The northern and northeastern parts of Iraq are mountainous area with very rugged topography that includes high and steep cliffs, deep valleys; locally canyon shape, and rare wide and flat plains. The main exposed rocks over all the area are the carbonates, especially limestone and dolostone of different varieties. Tens of geological formations consist of very think limestones and/ or dolostone. This article deals with the origin of a circular form developed in one of the main valleys called Lolan Valley in Khwakurk area, northern part of Iraq. Different geomorphological, lithological, structural and stratigraphical indications are used to conclude the origin of the circular form, which is confirmed to be a sinkhole due to karstification of thick carbonate rocks. The outer diameter of the circular form is 386 m; the width of the valley ranges from (35 – 150) m, the length of the circular form is 1045 m, which means the length to valley width ration is 20.9 times, the ratio of the radius to the width is 4 times. These two ratios are other indications that the meander of Lolan valley is not a normal meander, but a meander formed due to the collapse of existed sinkhole alongside the valley.