1. Faculty of Geosciences, Utrecht University, Postbus 80115, 3508 TC, Utrecht, The Netherlands
2. Present address: Department of Geosciences, Virginia Polytechnic Institute and State University, 4044 Derring Hall (0420), Blacksburg, Virginia 24061, USA.

Correspondence to: Erin R. Kraal^1,2 Correspondence and requests for materials should be addressed to E.R.K. (Email: ekraal@vt.edu).

Deltas and alluvial fans preserved on the surface of Mars provide an important record of surface water flow^{1, 2, 3}. Understanding how surface water flow could have produced the observed morphology is fundamental to understanding the history of water on Mars. To date, morphological studies have provided only minimum time estimates for the longevity of martian hydrologic events, which range from decades to millions of years^{4, 5, 6, 7}. Here we use sand flume studies to show that the distinct morphology of martian stepped (terraced) deltas^{8, 9, 10, 11} could only have originated from a single basin-filling event on a timescale of tens of years. Stepped deltas therefore provide a minimum and maximum constraint on the duration and magnitude of some surface flows on Mars. We estimate that the amount of water required to fill the basin and deposit the delta is comparable to the amount of water discharged by large terrestrial rivers, such as the Mississippi. The massive discharge, short timescale, and the associated short canyon lengths favour the hypothesis that stepped fans are terraced delta deposits draped over an alluvial fan and formed by water released suddenly from subsurface storage.

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