West Coast volcanic ashes provide a new continental-scale Lateglacial isochron

The ‘Lateglacial’ period (∼14.7–11.7 cal ka BP) eruptions of Mount St Helens and Glacier Peak in the Cascade Range deposited ash layers (tephras) within a short time span across much of western North America where they form event-stratigraphic marker layers or isochrons. They were deposited at a time which has long been of interest because it represents the transition between two fundamental states of the climate system: the late Pleistocene...