Just about everyone is familiar with the typical hazards of volcanoes - explosive eruptions, lava flows, giant ash clouds reaching altitudes of 10s of thousands of feet. However, most people don't realize that volcanic eruptions can cause tsunamis... really really big tsunamis in fact.
A recent article published in Science Advances shows evidence of a megatsunami that was caused by a large scale flank collapse of a volcano in Fogo, an island in the Cape Verde Islands, located about 600 km west of Senegal.
Geologists have long hypothesized that flank collapse of a volcano can set off a megatsunami. Flank collapse can simply be defined as a side of a volcano falling off. We saw something similar to this when Mt. St. Helens erupted in 1980. The entire north face of the volcano collapsed moments before the eruption occurred. Unlike the volcano in Fogo, Mt. St. Helens didn't set off a tsunami because it is landlocked.
Geologists noticed that there were huge boulders (the size of a bus) originating from oceanic deposits located too far inland and too far above sea level on the island of Santiago (an island about 50 km east of Fogo). Something was not right here. The boulders did not belong here; therefore, something had to have transported them to their final destination.
That transporting mechanism was a megatsunami. The authors conclude that the huge landslide off the volcano in Fogo caused an enormous tsunami (as large as 270 m tall) that crashed into Santiago, thus transporting and depositing the giant boulders that shouldn't be there.
These conclusion are significant because this is the first time that geologists have seen evidence for a megatsunami that was caused by the side of a volcano falling off and crashing into the ocean. They have long hypothesized that it was possible, but this is the smoking gun that it can indeed happen.