Waves that radiate out from a single point, like ripples on a pond, decrease in height as they travel. But it would still be a monster. If the La Palma collapse produced a single tsunami, it would be 40 to 50 metres high when it reached the American coast. Given the evidence that the Cumbre Vieja is poised to collapse and the catastrophic consequences of such an event, Day had to find out when the volcano might let go. First, he wanted to know if the fault that appeared in 1949 is still moving.
Day believes that water trapped in the volcano is the key.
Day realised that when magma rises towards the surface through wet rock, the water in the pore spaces within the rock is heated and expands. Because liquid water is incompressible, small increases in water temperature can significantly increase the water pressure in a confined space. Working with Derek Elsworth of Pennsylvania State University, Day performed some calculations to see if the pressure generated by heating water would be enough to make the rock fracture. Sure enough, relatively modest warming gave huge increases in water pressure. Everywhere we look on the sea floor around the Hawaiian islands, we see volcanic ash.