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Reply to comment on “Periodic jökulhlaups from pleistocene glacial Lake Missoula—New evidence from varved sediment in northern Idaho and Washington”
QUATERNARY
RESEARCH
24, 357-360
(1985)
Reply to Comment on “Periodic J6kulhiaups from Pleistocene Glacial Lake Missoula-New Evidence from Varved Sediment in Northern Idaho and Washington” If the 28 graded beds at the Latah Creek section are all of late Wisconsin age (Waitt, 1984), varves separating the 16 lowest beds corroborate my contention that the great Missoula floods were dozens of colossal jokulhlaups (Waitt, 1980). Kiver and Stradling have three objectives: (1) the varveseparated floodlaid beds may be older than late Wisconsin, for hypothetical soils may have been removed by hypothetical erosion; (2) the uppermost 12 graded beds may have formed by intraflood “surging,” for varves or other evidence of hiatus is lacking between them and floodwater may have reached the site by different routes; and (3) the number of Missoula floods may have been limited to the 16 that can be demonstrated near Spokane. I answer these in order. 1. There are no soils, weathered zones, much-weathered stones, extensive cementation, or other suggestion that any part of the Latah Creek section is pre-late Wisconsin in age or that long hiatuses lurk within the section. Several other sections in the region having similar characteristics include intercalated tephra or radiacarbondated material indicating ages of about 14,500 to 13,000 yr B.P. (Mullineaux et d., 1978; Waitt, 1980, in press; Atwater, 1984a). 2. Kiver and Stradling agree that some graded beds are deposits of separate floods, but they suggest that other similar beds may have formed by intraflood “surging.” How could a prodigious incoming flood sweeping mainly over dry land on the one hand, and a later “surge” causing a modest increase to already deeply ponded water on
the other hand, produce bottom currents so similar as to deposit almost identical beds? Hypothetical surging is not based on field evidence; it diverts attention from the many lines of positive field evidence that show that most and probably all mujor graded beds at several sections in southern Washington are deposits of separate floods spaced decades apart (Waitt, 1980, pp, 661668). I agree that the idea of intraflood surging should be kept open; indeed minor deviations in grading within some beds almost certainly were caused by currents varying during a flood. But tield evidence weighs heavily against the major graded beds having been produced in this way. 3. Most stratigraphic sections in the region are incomplete and expose fewer than 20 beds; the maximum number of floods must be inferred at the few exposures that are most complete. In southern Washington and northern Oregon at least five stratigraphic sections have more than 35 flood beds uninterrupted by soils or weathering zones, one section showing more than 60 separate beds (Waitt, 1980, in press). The bottom sediments of last-glacial Lake Missoula independently show that the lake rose gradually and fell abruptly at least 40 times (Chambers, 1971; Waitt, 1980, Fig. 13). In north-central Washington, Atwater (1983, 1984b) delineates at least 80 Missoula flood beds alternating with varved sediment. Kiver and Stradling’s limitation of evidence to that near Spokane ignores the more complete sections scattered about the rest of the flood-swept region. Kiver and Stradling’s present objections seem to be based on a history that they and 357 0033-XW8.5
$3.00
Copyright 0 1985 by the Umvers~ty of Washmgtm All rights of reprcduction in my form rewrwd
3%
LETTERS
1HE TO --*-
their colleague J. Rigby have inferred. Kiver and Stradhng (1981, 1982) proposed four Wisconsin-age “glaciations” and inferred an episode of catastrophic flooding between 42,000 and 30,000 yr B.P. They assigned the beds above and below the minor unconformity at Latah Creek to separate glaciations, and Rigby (1982) suggested an age of 37,000 to 18,000 yr B.P. for the varve-separated beds below the unconformity. Yet a glacial lake at Latah Creek and glacial Lake Missoula are both impossible between 45,000 and 17,500 yr BP, when southern British Columbia remained continually free of continental ice (Clague, 1981). Kiver and Stradling (1982) and Rigby (1982) correlate the upper beds at Latah Creek with backflood beds of southern Washington because they are similar in grain size and thickness; the iower beds, being coarser and beneath an unconformity,
MJllUK ------
must not correlate. Such distinctions based mainly on grain size and bed thickness ignore the enormous lateral variations of backflood beds in all valleys (Baker, 1973, Fig. 31; Waitt, 1980, Fig. 3). Rhythmic backflood beds in the upper Tucannon Valley are relatively thin and fine grained (Fig. I) and resemble the fmer upsection beds at Latah Creek (cf. Waitt, 1984, Fig. 7); down the Tucannon Valley the beds become thicker and coarser (Fig. 2) and resemble the coarse downsection beds at Latah Creek. Sections that expose more than 20 beds-including the prototype section near Touchet in southern Washington (Waitt, 1980, Fig. 6)-show thin, fine graded beds upsection and thick, coarser beds downsection. Thus both the downsection and upsection beds at Latah Creek resemble the backflood beds of southern Washington.
