Introduction: The topographic signature of a landform can give important clues as to its formation process. Since their discovery [1] the formation pro-cess of gullies on Mars has been under debate; ranging from completely dry processes [2], through hypercon-centrated flow and debris flow [3] to pure water runoff. Each of these processes involves a different amount and configuration of water and hence confirmation of one or another of these theories affects how we under-stand Mars' recent hydrosphere. Here, we have used topographic long profiles to study the process of gully formation on Mars. First, though, we studied topo-graphic long profiles of gullies on Earth to both con-firm previously published generalisations of how long profile shape varies with process [4–6] and also to use them as a direct comparison to the martian data. Figure 1: Example of points making up a long profile of a gully on Mars, showing the different components: alcove, channel and debris apron. HiRISE image: PSP_003583_1425. Credit: NASA/JPL/UofA.