Deep Secrets: Discovery of a giant mega-slide in the North Sea Fan, offshore Norway

The Mid-Norwegian continental margin is home to multiple submarine landslides of prodigious volume (mega-slides), thought to have occurred once each glacial cycle over the last ∼500 kyr. Here, we present new 2D seismic reflection data that image the headwall of a previously unknown mega-slide buried beneath Quaternary sediment in the North Sea Fan. The deposits linked to this mega-slide, named the Solsikke Slide, have a volume exceeding 15,000 km 3 . This is five times greater than the neighboring tsunamigenic Holocene Storegga Slide's volume, and makes the Solsikke Slide one of the largest landslides yet discovered on our planet. The Solsikke Slide remobilized deposits from the previous three mega-slides within the North Sea Fan, including the Tampen Slide that is thought to have occurred ca. 120 kyr BP. Together with the overlying deposits, this constrains the timing of the Solsikke Slide to between 120 and 57 kyr BP (MIS 5–3), which indicates that mega-slides may happen more frequently than previously thought along this margin. Furthermore, we identify a network of faults that extend up from the acoustic basement to the base of the Solsikke headwall, and seismic evidence of lateral fluid migration within the underlying unit. These observations suggest seismic shaking and fluid migration, together with sediment loading, likely played an important role in pre-conditioning and/or triggering failure. Our findings thus have significant implications for understanding the hazard posed by mega-slides in the Northern Atlantic, in terms of their frequency, potential magnitude, and pre-conditioning factors. • Discovery of a previously unknown, buried mega-slide (Solsikke) headwall on the Norwegian continental margin • Correlation of slide deposits with previous work suggests a prodigious slide volume exceeding 15,000 km 3 • Solsikke Slide occurred between the Tampen Slide (∼120 kyr) and the onset of MIS 2 (29 kyr) • Seismic shaking and lateral fluid migration most likely played a role in preconditioning and triggering the Solsikke Slide • Mega-slides on the Norwegian Margin occur more often than once per glacial-interglacial cycle