The lifecycle of mid-ocean ridge seamounts and their prodigious flank collapses

Volcanic seamounts are spectacular bathymetric features representing ‘undersea mountains’ comparable in size to volcanic islands. They are often sites of active volcanism, represent major marine habitats, and contain potentially globally significant commodities of trace metals. However, we know comparatively little about how they form, the extent of their volcanic lifecycle, and what risks they pose from periodic flank collapse. Here, we study a uniquely extensive 43 Myr record of volcaniclastic and calciclastic turbidites accumulated on the Madeira Abyssal Plain in the NE Atlantic, which originate from large submarine landslides from the adjacent Great Meteor-Cruiser seamount complex on the flanks of the Mid-Atlantic Ridge. These turbidites present the first long-term temporal record of the recurrence, magnitude, and emplacement mechanism of seamount flank collapses from a single seamount complex throughout its lifecycle. Landslides from the Great Meteor-Cruiser seamount complex are comparable size to those from the Canary Islands, with average volumes of 30-40 km3 but can be as large as 130 km3, comparable to many volcanic island landslides. These seamount landslides were predominantly multi-stage failures similar to those form neighbouring volcanic islands, but in contrast occurred preferentially during sea-level lowstands. We show that volcanic seamounts above mantle plumes have long protracted lifecycles and that substantial flank failures are capable of occurring at all stages of development. Temporal change in turbidite composition has, for the first time, enabled reconstruction of the inception (around 43-45 Myrs ago), ascension (taking around 20-25 Myrs), emergence (after 30 Myrs) and later recession (last 9 Myrs), cessation in volcanism (last 4 Myrs) and subsidence of the seamounts (from 2 Myrs onwards). These seamounts above a mantle plume have taken around 26 Myrs to emergence above sea level from inception, while their volcanic island contemporaries only took 2-to-5 Myrs. Here, we use the history of turbidites derived from landslides from the seamounts to show how the seamounts developed and suffered mass wasting during their life cycles.