Newsflash: Mt Tongariro erupts

There are 9 comments on the Hawkes Bay Today story from Nov 20, 2012, titled Newsflash: Mt Tongariro erupts. In it, Hawkes Bay Today reports that:

GNS Science says there has been an eruption at Mt Tongariro in the central North Island with an ash cloud blowing about 2km above the mountain.

Join the discussion below, or Read more at Hawkes Bay Today.

“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#1 Nov 21, 2012
This one was fun.

Looks like the short magma filled fracture squeezing into Tongariro from the SW. emerges at te Mari. In the future as the small magma filled fracture squeezes in, the result may be emission of a small amount of juvenile andesite ash once the groundwater has been baked out of the system.

For the record the long fracture from the NE. emerged at Ngaruhoe. That one appears thus far to have been squeezed flat but others are possible in this direction.

The fractures formed during the Rebound/long duration, mercalli X (r/lx) event "Hao Whenua" in 1460ADproducing an earthquake & bloody great big tsunami while relaxing the crust of the north island via the megathrust.

Ruapehu has a short (SW) fracture set so far. The volcano also has a high level magma chamber with base squeezed by tectonics resulting in the "zit" effect and constant heating @ the crater.

Will keep watching that space.

have a nice day: Ag

“Educating Utus”

Since: Aug 10

Wanganui, New Zealand

#2 Nov 21, 2012
Do you think this could be the Maori Gods protesting that they want more handouts?

Since: Nov 08

Auckland

#3 Nov 21, 2012
Torqueing Heads wrote:
Do you think this could be the Maori Gods protesting that they want more handouts?
Possibly, but I reckon any bills that might be incurred for ash clean up should be handed in for the local iwi to pay.

“Educating Utus”

Since: Aug 10

Wanganui, New Zealand

#4 Nov 21, 2012
Gutsfull wrote:
<quoted text>
Possibly, but I reckon any bills that might be incurred for ash clean up should be handed in for the local iwi to pay.
Yes and if they want ownership of the air and water it should be fair to expect them to pay for the damage incurred when too much of both occurs.
Tweeter

Auckland, New Zealand

#5 Nov 21, 2012
Adrian Godsafe MSc wrote:
This one was fun.
Looks like the short magma filled fracture squeezing into Tongariro from the SW. emerges at te Mari. In the future as the small magma filled fracture squeezes in, the result may be emission of a small amount of juvenile andesite ash once the groundwater has been baked out of the system.
For the record the long fracture from the NE. emerged at Ngaruhoe. That one appears thus far to have been squeezed flat but others are possible in this direction.
The fractures formed during the Rebound/long duration, mercalli X (r/lx) event "Hao Whenua" in 1460ADproducing an earthquake & bloody great big tsunami while relaxing the crust of the north island via the megathrust.
Ruapehu has a short (SW) fracture set so far. The volcano also has a high level magma chamber with base squeezed by tectonics resulting in the "zit" effect and constant heating @ the crater.
Will keep watching that space.
have a nice day: Ag
Tsunami caused by inland volcanic activity ? Sorry, not going to happen .

“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#6 Nov 26, 2012
Tweeter wrote:
<quoted text>
Tsunami caused by inland volcanic activity ? Sorry, not going to happen .
Other way round.

The bloody great big tsunami comes 1stand relaxes the crust.The crustal relaxation caused by r/lx results in fractures through the solid crust which in the arc & backarc imports magma from the magma discs ponded @ the base of the crust which are fed by magma extracted from the dewatering descending plate.

Following r/lx the continued descent of the descending plate versus the now locked and welded megathrust results in a horizontal compression regime,which then squeezes the overlying crust together. The magma imported into the fractures in the lower crust (30-120Km down,so includes solid upper mantle),the nrespondsto horizontal stress by floowing the fracture path sideways at depth into the least compressed bit.
As the convergence rate for NZ and the Rumbles arc is fastest in the N. the arc & backarc magma fractures transfer preferentially from NNE to SSW. Long fractures such as the one that built Ngaruhoe cross several segments and will squeeze in for a long time. Short fractures are produced between the volcano and the arc front (hence they are short), the reason they erupt @the volcano rather thanthe arc graben is because the S. boundary of the fracture is a tectonic segment boundary,and this squeezes together faster @the edge than in the centre.

