Stratigraphic disruption of piston cores, known as flow-in, often occurs in basal portions of cores, but also can form within a core between undisturbed sediment layers, or at the top of cores. Flow-in is caused by piston movement upwards, either abruptly during corer penetration or slowly during corer pull-out from the sea floor. Sedimentary structures indicative of flow in are usually noticeable by vertical streaking of sediments in contrast to horizontal layers that result from natural depositional processes. If, however, piston movement is brief or the cored sediment has no obvious layering, smeared and disrupted sections may not be apparent, resulting in unnaturally thick sediment layers in the middle or top of the core. Such stretched stratigraphic sections could be difficult to detect, and, consequently, could lead to misinterpretation of stratigraphic data.