Mt Churchill Lena Tephra
Start: 300 yBP [1]
Event Type: Explosive
Description: From Payne and others (2008): "The internal comparisons suggest correlation among ECR 32, LNA 39, and SPM 26 layers. All of these tephras show strong similarity to the White River Ash (WRA). SCs are as great as 0.99 with proximal WRA deposits and 0.96 with distal deposits (Table 4 [in original text])."
"The CHP 33 tephra has been directly radiocarbon dated. A sample of Sphagnum leaves gave an age estimate of 280-320 cal yr BP (Table 6 [in original text]) and a sample of Sphagnum stems gave a marginally less precise date with a calibrated age range of 290-460 cal yr BP, supporting the choice of Sphagnum leaves for the other dates. The CHP 33 tephra was therefore deposited around 300 cal yr BP. Although the CHP 33 tephra does not have EPMA data, the balance of probability suggests that a single tephra layer was deposited at all five sites around 300 cal yr BP, or approximately AD 1650."
"All of the sites contain a tephra layer dating to ca. 300 cal yr BP (AD 1650) with a major element geochemistry similar to that of the White River Ash. Both the eastern and northern lobe WRA deposits are considerably older, around 1147 and 1890 cal yr BP, respectively (Lerbekmo and others, 1975; Clague and others, 1995). Accumulation rates of ombrotrophic mires are usually in the range 10-20 yr cm. Robinson and Moore (1999) reported the depth of the WRA tephra in western Canadian peatlands; in ombrotrophic sites, the mean depth of the tephra was 68 cm whereas in poor fens it was 54 cm. The sites in this study are farther south in a more climatically favourable location for peat accumulation. It is therefore extremely unlikely that a tephra at this depth could be a correlative of either of the WRA deposits. No younger eruptions are known from Mt. Churchill. The only volcano in the Wrangell Volcanic Field to have had historic-age eruptions is Mt. Wrangell. However, there are no known eruptions near the probable age of this tephra, and the high degree of geochemical similarity to the WRA means a different source is improbable. The most likely source of the tephras is therefore a previously unknown eruption of Mt. Churchill, within the last 600 yr, and most probably around AD 1650. We propose the name ‘Lena tephra’ for this layer following the convention of naming previously unknown tephras after the site in which they were first located."
From Preece and others (2014): "...cores in southeastern Alaska contain two other tephra beds with compositions similar to WRA. These are the ca. 300 yr B.P. (ca. A.D. 1650) Lena ash preserved at sites A and B (Fig. 1 [in original text]) and the ca. 6330 cal yr B.P. MTR-146 ash preserved at site B (Fig. 1 [in original text]) (Payne and others, 2008)."
"The CHP 33 tephra has been directly radiocarbon dated. A sample of Sphagnum leaves gave an age estimate of 280-320 cal yr BP (Table 6 [in original text]) and a sample of Sphagnum stems gave a marginally less precise date with a calibrated age range of 290-460 cal yr BP, supporting the choice of Sphagnum leaves for the other dates. The CHP 33 tephra was therefore deposited around 300 cal yr BP. Although the CHP 33 tephra does not have EPMA data, the balance of probability suggests that a single tephra layer was deposited at all five sites around 300 cal yr BP, or approximately AD 1650."
"All of the sites contain a tephra layer dating to ca. 300 cal yr BP (AD 1650) with a major element geochemistry similar to that of the White River Ash. Both the eastern and northern lobe WRA deposits are considerably older, around 1147 and 1890 cal yr BP, respectively (Lerbekmo and others, 1975; Clague and others, 1995). Accumulation rates of ombrotrophic mires are usually in the range 10-20 yr cm. Robinson and Moore (1999) reported the depth of the WRA tephra in western Canadian peatlands; in ombrotrophic sites, the mean depth of the tephra was 68 cm whereas in poor fens it was 54 cm. The sites in this study are farther south in a more climatically favourable location for peat accumulation. It is therefore extremely unlikely that a tephra at this depth could be a correlative of either of the WRA deposits. No younger eruptions are known from Mt. Churchill. The only volcano in the Wrangell Volcanic Field to have had historic-age eruptions is Mt. Wrangell. However, there are no known eruptions near the probable age of this tephra, and the high degree of geochemical similarity to the WRA means a different source is improbable. The most likely source of the tephras is therefore a previously unknown eruption of Mt. Churchill, within the last 600 yr, and most probably around AD 1650. We propose the name ‘Lena tephra’ for this layer following the convention of naming previously unknown tephras after the site in which they were first located."
From Preece and others (2014): "...cores in southeastern Alaska contain two other tephra beds with compositions similar to WRA. These are the ca. 300 yr B.P. (ca. A.D. 1650) Lena ash preserved at sites A and B (Fig. 1 [in original text]) and the ca. 6330 cal yr B.P. MTR-146 ash preserved at site B (Fig. 1 [in original text]) (Payne and others, 2008)."
References Cited
[1] Using cryptotephras to extend regional tephrochronologies: an example from southeast Alaska and implications for hazard assessment, 2008
Payne, Richard, Blackford, Jeffrey, and van der Plicht, Johannes, 2008, Using cryptotephras to extend regional tephrochronologies: an example from southeast Alaska and implications for hazard assessment: Quaternary Research, v. 69, n. 1, p. 42-55.[2] Chemical complexity and source of the White River Ash, Alaska and Yukon, 2014
Preece, S.J., McGimsey, R.G., Westgate, J.A., Pearce, N.J.G., Hart, W.K., and Perkins, W.T., 2014, Chemical complexity and source of the White River Ash, Alaska and Yukon: Geosphere, v. 10, n.5., p. 1020-1042, doi: 10.1130/GES00953.1Complete Eruption References
Chemical complexity and source of the White River Ash, Alaska and Yukon, 2014
Preece, S.J., McGimsey, R.G., Westgate, J.A., Pearce, N.J.G., Hart, W.K., and Perkins, W.T., 2014, Chemical complexity and source of the White River Ash, Alaska and Yukon: Geosphere, v. 10, n.5., p. 1020-1042, doi: 10.1130/GES00953.1
Using cryptotephras to extend regional tephrochronologies: an example from southeast Alaska and implications for hazard assessment, 2008
Payne, Richard, Blackford, Jeffrey, and van der Plicht, Johannes, 2008, Using cryptotephras to extend regional tephrochronologies: an example from southeast Alaska and implications for hazard assessment: Quaternary Research, v. 69, n. 1, p. 42-55.
