Giant Current Ripples at Omak, WA

Lidar hillshade image. Giant current ripples atop a terrace surface near Omak, WA. Hwy 97 is at the center of the image. The ripple field is located on the second-highest terrace surface and is truncated on its east side by the next-lower surface. The south end of the ripple field, mostly off the image, appears partially buried by windblown sediment, likely post-glacial loess and dune sand.

I discovered these giant current ripples in 2019 and emailed this image out to folks I thought might be interested. I showed them to Jerome Lesemann in July 2020 via email, to Jim O'Connor in June 2021 in Upper Grand Coulee, and to Richard Waitt in May 2022 during breakfast at a Walla Walla Starbucks.

The unusual bedforms are of similar scale to features found at West Bar, WA and Camas Prairie, MT, two classic Missoula flood localities. The giant ripples at Omak are Pleistocene in age and produced by a sizeable flood down the Okanogan Valley, but one smaller than a Missoula megaflood.

Aerial photo. Giant current ripples at West Bar, WA. Scale bar shown.

Aerial photo with lidar footprint. Giant current ripples at Pogue Flat near Omak, WA. Photo is same scale as West Bar image.

Aerial photo with lidar image overlay. Giant current ripples at Pogue Flat in the Okanogan Valley are smaller and lower-relief than those at West Bar in the Columbia Valley. The flood that created them was certainly less voluminous than any of the Missoula floods, but it was still pretty large.

The source of the water is not currently known, only that it came from somewhere to the north. Potential sources for the water are near and far. Perhaps an outburst flood released from behind an ice-dammed lake in a nearby tributary valley, consistent with Holden (2007) who suggested, "The Pogue Flat terrace sediments were most likely derived from the Conconully drainage system to the west..." Perhaps water came from beneath the Cordilleran Ice Sheet, as proposed by Canadian geologists for other deposits and features in the region (Lesemann and Brenand, 2009). Perhaps a flood made its way south out of Canada through a system of bedrock channels and down the valley trough (i.e., Loomis-Palmer Lake-Sinlahekin-Similkameen).

Historic photo. Four or more terrace levels at Fish Lake near Conconully, WA. Matsura photo (#6578). Okanogan County Historical Society archives.

Landforms consistent with local outburst floods spilling from a side canyons into the main Okanogan Valley were noted by early geologists (Russell, 1893, 1898; Dawson, 1898; Waters, 1933), but none mentions giant current ripples. Flint (1935) came close with his "undulatory topography", but lacking a hot air balloon appears not to have found the ripples at Omak,

The upper surface of this terrace is marked by meander scarps and meander channels, some of them broad and deep, by extensive fans apexing at tributary mouths, by groups of kettles individually reaching half a mile in length, and locally by undulatory topography with closed depressions, suggesting irregular letting-down of sediment over deeply buried, wasting ice.

Historic photo. Pogue Flat near Omak c.1909 with glacially-sculpted Three Buttes and the Limebelt hills beyond. Matsura photo (#7735). Okanogan County Historical Society archives.

The giant ripples in the lidar image above appear related to a flood spilled from nearby Johnson Creek and sourced near Conconully. Johnson Creek is a tributary that enters the Okanogan Valley from the west just north of Omak, WA. Energetic overland flows formed "The Prow" east of the Omak Airport (Johnson Creek Rd and Blue Heron Ln) and covered Sand Flat-Pogue Flat in boulders (Omak Airport area). I lived in Omak for 5 years, right next to the airport, commuting 55 miles to Nespelem for work each day.

The Okanogan Valley contains an extensive kame and outwash terrace system. Flights of terraces composed of sand and gravel line the entire valley from Osoyoos to Brewster. Some are pocked with kettles, others are scoured by ancient streams. Sediments in the terraces are the preserved record of glacial ice of the Okanogan Lobe retreating north at the end of the last Ice Age. Enormous volumes of water flowed along the margins of stagnant(?) and downwasting ice, transporting sediment downvalley toward the Columbia River. A group of local geologists - bright, observant, amateurs - used to tell me that there's a lot more lake sediment stored in the Okanogan Valley than people think. Those gentlemen also spoke of boulder-sized erratics perched on hillsides far above the valley floor. The terrace and incision history, the architecture of ice-marginal deposits, and the contours of ice marginal lakes remain a frontier for discovery.

The talented geology Professor Jerome Lesemann of Vancouver Island University, is now working in the Okanogan and beginning to sort things out. I hope to soon meet up with him in the field. Nick Zentner recently did some filming with Dr. Lesemann near Omak. Check out their YouTube video, below.

The geological community has, in general, resisted the idea that large glacial floods coming from the Okanogan Valley (or other northern valleys). The current consensus is neither the Okanogan nor the Sanpoil contributed water scoured the Channeled Scablands. A satisfactory hydrologic connection between northern valleys and southern scablands has not been made. However, few flood geologists alive today have spent a significant amount of time examining the Okanogan Valley's glacial geology. Field evidence there, Omak's giant current ripples being just one example, seems to hint at new chapter in megaflood research.

Bretz's triumph over the East Coast naysayers came down to boot leather field work and first-hand observations. Not fancy models, not sophisticated theories, not elegant deduction. The doubters who found his evidence so easy to dismiss from their office chairs, were dumbstruck at the Dry Falls rim. While the Okanogan Valley will never be the Channeled Scablands and there is no modern day J Harlan Bretz, the valley is there. Its evidence is there. Someone just needs to go look and see if there's something to discover.

Aerial photo. Pogue Flat-Sand Flat area north of Omak, WA.

Aerial photo. Zooming in on a Pleistocene-age landform called "The Prow". The feature is several meters high, composed of coarse gravel, and was clearly formed by rushing water moving east out of the Johnson Creek Valley toward the Okanogan Valley.

Aerial photo. Energetic, east-directed flow and scour patterns orthogonal to Okanogan Valley trends are also prominent in the lower Pine Creek drainage, a tributary to the Okanogan Valley located north of Omak, near Tonasket.

Aerial photo. Zooming in. Flutes on the floor of Pine Creek Valley have upcurrent-pointing noses and were formed by rushing water moving toward the Okanogan Valley. They are remnant Pleistocene features. The horseshoe-shaped features are 10s of meters in size and highlighted by soil moisture and vegetation differences. Ranch buildings and gravel roads for scale.

Aerial photo. More fluted forms in glacial sediments along Pine Creek.

YouTube video. Professor Nick Zentner of Central Washington University meets up with geology Professor Jerome Lesemann in the Okanogan Valley to talk giant current ripples, terraces, and other aspects of the area's glacial geology.

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