Mount Pagan in the Mariana Islands erupting on April 15, 2009. Image courtesy of the NASA Earth Observatory.
Up until fairly recently, a lot of volcanoes got away with erupting without anyone knowing the better. However, with all the "eyes in the sky" we have these days, even remote oceanic volcanoes get caught in the act of erupting. Case in point is this image (above) of Mt. Pagan in the Mariana Islands erupting. It was captured by the MODIS satellite yesterday and it shows a health ash plume emanating from the volcano. Pagan is an oceanic stratovolcano on the sparsely populated island of the same name and it really two volcanoes (overflight video on this link) bridged by land. The last known eruption was in 2006, but most of the historic eruptions are small (VEI <2) consisting of small explosions and ash plumes, some lahar generation. However, in 1981, the volcano experienced a VEI 4 eruption that prompted evacuations due to pyroclastic flows, lava flows and fissure vent eruptions. This eruption also produced an 18-20 km / ~60,000 foot ash column, so it was definitely significant. It is good to know that even in places where some minor events might go unnoticed, there are resources that help us keep track of many of the potential volcanic threats on the planet.