[kneexyFreedly]

Bizarre rock 'ice shelf' found in Pacific
August 10, 2012




A huge cluster of floating volcanic rocks covering almost 26,000 square kilometres (10,000 square miles) has been found drifting in the Pacific, the New Zealand navy said Friday.



The strange phenomenon, which witnesses said resembled a polar ice shelf, was made up of lightweight pumice expelled from an underwater volcano, the navy said.

An air force plane spotted the rocks on Thursday about 1,000 kilometres (600 miles) offshore from New Zealand and warned a navy warship that it was heading towards them.


Lieutenant Tim Oscar said that while he knew his ship the HMNZS Canterbury was in no danger from the pumice, which is solidified lava filled with air bubbles, it was still "the weirdest thing I've seen in 18 years at sea".


"As far ahead as I could observe was a raft of pumice moving up and down with the swell," he said.




"The rock looked to be sitting two foot (half a metre) above the surface of the waves and lit up a brilliant while colour in the spotlight. It looked exactly like the edge of an ice shelf."

Scientists aboard the ship said the pumice probably came from an underwater volcano called Monowai, which has been active recently.

They said the phenomenon was unrelated to increased volcanic activity in New Zealand this week, including an eruption at Mount Tongariro that sent an ash cloud 20,000 feet into the atmosphere.





http://phys.org/news/2012-08-bizarre...f-pacific.html

[FUNALA]

Don't know that it is "bizarre". It's not as if it hasn't happened and been observed many times before. I can remember, as a young'un, seeing pumice drifting on the sea at Magnetic Island; not in large amounts like this, but not just isolated pieces, either.

[nickayary]

Some interesting images if you google for pumice raft.

[Zptmsemk]

Was it in one of the sailing blogs that you introduced this stuff to us, geoff d.

someone sailing a rather beautiful yacht?

What an experience though; I saw yesterday that one of NZ's Orions had spotted it while returning from patrol / exercises.

[Patgaepx]

Some of the beaches on Cape York are metres deep in pumice blown across the Pacific, and thongs, I reckon there must be an underwater volcano spewing thongs.

http://www.cairns.com.au/article/201...ocal-news.html

FOR a coastal strip seldom trampled by human feet, Chili Beach has somehow racked up an incredible number of thongs.

Environmental volunteers collected more than 4500 pieces of the footwear during a five-day clean-up blitz at the remote beach, north of Lockhart River.

[Vikonbarius]

> an underwater volcano called Monowai



A sufficiently powerful landslide there would give a tidal wave from Sydney to Brisbane.

[BriKevin]

I did a little hunting for Monowai to see if it was shallow, guessing it should be if the gas bubbles were to become actual gas such that the rock would be capable of floating. It turns out it's only a little over 100m deep.

http://www.volcano.si.edu/world/volc...?vnum=0402-05-

Probably not a good idea to sail over the top of it either:-

http://www.bbc.co.uk/news/science-environment-18040658

I imagine it's probably safe to sail over the top of deep active volcanoes though as the pressure will be so great that no gas will get out in the form of gas - it'll just stay liquid. Even a major erruption might show no signs at all at the surface, although it could cause tsunamis which would show up at a distance where the sea becomes shallow.

[BriKevin]

The finger's now being pointed at a different volcano - Havre Seamount:-

http://www.dailymail.co.uk/sciencete...f-Pacific.html

Interestingly, the summit depth for that volcano is over 1km below the surface of the sea:-

http://volcanolive.com/havre.html

This makes me wonder how deep a volcano has to be before the "gas" can't turn into a gas and remains liquid.

[Patgaepx]

The gas would most likely be steam so it shouldn't be too hard to figure. At the depth they are quoting for that new volcano though it must be hellish hot to do it.

[BriKevin]

Having had more time to think about it, it must be possible for a jet of hot water (hundred's of degrees) to punch straight up to the surface, carrying liquid or semi-liquid rock with it. The water would only turn to gas near the surface and create the bubbles in the rock needed to make it float.

[xquFzpNw]

Having had more time to think about it, it must be possible for a jet of hot water (hundred's of degrees) to punch straight up to the surface, carrying liquid or semi-liquid rock with it. The water would only turn to gas near the surface and create the bubbles in the rock needed to make it float.

I don't think so. a) the rock would quickly cool and solidify, and b) unless it's constrained, the rock will separate from the plume of water.

[Patgaepx]

What if you had a massive explosive eruption at that depth, could the explosion counter the pressure of the sea and allow the pumice to expand before cooling.
The more I think about that the less likely it seems but I will throw it in anyway.

[FUNALA]

Seems to me that there is a deep lack of understanding of the mechanisms involved in explosive eruptions. Unfortunately, I am not well enough informed to give any definitive answers. Need a vulcanologist on the forum 'team'.

[FUNALA]

What if you had a massive explosive eruption at that depth, could the explosion counter the pressure of the sea and allow the pumice to expand before cooling.
The more I think about that the less likely it seems but I will throw it in anyway.

You are on the right track, Wataday.

[Patgaepx]

Seems to me that there is a deep lack of understanding of the mechanisms involved in explosive eruptions. Unfortunately, I am not well enough informed to give any definitive answers. Need a vulcanologist on the forum 'team'.

I think you are right geoff, I am not even sure that explosive eruptions can occur at a Km depth, I was just off googling around a bit but haven't found anything yet.

[FUNALA]

If you take Tambora (on Sumbawa) as an example, albeit terrestrial, of a massive explosive eruption, the column of hot gas rising from that was of such a magnitude that it punched right through the atmosphere into the stratosphere without significant cooling, carrying fine dust with it. A big eruption like this creates conditions similar to a nuclear explosion (but many orders of magnitude larger) including a 'mushroom cloud'. The energy involved is enormous.

[FUNALA]

http://news.cnet.com/2300-11386_3-10002050.html

Images of an explosive undersea eruption, 1km deep.

[xquFzpNw]

http://news.cnet.com/2300-11386_3-10002050.html

Images of an explosive undersea eruption, 1km deep.

It does look like the energy gets dissipated pretty quickly.

[FUNALA]

But that's only a little one, a vent. Still, enough to produce pumice if the magma is of the right type (which it is).

[Thomas12400]

http://news.cnet.com/2300-11386_3-10002050.html

Images of an explosive undersea eruption, 1km deep.

Thanks for that, Mr D.