BJ Deming

Guest Videos: A Newbie Too Shortlived To Get a Name

Check out the birth of a new volcanic island recently in Japan’s Ogasawara archipelago, far to the south of Tokyo —

Nice Surtseyan eruptions!

This happened just off the coast of Iwojima — a/k/a Ioto, Iojima, or Ogasawara-Iojima, per the Global Volcanism Program, and “that place where US Marines planted a flag back in the 1940s?” to many of us.

This is a huge, mostly submarine volcano whose summit was the site of that famous World War 2 battle.

Here’s more video of the 2023 newbie in action:

But volcanism has not been strong enough to build a stable island structure, and the unnamed island is almost gone now, making it an appropriate subject for the last Sunday Morning Volcano post of 2023!

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The Japan Coast Guard conducted an overflight on 14 December of Ioto (Iwo-jima) to inspect the new island formed by an eruption from a submarine vent about 1 km off the SE coast at Okinahama. No eruptive activity was detected, but the shape of the island had notably changed due to erosion and wave action. During the previous 10 days deposits at the N part of the “J” shaped island had separated and migrated N, connecting to the Okinahama coast, and the curved part of the “J” had eroded into two smaller islands.

— Latest GVP activity report

What is Iwojima Volcano?

It is one of the many geological complexities that go way beyond my abilities to describe.

There is much research ongoing for the whole group of volcanic islands.

As far as basics go, these researchers report in their PDF that:

…only the elevated summit region of a larger stratovolcano named Iwojima volcano, with a basal diameter of about 40 km (Kaizuka et al., 1985) appears above the sea surface. The bulk of the volcano, with 1500–2000 m elevation, was built below sea level. Because the summit region appeared above the sea surface due to rapid upheaval,
it suffered from marine erosion that formed an ablation platform around its perimeter…

Unlike the 2023 newbie, though, Iwojima Island is big enough to withstand the waves and wind. According to those authors, “…Iwojima Island was formed during the Holocene and consists of three main parts: (1) Motoyama stratovolcano, a central cone within a summit caldera that is hidden by the sea; (2) Suribachiyama, a pyroclastic cone with a crater of 300 m diameter and 60m depth; and (3) Chidorigahara plain, which connects the two volcanic centers.”

The famous World War 2 picture was taken atop Suribachiyama, or Mount Suribachi.

Iwojima has frequent small eruptions along the lines of this November-December island-forming event, but there is also a caldera there (whose history I don’t know) and the major uplift at Iwojima, as I understand it, might be due to caldera resurgence.

How major?

The point where Captain Cook’s crew came ashore in 1779 is now more than 130 feet above sea level.

And this happened in 2021:

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This layperson’s impression is that Iwojima probably will go on having minor eruptions like those of past centuries, while boffins continue to work there in the hope of finding out why this magma is just piling up instead of blowing out with an earth-shattering kaboom.

Some lagniappe:

Seventy years after the battle…

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