Iwo-Jima, well-known to historians as the site of a Pacific War battle in 1945, is also a volcanic island prone to regular eruptions. On October 29, a volcanic eruption began off the southern coast of the island. This eruption is underwater but at a shallow depth, causing ashes and blocks to be ejected to a height of several tens of meters. Interestingly, a new island is already forming as a result of this eruption.
Underwater volcanic eruptions can be challenging to monitor. It’s not uncommon to observe discolored waters with a milky blue hue along the southern coast of this island, which is part of the Ogasawara archipelago, approximately 1,000 kilometers south of Tokyo. Such discolored water often hints at eruptive or volcanic degassing activity, but little is known until the eruptive vent gets closer to the ocean’s surface, making the activity visible. This recent event occurred in the same area where volcanic activity had been observed several times last year.
A satellite image from October 29 identified a thermal signal a few hundred meters off the southern coast of Iwo-Jima, indicating elevated magma temperatures and, consequently, subsurface eruptive activity. On the following day, October 30, individuals aboard an aircraft observed this eruption. It’s a relatively modest, classic Surtseyan-type activity for now, with ash and blocks being ejected to heights of up to around thirty meters every few minutes. Additionally, near this eruptive vent, a small island approximately ten meters in diameter was seen, along with fields of pumice stones within a broader area.
Nonetheless, the future is challenging for this newly forming island. Although it will continue to grow as long as the eruption persists, once the eruption ceases, erosion will begin to wear away the island’s surface, potentially causing it to disappear beneath the ocean’s depths once again.