plaster, Not-Pumice pic 1 - Christchurch ~May 2011

Plaster, not-pumice pic 1 - Christchurch ~May 2011

This autumn/winter in Christchurch there is chatter about the appearance of the above strange substance on Christchurch beaches. Since there have been recent earthquakes below the extinct volcanic crater of Lyttelton Harbour, and new warm spring flows and sulphur smells in the vicinity, people have become concerned that the ancient volcano could be soon to erupt again. With the appearance of large pumice-like chunks of light and porous ‘rock’ on south Pegasus Bay beaches, some are seeing it as more evidence. And so I present today’s documentary case – to the contrary – that Lyttelton ex-volcano is well and truly safe.

Note for a start the moulding line prominent in the piece at left. Other collectors have reported finding samples with this lining effect too – some with a red, plastic-like residue still attached within it. Source: Woodend Beach.

Plaster, not-pumice pic 2 - Christchurch ~May 2011

Plaster, not-pumice pic 2 - Christchurch ~May 2011


The second view shows what looks like residual concrete attached. I expect this is demolished building material that has escaped from the recent earthquake rubble-dump, the poorly-contained infill of Port Lyttelton, and that has been quickly rounded smooth in the surf. These samples are 10 to 15 centimetres in length.

Plaster, not-pumice pic 3 - Christchurch ~May 2011

Plaster, not-pumice pic 3 - Christchurch ~May 2011


The bubble holes in this material appear unnaturally large – indicating it to be manufactured, I would say.

For comparison, here we have a picture of some real pumice found on Spencer Beach, south Pegasus Bay:

Pumice - Christchurch 2009

Pumice - Christchurch 2009

This pumice came from a wind-separated drift accumulation between eroding sand-dunes. I was soon able to ask a fellow ECan councillor at the time, Geography Emeritus Professor Bob Kirk, what this material was. Bob had seen it and been asked the question many times before, because this pumice was spread along our beaches from a volcanic eruption on the other side of the Southern Hemisphere decades ago – probably 1962 – at the South Sandwich Islands.[1] The floated debris keeps turning up, dropped by the moving sands that caught it at the time. These fragments are just a few millimetres long; I don’t know if there are larger pieces about.

So I maintain the case, that we do not have any new deposits of pumice, for any reason. Confirmation by scientific testing of the new material awaits, however. New hotspring flows and sulphur smells are what we would expect from the steady shattering of Banks Peninsula, as this process provides new routes to surface for normal undercone heat and long-trapped chemical deposits.

You may quote me this way: “Geo-historically, you can have the Southern Alps as a long transform fault, or you can have an active volcano nearby – you cannot have both. The tectonic plate collision very long ago that built up the Alps extinguished Banks Peninsula early in the process.” Ref. Pushing New Zealand’s Boundaries GNS.

We may quote GNS Science this way: “about 1,800 years ago.. The Taupo eruption was the most violent eruption in the world in the last 5,000 years; it was a complex series of events. The first phases of the eruption produced a series of five pumice and ash fall deposits over a wide area of the central North Island, especially east of Taupo and beyond Napier into Hawke Bay. The eruption culminated with a large and very energetic pyroclastic flow that devastated an area of about 20,000 km2 and filled all the major river valleys of the central North Island with pumice and ash. These pumice deposits can still be seen today and many of the major rivers in the North Island carry large amounts of this pumice when in flood. Rounded pumice found on the beaches of the North Island have come from this eruption. The Taupo eruption took place from a line of vents near the eastern side of the modern lake.”

[1] Also see: South Sandwich Islands Wikipedia and January 1956 eruption ;
Lava and ice mingle in the South Sandwich Islands “the most horrible coast in the world.. doomed by nature never once to feel the warmth of the Sun’s rays” – Captain James Cook “..the South Sandwich chain features an active submarine vent, Protector Shoal. Just 30 yards below the surface, Protector Shoal erupted in 1962 and created a giant raft of floating pumice, which drifted several thousand miles and reached New Zealand” USGS October 2008 ; Volcanoes At Both Poles Erupting Now January 2006 etc.

Magnitude 6.5 – SOUTH SANDWICH ISLANDS REGION 2011 March 06 14:32:35 UTC USGS
etc …
Magnitude 5.2 – SOUTH GEORGIA ISLAND REGION 2011 June 24 19:28:56 UTC USGS
Magnitude 5.4 – SOUTHERN EAST PACIFIC RISE 2011 June 27 17:02:36 UTC USGS
Magnitude 5.5 – BALLENY ISLANDS REGION 2011 June 27 20:04:16 UTC USGS
Magnitude 5.2 – BALLENY ISLANDS REGION 2011 June 27 20:31:46 UTC USGS
Magnitude 4.9 – BALLENY ISLANDS REGION 2011 June 30 04:21:17 UTC USGS
[… to be continued in new blog post]

The Southern Ocean is teeming with tectonic life, of late. Connecting with greater energy from the north?
Magnitude 5.0 – KERMADEC ISLANDS REGION 2011 June 24 13:18:19 UTC USGS
Magnitude 5.2 – SOUTH OF THE KERMADEC ISLANDS 2011 June 27 13:39:10 UTC USGS
Magnitude 5.5 – OFFSHORE VALPARAISO, CHILE 2011 June 29 05:36:49 UTC

Alaska mag' 7.2 - USGS 250611

Alaska mag' 7.2 - USGS 250611


Kermadec Arc mag' 5.2 - USGS 280611

Kermadec Arc mag' 5.2 - USGS 280611


Balleny Islands mag' 5.4 - USGS 280611

Balleny Islands mag' 5.5 - USGS 280611


southern East Pacific Rise mag' 5.4 - GIM 290611

southern East Pacific Rise mag' 5.4 - GIM 290611


South Sandwich Islands mag' 5.2 - USGS 290611

South Sandwich Islands mag' 5.2 - USGS 290611


Chile mag' 5.5 - GIM 290611

Chile mag' 5.5 - GIM 290611

Volcanic ash and pumice do partly shape New Zealand’s past and future – Chile’s volcano has our airspace shut down yet again this week. …

~ Kia ora

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