CGRG Bibliography of Canadian Geomorphology
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Author : Atwater, B.F.; Smith, G.A.; and Waitt, R.B.
Date : 2000.
Title : The Channeled Scabland: Back to Bretz?: Comment
Publication : Geology
Issue : 28(6):
Page(s) : 574-576.
Abstract
Shaw et al. (1999) say that only one big flood went through the Channeled Scabland during the last glaciation. They also say this flood did not come from Glacial Lake Missoula; they propose that the water flowed southward from a reservoir beneath the Cordilleran ice sheet. These ideas clash with a wealth of evidence that Lake Missoula sent dozens of big floods through the Channeled Scabland (numbered examples in Figs. 1 and 2, and in Table 1). At the site of that lake, varved deposits record at least 34 occasions when Lake Missoula drained partly or completely after having filled for several decades (1–3). West of Lake Missoula, on the north margin of the Channeled Scabland, varve-bounded beds record dozens of floods into other lakes, particularly Glacial Lake Columbia (4–6). Varve counts show that most of these floods—like the drainings of Lake Missoula—repeated at intervals of several decades (10). In three valleys headed by ice sheet lobes, current indicators show that major floods entered those valleys from the south and initially ran northward, toward the Cordilleran ice sheet (7–9). One such valley contains a 115 m section in which 2000–3000 of Lake Columbia’s varves are regularly intercalated with the deposits of 89 last glacial floods that probably came from Lake Missoula (5). At least 60 of these floods are probably recorded by deposits in Pasco Basin (16–18)—where time between floods is evidenced by sev-eral widespread tephra layers: by loess, colluvium, and mud cracks, and, most abundantly, by animal burrows (12–15). East of Pasco Basin, about 20 last glacial floods crossed a high divide in the Channeled Scabland (19). Six floods below Pasco Basin probably exceeded 6 x 10 6 m 3 /s (20). Most scabland floods from non-Missoula sources were probably confined to the lowest scabland channels. An example is a series of some 45 non-Missoula floods that entered Lake Columbia late in the last glaciation (11). These floods were probably smaller than any Missoula flood of their time. But they unavoidably went through the Grand Coulee—not because of their size, but because that scabland channel served as Lake Columbia’s usual outlet (3).
Bibliography of Canadian Geomorphology