Valley Deposits Immediately East of the Channeled Scabland of Washington. I
1929; University of Chicago Press; Volume: 37; Issue: 5 Linguagem: Inglês
10.1086/623636
ISSN1537-5269
Autores Tópico(s)Geology and Paleoclimatology Research
ResumoForty-one valleys whose drainage enters the eastern margin of scabland spillways are known to contain deposits made by glacial waters. Thirty-nine of these valleys never have carried drainage from glaciated areas, and the glacial waters in them must have been backed up from the scabland. These deposits possess such extraordinary features and relations that they, like the scabland topographic forms, are considered unique. 1. Each separate area of backwater is recorded by a widespread mantle of silt containing abundant grains of unweathered basalt (the country rock) and pebbles of foreign rock. 2. In each, this mantle extends up to a definite upper limit on the valley slopes and along the valley lengths. 3. These upper limits in each case agree closely with the upper limit of scabland where the valley enters. 4. The altitudes of the upper limits, constant throughout any one backwater area, vary with different pondings, forming a descending series from north to south along the scabland gradient. 5. Remarkable large mounded gravel deposits in the tributary valley debouchures possess foreset strata which dip out of the scabland and up the valleys. The composition, topography, topographical relations, structure, and size of these deposits are in explicable without great reverse currents. 6. In no case could these reverse currents continue through and escape from the valleys they entered. They are simply a record of the rapid backflow into these valleys. It is concluded that these glacio-aqueous deposits cannot be explained by conditions associated with ordinary glacial ablation or by a sequence of several Pleistocene epochs. They require the volume and rapid rise of glacial rivers across the plateau, which the writer has previously read from the scabland itself.
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