Tongariro eruption 2012 - updates & current activity

Scientists think Tongariro will stay calm is most likely scenario
Update Mon 13 Aug 11:58
In its latest report, GeoNet writes:
"Volcanic activity remains low. There has been no significant seismic activity at Tongariro for several days. Heavy rain on Sunday produced minor lahars which affected State Highway 46. No further reports have been received since Sunday. Of the three eruption scenarios deemed possible over the next seven days, the scenario considered most likely is that there will be no further eruptions, the next likely is that any eruptive activity will be of similar magnitude to that on August 6, and the least likely that larger eruptions will occur."
Update Sat 11 Aug 09:09
Overnight the activity from Tongariro Volcano remained weak and seismicity is low.
Tongariro calm for the moment, gas measurements suggest magma presence underneath
Update Fri 10 Aug 10:55
Overnight there was no further activity from Tongariro and seismicity has remained low.
A very minor amount of ash is reported from some of the new steam vents. GNS scientists measured around 2,100 tons per day of sulphur dioxide (SO2) and elevated quantities of carbon dioxide (CO2) and hydrogen sulphide (H2S), which confirms that magma is accumulating beneath the volcano.
It is possible, that the Aug 6 eruption was only a precursor to a pending magmatic eruption, which could even be large, if the size of initial phreatic activity is in proportion to the proper magmatic eruption.
Update Thu 09 Aug 07:39
Seismic activity has been calm during the past 24 hours (GeoNet)
Seismic activity has been calm during the past 24 hours (GeoNet)
Tongariro has stayed calm.
In the meanwhile, first analysis of the ash from the erution were published: they showed it contains moderate levels of fluorine and that there was little or no new magma erupted on Monday night, confirming the initial hypothesis that the eruption was phreatic in nature.
Update Wed 08 Aug 07:09
Eruption source area looking up hill. Main steaming area is a new vent west of Upper Te Maari Crater. Steam in the lower left is part of Lower Te Maari Crater, and appears unchanged by the eruption. (GeoNet)
Eruption source area looking up hill. Main steaming area is a new vent west of Upper Te Maari Crater. Steam in the lower left is part of Lower Te Maari Crater, and appears unchanged by the eruption. (GeoNet)
Current seismic signal at Tongariro (GeoNet)
Current seismic signal at Tongariro (GeoNet)
This morning, NZ scientists could use a brief window of clear weather to make an overflight of the eruption area which was found to be just below the Upper Te Mari crater, where new steam vents were observed. No fresh lava bombs appear to have been observed, but numerous ballistic impacts of (older) blocks in up to 2 km distance around the vent. In addition, a debris flow deposit was observed. The lack of obvious fresh lava bombs supports the idea that the violent eruption was probably phreatic, i.e. caused by overheated ground water, and no fresh magma (so far) has reached the surface.
At the moment, Tongariro is calm, but eruptions could resume any time.

This is from the latest report from GeoNet:

"Current activity is weak with some steaming vents visible below the cloud level. Explosions at a new vent area below the Upper Te Māri crater have thrown blocks out more than 1.5 km. Current eruptive activity is low level but could re-commence at any time."

"No vents have opened in or around the Lower Te Māri crater, or at lower elevations on the mountain. There are no new vents or craters at the Ketetahi thermal area. Previously steaming ground at Ketetahi and Lower Te Māri crater appears more vigorous, but there were no obvious major changes there.

Blocks of old lava and hydrothermally altered lava up to approximately 1 metre size have been ejected by the eruption. There are extensive areas to the east and west of the new vents where falling blocks have formed impact craters in the ground. No burnt vegetation was seen. No steaming hot blocks were visible and all appeared to be angular shapes more typical of existing old rock, rather than fresh lava or scoria. Most blocks were covered by grey ash but many on the western slopes were not, which suggests that they were ejected after the main ash-producing phase of the eruption had finished. Blocks had reached 1.5 km to 2 km from the Te Māri craters area.

A flow of rock and soil debris generated by the eruption partly fills a stream valley draining north-west from Upper Te Māri crater area. The deposit has blocked some stream tributaries but most water appears to be diverted around the edges. Ash has slumped from the banks into this stream valley and in other stream valleys ash has been re-mobilised in slurry flows. No lahars were generated by the eruption.

New rock falls were visible around the walls of the new vent area and Lower Te Māri craters and in some stream valley walls near the craters. This is a sign that significant ground shaking took place during Monday night's eruption."
Facts about the eruption summarized by GNS Science
Update Tue 07 Aug 13:02
GNS Science gave a highly informative and easy to understand press conference. The facts of the eruption so far summarized:

- The eruption started at 11:52 PM (NZ time) and lasted about 30 minutes
- There was no significant precursory activity (such as sudden tremor) indicating an immediate eruption (although seismic activity had been increased since a few weaks ago).
- The eruption WAS followed by 15-20 minutes of strong seismic activity instead.
- The eruption was explosive and produced a 7 km tall ash plume and threw ballistic blocks of up to 1 m diameter to 1.5-2 km distance.
- Ash drifted about 200 km towards Napir and caused some domestic flight cancellations.
- The vent was at an area below the Upper Te Mari crater.

At the moment, the nature of the eruption (whether phreatic or phreatomagmatic) is not clear. Ash samples have been collected and their analysis will probably solve this question soon. GNS Science has said they think the eruption was a hydrothermal (phreatic) explosion, which makes sense with the idea that the eruption was very short and discrete, Eric Klemetti writes on his excellent update.
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