Volcanism eventually occurs when the magma from the fracture set is transferred in lower crustal depths via fractures and hits an area more compressed then the sector it is in. At that point the only way to go is up (volcano then goes "pop").

Short fractures tend to be shortlived, but fractues held @ depth in the lower crust foralong time will crystallise & exsolve gas. The Ruapehu short fracture set definitely "popped" rather well despite not being very productive. The same situation is currently hitting Tongariro. This is occasional @ Tongariro and it appears here that the short fracture set appears @ Te Mari. The amount of magma appearing from the fracture is rather small but it definitely seems to be good at exsolving & erupting gas.

Long magma filled fractures from the NNE @ NZ will squeezein for along time when they finally transfer to the surface. If nothing gets in the way, they will eventually produce a substantial stratovolcano. The tendency of fractures to remain hot & weak means that fractures can be re used during successive r/lx; Ngaruhoe has been built over 2 r/lx cycles and is now the highest part of the tongariro massif.
If a high level magma chamber gets in the way of a long magma filled fracture,the result is a particularly large volcanic eruption. In large part the result is an ash marker bed and a large blast crater formed by a plinian eruption.
The difference here is that VERY long fractures full of magma stored for a long interval of time can come down from the backarc basin from both the Rumbles backarc rift & also the Backfault region of the kermadec & Tonga backarc basin,jogging from one sector to another via r/lx which is fastest in the N. due to its faster convergence rate modified by the greater size of the backarc basin and longer runout (greater relaxation & more fractures). The result in these cases is that a giant eruption can occur instantly once such a fracture strikes the arc graben. A recent one (basalt) hit Tarawera. Ancient ones have struck high level magma chambers mixing in the gas with the rhyolite and producing large lava domes, large calderas & ignimbrite sheets.

NZ is still relatively decompressed following the ~4250AD Hao Whenua r/lx, which resulted in the backarcmagma missing Okataina. Later magma filled fractures encountering a more compressed arc will emerge through the high level rhyolite magma chambers sitting atmid to high levels in the crust of the arc.

Have a nice day: Ag

“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#7 Nov 26, 2012
Rebound/long duration, mercalli X (r/lx) as desribed in the last treatise & its bloody great big tsunami,is the start of a volcanism cycle.

Recent r/lx listed below.

The 2004 r/lx was a classical backarc basin r/lx runout ~35m vector SSW. The resulting tsunami killed a lot of people.

The 2010 r/lx of the central chile arc was a classical arc with runout ~12m and vector varying from WNW.to W.depending on where the GPS measurements were taken due to jogs around the tectonic segment boundaries affected by the r./lx.

The 2011 Tohoku r/lx was a zygomorph. There is a megathrust on both sides of northern Honshu,with the W.megathrust far stronger then the E. The e>Megathrust broke resulting in the R/lx with runout variable from ~35m @ Iwate in the N. through to ~12m in the southernmost segment. The result was a spectacular local tsunami, but fortunately as the arc was relatively short,the pan oceanic tsunami was relatively low and few deaths outside of the local zone occurred.

In all 3 cases magma has now been imported from the discsof magma @ the base of the crust & incorporated into the lower crust. In all cases the megathrust is now locked,weldedand the r/lx sector is recompressing @the start of the recompression cycle.
In all 3 cases tha magma has not yet reached the volcanoes & all volcanoes in the sector are dormant (with the possible exception of Villarrica, chile).

One exception was Barren island which sunk during the r/lx of 2004 and has re adjusted its stress field by squirting out magma from its high level magma chamber through its summit vent following the 2004 r/lx.

Those spaces will be interesting to watch in the near future. The most interesting bit will be the N.part of the Tohoku arc near Iwate & Towada.

