Image by IGNS Ltd.
As most of you know 2012 had up until a couple of days ago been rather free from significant eruptions, but that has now changed. As the ash and smoke starts to clear we now know that the explosions at both Whaakari and Tongariro was not the main events.
Tongariro
Image by Lurking showing ash column height and ash spread radius. This plot was also made at the same time as Lurking became the 1 millionth viewer. Quite fitting really.
The eruption that happened during last night was mainly driven by water pushed past the steam flash point. That in turn caused a large steam driven explosion that hurled incandescent stones out of no less than 3 new vents in the mountain close to the Te Mari craters. The steam also lofted ash and steam up to a height of 6 000 meters (20 000 feet, or FLA 200 as the VAAC terminology goes).
Photograph by Diana Booth. Rare image of an ash and steam cloud taken from below as it rises into the heavens after an explosive phase ends.
The steam explosion was caused by rising magma hitting the permanent water table, also, the magma from Tongariro contains a lot of water, and that most likely decompressed into a steam explosion.
The event was rather short in duration. According to the seismograph plots the actual explosion was about 1 minute long, and the main eruptive phase was about 20 minutes long. After that there was mainly steam being ejected. The steam phase lasted for about 20 hours when a second smaller steam driven ash explosion occurred.
Image by Geonet.
Risks at Tongariro
This is most likely not the main event, this is just a pre-cursor activity as magma rises. It is quite normal for andesitic subduction volcanoes to have an initial phase of steam driven ash explosions like this. This phase can last for a day or two up to a few weeks before the real eruption starts.
Quite often the size of the steam explosions are indicative of what will come during the main event, and a steam driven ash explosion that lofts up material to 6000 meters height is telling us that there can be something rather large in the making. My best guess is that this will be around a VEI-3 eruption.
Earlier today I read an interview with a local woman living close to the volcano. I was taken rather aback when I read that she felt safe where she was living. She was telling about seeing ash and steam rolling down the side of the volcano into the valley she lived in. Apparently she and other locals think this is as bad as it gets. This is rather ignorant since the main dangers are lahars and the even worse pyroclastic flows running down the mountain into the valleys.
I hope that the valleys will be evacuated in time. One should though not forget that the eruption can change pace rapidly, and that it is better to be safe than sorry. Dead is a rather permanent position in life.
http://www.stuff.co.nz/national/7426862/First-Tongariro-eruption-in-over-100-years
Whaakari (White Island)
Image by Geonet. Moonlighting volcano at its best! Beginning of the nightly steam explosion at Whaakari (White Island) back lighted by the wonderful moonligh.
Whaakari is also a member of the TVZ (Taupo Volcanic Zone). It is a very large volcano built up by no less than 78 cubic kilometers of material. It is a complex volcano containing multiple vents and craters. A few days ago the Crater Lake went from being a small mud pool into being a sizeable lake as the water level rose 6 meters over night due to increase in hydrothermal pressure. A day later (also at night) a steam driven explosion hurled up ash and mud covering the new crater, the same area that killed eleven sulphur miners during the end of the mining epoch at Whaakari.
Image by Geonet. The man activity was on the fourth of August, but the level of tremor is still above normal, a probable sign of rising magma in the system causing steam explosions during its progress.
White Island is well known for its high rate of eruptions. It normally erupt very complex lavas pointing to either a mixed heritage of basaltic and andesitic feeder sources, or a complex magmatic system with high fractioning of the magmas. This produces the famous “clean” and “dirty” andesites. The volcano is at best highly unpredictable and can erupt without giving any untoward signs beyond the normal high background level of activity. To go there during an eruptive phase is to be considered very dangerous.
Image by Global Volcanism Program taken by Richard Waitt, 1986 (U.S. Geological Survey). The current active area, photograph is from 1986.
The same goes for Whaakari as for Tongariro; this is most likely only a pre-cursor phase before the real activity starts. Historically Whaakari has slightly stronger eruptions than Tongariro with the norm being VEI-2 eruptions, but with an upwards trend in strength of the eruptions during the last 170 years with the norm now being medium sized VEI-3s. The last eruption was in 2001 and rated as a VEI-2. But the year before there was a short and brutal VEI-3. And it is fairly indicative of the volcano that it has an upwards trend as the volcanic system evolves. What makes this volcano more prone for larger eruptions than Tongariro is the large (almost limitless) access to water to drive the hydro magmatic processes going on down in the volcano. The currently active crater floor is only 13 meters above sea level.
1 million viewers!
Image by Spica.
It is rather insane that it took us this short time to have 1 million viewers. From the beginning this has been a rather nutty experience. As I was convinced by a few others to create this place I expected a couple of hundred views per day, and a few comments. I never expected to start with 5000 viewers on the first day… And it just continued like that. As I have said many times, this is a group efforts and during the last half a year (slightly more) had a tremendous amount of posts published by many of our members. Keep those lovely posts coming and we will soon pass 2 million!
Little known fact, this is also Swedens largest blog… How about that?
CARL
