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Radiocarbon and dendrochronological dating of glacially overridden stumps and detrital wood indicates that two outlet glaciers of the Juneau Icefield advanced shortly before the 'Little Ice Age'. Tulsequah Glacier advanced to within 2.4 km of its all-time Holocene limit between ad 865 and ad 940. Llewellyn Glacier, one of the largest glaciers in British Columbia, advanced sometime between ad 300 and ad 500, and reached to within 400 m of its Holocene limit between ad 1035 and ad 1210, well before the climactic, 'classical' 'Little Ice Age' advances of the past several centuries. Our data show that some glaciers in western North America were extensive and expanding at times when alpine glaciers have, in the past, been assumed to be restricted. The evidence raises questions about how to define the time of the beginning of the 'Little Ice Age' and, perhaps more importantly, about the utility of the term. [ABSTRACT FROM AUTHOR]

Accelerator radiocarbon dating of 147 charcoal samples recovered from colluvial and alluvial fan deposits at 29 sites was used to reconstruct the Holocene fire history of an inland temperate rainforest watershed in east-central British Columbia (BC), Canada. Radiocarbon dates ranged from 182 to 9558 cal. yr BP, with prominent peaks in the probability distribution of calibrated dates at c. 7100, 3900, 2300, 1600 and 250–1000 cal. yr BP. The inferred median fire return interval (FRI) was 800–1200 cal. yr, depending on the extent of inbuilt age errors resulting from charring of wood pre-dating actual fire ages. This FRI is likely an overestimate, as less severe events may not have created sufficient erosion and slope instability to preserve a record of charcoal in buried soils and slope deposits. Median time since fire was 467 cal. yr based on ages of the uppermost charcoal found at each site, but the severity of heart-rots in the dominant redcedars (Thuja plicata Donn ex D. Don) prevented independent confirmation of stand ages by dendrochronology. Sites with multiple charcoal-containing layers having similar radiocarbon ages can be explained with reference to contemporary post-fire mass-wasting processes. Peaks in fire-related sedimentation probability coincided broadly with periods of higher fire frequency c. 600–1000, 1300–2400 and 3500–4500 cal. yr BP inferred from sedimentary charcoal records at subalpine sites in southwestern BC. Correspondence with fire records from more distant sites in northwestern North America was less clear. [ABSTRACT FROM AUTHOR]

Jökulhlaups from lakes dammed by Tulsequah Glacier in northwestern British Columbia have occurred regularly since the early twentieth century. The floods commenced after decades of downwasting and retreat of the glacier from its Holocene maximum position, which it achieved in the nineteenth century. Hydrometric data and other records are used to reconstruct the times and peak discharges of floods from two glacier-dammed lakes. Tulsequah Lake formed in the early 1900s when a tributary glacier separated from Tulsequah Glacier, creating an ice-free embayment between the two. The lake grew rapidly in surface area and volume in the first half of the twentieth century, but later, with continued glacier retreat, it decreased in size. The first jökulhlaups from Tulsequah Lake were the largest. Peak and total discharges decreased as the lake became smaller. Today, Tulsequah Lake is small, and it will disappear completely if Tulsequah Glacier retreats any further. A second lake (Lake No Lake), however, has formed and grown in size as Tulsequah Lake has diminished. Lake No Lake developed from a subglacial water body in a tributary valley, 7 km upglacier from Tulsequah Lake. Like Tulsequah Lake, Lake No Lake rapidly grew in area and volume during its youth, and in the 1970s it began to generate its own jökulhlaups. Lake No Lake appears to be following the same evolutionary path as Tulsequah Lake – its volume is now decreasing due to downwasting of Tulsequah Glacier, and its jökulhlaups are beginning to diminish. As Tulsequah Glacier continues to shrink in response to climatic warming, additional glacier-dammed lakes may form, renewing the cycle of outburst flood activity. Such behaviour can be expected in other high mountains because most alpine glaciers are retreating in response to global warming. [ABSTRACT FROM AUTHOR]