Over the last few decades, a lot of attention has been concentrated on the consequences of marine impacts, especially those caused by the tsunami wave train. Internal solitary waves are similar to the surface waves that commonly occur in the waters of the ocean or large lakes and can have significant effects on oceanic mixing, climate change, the movement of submerged plankton, and the weathering of geological structures. This motion can be severe enough to create natural hazards, such as submarine tsunamis in the ocean. These could also even occur in large lakes. Numerical modeling has shown that the waveform of a soliton that interacts with others of a similar kind would emerge unchanged from the collision, except for a phase shift. However, the results from laboratory experiments are rather limited, despite the successful generation of ISWs using a collapse mechanism in a wave flume. This paper reports on some interesting facts compiled from the results of a series of laboratory experiments on the investigation of the head-on collision of two ISWs. Our results confirm that the waveforms of two depression ISWs will more or less retain their initial shape after a head-on collision. However, the transmitted wavelength will broaden when two elevation ISWs collide, perhaps affected by bottom friction. Overall, the resulting waveforms induced by such head-on collisions agree well with the theoretical predictions for depression ISWs, regardless of their scale of amplitude, but the results are only valid for elevated waveforms of large amplitude. © 2012 Springer Science+Business Media B.V.