Submarine volcanic vents and pumice rafts....

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Discussion Overview

The discussion centers around the conditions under which submarine volcanic vents can generate significant pumice rafts. Participants explore the depth of such vents, the mechanisms of pumice formation, and the relationship between eruptions and surface visibility. The conversation includes references to specific eruptions and geological studies, as well as the implications of these phenomena in various contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that deep submarine vents may produce pumice, but it typically does not reach the surface and remains on the vent's flanks.
  • Others argue that significant pumice rafting requires an eruption that breaches the ocean surface, as evidenced by historical eruptions like those in the Tongan Islands and the Havre Seamount.
  • A participant mentions that the eruption dynamics, such as magmatic explosivity and cooling processes, are crucial for pumice to float and form rafts.
  • There is a suggestion that the absence of an atmosphere may prevent pumice formation below sea level, with a call for further investigation into this claim.
  • Links to various articles and studies are shared, although some participants note that many are paywalled and not easily accessible.
  • One participant reflects on the implications of deep-sea eruptions and compares them to other geological events, such as the Gulf Oil Spill, highlighting the complexities of pressure changes in these contexts.

Areas of Agreement / Disagreement

Participants express differing views on whether pumice can be produced by deep-sea eruptions without breaching the surface. While some agree that surface visibility is necessary for significant pumice rafting, others suggest that deeper eruptions may still contribute to pumice formation under certain conditions. The discussion remains unresolved regarding the exact mechanisms and conditions required for pumice generation.

Contextual Notes

Limitations include the reliance on specific geological studies that are paywalled, which may restrict access to detailed evidence. Additionally, assumptions about the relationship between eruption depth and pumice formation are not universally accepted among participants.

Who May Find This Useful

This discussion may be of interest to geologists, volcanologists, and researchers studying submarine volcanism, as well as those curious about the dynamics of volcanic eruptions and their environmental impacts.

Nik_2213
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How deep can a submarine volcanic vent be and still generate a significant pumice raft ?

Sadly, Wiki is a stub, and most of the relevant literature is pay-walled.

As I understand it, deep vents may generate a lot of pumice, but it never reaches the surface, just stays on the vent's flanks. The famous mega-rafting in 'South Pacific' came from a transient volcanic island, clearly visible on the bemused yachties' photos. Unlike Surtsey, it didn't endure...

Would a kilometre-submerged rifting event, eg in Canary chain, produce significant, persistent rafting ??
 
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jedishrfu said:
Here's a Wired article on them but I don't think it answers your question:
...

The paper that the Wired article references does:

Rapid, Long-Distance Dispersal by Pumice Rafting
Scott E. Bryan , Alex G. Cook, Jason P. Evans, Kerry Hebden, Lucy Hurrey, Peter Colls, John S. Jell, Dion Weatherley, Jennifer Firn
Published: July 18, 2012

The main eruption appears to have been driven principally by magmatic explosivity, with hot pumice and ash largely excluded from the shallow water column by the erupting jet. Airborne cooling of the pumice in the eruption column was therefore important to cool pumice to form the floating pumice raft as experimental studies have shown hot pumice rapidly ingests water, becomes negatively buoyant and sinks. ​

I've never heard of "pumice" being associated with deep sea vents.
But I'm not a geologist, so that doesn't mean much.

@davenn and @billiards , have you ever heard of such a thing?
 
OmCheeto said:
I've never heard of "pumice" being associated with deep sea vents.

no, nor have I. From all I have so far read, the pumice isn't formed unless the eruption breaches the ocean surface

...
The paper that the Wired article references does:

Rapid, Long-Distance Dispersal by Pumice Rafting
Scott E. Bryan , Alex G. Cook, Jason P. Evans, Kerry Hebden, Lucy Hurrey, Peter Colls, John S. Jell, Dion Weatherley, Jennifer Firn
Published: July 18, 2012

The main eruption appears to have been driven principally by magmatic explosivity, with hot pumice and ash largely excluded from the shallow water column by the erupting jet. Airborne cooling of the pumice in the eruption column was therefore important to cool pumice to form the floating pumice raft as experimental studies have shown hot pumice rapidly ingests water, becomes negatively buoyant and sinks.

The publication date of that article made me do a double take and reread of the contents ... the research in that article was referring to eruptions in ~ 2006 in the Tongan Isl. region.
That publication date happens to correspond to a more massive eruption 1000km or so further south in the southern Kermadec Isl. region that was very much deeper undersea and produced large pumice rafts. The approximate depth to the top of the Havre Seamount is around 1100m. The eruption was not initially reported and it was only the pumice rafts, observed by several aircraft crossing the area on the 20th July, 2012, that has scientists going back over prior days satellite images to find the eruption imagery. They also found corresponding seismograms of some 157 events that were centred around the Havre Seamount.

From everything I have so far been able to find, this is the deepest undersea eruption that has produced pumice. BUT the main point being that the eruption was large enough to breach the ocean surface and produce pumice.

I haven't found any publication, so far, that suggests that pumice can be produced below sea level in the absence of an atmosphere.
I would be interesting to see if anything can be found to confirm or deny that :smile:Dave
 
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davenn said:
... The approximate depth to the top of the Havre Seamount is around 1100m.
...
Wow! I didn't see that number in my research. This kind of reminds me of the numbers from the "Gulf Spill" back in 2010.

This means that the gas is 400 times the volume of oil being collected.
[ref: PF, younger Om]

Things sure get weird when you move things from a high pressure area to a lower one.

The eruption was not initially reported and it was only the pumice rafts, observed by several aircraft crossing the area on the 20th July, 2012, that has scientists going back over prior days satellite images to find the eruption imagery. They also found corresponding seismograms of some 157 events that were centred around the Havre Seamount.

From everything I have so far been able to find, this is the deepest undersea eruption that has produced pumice. BUT the main point being that the eruption was large enough to breach the ocean surface and produce pumice.

I haven't found any publication, so far, that suggests that pumice can be produced below sea level in the absence of an atmosphere.
I would be interesting to see if anything can be found to confirm or deny that :smile:

Dave

Fun topic.

I just found this article:
Havre Seamount
October 2012 cruise confirms Havre as pumice source. On 26 October 2012 the New Zealand National Institute of Water and Atmospheric Research’s (NIWA) Research Vessel Tangaroa mapped Havre submarine volcano. NIWA ocean geology scientist Joshu Mountjoy announced finding a new volcanic cone which has formed on the edge of the volcano, towering 240 m above the crater rim that was first mapped in 2002 (Wright and others, 2006). The 2012 Havre eruption was strong enough to breach the ocean surface from a depth of more than 700 m by producing an ash plume, thermal alert, and a pumice raft that covered an area of 22,000 km2, all visible by satellite.​

Sounds like a homework problem from hell.
 
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Here's the abstract that piqued my curiosity...
http://geology.gsapubs.org/content/38/5/391.abstract
Paywalled, of course

My understanding of the erudite comments and linked articles in this thread suggest that, for significant pumice rafting, you'd need either a volcanic island, however transitory, or a submerged eruption that sent something resembling a pyroclastic flow all the way to the surface. The former is photogenic provided you can keep engine intakes clear. The latter is surely a 'Be Not There' event...

Fortunately, this is not a homework question. I began wondering about the first indications if the hypothesised embryonic subduction zone off Gibraltar 'went live'...
http://geology.gsapubs.org/content/early/2013/06/05/G34100.1.full.pdf+html
Paywalled, of course, of course...