North Manchester FM
During the initial media excitement about the Eyjafjallajokull eruption I gave a number of radio and newspaper interviews about the state of the volcano and subglacial eruptions. Of the lot, my favourite was easily the one that I did for the Science and Technology Show on North Manchester FM. It lasted nearly 20 minutes and covered not just the Eyjafjallajokull eruption, but a discussion of volcanology in general.
They were kind enough to send me an mp3 of the interview, which you can download and listen to by clicking on THIS LINK (Best to right-click, then press 'Save link as' or whatever option your browser gives). There were plenty mmms and errrs, and I was trying to remember a lot of figures off the top of my head, so don't quote any of them without checking them first, but the general idea is there.
The Science and Technology Show is hosted by Paul Lynock and is on Wednesday from 12:00-14:00hrs. You can listen on 106.6 FM in the Manchester area, or at http://www.northmanchesterfm.org.
Eruption update
The latest updates from the Nordic Volcanological Centre show that the eruption is continuing at a low level. The volcano has built a cone about 150 m tall within the hole that it melted through the glacier. It continues to produce lava, which flows northwards, and small amounts of ash, which rises to heights of about 4 km (as opposed to 10 km during the explosive phase), and which have caused closures of Keflavik (international) and Reykjavik (domestic) airports. The tremor is still going steadily, so the eruption doesn't look like stopping soon. Katla remains quiet.
This post is a follow-up to: http://johnalexanderstevenson.blogspot.com/2010/04/eyjafjallajokull-update-more-on.html
Tuesday, 27 April 2010
Tuesday, 20 April 2010
Eyjafjallajokull Update - More on subglacial intermediate volcanism
What is happening now?
Over the past three days less ash has been produced, and the ash plume has got smaller. This is mainly because there is less ice above the vent, as described on Monday. Analysis of ash composition shows that a reduction in silica content also had an effect.
When the eruption was at its most violent on Thursday, it was erupting 'trachyandesite' magma. Monday's post also explained that trachyandesite is an 'intermediate' composition, and that this means that it is stickier (more viscous) and can erupt explosively and produce fine ash, irrespective of the presence of a glacier/meltwater. Since Sunday, the magmas have a less-sticky basaltic composition, and consequently the eruption is less explosive.
Meanwhile, seismometers around the volcano continue to register significant vibrations (tremor), caused by the movement of magma beneath the volcano, and this suggests that the eruption is likely to continue for some days at least.
What do the deposits of these eruptions look like?
During my PhD, I studied deposits from an intermediate-composition subglacial eruption of at Kerlingarfjoll volcano, Iceland. This eruption was also explosive, with explosions driven by steam formation as the hot magma encountered meltwater. The deposits consist thick piles of a rock called 'hyaloclastite', formed by the quenching and fragmentation of magma by meltwater. If we could somehow see under the ice at Eyjafjallajokull, we would probably find something like this.
Hyaloclastite looks like shiny black gravel. When magma is rapidly quenched, and solidifies too quickly to form crystals, it produces a type of glass. Obsidian is the best known example of this. The hyaloclastite contains fragments of this glass ranging in size from about 2 cm down through sand to fine ash. This is the same type of material that was ejected by Eyjafjallajokull, and much of the fine ash was carried away by the wind.
The deposits at Kerlingarfjoll also show that magma that didn't meet ice or meltwater didn't explode. Instead, it managed to push its way into the pile of glassy gravel and formed intrusive lava lobes with irregular and grotesque forms. At Eyjafjallajokull, it is probable that magmas being erupted in the absence of ice/water will come out on top of the hyaloclastite and produce lava flows.
Where would any lava go?
Below is a radar image collected by the Icelandic Coast Guard, and released by the Nordic Volcanological Centre that reveals how the 200 m thick glacier has melted during the eruption (Click image to enlarge). It shows 3 main holes in the ice above three vents. It also shows a series of smaller holes forming skylights to a subglacial channel, formed where the meltwater drained towards the north.
Lava is not very good at melting ice, as once the outside forms a chilled skin, the interior is fairly well insulated. Witnesses to the flank eruption last month said that where the snow was covered with a thin layer of ash, the lava was able to flow right across it, despite probably having an internal temperature of over 800 degrees C!
