Cycles and trends in the recent eruptive behaviour of Mount Etna (Italy)

Mount Etna is among the few volcanoes on Earth that erupt nearly continuously, but its activity (in terms of output rate and flank eruption frequency) undergoes significant fluctuations in time. Such fluctuations do not occur in a random manner but represent various stages of cycles on a scale of decades and centuries. Recurrent patterns are particularly evident since 1865 with four complete cycles and a fifth one initiated in 1993. Each cycle consists of three phases beginning with low-level activity followed by near-continuous summit activity and culminating with a series of flank eruptions of which the last is commonly the most voluminous. A distinct increase in the output rate of Etna and more frequent and voluminous summit and flank eruptions since 1950 may be interpreted as part of a longer cycle that began after a large eruption in 1669 and has not yet reached its culminating phase. If that trend continues, the activity of Etna might become similar to that of the 17th century, when flank eruptions were more voluminous than ever since; however, it is difficult to assess when this will take place