Eruptions Newsletter #19 for September 19, 2025

So, hey! I think I have a schedule settled now that the semester is started. So, this biweekly newsletter will be exactly that for now: every two weeks. This is, of course, allowing for a newsletter in between should something volcanically important happen.

Activity News

Mount St. Helens, Washington and Katmai, Alaska

You might be thinking “uh oh, that’s not a good combination.” Fear not, for the news from both these famous volcanic areas is that windy conditions have blown volcanic ash from past eruptions back up into the air.

This is not uncommon at Katmai, where the copious ash from the 1912 eruption still covers the mostly barren landscape of the Alaska Peninsula. Strong winds, especially in the fall when the ground is snow-free, can send ash thousands of feet up into the air. This makes them potentially hazardous for anyone (although few) on the ground, as breathing in volcanic ash is bad news.

You can see in images of resuspended ash from 2015 that you might be fooled into thinking something in the Katmai area was actually erupting, but even 110+ years after the event, the ash can get blown around easily.

Over in Washington, the same thing was happening at Mount St. Helens. Strong winds this week caused enough ash from the 1980 eruption to blow around that commercial pilots flying over the area noted it and people in the area were concerned the volcano was erupting. Without any snow or plant cover, the ash will move in strong winds, especially after hot, dry summers. KGW posted video showing just how intense the old ash was in the air around Mount St. Helens and the GOES-18 satellite image (above) shows how the ash was spreading almost up to the border with British Columbia, causing impressive sunsets in Victoria!

Ioto (Iwo Jima), Japan

Some new explosive activity occurred in early September on the remote Japanese island of Ioto (Iwo Jima). Some images taken show incandescent bombs and dark grey ash from a vent that is just on the western edge of the small island, while satellite images clearly show discolouration in the ocean surrounding (above).

This is the second eruption of the year at Iwo Jima. The explosivity of these eruptions is likely helped along by interaction with water (phreatic or phreatomagmatic) as the vents are just on and off shore of the island. Small submarine eruptions occur frequently off the coast with the occasionally explosive eruptions sending ash and debris into the air disrupting the pattern.

One “fun” fact about Ioto is that it sits in a “resurgent” caldera (see below) that has been rising for nearly 700 years. This is common at calderas where new magma is filling in beneath the surface that was created when the caldera was formed. It doesn’t mean we are headed towards another big blast, but it does betray the continued magmatic activity beneath the waves.

Akan, Japan

Meanwhile, in the far north of Japan, Akan on Hokkaido is showing renewed signs of unrest. This volcano, also a caldera system, hasn't erupted since 2008, but it has a long history of relatively small eruptions (VEI 1). Steam and gas plumes from the Ponmachineshiri Crater area have become much more vigorous with hints of possible ash. The JMA has increased the volcanic alert to Level 2 (of 5). Most of the historic activity at Akan has been very mild (as VEI 1 would imply) and likely helped by access to surface and ground water at the volcano.

Krasheninnikov, Russia

The eruption at Krasheninnikov that started not long after the monster M9 earthquake off the coast of Russia’s Kamchatka Peninsula in late July continues unabated. Sentinel-2 images of the volcano taken early and mid-September show long, dark lava flows on the northern and eastern slopes of the volcano. Infrared images reveal that the flows are still hot and growing from September 3 to September 17 (below).=

It is fun to swap back and forth between a clear shot of the volcano taken just before the earthquake and the recent one from early September. The new flows are clear, filling in some channels on the volcano. How the M9 earthquake “triggered” this eruption will be fascinating to discover.

Kīlauea, Hawai’i

Just for good measure, the latest eruption at the summit of Kīlauea looks to be beginning as I write on September 18. This would be the 33rd episode since activity resumed at the summit in December 2024. An update from the Hawaii Volcano Observatory on September 17 noted that a new eruption was likely to begin in the next 1-4 days, so signs that this is the case are too surprising. You can watch the action on the USGS/HVO summit livestream.

Volcano Word of the Week

This week’s word is “resurgent caldera.” Ok, that is, indeed, two words. However, it is one concept. Calderas are formed by a collapse after an eruption that released large volumes of erupted material. In the case of resurgent caldera, it is usually in the form of an explosive eruption of high-silica ash and debris.

A caldera like Yellowstone is a prime example. The >1000 cubic kilometers that erupted during the Lava Creek eruption ~640,000 years ago left a big, empty space under the land surface. This meant the surface had no support, so it collapsed to form the modern 45 by 85 kilometer caldera.

After the collapse, the magmatic system under Yellowstone has slowly been rebuilding itself and in doing so, the land that collapse rises back up. As I mentioned above, this doesn’t mean it is building towards some new massive blast, but as new magma arrives in the system, it needs to go somewhere. So, it fills in the crust and causes the land surface to rise.

The Valles Caldera in New Mexico has a prominent resurgence (see above and below) that formed after the 1.24 million year old caldera-forming eruption. The floor of the caldera used to be much lower, but the center of the resurgence is almost 1,000 meters higher than the original caldera floor.

Sometimes that new magma will leak out to cause eruptions. The rhyolite domes that you find at Yellowstone that formed 180,000 to 70,000 years ago are evidence of that magma under the caldera. What we are seeing at Iwo Jima is likely the same thing. “Resurgent” just means that the land is rising again after the big collapse that formed the caldera.

Odds & Ends

Most people are unaware that volcanoes are close to San Francisco and the Bay Area. Sure, earthquakes are a hazard, but Clear Lake volcano lies only ~140 kilometres (86 miles) from downtown San Francisco. SFGate had a nice piece on Clear Lake discussing the hazards and monitoring of the volcano by the USGS. It erupted as recently as 11,000 years ago, which is not that long in the timescales of volcanoes. These days it is best known for the geothermal energy plant (The Geysers) nearby that causes a slew of small earthquakes (mostly unnoticeable to anyone who isn’t a seismometer) from pumping fluids into the crust to drive turbines.

Over on EOS, there is a fun article about the potential of “metal volcanoes” on asteroids like Psyche. We have no direct observations of such events, but they are theoretically possible according to a new study. I remember reading about a supposed magnetite lava flows from El Laco in Chile. Turns out that iron-rich flow wasn’t a metallic lava as much as an andesite flow that was intensely hydrothermally altered, depositing lots and lots of magnetite.

Sounds of the Week

To mark this week’s ash fall in Washington, why not an ode to wind:

Questions? Comments? Thoughts? Feel free to leave a comment, send me a note or follow me on Bluesky (@erikklemetti.bsky.social).

Be sure to check out my podcast, 5 Minute Volcano and the Patreon page for the Eruptions Newsletter/5 Minute Volcano Podcast.