This means that if this eruption goes on to produce lava, it will follow the channels created by the meltwater. The resulting deposits will be long and thin, and consist of glacial sediments, overlain by ash deposited by the flowing water and finally lava. This pattern can be seen elsewhere on Eyjafjallajokull and was described by Dr Sue Loughlin in her PhD thesis. The rocks record how large parts of the volcano were built of the products of ancient subglacial eruptions.
What about air travel?
It is hard to say how long the eruption will continue. The amount of ash being produced, and the height of the plume are lower now. These conditions may remain until the end of the eruption.
However, more explosive eruptions could resume at short notice if
- a) meltwater regains access to the vent, or a new vent opens under the ice,
- b) another source of more-evolved (trachyandesite) magma is tapped, or
- c) there is a significant increase in eruption rate.
Fortunately, low pressure moving in from the Atlantic at the end of the week will begin to push ash to the north, thus limiting the effect on the UK of any increase in activity. (Not so fortunate for Scandinavia, however...)
This post is a follow up to: http://johnalexanderstevenson.blogspot.com/2010/04/eyjafjallajokull-update-more-musings.html
Over the past three days less ash has been produced, and the ash plume has got smaller. This is mainly because there is less ice above the vent, as described on Monday. Analysis of ash composition shows that a reduction in silica content also had an effect.
When the eruption was at its most violent on Thursday, it was erupting 'trachyandesite' magma. Monday's post also explained that trachyandesite is an 'intermediate' composition, and that this means that it is stickier (more viscous) and can erupt explosively and produce fine ash, irrespective of the presence of a glacier/meltwater. Since Sunday, the magmas have a less-sticky basaltic composition, and consequently the eruption is less explosive.
Meanwhile, seismometers around the volcano continue to register significant vibrations (tremor), caused by the movement of magma beneath the volcano, and this suggests that the eruption is likely to continue for some days at least.
What do the deposits of these eruptions look like?
During my PhD, I studied deposits from an intermediate-composition subglacial eruption of at Kerlingarfjoll volcano, Iceland. This eruption was also explosive, with explosions driven by steam formation as the hot magma encountered meltwater. The deposits consist thick piles of a rock called 'hyaloclastite', formed by the quenching and fragmentation of magma by meltwater. If we could somehow see under the ice at Eyjafjallajokull, we would probably find something like this.
Hyaloclastite looks like shiny black gravel. When magma is rapidly quenched, and solidifies too quickly to form crystals, it produces a type of glass. Obsidian is the best known example of this. The hyaloclastite contains fragments of this glass ranging in size from about 2 cm down through sand to fine ash. This is the same type of material that was ejected by Eyjafjallajokull, and much of the fine ash was carried away by the wind.
The deposits at Kerlingarfjoll also show that magma that didn't meet ice or meltwater didn't explode. Instead, it managed to push its way into the pile of glassy gravel and formed intrusive lava lobes with irregular and grotesque forms. At Eyjafjallajokull, it is probable that magmas being erupted in the absence of ice/water will come out on top of the hyaloclastite and produce lava flows.
Where would any lava go?
Below is a radar image collected by the Icelandic Coast Guard, and released by the Nordic Volcanological Centre that reveals how the 200 m thick glacier has melted during the eruption (Click image to enlarge). It shows 3 main holes in the ice above three vents. It also shows a series of smaller holes forming skylights to a subglacial channel, formed where the meltwater drained towards the north.
Lava is not very good at melting ice, as once the outside forms a chilled skin, the interior is fairly well insulated. Witnesses to the flank eruption last month said that where the snow was covered with a thin layer of ash, the lava was able to flow right across it, despite probably having an internal temperature of over 800 degrees C!This means that if this eruption goes on to produce lava, it will follow the channels created by the meltwater. The resulting deposits will be long and thin, and consist of glacial sediments, overlain by ash deposited by the flowing water and finally lava. This pattern can be seen elsewhere on Eyjafjallajokull and was described by Dr Sue Loughlin in her PhD thesis. The rocks record how large parts of the volcano were built of the products of ancient subglacial eruptions.
