Frost Polygons in the Laptev Sea (IMAGE) British Antarctic Survey Caption This polygonal or geometric patterns on the shallow seafloor (10-17 m water depth) here shown on a side-scan sonar image, were formed when the area was emergent (land) during the last glacial and was permanently frozen but not covered by glaciers. Thermal contraction of the ground causes cracks with these geometric shapes with the high parts being raised about 1 m from the surrounding seafloor. The area was probably submerged again around 7 or 8 thousand years ago. Credit Atlas of Submarine Glacial Landforms (2017) Usage Restrictions With appropriate caption and credit only. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.