| Popis: |
Volcanic hazards associated with lava flows advancing on a snow cover are often underrated. On 16 March 2017, during a mild effusive-explosive eruption at Mt Etna (Italy) a slowly advancing lava lobe interacted with the snow cover producing a sudden, short-lasting sequence of explosions. White vapor, brown ash and coarse material were suddenly ejected, and the products hit a group of people, injuring some of them. The proximal deposit formed a continuous mantle of ash, lapilli and decimetric-sized bombs, and the ballistic material reached up to 200 meters away from the lava edge. A total deposit mass of 7.1 ± 0.8 × 104 kg was estimated, corresponding to a lava volume removed by the explosion of 32.0 ± 3.6 m3. Textural and morphological data on the ejected clasts were used to constrain a model of lava-snow interaction. Results suggest that the mechanism responsible for the explosions was the progressive pressure build-up due to vapor accumulation under the lava flow, while no evidence was found for the occurrence of fuel-coolant interaction processes driving the explosions. Although these low-intensity explosions are not too frequent, the collected data represent a unique dataset which provides useful information on the involved processes and the associated hazard, but also on possible measures of mitigation to prevent potentially dramatic accidents at volcanoes like Etna, recording up to thousands of visitors per day. |
