Effusion rate estimations during the 1999 summit eruption on Mount Etna, and growth of two distinct lava flow fields

Detailed studies of the evolution of two major flow fields during the 1999 eruption on Mount Etna provide useful insights into the development of different types of flow fields. During this eruption, two large lava flow fields were emplaced. The Eastern flow field, which formed between February and November, was erupted from three primary vents at the base of the Southeast Cone, one of four eruptive centres in the summit region of Mount Etna. This compound flow field was characterised by a complex tube network, skylights, ephemeral vents and tumuli. Between mid-October and early November, while the Eastern flow field was still active, another flow field was erupted from the western rim of the Bocca Nuova, one of the other eruptive centres. This Western flow field was emplaced during one month of discontinuous activity and is composed of discrete, channel-fed a'a flow units that formed a fan-shaped flow field. Major periods of flow advance within this flow field took place during phases of relatively high flow rate that lasted a few hours to days. The discontinuous supply prevented the formation of lava tubes within this flow field. The Eastern and Western lava flow fields from the Southeast Cone and Bocca Nuova have distinctive morphologies that reflect their emplacement mechanisms. Many of these morphological features are large enough to be seen on aerial photographs. This has implications for assessing the emplacement conditions of older flow fields on Earth and on other planets. (C) 2002 Elsevier Science B.V. All rights reserved.