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Publication - Dr Caroline Williams

    Observations of a stratospheric aerosol veil from a tropical volcanic eruption in December 1808

    is this the Unknown ~1809 eruption?

    Citation

    Guevara, A, Williams, CA, Hendy, E, Rust, AC & Cashman, KV, 2014, ‘Observations of a stratospheric aerosol veil from a tropical volcanic eruption in December 1808: is this the Unknown ~1809 eruption?’. Climate of the Past, vol 10., pp. 1707-1722

    Abstract

    The Unknown eruption of 1808/1809 was the second most explosive SO2-rich
    volcanic eruption in the last two centuries, eclipsed only by the
    cataclysmic VEI 7 Tambora eruption in April 1815. However, no eyewitness
    accounts of the event, and therefore its location, or the atmospheric
    optical effects associated with its aerosols have been documented from
    historical records. Here we report on two meteorological observations
    dating from the end of 1808 that describe phenomena we attribute to
    volcanic-induced atmospheric effects caused by the Unknown eruption. The
    observations were made by two highly respected Latin American
    scientists. The first, Francisco José de Caldas, describes a
    stratospheric aerosol haze, a "transparent cloud that obstructs the
    sun's brilliance", that was visible over the city of Bogotá, Colombia,
    from 11 December 1808 to at least mid-February 1809. The second, made by
    physician José Hipólito Unanue in Lima, Peru, describes sunset
    after-glows (akin to well-documented examples known to be caused by
    stratospheric volcanic aerosols) from mid-December 1808 to February
    1809. These two accounts provide direct evidence of a persistent
    stratospheric aerosol veil that spanned at least 2600 km into
    both Northern and Southern Hemispheres and establish that the source was
    a tropical volcano. Moreover, these observations confirm that the
    Unknown eruption, previously identified and tentatively assigned to
    February 1809 (±4 months) from analysis of ice core sulfate records,
    occurred in late November or early December 1808 (4 December 1808 ±7
    days). This date has important implications for the associated
    hemispheric climate impacts and temporal pattern of aerosol dispersal.

    Full details in the University publications repository