354-9 The Viability of Fulgurite Vesicles to Capture Atmospheric Conditions at the Time of a Lightning Strike

Abstract:

When a lightning strike comes in contact with sand, the rapid heating and subsequent quenching of the sediments forms natural glass structures called fulgurites. The extreme conditions of formation produce vesicles within the fulgurite walls, which may encapsulate gases from the environment surrounding the strike. Previous studies have gleaned paleoecological information from the composition of the trapped gases confirming the presence of organic matter in the original soil as well as the production of NO along the lightning channel. However, there still lacks understanding of whether the gases contained accurately reflect the atmospheric or soil conditions at the time of the strike. Fulgurites gathered from two sand mines along the Lake Wales Ridge (Florida, USA) were examined, and the presence of vesicles was confirmed using microscopy. The sand mines from which the samples were collected are fairly young (est. 1998), but the sediment itself is estimated to have been deposited in the Plio-Pleistocene. Trapped gases were released by mechanical decrepitation and analyzed by a quadrupole mass spectrometer. A known mixture of gas was used to create a calibration curve for the major atmospheric species before the samples were crushed; these species were then quantified at mass-to-charge (m/z) ratios 14, 32, 40, and 44 (N2, O2, Ar, and CO2, respectively). We also monitored m/z 30 as previous research confirms the production of NO when the energy generated by lightning breaks N2 and O2 bonds. If the gases observed do not reflect known atmospheric ratios, the observed ratios can give more insight into the chemical reactions that occur along the lightning channel whose products may have been sealed into the vesicles. Preliminary results reveal variable gas compositions between samples, which appear near but not quite atmospheric, with higher mole fractions of N2 and lower mole fractions of O2. These observations may indicate O2 consumption resulting from NO formation during the chemical processes of the strike or the denitrification of organic matter in the sand. Ongoing experiments are expected to show similar trends across the fulgurite samples and should confirm N2/Ar, O2/Ar, and CO2/Ar ratios, which will give further insight into the viability of fulgurites to capture the surrounding atmosphere.

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