Evaluating Reflectance Spectroscopy as a Method of Rapid Cryptotephra Identification: Tephrochronology Of the Lesser Antilles Arc.
Fisher, Elizabeth A.
- The recent reactivation of Montserrat’s South Soufrière-Soufrière Hills volcanic complex presents significant risk to local populations, and hazard assessments vital to their safety depend on a thorough understanding of the eruptive history of the island (Le Friant et al., 2011). Development of a comprehensive volcanic record, dependent on identifying volcanically deposited tephra layers preserved ... read morein hemipelagic sediment, is currently hindered by the lack of a rapid, non-destructive method of identifying cryptotephra (tephra layers invisible to the naked eye) in marine sediment cores. This work evaluates reflectance spectroscopy as a rapid, non-destructive method of identifying cryptotephra in ~7.5 m of marine core drilled during Integrated Ocean Drilling Program (IODP) mission 340 at site U1396 (IODP E340-PR). Vis-NIR [0.4-2.5 μm] reflectance spectra were collected at 0.5 cm down-core resolution using an ASD Fieldspec© spectrometer, and locations of potential cryptotephra layers identified using spectral summary parameters sensitive to iron content (0.95 μm integrated band depth) and clay minerals (2.202 μm band depth) (McCanta et al., 2014). Component analysis of the volcanic sediment fraction found at these locations reveals that spectral signatures indicative of tephra correlate with increased percentages of pumice and juvenile/angular volcanic materials likely emplaced by explosive eruptions. This suggests that reflectance spectroscopy is an effective means of identifying cryptotephra in situ. When employed in concert with other core scanning techniques, Vis/NIR spectroscopy could facilitate rapid shipboard identification of cryptotephra on future IODP missions.read less