Exceptionally Long Distance Transport of Volcanic Ash: Implications for Stratigraphy, Hazards and the Sourcing of Distal Tephra Deposits
Abstract:Cryptotephras (tephra not visible to the naked eye) form the foundation of the tephrostratigraphic frameworks used in Europe to date and correlate widely distributed geologic, paleoenvironmental and archaeological records. Pyne-O’Donnell et al. (2012) established the potential for developing a similar crypto-tephrostratigraphy across eastern North America by identifying multiple tephra, including the White River Ash (east; WRAe), St. Helens We and East Lake, in a peat core located in Newfoundland. Following on from this work, several ongoing projects have examined additional peat cores from Michigan, New York State, Maine, Nova Scotia and Newfoundland to build a tephrostratigraphic framework for this region. Using the precedent set by recent research by Jensen et al.(in press) that correlated the Alaskan WRAe to the European cryptotephra AD860B, unknown tephras identified in this work were not necessarily assumed to be from “expected” source areas (e.g. the Cascades).
Here we present several examples of the preservation of tephra layers with an intercontinental distribution (i.e. WRAe and Ksudach 1), from relatively small magnitude events (i.e. St. Helens layer T, Mono Crater), and the first example of a Mexican ash in the NE (Volcan Ceboruco, Jala pumice). There are several implications of the identification of these units. These far-travelled ashes:
(1) highlight the need to consider “ultra” distal source volcanoes for unknown cryptotephra deposits,.
(2) present an opportunity for physical volcanologists to examine why some eruptions have an exceptional distribution of ash that is not necessarily controlled by the magnitude of the event.
(3) complicate the idea of using tephrostratigraphic frameworks to understand the frequency of eruptions towards aiding hazard planning and prediction (e.g. Swindles et al., 2011).
(4) show that there is a real potential to link tropical and mid to high-latitude paleoenvironmental records.
Jensen et al. (in press) Transatlantic correlation of the Alaskan White River Ash. Geology.
Pyne-O'Donnell et al. (2012). High-precision ultra-distal Holocene tephrochronology in North America. Quaternary Science Reviews, 52, 6–11.
Swindles et al. (2011). A 7000 yr perspective on volcanic ash clouds affecting northern Europe. Geology, 39, 887–890.