FIG. I. About 15 graded sand-to-silt distal rhythmites in the Tucannon Valley about 20 km above the valIey mouth. LJpvalJey is to the left. Shovel handIe is 43 cm long.
LETTERS
TO THE EDITOR
3%
FIG. 2. Four proximal rhythmites in the Tucannon Valley 5 km above the valley mouth. Each rhythmite consists of a couplet of gravel topped by a graded sand-to-silt bed. Foresets in gravel dip upvalley (to right). Shovel handle is 43 cm long.
REFERENCES
Lake Missoula.” Unpublished sity of Montana. Missoula.
Atwater, B. F. (1983). “Jokulhlaups into the Sanpoil Arm of Glacial Lake Columbia, Washington.” U.S. Geological Survey Open-File Report 83-4.56. (Guidebook for 1983 Rocky Mountain. Friends of the Pleistocene Field Conference.) Atwater, B. F. (1984a). Periodic floods from glacial Lake Missoula into the Sanpoil arm of glacial Lake Columbia. northeastern Washington. Geo/ogy 12, 464-461. Atwater, B. F. (1984b). Number, frequency, and relative magnitude of last-glacial floods from Pleistocene Lake Missoula, Montana-Evidence from the Sanpoil River valley. northeastern Washington. EOS,
Trunsactions
American
Geophysicul
Union
65, 893. Baker, V. R. (1973). Paleohydrology and sedimentology of Lake Missoula flooding in eastern Washington. Geological Society of America Speciul Puper
144.
Chambers,
R. L. (1971). “Sedimentation
on Glacial
M.S. thesis, Univer-
Clague, J. J. (1981). Late Quaternary geology and geochronology on British Columbia: Part 2. Geo/ogiw/ Survey of Cunuda Puper 80-35. Kiver, E. P,, and Stradling, D. F. (1981). Catastrophic flood deposits from Lake Missouia in the Spokane area. Northwest Scientific Associution, Ab.xtroct.s w,ith Programs
46.
Kiver, E. P., and Stradling, D. F. (1982). Quaternary geology of the Spokane area. Tobacco Root Geological Society Guidebook (S. Roberts and D. Fountain, Eds.), pp. 26-44. Spokane, Washington. Mullineaux, D. R., Wilcox. R. E., Ebaugh, W. F., Fryxell, R., and Rubin M. (1978). Age of the last major Scabland flood of the Columbia Plateau in eastern Washington. Quuternary Research 10, l?l180. Rigby, J. G. (1982). ‘-The Sedimentology, Mineralogy, and Depositional Environment of a Sequence of Quaternary Catastrophic Flood-Derived Lacustrine Turbidites near Spokane, Washington.” Unpublished M.S. thesis, University of Idaho. Moscow.
360
LETTERS TO THE EDITOR
Waitt, R. B., Jr. (1980). About forty last-glacial Lake Missoula jokulhlaups through southern Washington. Journal of Geology 88, 653479. Waitt, R. B., Jr. (1984). Periodic jokulhlaups from Pleistocene glacial Lake Missoula-New evidence from varved sediment in northern Idaho and Washington. Quaternary Research 22, 46-58. Waitt, R. B., Jr. (in press). Case for periodic, colossal
jokulhlaups from Pleistocene glacial Lake Missoula. Geological Society of America Bulletin %.
RICHARD
B. WAITT,
JR.
