Are large submarine landslides temporally random or do uncertainties in available age constraints make it impossible to tell?

• Causes of apparent randomness of submarine landslides are examined.
• Large age uncertainties are shown to make non-random landslide ages appear random.
• Integrating multiple non-random datasets can result in apparent randomness.
• Global event datasets are likely to have a random distribution of events.
• The number of events needed to link landslides to sea level change is shown.

Large (> ~ 1 km3) submarine landslides can potentially generate very destructive tsunamis and damage expensive sea floor infrastructure. It is therefore important to understand their frequency and triggers, and whether their frequency is likely to change significantly due to future climatic and sea level change. It is expensive to both collect seafloor samples and to date landslides accurately; therefore we need to know how many landslides we need to date, and with what precision, to answer whether sea level is a statistically significant control. Previous non-statistical analyses have proposed that there is strong correlation between climate driven changes and landslide frequency. In contrast, a recent statistical analysis by Urlaub et al. (2013) of a global compilation of 41 large (> 1 km3) submarine landslide ages in the last 30 ka concluded that these ages have a temporally random distribution. This would suggest that landslide frequency is not strongly controlled by a single non-random global factor, such as eustatic sea level. However, there are considerable uncertainties surrounding the age of almost all large landslides, as noted by Urlaub et al. (2013). This contribution answers a key question that Urlaub et al. (2013) posed, but could not address — are large submarine landslides in this global record indeed temporally random, or are the uncertainties in landslide ages simply too great to tell? We use simulated age distributions in order to determine the significance of available age constraints from real submarine landslides. First, it is shown that realistic average uncertainties in landslide ages of ± 3 kyr may indeed result in a near-random distribution of ages, even where there are non-random triggers such as sea level. Second, we show how combination of non-random landslide ages from just 3 different settings, can easily produce an apparently random distribution if the landslides from different settings are out of phase. Third, if landslide frequency was directly proportional to sea level, we show that at least 10 to 53 landslides would need to be dated perfectly globally — to show this correlation. We conclude that it is prudent to focus on well-dated landslides from one setting with similar triggers, rather than having a poorly calibrated understanding of ages in multiple settings.