In a programme transmitted by the British Broadcasting Corporation BBC "Horizon" broadcast on 12 October 2000, two geologists (Day and McGuire) cited this crack as proof that half of the Cumbre Vieja had moved towards the Atlantic Ocean (Day et al.; 1999, and Ward and Day, 2001). They postulate that this process was driven by the pressure caused by the rising magma heating water trapped within the structure of the island. They hypothesised that during a future eruption, the western flank of the Cumbre Vieja, with a mass of approximately 1.5 x1015 kg, could slide into the ocean. This could then potentially generate a giant wave which they termed a "megatsunami" around - high in the region of the islands. The wave would radiate out across the Atlantic and inundate much of the eastern seaboard of North America about 7 hours later, many of the islands in the Caribbean and northern coasts of South America between six and eight hours later. They estimate that the tsunami will have waves possibly or higher causing massive devastation along the coastlines. Modelling suggests that the tsunami could inundate up to inland – depending upon topography. The basis for Ward and Day (2001) modelling the collapse of a much larger portion of the western flank than what the currently visible surface crack indicates as being potentially unstable, was based on geological mapping by Day et al.; (1999). In this paper they argue that a large part of the western flank has been constructed in the scar of a previous collapse and therefore sits upon unstable debris.