U.S. Geological Survey 5400 MacArthur Boulevard Vancouver, Washington 98661
RESEARCH
24, 357-360
(1985)
Reply to Comment on “Periodic J6kulhiaups from Pleistocene Glacial Lake Missoula-New Evidence from Varved Sediment in Northern Idaho and Washington” If the 28 graded beds at the Latah Creek section are all of late Wisconsin age (Waitt, 1984), varves separating the 16 lowest beds corroborate my contention that the great Missoula floods were dozens of colossal jokulhlaups (Waitt, 1980). Kiver and Stradling have three objectives: (1) the varveseparated floodlaid beds may be older than late Wisconsin, for hypothetical soils may have been removed by hypothetical erosion; (2) the uppermost 12 graded beds may have formed by intraflood “surging,” for varves or other evidence of hiatus is lacking between them and floodwater may have reached the site by different routes; and (3) the number of Missoula floods may have been limited to the 16 that can be demonstrated near Spokane. I answer these in order. 1. There are no soils, weathered zones, much-weathered stones, extensive cementation, or other suggestion that any part of the Latah Creek section is pre-late Wisconsin in age or that long hiatuses lurk within the section. Several other sections in the region having similar characteristics include intercalated tephra or radiacarbondated material indicating ages of about 14,500 to 13,000 yr B.P. (Mullineaux et d., 1978; Waitt, 1980, in press; Atwater, 1984a). 2. Kiver and Stradling agree that some graded beds are deposits of separate floods, but they suggest that other similar beds may have formed by intraflood “surging.” How could a prodigious incoming flood sweeping mainly over dry land on the one hand, and a later “surge” causing a modest increase to already deeply ponded water on
the other hand, produce bottom currents so similar as to deposit almost identical beds? Hypothetical surging is not based on field evidence; it diverts attention from the many lines of positive field evidence that show that most and probably all mujor graded beds at several sections in southern Washington are deposits of separate floods spaced decades apart (Waitt, 1980, pp, 661668). I agree that the idea of intraflood surging should be kept open; indeed minor deviations in grading within some beds almost certainly were caused by currents varying during a flood. But tield evidence weighs heavily against the major graded beds having been produced in this way. 3. Most stratigraphic sections in the region are incomplete and expose fewer than 20 beds; the maximum number of floods must be inferred at the few exposures that are most complete. In southern Washington and northern Oregon at least five stratigraphic sections have more than 35 flood beds uninterrupted by soils or weathering zones, one section showing more than 60 separate beds (Waitt, 1980, in press). The bottom sediments of last-glacial Lake Missoula independently show that the lake rose gradually and fell abruptly at least 40 times (Chambers, 1971; Waitt, 1980, Fig. 13). In north-central Washington, Atwater (1983, 1984b) delineates at least 80 Missoula flood beds alternating with varved sediment. Kiver and Stradling’s limitation of evidence to that near Spokane ignores the more complete sections scattered about the rest of the flood-swept region. Kiver and Stradling’s present objections seem to be based on a history that they and 357 0033-XW8.5
$3.00
Copyright 0 1985 by the Umvers~ty of Washmgtm All rights of reprcduction in my form rewrwd
3%
LETTERS
1HE TO --*-
their colleague J. Rigby have inferred. Kiver and Stradhng (1981, 1982) proposed four Wisconsin-age “glaciations” and inferred an episode of catastrophic flooding between 42,000 and 30,000 yr B.P. They assigned the beds above and below the minor unconformity at Latah Creek to separate glaciations, and Rigby (1982) suggested an age of 37,000 to 18,000 yr B.P. for the varve-separated beds below the unconformity. Yet a glacial lake at Latah Creek and glacial Lake Missoula are both impossible between 45,000 and 17,500 yr BP, when southern British Columbia remained continually free of continental ice (Clague, 1981). Kiver and Stradling (1982) and Rigby (1982) correlate the upper beds at Latah Creek with backflood beds of southern Washington because they are similar in grain size and thickness; the iower beds, being coarser and beneath an unconformity,
MJllUK ------
must not correlate. Such distinctions based mainly on grain size and bed thickness ignore the enormous lateral variations of backflood beds in all valleys (Baker, 1973, Fig. 31; Waitt, 1980, Fig. 3). Rhythmic backflood beds in the upper Tucannon Valley are relatively thin and fine grained (Fig. I) and resemble the fmer upsection beds at Latah Creek (cf. Waitt, 1984, Fig. 7); down the Tucannon Valley the beds become thicker and coarser (Fig. 2) and resemble the coarse downsection beds at Latah Creek. Sections that expose more than 20 beds-including the prototype section near Touchet in southern Washington (Waitt, 1980, Fig. 6)-show thin, fine graded beds upsection and thick, coarser beds downsection. Thus both the downsection and upsection beds at Latah Creek resemble the backflood beds of southern Washington.
