The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels,
coulees and
cataracts eroded into Palouse
loess
Loess (, ; from german: Löss ) is a clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loess or similar deposits.
Loess is a periglacial or aeolian ...
and the typically flat-lying basalt flows that remain after cataclysmic floods within the southeastern part of
Washington.
[Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ] The Channeled Scablands were scoured by
more than 40 cataclysmic floods during the
Last Glacial Maximum
The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent.
Ice sheets covered much of Northern North America, Northern Eur ...
and innumerable older cataclysmic floods over the last two million years.
These floods were periodically unleashed whenever
a large glacial lake broke through its ice dam and swept across eastern Washington and down the
Columbia River Plateau during the
Pleistocene epoch. The last of the cataclysmic floods occurred between 18,200 and 14,000 years ago.
[Balbas, A.M., Barth, A.M., Clark, P.U., Clark, J., Caffee, M., O'Connor, J., Baker, V.R., Konrad, K. and Bjornstad, B., 2017]
''10Be dating of late Pleistocene megafloods and Cordilleran Ice Sheet retreat in the northwestern United States.''
''Geology,'' 45(7), pp. 583-586.
Geologist J Harlen Bretz defined "scablands" in a series of papers written in the 1920s as lowlands diversified by a multiplicity of irregular channels and rock basins eroded into basalt. Flood waters eroded the loess cover, creating large
anastomizing channels that exposed bare basalt and creating
butte-and-
basin topography. The buttes range in height from , while the rock basins range from in width up to the long and 30 m deep
Rock Lake. Bretz further stated, "The channels run uphill and downhill, they unite and they divide, they head on the back-slopes and cut through the summit; they could not be more erratically and impossibly designed."
The debate on the origin of the Scablands that ensued for four decades became one of the great controversies in the history of
earth science
Earth science or geoscience includes all fields of natural science related to the planet Earth. This is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of Earth's four spheres ...
. The Scablands are also important to planetary scientists as perhaps the best terrestrial analog of the Martian
outflow channels.
[Carr, M. H. (2006), ''The Surface of Mars''. Cambridge Planetary Science Series, Cambridge University Press.]
History
Bretz conducted research and published many papers during the 1920s describing the Channeled Scablands. His theories of how they were formed required
short but immense floodsfor which Bretz had no explanation. His theories of apparent
catastrophism
In geology, catastrophism theorises that the Earth has largely been shaped by sudden, short-lived, violent events, possibly worldwide in scope.
This contrasts with uniformitarianism (sometimes called gradualism), according to which slow increment ...
met with vehement opposition from geologists of the day, who tried to explain the features with
uniformitarian theoriesthat they were shaped by processes still acting today.
J. T. Pardee first suggested in 1925 to Bretz that the draining of a
glacial lake
A glacial lake is a body of water with origins from glacier activity. They are formed when a glacier erodes the land and then melts, filling the depression created by the glacier.
Formation
Near the end of the last glacial period, roughly 10,0 ...
could account for flows of the magnitude needed. Pardee continued his research over the next 30 years, collecting and analyzing evidence that eventually identified
Lake Missoula as the source of the floods (now the
Missoula floods) and creator of the Channeled Scablands.
Pardee's and Bretz's theories were accepted only after decades of painstaking work and fierce scientific debate. Research on open-channel hydraulics in the 1970s put Bretz's theories on solid scientific ground. In 1979 Bretz received the highest medal of the
Geological Society of America, the
Penrose Medal, to recognize that he had developed one of the great ideas in the earth sciences.
Geology
Distinct
geomorphological features include coulees, dry falls, streamlined hills and islands of remnant loess, gravel fans and
bars, and
giant current ripples
Giant current ripples are active channel topographic forms up to 20 m high, which develop within near-thalweg areas of the main outflow valleys created by glacial lake outburst floods. Giant current ripple marks are large scale analogues of small ...
.
The term scabland refers to an area that has experienced fluvial erosion resulting in the loss of loess and other soils, leaving the land barren.
River valleys formed by erosional downcutting of rivers create V-shaped valleys, while
glaciers carve out
U-shaped valleys. The Channeled Scablands have a rectangular cross section, with flat plateaus and steep canyon sides, and are spread over immense areas of
eastern Washington. The morphology of the scablands is butte-and-basin.
The area that encompasses the Scablands has been estimated between , though those estimates still may be too conservative.
They exhibit a unique
drainage pattern that appears to have an entrance in the northeast and an exit in the southwest. The
Cordilleran ice sheet dammed up Glacial Lake Missoula at the Purcell Trench Lobe.
A series of floods occurring over the period of 18,000 to 13,000 years ago swept over the landscape when the ice dam broke. The eroded channels also show an
anastomosing, or braided, appearance.
The presence of
Middle
Middle or The Middle may refer to:
* Centre (geometry), the point equally distant from the outer limits.
Places
* Middle (sheading), a subdivision of the Isle of Man
* Middle Bay (disambiguation)
* Middle Brook (disambiguation)
* Middle Creek (d ...
and
Early Pleistocene
The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...
