a time anchor in the 2nd millennium BCE that is inherently independent of archaeology and political history. It was a geological event. Yet the dimension of time in geology is not different than in archaeology or human history. Why then does archaeological dating usually place the Minoan Santorini eruption in the 18th Dynasty around 1500 BCE, whilst radiocarbon dating of the volcanic event at Akrotiri (Thera) yielded a calibrated age of 1646–1603 cal BCE, a difference of more than a century? The crux of the problem lies apparently in the correlation between archaeological strata and political history. We present radiocarbon dates of Ashkelon Phases 10 and 11 in comparison to Tell el-Dabca and the Santorini eruption, based only on14C dating. Tell el-Dabca Phase D/2 is slightly older than the volcanic event. But Phase D/1 or Phase C/2-3 could have witnessed the eruption. Ashkelon Phase 11 has similar radiocarbon dates as Tell el-Dabca Phases E/2, E/1 and D/3, all being significantly older than the Minoan eruption. It seems that the duration of Ashkelon Phase 10 includes the temporal occurrence of the Minoan Santorini eruption within the Second Intermediate Period.

ROCK MAGNETIC AND PALAEOMAGNETIC ANALYSES ON LITHIC FRAGMENTS FROM THE ARCHAEOLOGICAL SITE OF AKROTIRI, SANTORINI

Rock magnetic and palaeomagnetic analyses on lithic clasts collected from the pumice fall deposited inside the archaeological site of Akrotiri have been applied in order to estimate the deposition temperature of the first volcanic products of the Minoan eruption. A total of 50 lithic clasts have been collected from four different locations inside the excavation of Akrotiri. All samples have been stepwise thermally demagnetized and the obtained results have been interpreted through principal component analysis. The equilibrium temperature obtained after the deposition of the pumice fall varies from sample to sample but generally shows temperatures around 240-280oC. These temperatures are in good agreement with those estimated from lithic clasts from the Megalochori Quarry while they are higher compared with those from ceramic fragments from Akrotiri. The new temperature data presented here show that the pumice fall was still relatively hot when deposited inside the archaeological site and even if it interacted with the buildings, often causing the collapse of roofs, it still remained hot with mean temperature around 260oC.

Late bronze age pottery as indicator of the deposition temperatures of the Minoan pyroclastic products, Santorini, Greece.

The Minoan eruption of Santorini volcano (Greece) took place in the Late Bronze Age (17th century BC) and produced a great volume of volcanic products that covered the whole island and buried every human settlement under meters of pyroclastic deposits. In this study we used thermal analysis of the magnetic remanence carried by pottery fragments buried under the pyroclastic deposits in order to estimate the thermal effect of the Minoan volcanic products on the pre-eruption habitation level. A total of 70 samples, prepared from 45 independent pottery fragments, have been studied. Samples were collected from three different sites, situated at the southern part of the island. Stepwise thermal demagnetizations reveal that the pottery fragments generally carry a two-component remanent magnetization. Interpretation of the demagnetization results using the normalised intensity decay curves and the orthogonal projection diagrams indicates that most samples were re-heated at temperatures around 160-260o C. The obtained results represent the equilibrium temperatures reached after the deposition of the pyroclastic fall and show that the pyroclastic fall deposits at distances around 6 to 9 km from the eruption vent were still hot enough to reheat the buried pottery at such temperatures.