FIG. I. About 15 graded sand-to-silt distal rhythmites in the Tucannon Valley about 20 km above the valIey mouth. LJpvalJey is to the left. Shovel handIe is 43 cm long.
LETTERS
TO THE EDITOR
3%
FIG. 2. Four proximal rhythmites in the Tucannon Valley 5 km above the valley mouth. Each rhythmite consists of a couplet of gravel topped by a graded sand-to-silt bed. Foresets in gravel dip upvalley (to right). Shovel handle is 43 cm long.
REFERENCES
Lake Missoula.” Unpublished sity of Montana. Missoula.
Atwater, B. F. (1983). “Jokulhlaups into the Sanpoil Arm of Glacial Lake Columbia, Washington.” U.S. Geological Survey Open-File Report 83-4.56. (Guidebook for 1983 Rocky Mountain. Friends of the Pleistocene Field Conference.) Atwater, B. F. (1984a). Periodic floods from glacial Lake Missoula into the Sanpoil arm of glacial Lake Columbia. northeastern Washington. Geo/ogy 12, 464-461. Atwater, B. F. (1984b). Number, frequency, and relative magnitude of last-glacial floods from Pleistocene Lake Missoula, Montana-Evidence from the Sanpoil River valley. northeastern Washington. EOS,
Trunsactions
American
Geophysicul
Union
65, 893. Baker, V. R. (1973). Paleohydrology and sedimentology of Lake Missoula flooding in eastern Washington. Geological Society of America Speciul Puper
144.
Chambers,
R. L. (1971). “Sedimentation
on Glacial
M.S. thesis, Univer-
Clague, J. J. (1981). Late Quaternary geology and geochronology on British Columbia: Part 2. Geo/ogiw/ Survey of Cunuda Puper 80-35. Kiver, E. P,, and Stradling, D. F. (1981). Catastrophic flood deposits from Lake Missouia in the Spokane area. Northwest Scientific Associution, Ab.xtroct.s w,ith Programs
46.
Kiver, E. P., and Stradling, D. F. (1982). Quaternary geology of the Spokane area. Tobacco Root Geological Society Guidebook (S. Roberts and D. Fountain, Eds.), pp. 26-44. Spokane, Washington. Mullineaux, D. R., Wilcox. R. E., Ebaugh, W. F., Fryxell, R., and Rubin M. (1978). Age of the last major Scabland flood of the Columbia Plateau in eastern Washington. Quuternary Research 10, l?l180. Rigby, J. G. (1982). ‘-The Sedimentology, Mineralogy, and Depositional Environment of a Sequence of Quaternary Catastrophic Flood-Derived Lacustrine Turbidites near Spokane, Washington.” Unpublished M.S. thesis, University of Idaho. Moscow.
360
LETTERS TO THE EDITOR
Waitt, R. B., Jr. (1980). About forty last-glacial Lake Missoula jokulhlaups through southern Washington. Journal of Geology 88, 653479. Waitt, R. B., Jr. (1984). Periodic jokulhlaups from Pleistocene glacial Lake Missoula-New evidence from varved sediment in northern Idaho and Washington. Quaternary Research 22, 46-58. Waitt, R. B., Jr. (in press). Case for periodic, colossal
jokulhlaups from Pleistocene glacial Lake Missoula. Geological Society of America Bulletin %.
RICHARD
B. WAITT,
JR.
U.S. Geological Survey 5400 MacArthur Boulevard Vancouver, Washington 98661