The plume from the November 20, 2012 eruption of Tongariro in New Zealand, as seen from Emerald Lakes. Image: Brad Scott, courtesy of GeoNet NZ. Sure, enough, I go away for the week with only my iPhone and something interesting happens. I had mentioned on Monday before I left that volcanologists in New Zealand were concerned about signs of an eruption from Ruapehu but then Tuesday (November 20), almost out of the blue, Tongariro had its second significant explosive eruption of the year. This eruption was from the same Te Maari craters that was the source of the August activity, but this eruption occurred during daylight hours, so the ~3-4 km / 9,800-13,200 foot plume was clearly seen -- especially by hikers caught unawares along the Tongariro Crossings trail (see above). You can see the whole eruption develop on this time lapse of images taken from GNS Science's webcam pointed at the Te Maari crater. However impressive the explosion seems, reports and images of overflights of the craters say very little changed at the active area of Tongariro. Now, much of the information released by GNS Science about the singular, 5-minute-long explosion on 11/20 suggests that like the August activity, this eruption had little-to-no juvenile magma in the ash (but further analyses of the ash will hopefully confirm this). This means that much of the explosivity was driven by steam pressure buildup at the crater, either by flash-heating of circulating groundwater or possibly gases being released by the magma. However, there was little in the way of precursory signs that an explosion could occur (Something GNS Science has been saying about Tongariro since the August activity - an explosion could occur without warning). After the Tuesday explosion, which briefly shifted the volcano to "Red" on the warning system, there hasn't been much in activity at the Te Maari craters and by Friday, the volcano was merely emitting volcano gases with no ash. This settling has prompted GNS Science to lower the alert to Yellow. One has to be a little concerned about complacency about the activity at Tongariro after this mostly harmless eruption - political figures in New Zealand are already calling the reactions by the government (raised alert status, flight cancellations, exclusion zones, etc.) "overreaction", which doesn't bode well for future eruptions that may be more significant. It is very easy to say after the fact that you think that the precautions were too, well, cautious, but at the time the eruption occurred, it can be very unclear where the activity might lead. With that in mind, it is always better to overreact than under. Tongariro is an active volcano that is capable of producing these types of eruptions with little notice, so the question of how much danger (which is relatively low) this represents will likely be hotly debated as tourists flock to New Zealand to catch the action. A final note: I have heard some suggestion about a connection between the rumblings reported over the weekend at Ruapehu and this explosion at Tongariro. In all likelihood, these events were merely a coincident -- that is, there is no evidence that Tongariro and Ruapehu are directly connected at shallow levels under the volcanoes. However, it will definitely be an interesting field of study to examine this potential contemporaneous activity at the volcanoes.