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| Titel |
Estimation of CO2 flux from Lakes Monticchio, Mt Vulture, Southern Italy |
| VerfasserIn |
Agnes Mazot, Orlando Vaselli, Barbara Nisi |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050527
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| Zusammenfassung |
| Crater lakes act as huge condensers of fluids coming from volcanic-hydrothermal systems.
Water and dissolved gas composition and the flux of volatiles from lake surface provide
valuable information on the gas input from the sub-continental mantle. In quiescent and
extinct volcanoes, residual gases from degassing magmatic systems, such as CO2, may
interact with the surficial water bodies and produce vertical chemical stratification
(meromictic lakes) that may trigger limnic eruption as those occurred in Monoun and Nyos
(Cameroon).
Mt. Vulture, located in the southern Apennines, is the easternmost volcanic district of the
Roman Comagmatic Province and is a relatively small igneous complex consisting of lava
and tuff sequence and several parasitic cones, eccentric lava-plugs and domes. Basanite,
nefelinite, tephrite and phonolite are the main rock types with subordinate melilite-bearing
and carbonatitic rocks rocks. The last explosive activity of Mt. Vulture occurred 130 ka ago
with the formation of two maar craters (Lakes of Monticchio: Piccolo and Grande). In the last
200 years several gas bursts in the lakes have occurred with the last events occurring
between 1810 and 1820 when all the fish living in the Piccolo lake were killed. This
lake is permanently stratified because of the presence of a vertical water density
gradient with the deep layer not affected by seasonal mixing. A CO2 flux survey
was performed on the surface of both lakes by using the floating accumulation
chamber method. During this survey the water at different depth was also sampled for
geochemical analysis. The two lakes displayed a significant chemical stratification, mainly
consisting of an increase of the HCO3- and Ca2+ concentrations. The dissolved gas
composition was dominated by N2 in the epilimnion, whereas CO2 and CH4 were the
main gas compounds in the anoxic hypolimnion. Total CO2 emission rate from the
lakes was estimated to be 0.9 ± 0.02 t/day (Piccolo lake), and 1.9 ± 0.04 t/day
(Grande lake). The mean CO2 flux for both lakes was 4 g/m2/day. The flux measured
was quite low and homogeneous but some small areas of the Piccolo lake were
characterized by relatively high flux (up to 27 g/m2/d). The CO2 fluxes measured at Grande
lake were also confirmed by theoretical calculation carried out using an empirical
equation similar to the 1st Fick’s law equation and the chemical composition of the
water sampled. On the contrary, for Piccolo lake a CO2 flux of 0.2 g/m2/day was
calculated, i.e. more than one order of magnitude lower than that provided by direct
measurements. This suggests that the higher CO2 flux measured on this lake was
probably the consequence of another mechanism (i.e. “pockets” of CO2 coming
from the lake bottom to the surface). Further research will be carried out to have a
better understanding of the physicochemical processes occurring at Piccolo lake. |
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