Submarine landslides during the growth of volcanic islands

It is well established that the largest mass movements on Earth are submarine landslides.  These can be vast – 150 km³ is not unusual,  and landslides as large as 900 km³ have been detected.  But much remains undetermined about submarine landslides, primarily because they are so difficult to access on the floor of the deep oceans.  In an open access paper just published in Nature Communications (Hunt and Jarvis 2017), James Hunt and Ian Jarvis from the National Oceanography Centre in Southampton and Kingston University report on the analysis of cores recovered from the Ocean Drilling Programme some 500 km to the west of the Canary Islands.  These cores were recovered from the sea floor in an ocean that is 5,000 m deep in a mission that drilled three holes on the Madeira Abyssal Plain (see diagram below).  They record a succession of turbidites – the remains of submarine landslides – over a 43 million year period, which captures the formation and growth of the Canary Island volcanic island group.

The location of theODP drilling sites on the Madeira Abyssal Plain. Maps taken from the report of the Shipboard Scientific Party in 1995.

The cores record a long succession of large submarine landslides.  Hunt and Jarvis (2017) propose that these represent a succession of failures that occurred as the Canary Islands underwent ” inception, ascension and emergence during the seamount-phase of growth and later subaerial-phase of growth”.  In other words, as the islands formed the submarine slopes became oversteepened, and underwent failure (possibly triggered by a seismic event or by magma emplacement), generating these vast submarine landslides.  They find that on average a major landslide has occurred every 220,000 years over the last seven million years, which is more frequent than occurred prior to this point.  Interestingly, they have also been able to associate specific landslides to the formation of specific islands.  The authors suggest that the record indicates that the early growth phases of volcanic islands are associated with a high rate of submarine landslides.

Such large submarine can of course represent a hazard as they have the potential to be tsunamigenic. However, Hunt and Jarvis (2017) address this issue in what is I think the most important element of this piece of work.  They note that:

“These distal deposits representing failures of the submarine flanks of the Canary Islands and adjacent seafloor predominantly comprise two or more silt layers in the basal portion of the deposits (85% of those beds thicker than 10 cm), which are separated by centimetres to decimetres of turbidite mud. This implies that the slides were predominantly multi-stage, thus despite their large-volume, their tsunamigenic potential is reduced.”

In other words the deposits demonstrate that the failures did not occur as a single large event, but instead as a multistage failure, presumably through retrogression and lateral growth of the failure mass.

Reference

Hunt, J.E. & Jarvis, I. 2017.  Prodigious submarine landslides during the inception and early growth of volcanic islands.  Nature Communications 8, Article number: 2061. doi:10.1038/s41467-017-02100-3