The 2005 Landslide

The 2005 Landslide. . , What Happened? , In May of 2005, a landslide changed the face of the Rachel Carson Trail near Outlook 1. This singular event not only altered the appearance of the present landscape, but also changed the surrounding ecosystem permanently. Nevertheless, this landslide was not a sporadic event, It occurred as the result of four factors affecting banks of the Merriland River:, . winding river channel , . unconsolidated sediments , . high groundwater table , . a fault, The natural current along the outside edge of the Merriland River channel steadily removed sediment from the base of the cliff over a period of many years., Steep, unstable riverbank cliffs made up of heavy sediments, not bedrock, added to the unpredictability of the area. Cliff sediments were composed of a sand layer and a deeper marine clay layer that lacked any real cohesion. High water tables, prevalent in the record wet spring of 2005, kept the pore space in sediments saturated. This weakened the bond between particles. Increased pressure from penetrating rainfall forced the soil apart and created greater instability., These combined factors caused a shift along a "plane of failure", or fault, which created a domino effect of opening additional cracks. Underlying clay then extruded sideways into the river while the sand, soil and trees dropped straight down, in some areas settling 20 feet below the original bluff., What You Will See , Besides the obvious steepness of the area next to the Outlook 1 portion of the trail, additional evidence of the landslide can be found. Further along the trail, walkers will notice areas along the plateau where trees are leaning toward the bluff and are growing on a ledge well below the level of the trail. This is evidence of past landslides and demonstrates how the area will be transformed over time., So Now What? , A remaining question is how the course of the river and the existing marsh will be altered by the damming effect of the landslide. The tidal river patiently dredges new channels and seeks the path of least resistance to the open ocean. Years from now, visitors more than likely will be looking out across a new channel as the river continues its seaward flow., Water-Saturated Sediment , Water fills in the pore space between grains. Friction between grains holds sediment together. , Liquefaction , Water completely surrounds all grains and eliminates all grain to grain contact. Sediment flows like a fluid.