The activity of the Mapping Laboratory "MAP-LAB"
Staff: Stefano Branca (coordinator), Boris Behncke, Emanuela De Beni, Cristina Proietti
During an eruptive crisis, various activities in the framework of volcanological monitoring allow to define, in real time, the dynamics and evolution of the eruption under way. Among these monitoring activities, the mapping of an expanding active lava flow-field is fundamentally important for an accurate and timely response by Civil Defense and local authorities.
Fig. 1. Examples of the field activities carried out by the Mapping Laboratory "MAP-LAB" to measure the dimensions of new volcanic landforms (such as the cone of the New Southeast Crater, NSEC), and to determine the temperature of an active lava flow.
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Fig. 2 Two examples of lava fountaining episodes in 2011-2012 and map of the 25 lava flow-fields formed during the paroxysmal episodes at the NSEC from 12 January 2011 to 24 April 2012. |
The Mapping Laboratory “MAP-LAB” is in charge of mapping lava flows and morphologies associated with volcanic activity. The “MAP-LAB” staff has defined an operational procedure to be applied in the case of an effusive eruption of Etna, to permit swift and accurate mapping of lava flows, collection and cataloguing of field data, and definition of the main volcanological parameters. For this aim, a geodatabase has been created with ESRI "ArcInfo" for the visualization, analysis, editing and geoprocessing of spatial data. The geodatabase is optimized for the archiving and interrogation of data correlated with objects in space. High-precision mapping of lava flows is based on data collected during field and aerial (helicopter) surveys (Fig. 1). The recent purchase of two high-precision GPS-GIS, which can be connected via cable to laser range-finding binoculars, allows to acquire from a distance the position of targets that are potentially dangerous (such as eruptive vents) or difficult to approach. Lava flows can also be mapped by kinematic GPS surveys, by walking along portions of the perimeter of the lava flow-field. During the field surveys, samples are taken from the lava, which has to be instantly chilled with water or snow, to carry out chemical analyses of the glass in the laboratory. Also in the field, the temperature of the lava is measured with a thermal camera or a thermocouple. Each measurement or sampling point is recorded by the GPS along with its associated parameters. All this information is eventually uploaded, with a simple click, into the geodatabase created ad-hoc by the "MAP-LAB" staff, thereby obtaining complete and homogeneous records of the characteristics of each eruptive event. Aerial surveys (mostly in helicopter) allow to obtain photography of the entire lava flow-field, which represents the best auxiliary to the mapping. Unfortunately, aerial surveys are carried out only rarely due to the elevated costs, and are furthermore constrained by meteorological conditions. Etna - the "training volcano" The eruptive episode of 12 January 2011 allowed to test the operational procedure described above and to verify the usefulness and reliability of the instruments used by “MAP-LAB”. Thanks to the rather favorable meteorological conditions, it was possible also to perform an aerial survey; the acquired images were georeferenced and processed to eliminate distortions caused by the topographic variations and the fact that the photos were not acquired vertically to the terrain. The combined use of field data and photos taken from helicopter allowed mapping of the lava flow in unprecedented detail. Between 12 January 2011 and 27 April 2013, Etna produced 38 paroxysmal episodes of lava fountaining from its New Southeast Crater (NSEC), which generated lava flow-fields (Fig. 2) that extended downslope into the desert-like Valle del Bove without threatening any nearby human property. These lava flows reached maximum lenghts of little more than 4 km. A few smaller lava flows were emitted from fractures on the northern and southern flanks of the NSEC. In this way, Etna served as a perfect "training camp" for the "MAP-LAB" staff. |
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Fig. 3 a) and b) The pit crater before and after the first paroxysmal eruptive episode in January 2011 (dotted red line in b shows outline of the pit's rim); c)-d)-e) evolution of the pit crater shown on digital elevation model (DEM). - Fig. 4 a) and b) Evolution of the NSEC cone in 2011 and 2012, showing remarkable growth in height and width of the cone. c)-d)-e) Thickness of volcanic products constituting the cone shown on DEM.
A rapidly changing volcano
A fine example of the rapid changes that can occur in the morphology of a volcano has lately been furnished by Etna with the growth of a new scoria cone on the eastern flank of the Southeast Crater (SEC) cone. In early November 2009, a new pit crater (5 x 8 m in diameter) opened at the eastern base of the SEC (Fig. 3); following a series of collapse events, its diameter had increased about 40-fold. By August 2011, a dozen episodes into the latest series of paroxysms, the pyroclastic material ejected by the lava fountains had constructed a cone 110 m tall around the crater; in August 2012 this cone's height had increased to 190 m (Fig. 4), and in February-April 2013 it grew further to a height of approximately 245 m. Since growth of the cone occurred exclusively during the activity of lava fountaining, we can say that the entire NSEC grew in two-and-a-half days (that is, the total duration of the 38 lava fountains from 12 January 2011 until 27 April 2013, which together lasted about 60 hours).
Fig. 5. Map of the lava flows emitted during the series of paroxysmal episodes between February and April 2013.
"Training" for future emergencies
The work carried out during 2011-2013 on the NSEC and its lava flows has been for the "MAP-LAB" staff a rather precious occasion to perform excercises and be ready to respond to a future flank eruption that might threaten populated areas or cultivated land. Such eruptions occur at irregular intervals (from less than one year to several decades) from eruptive vents that open on the slopes of Etna, more commonly at elevations above 1500 m a.s.l. (above the sea-level), but more rarely at elevations of just a few hundred meters a.s.l., in areas that are now densely urbanized on Etna's southern and southeastern flanks. In the case of a potentially destructive lava flow, the main physical characteristics of this flow, such as the effusion rate and its expansion on the terrain, must be measured with the highest possible precision, and this information must be promptly communicated to the authorities and Civil Defense to facilitate the measures and actions to be undertaken. The task of measuring the essential parameters of a lava flow and of the eruptive vents can be made rather difficult and dangerous due to explosive activity and/or the morphology of the area; in such conditions the application of the new tools described above will be of significant aid.
Further reading (in Italian)