What about air travel?
It is hard to say how long the eruption will continue. The amount of ash being produced, and the height of the plume are lower now. These conditions may remain until the end of the eruption.
However, more explosive eruptions could resume at short notice if
- a) meltwater regains access to the vent, or a new vent opens under the ice,
- b) another source of more-evolved (trachyandesite) magma is tapped, or
- c) there is a significant increase in eruption rate.
Fortunately, low pressure moving in from the Atlantic at the end of the week will begin to push ash to the north, thus limiting the effect on the UK of any increase in activity. (Not so fortunate for Scandinavia, however...)
This post is a follow up to: http://johnalexanderstevenson.blogspot.com/2010/04/eyjafjallajokull-update-more-musings.html
Monday, 19 April 2010
Eyjafjallajokull update - more musings
Is the eruption coming to an end?
The Icelandic Met Office reported yesterday that the plume was no longer detectable by their radar, and other reports say that it is much lower than it was previously (3000 m versus 10000 m). Less ash is being produced and put into the atmosphere. However, geophysical data suggests that seismicity from the eruption is still going strong. Tremor is a continuous, low-frequency, seismic signal caused by the movement of magma beneath the volcano, and the data show that this has increased since yesterday. This would suggest that the eruption is not ending, and may not be likely to end soon.
So why is there less ash now?
The declining explosivity is probably caused by decreasing interaction with ice and meltwater. The eruption became explosive when a vent opened beneath the glacier in the central crater and steam explosions fragmented the magma into fine ash. Now it seems likely that all the ice near the vent has melted, or a cone of tephra has built up around the vent, which is limiting contact between the magma and the meltwater. The glacier was initially only ~200 m thick, which is relatively thin; there are a number of ancient subglacial volcanoes in Iceland that erupted through ice over 1000 m thick.
This hypothesis is corroborated by reports and photographs of incandescence at the vent last night and 'lumps' of lava ejected onto the crater rim. Rocks become red hot (incandescent) at temperatures of above 600 degrees C. If the magma was erupting through water, it would be chilled to beneath these temperatures very quickly. Overflights by Icelandic scientists will hopefully allow them to see the vent and confirm if this is the case. If the vent remains in the same position then the eruption may progress to photogenic red fire-fountains similar to those seen in the previous phase, but if it moves to another ice-covered location then the ash production will resume. This would result in more flight cancellations at short notice. Also, the possibility of an eruption of Katla in the near future remains.
What is trachyandesite?
The composition of recent ash is trachyandesite. This is a chemical definition used to describe the proportions of various oxides within the magma (e.g. SiO2, Al2O3, CaO, NaO, K2O etc). There are a plethora of different names and subdivisions, but the general evolution in terms of increasing silica (SiO2) content is basalt, andesite, dacite, rhyolite. The recent magma contains 60% SiO2. Silicic magmas are more viscous and associated with more explosive eruptions. This is a problem because their eruptions can produce large plumes with lots of fine ash irrespective of the presence of a glacier or meltwater.
The initial magma for volcanic eruptions is generated in the Earth's mantle. En route to the surface it may pass through a series of magma chambers in the crust, where the composition is changed as it partially crystallises or incorporates material from the walls. As a rule of thumb, the more time that magmas spend in the crust on their way to the surface, the more evolved they become. Both Eyjajfallajokull and Katla are long-lived volcanoes with magma chambers where silicic magmas are produced. The current production of trachyandesite magma suggests that material from one of these chambers is being tapped.
