Deposits related to the failure of the Malpasset Dam in 1959: An analogue for hyperpycnal deposits from jökulhlaups

Sediment cores collected in the Gulf of Fréjus (SE France) contain submarine deposits related to the failure of the Malpasset Dam in 1959. These deposits constitute a dark, sandy terrigeneous layer of 10–40 cm thickness lying above an erosion surface. The deposits are composed of ungraded, non-bioturbated sands and silts displaying no apparent sedimentary structure, but rich in organic matter and rock or shell fragments. During the event, this layer prograded onto the inner continental shelf and froze rapidly. These hyperconcentrated flow deposits are related to an unsteady inertia flow generated by a surge-like flood and bedload-dominated hyperpycnal flow. Rapid freezing on flow sides generated lateral, coarse-grained, levee-shape deposits. The deposits related to the failure of the Malpasset Dam are drastically different from classical suspended-load-dominated hyperpycnites deposited by a steady, flood-generated, hyperpycnal flow. However, they are comparable with present-day deposits on a volcanic, ice-covered margin (Icelandic jökulhlaups), with ancient deposits resulting from the pulsating output of subglacial lakes during a deglaciation, or with Martian landforms resulting from sporadic ice–melt events during early Martian times.