TEMPORAL PATTERNS IN THE TEPHROSTRATIGRAPHIC FRAMEWORK OF EASTERN NORTH AMERICA: WHAT CAUSED THE LATE-GLACIAL/EARLY HOLOCENE QUIESCENCE?

Networks of distal tephrostratigraphic records can be used to investigate the frequency and extent of past ash fall events. These studies provide a long view of regional volcanic hazards that exceeds the comparatively short historical archive. To date, the use of tephrostratigraphy in this way has been restricted to Europe; however, the rapid global expansion of tephrochronology means there is now potential to use this approach in new areas. The number and density of cryptotephra (non-visible volcanic ash deposits) records from eastern North America are unique in the continent, and provide an opportunity to investigate the controls of ultra-distal ash dispersal and deposition. Here, we present eight new cryptotephra records alongside previous findings in order to examine temporal patterns in the tephrostratigraphy of eastern North American throughout the last 17,000 years. An increase in the frequency of ash fall events is observed after ca. 7600 cal yr BP (calendar years before AD 1950), beginning with the deposition of the Mazama ash. We discuss this change in the frequency of tephra deposition in relation to volcanic and environmental controls of fine ash dispersal and preservation. We reject hypotheses relating to eruption frequency or taphonomic processes in favour of changing atmospheric influences on regional tephra dispersal - possibly caused by the retreat of the Laurentide Ice Sheet and associated shifts in atmospheric circulation.