The causes of a tsunami are found in phenomena capable of moving a large mass of water vertically, large enough to generate an ocean wave.
One of the main causes of tsunamis are underwater seismic phenomena (or at least where the epicentre is close to the coast), but we also know that the seismic origin is not the only one to consider.
Generally, it is common knowledge that a volcanic eruption is preceded and accompanied by seismic events, including of considerable intensity. This simple consideration leads us without a shadow of a doubt to catalogue volcanic phenomena as possible causes of tsunamis. This probability becomes a certainty if the volcanic structure is located on small islands or near the coast.
However, there are particular manifestations of volcanic activity that lend themselves to becoming the trigger of gigantic tsunamis. These are related to volcanic eruptions that can be defined simply as “explosive”, and occur near the sea.
In highly explosive eruptions accompanied by a massive expulsion of material, the magma chamber, i.e. the reservoir of the volcano, can empty. As a result of this, the walls of the volcanic cone collapse, forming a caldera, a large chasm, up to hundreds of square kilometres in size, which is usually circular or elliptical in shape. The caldera has near vertical walls, inside which it is not uncommon for a lake to form.
If an explosive eruption and the subsequent collapse affect volcanic structures on land, the consequences are especially seismic in nature, unlike when this phenomenon occurs in water. When volcanic magma comes into contact and interacts with water, whether from the sea or from underground aquifers, we talk about hydrovolcanic activity. The immediate effect of this interaction is the overheating, boiling and vaporisation of the water, a situation that results in an increase in pressure and the violent expansion or explosion of the gas produced. This transformation will have varying levels of efficiency, depending on the ratio between the quantities of magma and water that come into contact.
