Submarine megafans and their associated canyons have long attracted the attention of a large community in the earth sciences because they record the history of past erosional processes. As such, their morphology and sedimentary infill may be of use to unravel past climatic and tectonic evolution. Yet despite an important corpus of research on their structural characteristics we lack a well accepted quantitative description for the dynamics of the formation and growth of these sedimentary systems. One of the main reasons for this lies in our inability to successfully understand, reproduce, and predict the dynamics of the channel systems, tens to hundreds of meters deep, several kilometers in width, and hundreds of kilometers in length, that build submarine fans. Here we report on a series of small-scale laboratory experiments on the formation of subaqueous channels and lobes. Our experiments show that steady flow of a dense current on a bed of light particles can induce both spontaneous formation of channels longer than a few channel widths and spontaneous meandering.