Todd Glacier descends from the northern flank of the Todd Icefield (located at approximately 56° 13' N, 129° 46' W) and feeds the head of north-facing Todd Valley in the Boundary Ranges of north-western British Columbia. Until the mid-20th century its tongue merged with four neighbouring tributary glaciers, the composite snout ending about 2.5 km down-valley at roughly 1000m elevation; meltwater gives rise to Todd Creek, which drains to the Portland Canal fjord system. Since the 1970s every glacier in the valley has thinned and retreated, with aerial photographs showing terminus recession rates of roughly 9–76 metres per year between 1974 and 1997; Recession has exposed a fluted till forefield, small recessional moraines, deeply incised meltwater channels and steep lateral-moraine walls that rise to the Little Ice Agetrimline (roughly 1200m)—the valley-side boundary showing the glacier's maximum thickness during that period.[2]
Glaciological history
Dendroglaciological and radiocarbon studies carried out in the forefields of Todd, Two, Sage and Bug glaciers, together with work on the adjacent Surprise Glacier moraine, reveal a detailed late-Holocene record. Five principal advance intervals are recognised: (1) a pre-Tiedemann event older than 3000 14C yr BP (14C yr BP = radiocarbon years before present, where "present" is conventionally AD 1950); (2) the regional Tiedemann advance at ~3000 14C yr BP; (3) a lesser-known expansion about 2300 14C yr BP; (4) a two-phase First-Millennium advance centred on ~1700 and ~1450 14C yr BP; and (5) a multi-stage Little Ice Age sequence that began before 750 14C yr BP and culminated in two late bursts after roughly AD 1760 and around AD 1900. The work hinges on tree ring cross-dating of in situ stumps and detrital boles, supplemented by perimeter-ring radiocarbon ages, allowing individual kill events to be tied to glacier margins with annual precision.[2]
During the early Little Ice Age (roughly AD 883–1156) Two and Sage glaciers had already coalesced with Todd Glacier, filling the trunk valley; by 730–660 14C yr BP the combined front stood at the present forefield, as shown by buried forest horizons. Subsequent readvances in the eighteenth century felled trees on Surprise Glacier's lateral moraine (perimeter years 1746 and 1764), while a final surge in 1898–1899 pushed over mature subalpine fir on the west wall of Two-Glacier Valley. These events mark the greatest documented Holocene extent of the Todd Glacier system; the pronounced 20th-century retreat described above therefore represents a dramatic reversal from that late Little Ice Age maximum.[2]
1 2 3 Jackson, Scott I.; Laxton, Sarah C.; Smith, Jon J. (2008). "Dendroglaciological evidence for Holocene glacial advances in the Todd Icefield area, northern British Columbia Coast Mountains". Canadian Journal of Earth Sciences. 45 (1): 83–98.
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This article incorporates public domain material from "Todd Glacier". Geographic Names Information System . United States Geological Survey. 
