 Complete the following phrase:  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. 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 