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DeGroot Studies Offshore Seabed Sediments in Norway

Dr. Don DeGroot of the Civil and Environmental Engineering Department traveled to Oslo, Norway, in January to conduct research on characterization of offshore seabed sediments. This research was conducted at the International Centre for Geohazards of the Norwegian Geotechnical Institute as part of the UMass Amherst U.S. National Science Foundation Partnerships for International Research and Education (PIRE) project, a research and education collaboration among experts in offshore sediment geology, geotechnical engineering, and disaster mitigation. 

“The ultimate goal of our research plan,” as the project’s website (offshoregeohazards.org) explains, “is to develop protocols (e.g., design guidelines, standards, manuals of practice, public education documents) for the international community that can be used to accurately characterize offshore sediments and the role they play in assessment and mitigation of geohazards.”

Professor DeGroot's research experience is primarily in the area of soil behavior and environmental geotechnics, with special emphasis on laboratory and field measurements for site characterization programs.

One project in DeGroot's PIRE research has been studying the consequence of a sub-marine landslide, the Storegga tsunami, one of the largest of its type ever to occur. The slide and tsunami are believed to have taken place about 8,000 years ago in the Norwegian Sea, causing massive waves to run up on the surrounding coasts to elevations as high as 20 meters or 66 feet above sea level.

Soil deposits from coastal areas near the Norwegian and North seas have been studied to determine the age and run up of the tsunami. By examining the sandy soil, and the organic materials trapped within it, geologists have been able to estimate the age of the event with Carbon 14 dating. Dating the layer of sand deposited by the tsunami and the layers of peat immediately above and below proves that the sand is much older than the peat and that the seam of sand was deposited around the year 7,000 BCE (Bondevik et al. 2004).

The wave was generated by a massive sub-marine landslide that pushed the surrounding ocean waters in the Norwegian Sea in a south/southeast direction, with the main front of the wave being felt by the small Shetland Islands off the northern coast of Scotland (Bondevik et al. 2003). Global warming and deglaciation, occurring as the world exited the last major ice age, are believed to have created especially high rates of sediment accumulation on the sea floor in the area where the slide occurred.

Another PIRE project, performed by DeGroot with Professor Thomas Sheahan of Northeastern University, has been a study of the Grand Banks, a group of underwater plateaus southeast of Newfoundland on the North American continental shelf.

The North West Atlantic Ocean is not typically known for violent earthquakes, landslides, or tsunamis, but on November 18, 1929, the coastal areas of Newfoundland felt the destructive effects of all these natural phenomena. A magnitude 7.2 earthquake struck the Grand Banks, shaking the nearby coastal settlements of Newfoundland, and was experienced as far away as the New York and Montreal. The earthquake triggered an underwater landslide of about 200 km3 of material, which then generated a tsunami that crashed into Newfoundland and the Burin Peninsula.

Two and a half hours after the earthquake, the massive wave ran up the coast as much as 27 meters or 89 feet, killing a combined 29 people, the highest death toll attributed to an earthquake event in Canada's history. The most destructive component of the November 18 event was the underwater landslide; the slide greatly amplified the tsunami headed towards the coast, causing loss of human life, and also damaged sections of several strands of transatlantic cable that had to be repaired. (January 2011)