As a result of the dilation of soil matrix, dense submarine sand slopes can temporarily be steeper than the natural angle of repose. These slopes gradually fail by the detachment of individual grains and intermittent collapses of small coherent sand wedges. The key question is whether steep disturbances in a submarine slope grow in size (destabilizing breaching) or gradually diminish (stabilizing breaching) and thereby limit the overall slope failure and resulting damage. The ability to predict whether the breaching failure is stabilizing or destabilizing is also crucial for the assessment of safety of submarine infrastructure and hydraulic structures located along rivers, lakes, and coasts. Through a set of large-scale laboratory experiments, we investigate the validity of an existing criterion to determine the failure mode of breaching (i.e., stabilizing or destabilizing). Both modes were observed in these experiments, providing a unique set of data for analysis. It is concluded that the existing method has limited forecasting power. This was quantified using the mean absolute percentage error, which was found to be 92%. The reasons behind this large discrepancy are discussed. Given the complexity of the underlying geotechnical and hydraulic processes, more advanced methodologies are required.@en