Details on the Tongan Eruption

Now that people have been able to get a better look at the are about Hunga Tonga Hunga Ha'apai, we've been able to get a better idea of what sort of eruption occurred. The explosions and ash/tephra from the eruption have all but wiped out life on Hunga Ha'aapai, as the island contains one of the vents, while the other is only 100 meter off shore of the island - although the tephra erupted so far have joined the new vent and the island. You can clearly see ash mixing with the water around the island and the island itself has been blackened by the coating of ash. This is a classic volcanic atoll island-building event and the question will be how long will the enlarged Hunga Ha'apai last and how last will the eruption continue.

Of course, with any large eruption, there are a lot of, well, questionable things that go along with it, such as:

  • From the AFP report linked above: A local airline was reportedly planning to fly sightseers near the eruption site Friday. Probably not the best idea when other airlines are rerouting away from the volcano. As long as you stay below the ash, a plane should be OK (be it jet, turboprop or helicopter), but still, it doesn't seem like a good idea, unless you're into dodging flying boulders
  • The BBC is touting the idea that the earthquakes in the Tongan arc are directly connected to the volcano. This is absolutely terrible "science" journalism, only referring to "officials" who, on the basis of, well, nothing that I can tell, connected the earthquakes before the eruption with the volcano and adding a silly note of dread claiming the M7.7 earthquake hundreds of kilometers to the south could cause the eruption to intensity. Until someone can directly show me the volcanic tremors that followed the tectonic earthquakes, this is all conjecture.

Hopefully the media won't lose interest in this island-creating event if the eruption goes on for days as it is a wonderful opportunity to see the birth of a South Pacific island (or at least the growth of one) in action.

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"...long will the enlarged Hunga Ha'apai last..."

Not long, if the nearby Fonuafo'ou (a.k.a Falcon Island) predicts anything. It has been above the waves five times since 1885. Currently it is below, even tough at one time it was more than 100 metres high and several kilometres long. Metis Island/Shoal further north along the Arc is trying to do the same.

By Lassi Hippeläinen (not verified) on 20 Mar 2009 #permalink

It's reasonable to say that the earthquake might have altered the course of the eruption. Earthquakes have been suggestively correlated to changes in eruption activity before, at e.g. Merapi and Semeru, and this earthquake was well within the distance at which those observations were made. We also know that eruptions are a very wee slight bit more likely to begin immediately after large nearby earthquakes.

It's still stupidly irresponsible to write your headline as "quake may have caused eruption" - especially since the eruption was ongoing when the big quake occurred. But at least it's physically plausible conjecture this time, as opposed to the idea that the volcano caused the earthquake.

Also, have the BBC edited their report since you posted this? I can't find where they're citing "officials", and the only earthquake/volcano connection they mentioned in the video is pretty generic Ring of Fire stuff.

Maria - That is the key difference: whether earthquakes triggered vs. altered the eruption. The implication was that the earthquakes lead directly to the volcano. I haven't checked the most recent BBC audio on the video clip, but they definitely were pushing the direct link between the eruption and earthquakes both before and after the eruption began. You can take a look at the post over on Green Gabbro to see why the M7.7 earthquake likely has nothing to do with the Honga Ha'apai eruption as well.

Keep up the good work critiquing news reports on volcanic events. The general public takes these reports as authoritative and this contibutes to confusion on scientific subjects. I think what happens is that a journalist takes speculation by scientists as a definitive conclusion and reports it as such. The thing all scientists should remember is to never speculate to the media.

Now after that praise, I hate to nitpick you, but I don't think the term "atoll building event" is what you were looking for.


Don't worry about the reef. It will appear automatically, if the islands remains at the surface long enough. This could be the very early stage of atoll formation :-)

BTW, the islands in the main chain of Tonga are not atolls. They don't even have volcanic cores. They are coral-covered crumbs off the edge of the continental plate, lifted to surface by the creator god Tangaloa (or the subducting Pacific plate; opinions differ). Tonga is culturally a Polynesian country, but geologically it is very different from the rest of Polynesia.

By Lassi Hippeläinen (not verified) on 20 Mar 2009 #permalink