The eruption of Hunga Tonga Hunga Ha'apai volcano in Tonga looks to be a big one. Keleti Mafi, head of the Tongan geological service, calls this "a very significant eruption, on quite a large scale", which is no surprise considering some of the spectacular picture we saw of the eruption yesterday. In fact, the eruption is big enough that it has disrupted air traffic over Tonga, as Air New Zealand has issued a warning about the ash column - an ash column that has reached over 15,000 meters/50,000 feet! Luckily for the residents of Tongatapu, a [strike]mere 10 kilometers[/strike] 50 km to the [strike]southwest[/strike] SSE from the volcano, so far the trade winds have pushed most of the ash and volcanic emissions away from the island.
For those of you unfamiliar with the hazards that ash poses to aircraft, I'll point you to an excellent USGS report on the subject. With large eruption like the one we're seeing in Tonga, accurate predictions of ash column height and dispersal are vital in order to keep air traffic safe.
From the Auckland Art Gallery Collection
As for the eruption itself, it appears that some precursor seismicity was felt on the islands around the volcano, before the first sighting of the plume was made. Mafi mentions that there might actually be two vents involved (although this is unconfirmed) and that this eruption looks to be bigger than the last large eruption in Tonga in 2002. Fiji should expect large amounts of pumice to wash up on its shores in the near future as well. Tongan officials will "visit the area" (not sure how close that means) and fisherman have been told to stay away from the erupting volcano.
These types of eruption, although impressive, are not unheard of in the area. Just wandering around the interweb last night I found this amazing painting (see above) of an eruption in Tonga in 1886. The painting looks very similar to the pictures we've seen so far of the 2009 eruption (top).