QUANTIFICATION AND DIFFERENTIATION OF DELTA AND FLUVIAL FAN CHANNEL NETWORK MORPHOMETRICS

Fluvial fans and deltas are both fan-shaped landforms that contain complex channel networks. One difference between these two landforms is that only deltas systematically form along the shorelines of a standing body of water. Fluvial fans however, may or may not form along a standing body of water. Accurately identifying and distinguishing deltas from fluvial fans is crucial to understanding paleo-environments on Earth and also on Mars. Here we report on multiple quantitative morphological characteristics such as channel bifurcation and divergence angles, as well as channel lengths and widths between divergence nodes to establish differences between delta and fluvial fan channel networks. Differences in channel networks occur because fluvial fans form through channel avulsions and sediment aggradation in channels. Deltas form by channel avulsions as well as mouth bar growth and consequent channel bifurcation. Previous research has shown that delta bifurcation angles form at approximately 72°. Other studies on delta channel networks have demonstrated a distinct downstream decrease in channel reach length and in channel width with successive bifurcations. We demonstrate that fluvial fans form statistically significant smaller channel divergence angles averaging approximately 55°. Down-fan channel narrowing also shows no association to the order of divergence nodes. Results from our analysis also suggest that deltas maintain an average bifurcation angle of 72° which increases slightly to approximately 80° for bifurcations in arctic deltas. These results indicate that channel networks need to be carefully assessed if used for the estimation of the location of paleo-shorelines on planetary bodies, as only deltas systematically occur at shorelines. Additional evidence is also needed for the presence of shorelines as fluvial fans may also occur at shorelines.