Shallow Submarine, Non-emergent Eruptions Revisited: Constraining Eruption Dynamics from Sampling of Floating Lava Balloons and Proximal Deposit Facies Analysis. The 1998-2001 Serreta Eruption (Azores, Portugal)

Monday, 30 January 2017: 14:30
Sovereign Room (Hobart Function and Conference Centre)
Ulrich Kueppers1, Christoph Beier2, Janis Thal3, Wolfgang Bach3, Pedro Ferreira4, Andreas Kluegel3 and Scientific team of METEOR cruise M128, (1)Ludwig-Maximilians-Universität (LMU), Munich, Germany, (2)GeoZentrum Nordbayern, Erlangen, Germany, (3)University of Bremen, Bremen, Germany, (4)Laboratório Nacional de Energia e Geologia, Amadora, Portugal
Abstract:
Between December 1998 and April 2001, a submarine basaltic eruption occurred west of Terceira Island, Azores (Portugal). This eruption produced ellipsoidal basaltic bodies (up to 3 m long and 1 m in diameter) that were observed at the ocean surface. Worldwide, only four similar eruptions have been observed: in 2011-2012 at El Hierro, Spain (e.g. Troll et al., 2012), in 1993 at Socorro, Mexico (Siebe et al. 1995), in 1891 at Pantelleria, Italy (Riccò 1892; Conte et al. 2014) and in 1877 at Big Island, Hawai’i, USA (Moore et al. 1985). Floating “lava balloons” sampled commonly consisted of a single gas-filled cavity surrounded by a few cm thick shell of vesicular lava. Kueppers et al. (2012) proposed an eruptive scenario model suggesting a generally mildly explosive eruption style from a lava-lake-like setting.

In July 2016, the German research vessel Meteor (cruise M128) performed comprehensive bathymetric surveys and sampling programs in the Azores archipelago. Using MARUM’s ROV QUEST, the eruptive vents of the 1998-2001 eruption and the proximal to distal facies were observed, mapped and described during three dives. The eruption took place along a N 110° trending fissure of approx. 2.8 km length in water depth between 200 and 400 m.

In two localities bacterial mats were found but without any temperature anomaly or evidence for active hydrothermal venting. The deposits are characterised by two facies types that intercalate in places: 1) Extensive layers of volcanic ash and fine lapilli and 2) clast-supported heaps of porous pyroclasts, many of which show signs of fluidal deformation and a hollow interior. Based on clast size and frequency, eruptive vents could be determined. Furthermore, we found no indications for effusive activity or lava lakes. We can additionally rule out the existence of the NE-SW oriented fissure based on the area of balloons floating on the sea surface and conclude that the balloon distribution was solely due to wind and ocean currents.

These studies and investigations on the Serreta eruption represent a unique data set that includes direct observation and sampling during the eruption as well as detailed mapping and facies analysis after the end of the eruption by means of ROV and TV-grab. This combination allows for unprecedented insights into the dynamics of shallow submarine eruptions.

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