HR: 0800h
AN: V21E-0672    [Abstracts]
TI: Quantifying Sulphur Emissions and Atmospheric Aerosol Loading From the 1730-36 Lanzarote Eruption
AU: * Sharma, K
EM: k.sharma@open.ac.uk
AF: Volcano Dynamics Group, The Open University, Department of Earth Sciences The Open University Walton Hall , Milton Keynes, MK7 6AA United Kingdom
AU: Blake, S
EM: s.blake@open.ac.uk
AF: Volcano Dynamics Group, The Open University, Department of Earth Sciences The Open University Walton Hall , Milton Keynes, MK7 6AA United Kingdom
AU: Self, S
EM: stephen.self@open.ac.uk
AF: Volcano Dynamics Group, The Open University, Department of Earth Sciences The Open University Walton Hall , Milton Keynes, MK7 6AA United Kingdom
AB: The AD 1730-36 eruption of Lanzarote (Canary Islands) is the third largest basaltic fissure eruption known to have occurred in the last 1000 years, after the Icelandic events of Laki (AD 1783-84) and Eldgja (AD 934). Our new volume estimates suggest that the Lanzarote eruption produced ~6 km³ of alkali basalt magma along a 15-km long, E-W trending fissure. Eruptive activity occurred in five distinct phases. Each phase began with Strombolian fire fountain activity, building large spatter and scoria cones. This was accompanied and followed by effusive aa and pahoehoe lava flow emplacement. As studies in Iceland have shown, this type of sustained fissure eruption can release large amounts of SO₂ to the upper atmosphere, leading to the formation of sulphate aerosol clouds and causing widespread environmental damage and human suffering. Matrix glasses in scoria and surface lava samples have 80-300 ppm S (EMPA) and 300-600 ppm H₂O (FTIR), whereas glass inclusions in olivine have 420-2650 ppm S and 1000-5000 ppm H₂O. Low sulphur inclusions are believed to be partially degassed, representing melt that was trapped during degassing-induced crystallization that occurred as a result of shallow decompression. The inclusions with the highest sulphur contents trap the original un-degassed melt, as indicated by their consistent S/K₂O ratio (0.22). The high sulphur contents are also consistent with our finding, from olivine-spinel equilibria, that the magma was relatively oxidized (log fO₂ -4.8) therefore favouring the formation of sulphate species and preventing sulphide saturation. Our glass analyses indicate that 40 Mt of SO₂ was injected into the upper troposphere - lower stratosphere via 12-16-km-high eruption plumes and that over half this amount was released during the first year of activity. This figure correlates with published Greenland ice-core (GISP-2) data that shows an acidity spike in 1731, suggesting stratospheric transport of sulphate aerosol to the North during the first year of eruption. Historical records note the presence of a dry fog over much of Europe during 1733. This, together with proxy climate indicators such as a marked tree ring anomaly in 1732 and a known decrease in the Northern hemisphere surface temperatures suggests that the Lanzarote eruption had some impact on Northern Hemisphere climate in the years following the activity.
DE: 8408 Volcano/climate interactions (1605, 3309)
DE: 8409 Atmospheric effects (0370)
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8425 Effusive volcanism
DE: 8430 Volcanic gases
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005