Have a nice day: Ag

“Educating Utus”

Since: Aug 10

Wanganui, New Zealand

#8 Nov 26, 2012
Adrian Godsafe MSc wrote:
<quoted text>
Other way round.
The bloody great big tsunami comes 1stand relaxes the crust.The crustal relaxation caused by r/lx results in fractures through the solid crust which in the arc & backarc imports magma from the magma discs ponded @ the base of the crust which are fed by magma extracted from the dewatering descending plate.
Following r/lx the continued descent of the descending plate versus the now locked and welded megathrust results in a horizontal compression regime,which then squeezes the overlying crust together. The magma imported into the fractures in the lower crust (30-120Km down,so includes solid upper mantle),the nrespondsto horizontal stress by floowing the fracture path sideways at depth into the least compressed bit.
As the convergence rate for NZ and the Rumbles arc is fastest in the N. the arc & backarc magma fractures transfer preferentially from NNE to SSW. Long fractures such as the one that built Ngaruhoe cross several segments and will squeeze in for a long time. Short fractures are produced between the volcano and the arc front (hence they are short), the reason they erupt @the volcano rather thanthe arc graben is because the S. boundary of the fracture is a tectonic segment boundary,and this squeezes together faster @the edge than in the centre.
Volcanism eventually occurs when the magma from the fracture set is transferred in lower crustal depths via fractures and hits an area more compressed then the sector it is in. At that point the only way to go is up (volcano then goes "pop").
Short fractures tend to be shortlived, but fractues held @ depth in the lower crust foralong time will crystallise & exsolve gas. The Ruapehu short fracture set definitely "popped" rather well despite not being very productive. The same situation is currently hitting Tongariro. This is occasional @ Tongariro and it appears here that the short fracture set appears @ Te Mari. The amount of magma appearing from the fracture is rather small but it definitely seems to be good at exsolving & erupting gas.
Long magma filled fractures from the NNE @ NZ will squeezein for along time when they finally transfer to the surface. If nothing gets in the way, they will eventually produce a substantial stratovolcano. The tendency of fractures to remain hot & weak means that fractures can be re used during successive r/lx; Ngaruhoe has been built over 2 r/lx cycles and is now the highest part of the tongariro massif.
If a high level magma chamber gets in the way of a long magma filled fracture,the result is a particularly large volcanic eruption. In large part the result is an ash marker bed and a large blast crater formed by a plinian eruption.
The difference here is that VERY long fractures full of magma stored for a long interval of time can come down from the backarc basin from both the Rumbles backarc rift & also the Backfault region of the kermadec & Tonga backarc basin,jogging from one sector to another via r/lx which is fastest in the N. due to its faster convergence rate modified by the greater size of the backarc basin and longer runout (greater relaxation & more fractures). The result in these cases is that a giant eruption can occur instantly once such a fracture strikes the arc graben. A recent one (basalt) hit Tarawera. Ancient ones have struck high level magma chambers mixing in the gas with the rhyolite and producing large lava domes, large calderas & ignimbrite sheets.
NZ is still relatively decompressed following the ~4250AD Hao Whenua r/lx, which resulted in the backarcmagma missing Okataina. Later magma filled fractures encountering a more compressed arc will emerge through the high level rhyolite magma chambers sitting atmid to high levels in the crust of the arc.
Have a nice day: Ag
Yep got that. But will the Maoris need compensating for damage to their mountain?

“Geologist [I'm Climate Change]”

Since: Mar 07

formerly Nuneaton

#9 Nov 28, 2012
Torqueing Heads wrote:
<quoted text>Yep got that. But will the Maoris need compensating for damage to their mountain?
Probably not.

This is one of the acts of one of their gods. Most likely the one responsible for the Hao Whenua earthquake & bloody great big tsunami of ~1460AD. This one as an apocryphal (so far) tale appeared to have been a response to the major tribal wars that occurred in the century before the event. In most areas of island arcs & ranges, the locals appear to go gaga with major internecine gods & monsters wars before the r/lx (ie. Aceh prior to 2004, Burma/Bangladesh area prior to the r/lx of ~460BC (thugs being country wallahs were the only survivors), and Kashmir Pakistan/india border (ongoing; *NOTE* That will be a range r/lx affecting the Himalayan frontal thrust & will be a biggie).

The same case could also be argued for the sinter terraces at Tarawera which were destroyed by the basaltic fissure eruption last century; (Apparently the same god required the montain to be a different shape). Bit of a shame in the case of Tarawera as the sinter terraces looked rather pretty, & drew quite a few tourists.

Have a nice day: Ag

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