Fredback, D., Clark, D., Park, M. and Tucker, D., 2008, Coring for ash; a possible new tephra from Mount Baker Volcano: Abstracts with Programs - Geological Society of America, February 2008, Vol. 40, Issue 1, pp. 67

Coring for ash; a possible new tephra from Mount Baker Volcano

A small alpine lake northeast of Mount Baker volcano preserves what initial analysis suggest may be either a previously reported (Hyde and Crandell, 1978) but rarely preserved tephra from the volcano correlative to the SP tephra, 10870+ or -80 (super 14) C yr. B.P., or an unidentified tephra. Alternatively, the deposit may be eroded sediment from a Table Mountain columnar andesite outcrop present in the cliff above and to the east of the lake. In the fall of 2007, we collected three short sediment cores from a small, shallow, unnamed lake near the Heather Meadows Visitors Center. The lake is roughly circular, approximately 50 m in diameter with a maximum depth of 3.6 m. We cored the lake using a modified Livingstone piston corer (50.8 mm diameter barrel); all cores showed a similar upper stratigraphic sequence: organic mud (gyttja) interbedded with two known tephras (Mount Baker Set BA/OP, approximately 5740 (super 14) C yr B.P.; and Mazama O, approximately 6850 (super 14) C yr B.P.). Two of the cores also contain a dark, silty-to-sandy glass-bearing basal unit up to 12 cm thick that physically resembles other Mount Baker tephras. Initial Scanning Electron Microscope/Energy Dispersive Spectroscopy analysis of the glass shards in the basal unit suggests that the composition of the grains is within the compositional range of the SP tephra (average SiO (sub 2) value of 66.85%) and the BA tephra (average SiO (sub 2) value of 68.42%). A compositional analysis of glass from the Table Mountain andesite should help determine if it is a possible source for the basal unit. Of note, no unit correlating to this dark sand was found in Highwood Lake, which is only 1.4 km down-valley of our lake. Additional coring in several other alpine lakes in this area during winter, 2008, should help to constrain the distribution and composition of this unit.