Missoula flood deposits have been documented within the Channeled Scabland as other parts of the Columbia Basin, e.g. the Othello Channels, Columbia River Gorge, Quincy Basin, Pasco Basin, and the
Walla Walla Valley. Based on the presence of multiple
interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene in ...
calcrete
Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, ...
s interbedded with
glaciofluvial flood deposits,
magnetostratigraphy,
optically stimulated luminescence dating, and
unconformity truncated
clastic dikes, it has been estimated that the oldest of these megafloods flowed through the Channel Scablands sometime before 1.5 million years ago. Because of the fragmentary nature of older glaciofluvial deposits, which have been largely removed by subsequent Missoula floods, the exact number of older Missoula floods, which are known as ''Ancient Cataclysmic Floods'', that occurred during the Pleistocene cannot be estimated with any confidence.
As many as 100 separate, cataclysmic Ice Age floods may have occurred during the last glaciation.
[Waitt, RB, Jr. (1994) ''Scores of Gigantic, Successively Smaller Lake Missoula Floods Through Channeled Scabland and Columbia Valley'', in ''Geologic Field Trips in the Pacific Northwest: 1994 Geological Society of America Meeting'', Chapter 1K, D. A. Swanson and R. A. Haugerud (eds.), Geological Society of America, Boulder, Colorado.] There have been at least 17 complete interglacial-glacial cycles since about 1.77 million years ago, and perhaps as many as 44 interglacial-glacial cycles since the beginning of the Pleistocene about 2.58 million years ago. Presuming a dozen (or more) floods were associated with each glaciation, the total number of cataclysmic Ice Age Missoula floods that flowed through the Channeled Scablands for the entire Pleistocene Epoch could possibly number in the hundreds, perhaps exceeding a thousand Ancient Cataclysmic Floods.
There are also immense
potholes and
ripple marks, much larger than those found on ordinary rivers. When these features were first studied, no known theories could explain their origin. The
giant current ripples
Giant current ripples are active channel topographic forms up to 20 m high, which develop within near-thalweg areas of the main outflow valleys created by glacial lake outburst floods. Giant current ripple marks are large scale analogues of small ...
are between high and are regularly spaced, relatively uniform hills.
Vast volumes of flowing water would be required to produce ripple marks of this magnitude, as they are larger-scale versions of the ripple marks found on streambeds that are typically only centimeters high. Large potholes were formed by swirling vortexes of water called
kolk
Kolk may refer to:
People
* Douglas Kolk (1963–2014), American artist
* Hanco Kolk
Hanco Kolk (born 11 March 1957, Den Helder) is a Dutch cartoonist and comics artist. He is best known for his collaborations with Peter de Wit, with who he mad ...
s scouring and plucking out the bedrock.
The Scablands are littered with large boulders called
glacial erratics
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
that rafted on glaciers and were deposited by the glacial outburst flooding. The lithology of erratics usually does not match the rock type that surrounds it, as they are often carried very far from their origin.
See also
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Notes
Additional references
*Allen, John Eliot;
Marjorie Burns; and Sam C. Sargent. (1986) ''Cataclysms on the Columbia''. Portland, Oregon: Timber Press,
*Bjornstad, Bruce
Ice Age Floodscapes YouTube Channel*Bretz, J Harlen (1923), "The Channeled Scabland of the Columbia Plateau." ''Journal of Geology'', v.31, p. 617-649.
*Bretz, J Harlen (1925), "The Spokane flood beyond the Channeled Scablands." ''Journal of Geology'', v.33, p. 97-115, 236–259.
*Bretz, J H.; Smith, H.T.U.; and Neff, G.E., (1956) "Channeled Scabland of Washington — New Data and Interpretations." ''Geological Society of America Bulletin'', v.67, p. 957-1049.
''Spokane Outdoors''. N.p., n.d. Web. 9 October 2013.
*Soennichsen, John (2008), "Bretz's Flood: The Remarkable Story of a Rebel Geologist and the World's Greatest Flood", Seattle, Washington, Sasquatch Books,
External links
* United States Geological Surve
Five chapters with 23 illustrations and maps.
*Steven Dutch, University of Wisconsin - Green Bay
Channeled Scablands: Overview*
PBS's ''
NOVA
A nova (plural novae or novas) is a transient astronomical event that causes the sudden appearance of a bright, apparently "new" star (hence the name "nova", which is Latin for "new") that slowly fades over weeks or months. Causes of the dramati ...
''
''Mystery of the Megaflood'' Scablands in Google Mapsfrom the
National Park Service about the geologic origins of the scablands.
Sun Lakes-Dry Falls State Parkin the Channeled Scablands
Columbia Plateau Trail StateParkin the Channeled Scablands
- "Trailing an Apocalypse" - 30-Sep-2007
The channeled scabland a guide to the geomorphology of the Columbia Basin, Washington : prepared for the Comparative Planetary Geology Field Conference held in the Columbia Basin, June 5–8, 1978 / sponsored by Planetary Geology Program, Office of Space Science, National Aeronautics and Space Administration ; edited by Victor R. Baker and Dag Nummedal.
* Keenan Lee
Altai Flood*
{{Deserts
Geology of Washington (state)
Deserts of the United States
Megafloods
Landforms of Washington (state)