Eruptions Newsletter #21 for October 17, 2025

As we now approach a third week of the US government shutdown, I don’t have the help of the Global Volcanism Program’s Weekly Volcanic Activity Report to guide me. Thankfully, the USGS is still publishing volcanic activity reports because monitoring volcanoes is vital to national security. We will persevere!

Activity News

Lewotobi, Indonesia

I’ve written about explosive eruptions at Indonesia’s Lewotobi (aka Lewotobi Laki-Laki) already this year and it appears that these blasts have continued. Eruptions earlier this week produced ash plumes that reached ~10 kilometres (~32,000 feet) and prompted local authorities to reinforce a 7 kilometre (~4 mile) exclusion zone around the volcano.

Several villages near the volcano were blanketed in volcanic ash and debris. Beyond the exclusion zone, a number of nearby airports had to shut down due to the ash spread by the eruption. Located on Flores Island, almost 20,000 people live within the current exclusion zone and almost 1 million live with 100 kilometres (62 miles) of the volcano.

Kanloan, Philippines

Over in the Philippines, authorities have noted increased seismicity at Kanlaon. The volcano has been erupting intermittently for the past year with mostly small ash-rich explosions. The earthquakes under the volcano are likely related to new magma rising under Kanlaon according to PHIVOLCS. Whether or not this leads to more energetic eruptions is not known. Over the past few days, the volcano has produced a few small (100-150 meter) ash plumes. Kanlaon is currently one of three volcanoes (along with Bulusan and Taal) with aviation restrictions preventing airplanes from getting too close.

Reykjanes Peninsula, Iceland

In no-eruption-but-maybe-an-eruption-soon news, the Icelandic Met Office is reporting an increasing number of earthquakes near the Sundhnúkur Crater in Iceland on the Reykjanes Peninsula. The earthquakes along with measurements of the deformation of the Earth’s surface suggest to volcanologists at the IMO that we are indeed headed towards new eruptions near Grindavík. So far, the uplift in the area has exceeded what happened before the last eruption in July-August of this year. The IMO noted that eruptions have commenced once ~12 million cubic meters of magma has accumulated in the upper crust.

It has now been almost 2 years since eruptions began near Grindavík. This on-again/off-again pattern of eruptions means that the city itself has been in turmoil for that time as well. Businesses are suffering from evacuations and there is no clear end to the eruptions in sight. This makes mapping a path for a city like Grindavík is challenging to say the least. The Icelandic government has approved the construction of more lava defences around the city, but local residents are choosing not to move back to their old homes. This isn’t destruction like Pompeii getting wiped out by a pyroclastic flow, but instead it could be seen as destruction by a thousand cuts and the crisis lingers. Nevertheless, they are both volcanic disasters.

Taftan, Iran

I’m not sure if this counts as “current activity” or “volcano research” but …in the realm of potentially restless volcanoes, a new study in Geophysical Research Letters using satellite radar (InSAR) found that Taftan in Iran saw uplift on the order of 11 centimeters/year from July 2023 to May 2024. That is an impressive amount of deformation and the authors of the paper lead by Mohammadhossein Mohammadnia think the uplift is due to either a small magmatic intrusion under the volcano or changes in the hydrothermal system.

There is no real active monitoring of Taftan which is located near the border of Iran, Afghanistan and Pakistan. Little is known about its eruptive history either, but most indications suggest that the volcano may not have erupted in the past ~11,000 years. However, there are potentially reports of molten sulphur flows from the active hydrothermal system as recently as 1993, but this is unsubstantiated.

One note, though. I’m not thrilled with the LiveScience headline for this study: An Iranian volcano appears to have woken up — 700,000 years after its last eruption. You can likely guess why. First, we don’t have a long enough (or really, any) record of its typical behaviour to say this uplift means it has “woken up.” Second, we don’t know that it has been 700,000 years since its last eruption. I’m not even sure where that number comes from anyway. And not to be too grumpy, the LiveScience piece also says “volcanoes are considered extinct if they haven’t erupted in the Holocene era, which started 11,700 years ago.” Again, that just isn’t true — there is no strict definition for extinct or dormant for volcanoes.

Volcano Word of the Week

This week’s word is “ring fault,” which is admittedly two words, but we’re going with it. I chose ring fault because I saw a new paper in Science about the ring fault at the Campi Flegrei in Italy and the caldera’s current state of unrest. Needless to say, lots of people like to pay attention to this massive volcano in the Bay of Naples.

Before we get there, let’s talk about ring faults. When calderas form, they create a mostly circular set of faults (above) defined by the area of the land surface supported by the magma in the upper crust. The process of magma filling in the magmatic system, causing the land surface to bulge upwards can weaken the crust in a radial pattern. If an explosive eruption happens, many times they start along the ring fault as it is the path of least resistance. As the eruption continues, the vents might merge to the point where much of the ring fault is part of the eruption.

Once enough material has been erupted and the land surface starts to collapse into the void space created, it will sink like a piston with the boundary typically being along the ring fault. This fault also becomes a likely location for post-caldera lava domes and flows to erupt because, as I mentioned, it is that easiest path for magma to move. They might also help define the hydrothermal system at caldera systems.

This new study in Science by Tan and others looked at a large database of earthquakes over the past ~2 years. Tens of thousands of small to moderate earthquakes have occurred in and around the Campi Flegrei. With this size of data set, they utilised machine learning to have a faster and more robust way to analyse the seismicity with an eye for interpretation of future seismicity to help with monitoring.

What they found was some clearly defined parts of the ring fault system. This included the area underneath the Bay of Naples, an area where the ring fault had not been clearly defined (see above). Their interpretation of the seismicity across the last few years is that much of it is driven by Campi Flegrei’s hydrothermal system. They didn’t find any signs of rising magma or earthquakes deeper than ~3.7 kilometres, all of which suggests that there is not likely much/any resupply of new magma into the upper parts of the caldera’s magmatic system. That’s good news!

Odds & Ends

Not a lot to add from the last few weeks in our odds and ends. I did catch a glimpse of a Ford (?) ad with a shot of an eruption for … reasons? It did remind me of a local truck ad in the 2002 or 2003 that my Ph.D. advisor shot with some other real volcanologists in Oregon. It was obviously goofy, but had them all running into some big American 4 door pickup to get out of the path of an erupting volcano. If I remember correctly, it was shot out by Newberry Caldera southeast of Bend. Strange opportunities sometimes arise in life, right?

I also saw a post from ESA with an image of the most recent eruption at Kīlauea in Hawai’i from early October. What is most striking is just how much of the crater floor the lava flows and overflowing lava ponds at the vents cover. Needless to say, it is a cool shot. Be sure to keep an eye on the summit livestream as a new eruption looks to be around the corner.

This isn’t volcanoes, but it is cool Earth science … and baseball. The Pacific NW Seismic Network has been recording the seismic signal of the Mariners playoff games at T-Mobile park in Seattle. They recorded a good jolt (below) after Julio Rodriguez’s 1st inning home run in Game 3 of the ALCS against the Blue Jays. However, for Mariners fans, the rest of the game is best ignored.

Sounds of the Week

I was surprised this week by Bob Mould’s great band Sugar coming out of retirement with some new music. Sugar was one of those seminal high school/college bands for me so I’m thrilled that they are back together and still taking no prisoners.

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

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