'Describe how coastal mass movements can occur and explain why they pose a hazard to the economy'

Mass movement events, such as slumps and rock-falls, commonly occur in coastal zones. Cliff toes are almost ubiquitously subject to erosional processes relating to the work done upon them by wave action. The principle means by which this erosion occurs is hydraulic action creating pore water pressure within faults in cliff strata, resulting in interparticular stresses. Other forms of erosion can be related to the crystalisation of salts within pores in rock, as well as the saturation of weaker regoliths (such as clays) by heavy rain or the spray from waves. Ultimately this reduces the cohesiveness of cliff material at the toe, and subsequently the forces of basal resistivity supporting the mass of sediment above the base. Eventually, the base will be too weak to support the remaining material, causing the sediment matrix of the slope or cliff to come under the force of gravity, resultng in a mass movement. These can either be fast, dry movements such as rock falls, or be rotational in their movement along a 'slip plane' of more consolidated rock beneath the moving sediment- this occurs during slumping. 

Coastal mass movements can pose a hazard to economic systems because they are commonly large scale, catastrophic events. They are often difficult to predict and cause significant damage to infrastructure which supports economic activities, such as tourism. For example, the winter storms experienced in the UK, 2014, resulted in coastal storm surges along the south coast, with the increased hydraulic action incident on cliff bases causing large mass movement events. The main railway line through the town of Dawlish, Devon, cost £35 million and two months to repair and significantly impacted footfall to local businesses in the area. This was because less people were able to access the town. This is an economic impact over a relatively large temporal scale, despite being a soatially localised effect. Therefore, this emphasises that coastal mass movements can have wide ranging and significant impacts on the economy.