Underwater volcanoes! The sound of it piques our interests; it sounds exotic and rare. However, the occurrence of underwater volcanoes is actually more common than you might think. There are several active volcanoes constantly erupting on Earth's surface but we aren't aware of them because these eruptions occur underwater. These underwater volcanoes are not only special because of the interaction of lava and water, but also because they provide extreme environments for certain species of life to grow and flourish; these bacteria and living creatures are sometimes ONLY found in these hot, wet, and sulphuric conditions!

Figure above: Showing the formation of an underwater volcano and the emergence over time of the volcano as an island (Image credit to Zina Deretsky, National Science Foundation)

Around 80% of volcanic eruptions on Earth occur underwater! Unless there are earthquakes related to the eruptions, they usually erupt unmonitored and are only spotted after they've initially erupted. Sometimes we don't even know they are there until the volcano emerges as an island! Another way of spotting an underwater volcano is from the products produced from this eruption. One of the most common products of an underwater eruption are pumice rafts. Pumice, which is a highly vesicular volcanic rock, traps air in its vesicles, making it more bouyant than water, allowing it to float. During an eruption, large amounts of pumice can be created, which float up to form pumice rafts.

Figure above: Example of a pumice raft from the Krakatau Caldera eruption in Indonesia. (Photo credit to swisseduc.ch)

One really cool underwater volcanic eruption that was identified in this manner is the eruption of Iriomote-Jima, a submarine volcano off the southwest of mainland Japan. It formed on the 31st of October, in 1924, when it erupted underwater, producing 1 cubic km of rhyolitic pumice. At this point in time, it was the largest recorded historical eruption by volume in Japan. The resulting pumice raft ended up floating along the coast of Japan, being found as far as Hokkaido, over 2700 km away from the volcano!

Figure above: Location of Iriomate-Jima volcano marked by red X. Iriomate-Jima volcano is located off the coast of Iriomate-Jima island (same name), which is one of the southernmost islands of Ryuku islands, around 950 km SSW of Honshu, Japan, and 200 km east of Taiwan. (Photo credit to NASA and Global Volcanism Program)

Some of the pumice blocks found were recorded as being almost 2 m in diameter! Since the eruption, there have only been swarms of earthquakes recorded in the area, the most recent being in 1992. There has not been any activity recorded at Iriomote-Jima volcano since then, but that does not make this submarine volcano any less interesting. In fact, this only raises more questions related to submarine eruptions. Why do they occur where they do? In the case of Iriomote-Jima volcano, why has there been no recent volcanic activity? Was this a one time event? Unfortunately for us, this 1924 eruption was one of the few poorly recorded eruptions in volcano history, compounded by the fact that the volcano is almost 200 m below sea level.

With advancements in technology, however, we have been able to monitor other submarine volcanoes and their underwater action. We have even managed to record some eruptions live. With the ongoing research, we are getting closer and closer to finding answers about our underwater 'friends'.

Video above: Example of an underwater volcanic eruption as shown on the Discovery Channel.

For more information on Iriomote-Jima volcano, click here.

For cool and interesting information on submarine volcanoes in general, click here.