Resedimentation of the late Holocene White River ash, Yukon territory, Canada and Alaska, USA

Abstract

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Distal volcanic impacts on peatlands: palaeoecological evidence from Alaska

“…An exception to this is the White River Ash (Eastern Lobe), which is correlated with the LNA 100 layer in this study. West & Donaldson (2002) presented geomorphological evidence that this tephra was produced in late autumn or very early winter. If the impacts of winter eruptions are reduced, impacts across LNA 100 should be minimal but this is actually one of the two tephras associated with the most conclusive impacts.…”

“…If the impacts of winter eruptions are reduced, impacts across LNA 100 should be minimal but this is actually one of the two tephras associated with the most conclusive impacts. However, West & Donaldson (2002) worked on sites that are both further north and at higher elevation than Point Lena and it is therefore conceivable that Point Lena could still have been unfrozen and snow-free at the time of the White River Ash eruption.…”

Diatom ecological response to deposition of the 833-850 CE White River Ash (east lobe) ashfall in a small subarctic Canadian lake

“…The orientation of each WRA lobe was likely correlated with the prevailing seasonal wind patterns during each eruption (Hanson, 1965; West & Donaldson, 2002). Convincing evidence presented in several previous studies indicates that the eastward oriented WRAe eruption most likely occurred during late fall and winter, as winds in Alaska tend to trend eastward during winter (West & Donaldson, 2002). Winter emplacement of this tephra is also supported by the presence of anomalous steeply oriented deposits throughout the region (Hanson, 1965).…”

“…Deposition of this type can only occur when concentrations of ash become compacted under snow, as rain during warmer seasons of the year would have quickly dispersed the ash (Lerbekmo & Campbell, 1968). Moreover, West (2007) analyzed the stratigraphy of two deposits of the WRAe along Bock’s Brook and Danjek River in the Yukon Territory where deposition occurred onto a floodplain and concluded that the eruption probably occurred in the late fall-early winter, just prior to the first snowfall but when seasonal temperatures remained consistently below freezing. At Bock’s Brook, the ash is preserved as a distinct layer overlain by a gravel unit with no visible reworking of sediment, suggesting that the ash froze in place immediately after deposition.…”

“…The ash was subsequently buried during the following spring freshet when flood sediments buried and protected the WRAe deposits from being reworked. At Djenek River, West (2007) observed intact clasts of pumice embedded within the fluvial sediments deposited by the river, a type of deposition which requires frost in order to occur. As with the previous site, this material would have remained frozen until the spring.…”