Tekst: Yngve Vogt, Translated by: Kathrine Torday Gulden
Surprisingly sand and clay landslides can move at a much higher speed under water than above. Landslides can cross ocean floors with a tremendous speed and move several hundred kilometres in more than a hundred kilometres per hour.
"The speed of the landslides can be compared to the airport express in Oslo and the landslides “float” almost without any contact with the sea bed", says Professor Anders Elverhøi from the Department of Geosciences at the University of Oslo to the research magazine Apollon.
He has spent the last ten years studying underwater landslides.
His interest in underwater landslides began already at the end of the eighties, when the oil industry needed knowledge in regard to where they could place installations on the sea bed without there being a risk of them being ruined by landslides.
The oil industry has the last years begun the search for oil in the continental slope which ties together the continental shelf and the deep sea. Huge landslides have been observed in this area.
One example of this is the gas field at Ormen Lange, where the Storegga Landslide occurred approximately 8200 years ago. The landslide resulted in a 10-15 metre tidal wave which lead to the ruin of a Stone Age settlement on the west coast of Norway.
After the Ice Age a similar landslide occurred just outside Bjørnøya. The landslide moved 100 to 200 kilometres across the sea bed, even though the angle of inclination was only between a half and one degree steep, this being no steeper than Denmark.
Landslides in modern times
The most notorious landslide in modern time occurred outside Newfoundland in Canada in 1929. Cables on the sea bed were demolished. When researchers studied the damages they were able to establish that the landslide of one thousand cubic kilometres had moved at a speed of 60 to 100 kilometres an hour.
A thousand cubic kilometres is such a large amount that it could have covered Norway with more than three metres of deposit. The large landslides outside the coast of Norway were even bigger.
Underwater landslides are paradoxical in two ways.
"One paradox is how such huge amounts of deposit can move at such great speed. The other paradox is that the landslides travel across great distances even if the angle of inclination is slight", says Anders Elverhøi.
To be able to reveal the secrets concerning underwater landslides, Elverhøi and Dr. Carl Harbitz at the International Centre for Geohazards have worked together with American researchers at a laboratory in St. Anthony Falls in USA. The researchers have imitated a landslide in a small tank with a six degree angle of inclination. Advanced high speed cameras have documented the experiment by taking 250 video images per second.
The fundamental physical nature of the landslide has been researched, more specifically how the particles distribute and have an impact on each other.
The results of this experiment have been used to create a mathematical model of large landslides at sea.
Deposit landslides travel further in water than in air.
On one of the videos the landslide is similar to a train with its nose pointing upwards. The speed is as intense the entire time.
Due to the pressure which commences in front of the landslide, the landslide points upwards and moves above a thin layer of water, hardly in contact with the sea bed. The phenomenon is called hydroplaning and causes less resistance. This is especially apparent in regard to landslides with a high content of marine clay, such was the case in the notorious Storegga Landslide outside the west coast of Norway.
Stretches into two
Thanks to the experiments at the American laboratory, Anders Elverhøi has calculated that the front part of the Storegga Landslide travelled at three to four times the speed than the behind part.
- When a landslide stretches, the mass is distributed over long distances. This can be compared to a dispersing car queue. The cars in front race forward, while the queue still clutters together behind.
During the stretch, water is mixed into the landslide. This causes less “resistance within” the landslide which results in the landslide moving at a higher speed.
– The combination of hydroplaning up front, that the landslide stretches and that water mixes in to the landslide, has to do with the speed and distance the landslide travels. This also results in the underwater landslide meeting a smaller collected resistance than a landslide would in air. We had not foreseen these results.
In certain cases there is such a large stretch in the landslide that the front of the landslide escapes the back end of the landslide. In these cases the landslide is divided into two.
As of today pictures are only taken of the landslide’s surface.
– We are not sure that the surface of the landslide represents what is actually happening inside the landslide. To be certain of this we feel it is necessary to do research on the particle movement within the landslide.
This is the next step for their research project.
"We can learn more about safety in regard to underwater installations once we understand which mechanisms lead sand and clay to deep water. This understanding is also important to learn what sort of connection there is between landslides and tsunamis and what creates the basis for the oil reservoirs on the continental slope. This isn’t only interesting for Norway, but also for oil searches in other deep sea areas, such as on the outskirts of Nigeria, Angola and Brasil", Anders Elverhøi says.
Anders Elverhøi | alfa
Hundreds of bubble streams link biology, seismology off Washington's coast
22.03.2019 | University of Washington
Atmospheric scientists reveal the effect of sea-ice loss on Arctic warming
11.03.2019 | Institute of Atmospheric Physics, Chinese Academy of Sciences
DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.
The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...
Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.
The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
22.03.2019 | Life Sciences
22.03.2019 | Life Sciences
22.03.2019 | Information Technology