Background
On June 20, 1996 a major landslide of nearly one million cubic meters (with out runner blocks nearly 10,000 m3 big) of sediment occurred along the shore line of the Finneidfjord in northern Norway (Longva et al. 2003). The slide occurred mostly underwater (approximately 90% sub-marine) and consisted of two major layers of clay, the first or starting layer being holocene clay and the second late glacial clay.The slide began in the holocene layer alone; the initial slide is believed to be caused by a detachment in a weak soil layer as a result of excess pore pressures caused by the presence of free gas pockets (Best et al. 2003).
Failure of the first layer left a slope on the second that could not be supported causing the second phase of the land- slide. The slide left substantial damage on nearby infrastructure, homes, and the general landscape of both the land and seafloor. Experiments to determine shear strengths were conducted on core samples taken from the failure area. Cores were done on soils in different lateral locations and tests were conducted on the samples found.
In order to identify the weak layer the samples were segmented into different depths and tested separately, the outcome was a clear decline in shear strength for a specific layer within the soil (Ilstad et al. 2004). The main concern with this type of slide is its potential impact on nearby offshore and costal instillations and how to predict and prepare for these events so that these structures and their personnel can be kept safe and operational.
