Thursday, July 4, 2024

Chandler Narrows I

On my way to another venture I observed this road cut west of Benton City in the lower, eastern Yakima valley.

The location is mapped as an ice age flood deposit by Reidel and Fecht (1994). My interpretation of the road cut exposure is that both the lower silt and the upper gravel were deposited during a ice age flood events.

The silt would have been deposited when the site was temporarily inundated by the short lived Lake Lewis.

Map of Lake Lewis with water level at 305 meters.
White arrows show flow path of ice age flood waters into the lake from left to right: Columbia River, Drumheller Channel, Washtucna Coulee, and spill over into the Snake River.

Lake Lewis formed due to the restriction at the narrow gap at Wallula Gap through the Horse Heaven Hills. The backing up of water resulted in deposition of silt in the queit water areas of the temporary lake including extensive silt deposits around the area of Benton City and up in the Yakima Valley.

As the lake drained down, water that had filled the Yakima Valley had to pass through a relatively narrow exit at Chandler Narrows.

The relatively narrow lower Yakima Valley resulted in high flow velocity of the water as it drained out of the valley. The result was an area of classic eastern Washington scab land in the eroded basalt up stream of the gravel deposit.

Basalt cliffs with latge basalt blocks ripped off the cliffs along the 
Chandler narrows reach of the Yakima Valley

Patch of grapes in the scab land landscape
This are is a hot wine area just west of Red Mountain

Thick gravel deposits just belwo the Chandler Narrows

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