Since you cannot see it how do you know when the volcano is erupting?

All of the known eruptions of Kick-’em-Jenny since 1939 have been detected by seismographs. Kick-’em-Jenny, like many other submarine volcanoes, is a particularly efficient generator of acoustic signals which are transmitted through the ocean. These can be heard underwater (and on land close to the volcano) as a deep rumbling noise but more importantly they are recorded by seismograph stations, the data from which we are able to read at our headquarters in Trinidad. On several occasions they have been felt strongly in northern Grenada and the Grenadines and perceptibly as far away as Martinique. We refer to these signals as T-phase. Discrete volcanic earthquakes are also sometimes generated, but these are recorded only by seismograph stations very close to the volcano.