Kolk (vortex)

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One of many kolk-formed depressions or "potholes" in the channeled scablands in eastern Washington at
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46deg54'21.40''N 119deg16'47''W / 46.9059444degN 119.27972degW / 46.9059444; -119.27972
. Kolk plucked pothole.jpg
One of many kolk-formed depressions or "potholes" in the channeled scablands in eastern Washington at 46°54′21.40″N119°16′47″W / 46.9059444°N 119.27972°W / 46.9059444; -119.27972 .

A kolk is an underwater vortex causing hydrodynamic scour by rapidly rushing water past an underwater obstacle. High-velocity gradients produce a high-shear rotating column of water, similar to a tornado. Kolks can pluck multiple-ton blocks of rock and transport them in suspension for kilometres. [1] [2]

Contents

Kolks leave clear evidence in the form of kolk lakes, a kind of plucked-bedrock pits or rock-cut basin. Kolks also leave downstream deposits of gravel-supported blocks that show percussion but no rounding. [1]

Examples

Kolk from the 1717 Christmas flood in Horumersiel (de: Horumersiel) with information board Horumersiel Kolk.jpg
Kolk from the 1717 Christmas flood in Horumersiel (de: Horumersiel) with information board

Kolks were first identified by the Dutch, who observed kolks hoisting several-ton blocks of riprap from dikes and transporting them away, suspended above the bottom. [1] The Larrelt kolk near Emden appeared during the 1717 Christmas flood which broke through a long section of the dyke. The newly formed body of water measured roughly 500 × 100 m and was 25 m deep. In spite of the repair to the dyke, another breach occurred in 1721, which produced more kolks between 15 and 18 m deep. In 1825 during the February flood near Emden, a kolk of 31 m depth was created. The soil was saturated from here for a further 5 km inland.

Kolks are credited with creating the pothole-like features in the highly jointed basalts in the channeled scablands of the Columbia Basin region in Eastern Washington. Depressions were scoured out within the scablands that resemble virtually circular steep-sided potholes. [2] Examples from the Missoula floods in this area include: [1]

See also

Related Research Articles

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A pendant bar is a large, streamlined, fluvial bar that is typically composed of gravel which occurs just downstream of a bedrock obstruction within a river channel or floodway that has been scoured by either an outburst flood, megaflood, or jökulhlaup. They are often associated with giant current ripples. Malde introduced this to refer to streamlined mounds of gravel deposited by the Bonneville Flood that lie downstream of bedrock projections on the scoured valley floor of the Snake River. They are most common type of bar found within the Channeled Scablands created by the Missoula floods. The obstruction for the initiation of pendant bars in the Channeled Scablands is typically either a knob of basalt or the relict bend of a pre-flood meandering valley.

References

  1. 1 2 3 4 Alt, David (2001). Glacial Lake Missoula & its Humongous Floods. Mountain Press Publishing Company. ISBN   0-87842-415-6.
  2. 1 2 Bjornstad, Bruce (2006). On the Trail of the Ice Age Floods: A Geological Guide to the Mid-Columbia Basin. San Point, Idaho: Keokee Books. ISBN   978-1-879628-27-4.