Running rivers are very scarce in globally distributed hyperarid and arid coastlines (∼28,000 km worldwide), and it is ephemeral rivers that carry most terrestrial sediment into the sea in these regions. However, there is very little information regarding the contribution of terrestrial sediment and dynamics of transport of sediment that enter marine basins from these rivers. One hyperarid region, the Gulf of Aqaba received an exceptional number of flashflood events during the winter of 2012–2013. The results illustrate, for the first time, how the high volume of flashflood sediment influences the distribution of coral reefs; dwarfs the contribution of airborne dust; elevates floodwater densities to produce hyperpycnal flows, despite highest ocean salinities; and is subsequently transported to the deep basin where it may be preserved as a climate archive.