The evolution of lava flow-fields: observations of the 1981 and 1983 eruptions of Mount Etna,Sicily

The eruptions of Mount Etna in 1981 on the north flank and 1983 on the south flank of the volcano were of strikingly different character. The former was a short duration, high effusion rate eruption producing for the most part a simple flow-field; the latter was of relatively long duration and low effusion rate, producing a compound flow-field of overlapping flows.Despite the differences between the eruptive behaviour of these two events and the way in which the flow-field developed, both the flow-fields achieved about the same maximum length. This is considered fortuitous. The evidence suggests that the main 1981 flow stopped because the lava supply ceased and was thus volume controlled. The 1983 flow-field had a more complex history of branching, but in this case it appears that, for the longest individual flow, cooling played an important role in controlling the maximum extent of the flows.