From 19th-century topographic maps to modern drone surveys, a new study reconstructs the transformations of Etna's summit area from 1865 to 2024.
Over a century and a half of transformations of Etna's summit craters reconstructed through a sort of photogrammetric "time machine", capable of integrating the first topographic maps of the volcano with aerial photographs, satellite images, and modern surveys carried out with drones. This is what was presented in the study “160 Years of Etna summit craters through a photogrammetry-based time machine”, conducted by a team of researchers from theIstituto Nazionale di Geofisica e Vulcanologia (INGV), of theUniversity of Milan-Bicocca (GeoVires Lab) and dell 'University of Palermo and just published in the magazine International Journal of Applied Earth Observation and Geoinformation.
The research quantitatively reconstructs the morphological and structural evolution of Etna's summit area between 1865, the year the topographic map was created by the Military Geographic Institute (IGM), and 2024.
160 years ago the summit of the volcano was dominated by a single large Central Crater: through the integration and validation of 14 dataset, acquired with different techniques and resolutions, the researchers followed the progressive transformation of the crater area up to the current configuration, characterised by four active summit craters: Chasm, New Mouth, North-East Crater and South-East Crater.
“We have brought together in the same reference system data produced over a period of almost 160 years and with profoundly different techniques: from historical topographic maps to aerial photographs, up to satellite data and high-resolution drone surveys.”, explains Christine Proietti, INGV technologist and first author of the study. This allowed us to build a true topographic time machine to quantitatively observe how Etna's summit has changed. A key aspect of the research was the ability to compare highly heterogeneous sources: we developed a co-registration, validation, and statistical error propagation procedure that allows us to evaluate the uncertainties associated with different datasets and distinguish significant morphological variations from the errors inherent in different cartographic and topographic sources..
The reconstruction documents the transition from a predominantly monocentric configuration to a highly dynamic polycentric system, in which the four craters show different morphological behaviors. Chasm is characterized by recent construction growth; New Mouth and Northeast Crater instead, they show cycles of filling followed by subsidence; Southeast Crater, finally, is distinguished by a marked growth accompanied by a progressive expansion towards the east.
“The long-term perspective shows that the four craters, although belonging to the same summit system, have followed different morphological evolutions”, he adds Emanuela De Beni, researcher at INGV and co-author of the study. Their evolution appears consistent with the volcano's complex structural structure and, in particular, with the influence of the Northeast and South rift zones. The progressive eastward expansion of the Southeast Crater also fits into the context of the seaward deformation of Etna's eastern flank, already documented by geological and geodetic studies..
Research shows how the integration of historical cartography, photogrammetry and modern remote sensing techniques can extend the quantitative observation of a volcano well beyond the era of modern instrumental monitoringThe proposed method also constitutes a reproducible and potentially transferable approach to the study of the morpho-structural evolution of other active volcanoes around the world.
“The project also had an impact on accessible scientific dissemination”he concludes De Beni. “The digital models used to reconstruct the evolution of the craters were reproduced using 3D printing, allowing blind people to explore, by touch, the morphology of the summit of Etna and its transformations over time".
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Figure 1: Topographic map from 1865 produced by the Military Geographic Institute, the blue dots are points used to georeference historical maps
Figure 2: Shaded models of the Etna summit area from 1865 to 2024
Figure 3: Shaded models of the Etna summit area from 1865 to 2024