New Zealand Eruption Update for August 9, 2012: White Island and Tongariro

Steam seen on August 8, 2012 from one of the sources of the August 6 eruption of Tongariro in New Zealand. Image from OneNews.

The hits just keep on coming this week in New Zealand. We’re seen eruptions from both Tongariro and White Island this week – and White Island seems to be picking up the pace. Last night, reports of volcanic lightning from White Island abounded along the Bay of Plenty and a 300 meter eruptive plume was confirmed for the volcano, meaning. Ash fall was also reported at Papamoa, on the coast near Tauranga, the first ash produced from White Island since 2001. To my knowledge, tours of White Island have not been officially banned yet – even the wording of the GNS Science report suggests that tours are still going on: “GNS advises visitors to take a high level of caution.” This is fascinating because as Eruptions reader Claude G. pointed out, the New Zealand government quickly closed access to the Tongariro area after its eruption on Monday, but the same ban has not been produced for the more-vigourously active White Island. My post from Monday that was lost in tall the eruptive excitement gets into some of the issues of these tours to active volcanoes like White Island. The volcano is still at alert level 2 and aviation alert orange according to the latest GNS Science update.

Meanwhile, more of the results (video) of the Tongariro eruption have become apparent. At least three blast craters were formed along with a fissure on the volcano during the eruption and the volcanic tephra produced a small debris flow that travelled a few kilometers from the crater (like caused by a breached lake at the Te Mari crater and/or mixing with snow on the volcano). The GNS Science overflight also captured some cool images of impact craters from the bombs thrown from the vent area. Things have settled down at Tongariro, with only low levels of seismicity under the volcano, but new video footage of the Te Mari crater area shows the vigorous steaming (see above) around the area of the eruption. Be sure to check out the great gallery of images from Tongariro on the GNS Science Flickr stream. Some early analyses of the Tongariro ash show that is was somewhat fluorine rich – an issue especially important for agricultural interests near the volcano. However, this eruption didn’t produce sufficient volume of ash for the fluorine to be problematic, but a larger, sustained eruption might change that. I did find it frustrating how some media made it seem like fluorine in the ash was both surprising and dangerous. This isn’t really the case as almost all volcanic ash as some fluorine. More interestingly, these early ash analyses suggest that little to no juvenile (new magma) material present. Speaking of the ash plume, the NASA Earth Observatory posted a great night image of the plume from the eruption showing it stretching eastward across the North Island. GNS Science has left Tongariro at alert level 2/aviation alert yellow.

Now, one question that I’ve seen asked in a number of places is “are these eruptions related?”. The answer is yes and no. Yes, White Island and Tongariro are both part of the same volcanic arc, where the Pacific Plate is being subducted under the Australian Plate. This means that the processes that generate the primary magmas that feed the volcanoes are the same – as they are for all the volcanoes of New Zealand. However, White Island and Tongariro are geographically separated by over 220 km, so, no, their respective eruption did not cause/prompt the other. Instead, we’re just seeing another example of the random distribution of volcanic activity that produced a beguiling but ultimately false correlation. Now, if Tongariro erupted in quick succession with Ruapehu, only ~17 km away, then there could be more argument for a shared cause (think something like the Katmai eruption in Alaska in 1912). However, White Island and Tongariro are just too far apart to be directly connected in their magmatic systems.

from:    http://www.wired.com/wiredscience/2012/08/new-zealand-eruption-update-for-august-9-2012-white-island-and-tongariro/