Deltas and fluvial fans are two fan-shaped landforms with complex
channel networks. Deltas always occur where rivers enter a standing body
of water, such as lakes or oceans. Fluvial fans are inland terrestrial
landforms that may form thousands of kilometers from shorelines. Fluvial
fans may however also reach lakes and oceans. The current state of
knowledge lacks understanding of their morphometric differences or
recognition criteria, despite their socioeconomic significance,
vulnerability to natural hazards, and important differences in how these
landforms respond to global climate change. Moreover, numerous
fan-shaped landforms with channel networks have been identified on other
planetary bodies, such as Mars and the Saturn's moon Titan, where deltas
are important indicators of paleo-shorelines and offer attractive
targets for mission sites due to their habitability and high
biosignature preservation potential. Here we review the known
morphometrics of delta and fluvial fan channel networks, and the
differences in their formative processes, and develop morphometric
criteria for distinguishing deltas and fluvial fans. We present an
ensemble of quantitative metrics that distinguish deltas and fluvial
fans and test these criteria on 80 modern channel networks on Earth. Our
results improve mechanistic understanding of the fluvial record and
delta evolution, provide criteria for accurate recognition of these
landforms on planetary bodies and in the sedimentary record, and explain
differences in their vulnerabilities to global change.