9 February 2015
Simulating submarine landslides
Submarine landslides are deeply interesting – these are largest slides on earth in terms of both runout and volume. Recently, my twitter feed has been dominated by interest in a section through a Japanese landslide deposit that was tweeted to me:
Zane Jobe has a very nice blog post explaining that deposit. Submarine landslides typically generate these very complex deposits, primarily because of their complex dynamics. However, the processes involved in submarine landslides are rather hard to measure given the inaccessibility of the setting.
But, a very nice video has been published on Youtube by Joris Eggenhuisen showing an experiment to simulate the processes involved in submarine landslides. This is from the Eurotank Flume at Utrecht University:
For information, I have copied the supporting text from the Youtube page here:
This video shows a real-time recording of a scaled-down experiment of a subaqueous massflow, made with an under-water camera. The width of view is 0.5m, the depth of view is ~2.5m (considerable foreshortening due to low camera angle). The experiment demonstrates the sequence of events during mass transport events, which occur on the modern seafloor, and are recognized in geological deposits: A trigger (in this case an earthquake) destabilised the sediments near the seafloor. The down-slope pull of gravity then exceeded the strength of the seafloor sediment, and the sediment started to break-up, and slide down the slope, all the while transforming into a jumble of blocks. Near the bottom of the slope, where gradients decreased, the movement came to a halt. The change of light halfway through the video is associated with a time lapse of 24 hours during which the experiment was left untouched. Another earthquake was generated, which destabilised another patch of sediments on the upper slope. Some blocks could be seen to accelerate to much higher speeds due to a mechanism called “hydroplaning” in massflow literature. The deformation of the flowing sediment blocks completely transformed part of the massflow into a debrisflow. The massflow deposit of the previous day’s event acted as a buttress at the base of the slope, that was partly overriden by the 2nd flow. In the geological record, such a combination of deposits created by a number of consecutive massflow events coming from the same source area is called a Mass Transport Complex.
The video is really interesting, especially the way that the second slide develops a higher velocity because it is moving down the shear surface formed by the first failure, although its runout is short because of the block imposed by the deposit from the first slide. Noe the less it does over-ride the first landslide debris. And note also the very complex scar and deposit combination that is set up by even this small, simple landslide system.