ISLAND OF FIRE IN A SEA OF ICE--THE GROWTH OF MOUNT BAKER VOLCANO AND THE FRASER GLACIATION IN THE NORTH CASCADES

Late Pleistocene lava and lithic pyroclastic flows, with syneruptive lahars and their alluvial runouts, comprise the youngest deposits of the Mount Baker stratocone. These syneruptive assemblages overlie glacial deposits of the Vashon Stade of the Fraser Glaciation. Correlation with the Vashon, beginning before 20,000 ¹⁴C yrs BP, is verified by incorporated clasts of Baker andesite, thus probably excluding any older glaciation (W. Hildreth defines the beginning of the major period of growth of the present cone at ~40,000 yrs based on K-Ar lava ages). The apron of deposits around the southern half of the volcano shows that the Cordilleran Ice Sheet (CIS) surrounded the growing volcano, transporting erratics from faraway terranes and multiple directions, including dunite from Twin Sisters Mountain to the southwest.

Edifice growth was completed during the following Everson Interstade, at the time what we call Glacial Lake Baker filled the Baker River valley southeast of the volcano. The Sandy Creek beds are a varved lacustrine sequence--yielding a ¹⁴C age of 12,200+/-45 yrs BP--transitionally overlying erratic-bearing till like CIS diamicts elsewhere. Thus the CIS remained around the Baker edifice to near that time.

The edifice was entirely complete before an alpine re-advance correlating with the Sumas Stade or Younger Dryas. Soils on the flanks of the volcano yield ages of at least 11,020+/-180 ¹⁴C yrs BP and include Baker tephra SP, ca. 10,800 ¹⁴C yrs BP. The innermost in a sharply defined complex of terminal moraines in the Middle Fork Nooksack River yields these ¹⁴C ages: log at basal contact with Vashon deposits, 10,600+/-40 BP; logs within moraine, 10,510+/-40, 10,520+/-50, and near top, 10,550+/-40 BP. The moraines end 4.7 km downstream from the modern Deming Glacier, and only 3.0 km beyond the maximum extent of Neoglacial ice in the Middle Fork.