Eventually it would break through the surface of the ocean and then form an island.
you will get berned and die
The underwater volcano would eventually emerge from the sea and become an island. For example, each of the islands in the Hawaiian Islands chain were formed from vocanoes, and the Big Island of Hawai'i is STILL erupting. Iceland was created the same way. Many South Pacific islands were originally undersea volcanoes which erupted, formed an island, and the island became ringed with coral reefs.
all the fish would die
It would take a long time but eventually either a new island will form or if the underwater volcano is close enough to land a current island we become larger
In that case, the volcano would be referred to as dormant.
That would describe an active volcano.
If a tornado funneled into an erupting volcano, it could potentially intensify the eruption by supplying additional oxygen and heat to the volcanic plume. This could result in stronger and more widespread volcanic activity, posing a greater risk to surrounding areas.
lower magma reserves or the volcano tube has closed/shifted.
A submarine Volcano.
There is no way of predicting accurately when a volcano would next erupt. However, for Kilauea to have a "next" eruption, the current one has to stop. The volcano is erupting right now, and has been erupting continuously since 1983.
Tourism. Many people also have beliefs that some hazards would not happen because e.g. a volcano not erupting for 100 years.
An island