Precisely measure the morphological changes that characterized the summit of Etna between 2007 and 2010, thanks to a topographic map created with LiDAR technology from an airplane. The study, signed by INGV, was published in Geophysical Research Letters
Active volcanoes change their appearance over time, especially in the summit area in correspondence with the eruptive vents. Etna, the largest active volcano in Europe, certainly holds the record. This is demonstrated by the events that in recent months have profoundly changed not only the morphology but also the structures of its summit craters and its eastern flank. A team of researchers from the National Institute of Geophysics and Volcanology (INGV), from the Catania and Pisa sections, aims to measure the volume variations and morphometric changes of Etna with ever greater precision. Geophysical Research Letters the Lidar surveys reveal eruptive volumes and rates at Etna, 2007–2010, together with the new 2010 map, in electronic attachment.
How much lava was erupted? At what effusive rate? How much material was removed by an explosive eruption? These are just some of the questions that INGV volcanologists try to give precise answers to every day.
“The survey of land on an active volcano”, explains Marco Neri, researcher at INGV in Catania and coordinator of this study, “often provides results which by their very nature are subject to a certain degree of uncertainty. Today, modern technology provides us with ever more sophisticated tools, capable of acquiring extremely precise and precious information on the surface of a volcano remotely, i.e. without coming into direct contact with it".
To measure the extent of the morphological changes that affected Etna between 2007 and 2010, INGV researchers used LiDAR (Light Detection And Ranging) technology, an "active" remote sensing system for carrying out topographic surveys high-resolution by aerial means. A laser scanner consisting of a laser transmitter, a receiver and a data acquisition and processing system is installed on the aircraft. The peculiarity of LiDAR is the very high data acquisition speed (up to 100 points per second), associated with a high spatial resolution.
"Quantifying the changes that have occurred on Etna is of fundamental importance for understanding the recent eruptive dynamics", adds Alessandro Fornaciai, a researcher at the INGV in Pisa. “The aircraft LiDAR, thanks to the overview it provides and the accuracy it achieves, is of great help because it allows to obtain, through appropriate corrections and processing, temporal sequences of high resolution digital elevation models (DEM) of the investigated area".
Thanks to the LiDAR data, it was not only possible to create a DEM of Etna that reproduces its morphology in September 2010 and one in June 2007, but by comparing them, it was also possible to measure with great precision the volume variations and morphometrics occurred in the summit area of the volcano and along the Valle del Bove. In about three years, over 86 million cubic meters of volcanic products have accumulated in the area studied, most of which (about 74 million) were erupted by an eruptive fissure opened on the upper western flank of the Valle del Bove, which resulted profoundly modified.
"The new topography of 2010 also represents a starting point for calculating the subsequent morpho-structural changes of the volcano", concludes Boris Behncke, INGV researcher in Catania. “Important changes, such as those that occurred from January 2011 onwards, which gave rise to a long series of summit eruptive events, building, in the following years, the new cone of the South-East Crater, 300 m high and growing faster than any other volcano in recorded history”.
Figure 1 - 3D perspective view of Etna showing the thickness of the deposits (mostly lava flows) emitted between 2007 and 2010 calculated from the differences of successive LIDAR DEMs. Source DEMs have a resolution of 1m. The viewpoint has an azimuth of 105° and an elevation angle of 15°. Graphic elaboration: INGV Pisa.
Figure 2 – First light of dawn on 8 May 2007: it is the last eruption of the South-East Crater. From this moment on, this crater, which arose in 1971, will no longer be active until today, and the activity will migrate to a mouth located on the lower eastern flank of this summit cone, generating the New Southeast Crater. Photo: Marco Neri.
Figure 3 – Crater located along the eruptive fissure of the 2008-2009 eruption. Photo: Boris Behncke.
Figure 4 – Aerial view, from the east, of the summit area of Etna. On the left, the cone of the Southeast Crater can be seen, "holed" at its eastern base by the eruptive vent which, from 2011 onwards, will build the New Southeast Crater. On the right, we see the eruptive fissure that fed the lateral eruption of 2008-2009. Photo: Marco Neri.
Figure 5 – First light of dawn on 8 March 2009. Valle del Bove taken from Monte Fontane. The western wall (opposite in the photo) of the valley shows the enormous mass of lava (about 74 million cubic metres) which poured along its western wall during the 2008-2009 eruption. A rivulet of incandescent lava gently feeds the lava field. Photo: Boris Behncke.
Figure 6 – Extract of the topographic map updated to 2010. The complete map can be downloaded as an electronic attachment of the scientific publication, from: http://onlinelibrary.wiley.com/doi/10.1002/2016GL068495/abstract;jsessionid=041C67D87C30BCC155A9A9D10A0C16C7.f02t02