Kolk 5302890 202979912 2008-04-03T05:03:41Z Esprqii 1955864 /* Examples */ Oswego Lake is also mentioned in this book A '''kolk''' (also known as ''colc'') is an underwater [[vortex]] that is created when rapidly rushing water passes an underwater obstacle in boundary areas of high shear. High velocity gradients produce a violently rotating column of water, similar to a [[tornado]]. Kolks are capable of plucking multi-ton blocks of rock and transporting them in suspension for some thousands of meters. <ref name="Alt"> {{cite book|first=David|last=Alt|id=ISBN 0-87842-415-6|location= |title=Glacial Lake Missoula & its Humongous Floods|publisher=Mountain Press Publishing Company}} </ref><ref name="Bjornstad">{{cite book|author=Bjornstad, Bruce|title=On the Trail of the Ice Age Floods: A Geological Guide to the Mid-Columbia Basin |publisher=Keokee Books; San Point, Idaho |year=2006|id=ISBN 978-1-879628-27-4}}</ref> Kolks leave clear evidence in the form of plucked-bedrock pits, called [[Rock-cut basin]]s or lakes and downstream deposits of gravel-supported blocks that show percussion but no rounding.<ref name="Alt" /> ==Examples== Kolks were first identified by the Dutch, who observed kolks hoist several ton blocks of [[riprap]] from dikes and transport them away suspended above the bottom.<ref name="Alt" /> Kolks are credited with creating the pothole-type geographical 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.<ref name="Bjornstad" /> Examples from the [[Missoula Flood]]s in this area include<ref name="Alt" />: * The region below [[Dry Falls]] includes a number of lakes scoured out by kolks. * [[Sprague Lake]] is a kolk-formed basin created by a flow estimated to be 8 miles wide and 200 feet deep. * The Alberton Narrows on the [[Clark Fork River]] shows evidence that kolks plucked boulders from the canyon and deposited them in a rock and gravel bar immediately downstream of the canyon. * The south wall of [[Hellgate Canyon]] in [[Montana]] shows the rough plucked surface characteristic of kolk eroded rock. * Both the walls of the [[Wallula Gap]] and the [[Columbia River Gorge]] also show the rough plucked surfaces characteristic of kolk eroded rock. * [[Oswego Lake]], in the middle of [[Lake Oswego, Oregon]] (a [[Portland, Oregon|Portland]] suburb), was an abandoned channel of the [[Tualatin River]] that was scoured by a kolk ==References== <!--See http://en.wikipedia.org/wiki/Wikipedia:Footnotes for an explanation of how to generate footnotes using the <ref(erences/)> tags--> <div class="references-small"> <references/> [[Category:Oceanography]] [[Category:Geomorphology]] [[de:Kolk]] [[nl:Kolk (water)]]