Effect Of Volcanoes on Oceans

Volcanoes can have a number of effects on the ocean. Some of the most obvious would be when large eruptions generate tsunami. Collapse of the Krakatau caldera during the big 1883 eruption generated a tsunami that radiated outward and devastated coastlines on nearby islands. A large eruption-related collapse at Mt. Unzen (Japan) caused a smaller tsunami about 100 years before Krakatau.

Sometimes large explosive eruptions (such as that of Krakatau) will produce huge mats of floating pumice. Small fish are attracted to these matts because they offer places to hide. These small fish would never strike off across the wide ocean on their own, but hiding amongst the pumices they sometimes get rafted across the ocean without even realizing it. This will cause havoc for people trying to study fish distributions.

Underwater eruptions will release big amounts of gas into the water, producing big plumes of water with different chemical compositions. These eruptions will also release a lot of heat into the ocean. A geophysicist who recently retired from the University of Hawai'i has proposed that large eruptions on the East Pacific Rise (a mid-ocean spreading center) will heat enough water to cause currents in the Pacific to be changed, causing El Nino events. He has correlated earthquake activity along the East Pacific rise with El Nino and thinks that there is agreement. His ideas have not been accepted yet by most people who study El Nino. In fact, there has been at least one proposal that El Nino might cause increased activity on the East Pacific Rise!