Today marks the 25th anniversary of the massive eruption of Pinatubo in the Philippines. If you haven't looked at my post about the Pinatubo area before and after the eruption, head on over there now. You should also check out the US Geological Survey's marking of the anniversary and this excellent article in EOS about the ways the eruption changed modern volcanology. You should also check out this Manila Bulletin article about a new lake that formed after the eruption. Just to keep us all on our toes, Bulusan, one of the many active volcanoes in the Philippines, had a small explosive eruption this week that has left the region on alert for potential continued activity.

On to some updates on volcanoes around the world:

Colombia

Two volcanoes are catching people's attention. The (much) more immediate threat comes from the continued unrest at Nevado del Ruiz. Over the past month (and longer), the volcano has experienced intermittent explosive eruptions. Along with the eruptions, there is a constant din on earthquakes and a thermal anomaly at the summit Arenas crater, which suggests that magma is constantly present in the upper parts of the volcano. The steam/gas/ash plume from Ruiz doesn't get particularly high, reaching a couple kilometers over the volcano. The biggest concern, as it has been for decades at Ruiz, is that a larger eruption will produce mudflows from melting snow and ice like those experienced in the deadly 1985 eruption of the volcano. Colombia is much more prepared now than in 1985, mainly in its ability to closely monitor the activity at Ruiz, but it is still anybody's guess how events could unfold—both volcanologically and mitigation-wise when the next lahar-rich eruption occurs.

Down the road from Nevado del Ruiz is the small dome complex of Cerro Machín. I've discussed Machín here before and it poses a different challenge to Colombian volcanologists monitoring the volcano. The most recent known eruption at Machín was around 1180 AD, but based on the composition of the previous deposits, one might expect a new eruption could be quite explosive. The most recent domes sit inside a 3-km caldera and some of the pyroclastic flow deposits from Machín are found 40 kilometers (~25 miles) from the volcano. Considering that over 500,000 people live within 30 kilometers (~19 miles) from Machin, you can see why the SGC would closely watch this dome complex. This week, a magnitude 2.2 earthquakeoccurred near the volcano at a depth of ~4 kilometers, a region where the magma under the volcano could reside. While this, by no means, suggests an eruption is in the works, it is a reminder that there is likely magma lurking below Machín. The SGC currently has the volcano on elevated alert.

Similarly, a M3.3 earthquake occurred under Santa Isabel, another Colombian volcano that may not have had an eruption since ~850 BC. The volcano is close to Nevado del Ruiz and its other potentially active neighbor, Tolima.

Russia

On the other side of the Pacific Ocean, Kliuchevskoi on the Kamchatka Peninsula produced a 6 kilometer (~20,000 foot) ash plume, which happens fairly frequently at the perennially restless volcano. Tim Peake, one of the astronauts on the International Space Station, caught an image of a faint steam plume from Moyorodake on Iturup Island. This is a bit of a surprise as I haven't seen any reports of recent activity at the volcano and its last known eruption was back in 1999. This sort of wispy degassing can happen at many volcanoes when conditions are right even without changes to their state and very well could be merely fumaroles (hot gases) from the older Tukap volcano.

Nicaragua

InSAR images of Masaya in Nicaragua is showing that the volcano is inflating according to a report by the US Geological Survey given to the Nicaraguan government. InSAR is a method that compares two sets of satellite data to look for changes in the shape of the Earth's surface, so it is especially useful to look for inflation or deflation at volcanoes. Masaya currently has an active lava lake at its summit, so this inflation could merely be part of the normal activity at the volcano, but the USGS said that their Nicaraguan counterparts should keep a close eye on Masaya. The current activity at the volcano has been going since December 2011 and has been quite a tourist boon for Nicaragua. Masaya sits only 23 kilometers (~14 miles) from Managua.