Few volcanoes on Earth pose as much of a potential threat to human life as Taal in the Philippines. It's a caldera volcano that last erupted in 1977 and which has over 24 million people living within ~60 miles (100 km) of it. Taal has the potential for large explosive eruptions that could spread ash across much of the Philippines, including the capital, Manila.
On January 12, Taal woke up from its more than 40 year slumber, producing an explosive eruption from its central vent inside Lake Taal. The continuing explosions have been sending steam ash up over 32,000-49,000 feet (10-15 km) above the volcano. Ash fell on many towns near Taal and the international airport at Manila has closed in response. Thousands of people living on the shores of Lake Taal have been evacuated due to the threat of a potential tsunami in the lake if a larger eruption occurs.
The eruption has been producing some spectacular volcanic lightning as well - you can see lots of images of the eruption here. The PHIVOLCS webcam on Volcano Island in the caldera caught the eruption starting (until it was taken out by the eruption). NOAA also posted a time-lapse of the growing ash plume seen by the Himawari-8 weather satellite (above).
PHIVOLCS, the the Philippines' volcano monitoring agency, said the first of the new explosions was a phreatic eruption. This means they think the blast was being driven by steam in the vent area rather than new magma reaching the surface. Phreatic eruptions can happen unexpectedly even at volcanoes that are not restless as all they require is the heat inside the volcano and water.
Updates on the Eruption
PHIVOLCS recently released an image of a lava fountain (above) spotted at the main vent of the eruption. This clears up any doubt of magma reaching the surface.
A timelapse of the eruption (below) captured by Himawari-8 shows just how quickly the volcano went from quiet to a towering ash plume. The other feature that stands out, especially at night, is how the plume spread across such a highly populated area, covering much of Manila in ash overnight on January 12-13. The lake can be seen towards the bottom of the timelapse just south of Manila.
This image of the ash plume seen from an airplane near Taal during the eruption clearly shows the convective portion of the plume (the column) and then the spreading out of the material when neutral buoyancy is reached. This forms that classic umbrella shape of an explosive plume. You can also see on the left side of the plume dark grey ash falling as well.
The Independent has been running constant updates from the area. Most people have heeded the call for evacuations, although apparently tourists are still trying to get close to the volcano to see the eruption. Local residents are also trying to return home now that the eruption as waned some, although this is very dangerous. Estimates of the total evacuees range from 8,000 to 13,000, although it could be quite higher.
The most recent update from PHIVOLCS on January 13 says that the strong lava fountaining has ceased. The eruption has now waned considerably but continues in the main vent of the island in Lake Taal. There are still hundreds of earthquakes occurring and PHIVOLCS continues to call for the evacuation of the island and a 14-km radius around the volcano. The alert level remains at 4, so eruptions are expected to continue.
As an aside, Taal is not "the world's smallest volcano". I'm not sure how this meme in the news about this volcano started. It is a caldera volcano, so it is not very tall -- a few hundred meters above sea level at its highest on Volcano Island. The caldera itself, though, is over 10 miles across. This is a big volcano and a typical shape of a caldera. By this measure, Yellowstone is not a "big" volcano because it too lacks a large cone like Mt. Fuji or Shasta.
Unrest since 2019
Taal has been showing signs of unrest for the past year in the form of increasing gas emissions, earthquakes and deformation. This all could mean that new magma is moving under Taal and this phreatic blast is just another sign that Taal is heading towards a potential new period of activity or larger explosions. The fact that the eruption has continued for hours suggests that new magma is indeed being fed into the vent. If larger explosions occur, there is the potential for pyroclastic flows and heavy ash fall from the volcano.
Taal itself is a massive caldera tens of miles across (see above) with a volcanic cone in the lake. In 1965, Taal produced a VEI 4 eruption that covered tens of square miles with up to 10 inches (25 centimeters) of ash and killed hundreds of people. That eruption was from the central island in Lake Taal and was phreatomagmatic -- an eruption driven by mixing water and magma. Adding water can enhance the explosivity of an eruption, so more ash is produced.
Where Taal heads with this new activity will need to be closely watched. Hazard maps for Taal show the danger to those living near the volcano. The large population and potential for explosive eruption at this caldera mean that the ingredients are there for a disaster. Luckily, PHIVOLCS has been carefully monitoring the volcano, so hopefully people will listen when they say it could be time to leave.