Horses' mouths
Most of the information here has been obtained from other sources on the internet. The most useful sites include:
University of Iceland Earth Sciences
- Latest scientific results
http://www.earthice.hi.is/page/ies_Eyjafjallajokull_eruption
Icelandic Met Office
- Local earthquakes
http://www.vedur.is/skjalftar-og-eldgos/jardskjalftar/myrdalsjokull
- Geophysical monitoring data
http://hraun.vedur.is/ja/Katla2009
- News on the plume near the source
http://en.vedur.is/about-imo/news/2010
UK Met Office
- Computer predictions of plume behaviour
http://www.metoffice.gov.uk/aviation/vaac/vaacuk_vag.html
- Surface pressure chart
http://www.metoffice.gov.uk/weather/uk/surface_pressure.html
(The wind blows along the isobars, clockwise round Highs and anticlockwise round Lows)
Iceland Civil Protection Department
- Updates on activity and risks within Iceland
http://www.almannavarnir.is/displayer.asp?cat_id=413
Iceland Review
- The local perspective
http://icelandreview.com
This post is a follow-up to http://johnalexanderstevenson.blogspot.com/2010/04/fire-and-ice-again-baby.html
The Icelandic Met Office reported yesterday that the plume was no longer detectable by their radar, and other reports say that it is much lower than it was previously (3000 m versus 10000 m). Less ash is being produced and put into the atmosphere. However, geophysical data suggests that seismicity from the eruption is still going strong. Tremor is a continuous, low-frequency, seismic signal caused by the movement of magma beneath the volcano, and the data show that this has increased since yesterday. This would suggest that the eruption is not ending, and may not be likely to end soon.
So why is there less ash now?
The declining explosivity is probably caused by decreasing interaction with ice and meltwater. The eruption became explosive when a vent opened beneath the glacier in the central crater and steam explosions fragmented the magma into fine ash. Now it seems likely that all the ice near the vent has melted, or a cone of tephra has built up around the vent, which is limiting contact between the magma and the meltwater. The glacier was initially only ~200 m thick, which is relatively thin; there are a number of ancient subglacial volcanoes in Iceland that erupted through ice over 1000 m thick.
This hypothesis is corroborated by reports and photographs of incandescence at the vent last night and 'lumps' of lava ejected onto the crater rim. Rocks become red hot (incandescent) at temperatures of above 600 degrees C. If the magma was erupting through water, it would be chilled to beneath these temperatures very quickly. Overflights by Icelandic scientists will hopefully allow them to see the vent and confirm if this is the case. If the vent remains in the same position then the eruption may progress to photogenic red fire-fountains similar to those seen in the previous phase, but if it moves to another ice-covered location then the ash production will resume. This would result in more flight cancellations at short notice. Also, the possibility of an eruption of Katla in the near future remains.
What is trachyandesite?
The composition of recent ash is trachyandesite. This is a chemical definition used to describe the proportions of various oxides within the magma (e.g. SiO2, Al2O3, CaO, NaO, K2O etc). There are a plethora of different names and subdivisions, but the general evolution in terms of increasing silica (SiO2) content is basalt, andesite, dacite, rhyolite. The recent magma contains 60% SiO2. Silicic magmas are more viscous and associated with more explosive eruptions. This is a problem because their eruptions can produce large plumes with lots of fine ash irrespective of the presence of a glacier or meltwater.
The initial magma for volcanic eruptions is generated in the Earth's mantle. En route to the surface it may pass through a series of magma chambers in the crust, where the composition is changed as it partially crystallises or incorporates material from the walls. As a rule of thumb, the more time that magmas spend in the crust on their way to the surface, the more evolved they become. Both Eyjajfallajokull and Katla are long-lived volcanoes with magma chambers where silicic magmas are produced. The current production of trachyandesite magma suggests that material from one of these chambers is being tapped.
Horses' mouths
Most of the information here has been obtained from other sources on the internet. The most useful sites include:
University of Iceland Earth Sciences
- Latest scientific results
http://www.earthice.hi.is/page/ies_Eyjafjallajokull_eruption
Icelandic Met Office
- Local earthquakes
http://www.vedur.is/skjalftar-og-eldgos/jardskjalftar/myrdalsjokull
- Geophysical monitoring data
http://hraun.vedur.is/ja/Katla2009
- News on the plume near the source
http://en.vedur.is/about-imo/news/2010
UK Met Office
- Computer predictions of plume behaviour
http://www.metoffice.gov.uk/aviation/vaac/vaacuk_vag.html
- Surface pressure chart
http://www.metoffice.gov.uk/weather/uk/surface_pressure.html
(The wind blows along the isobars, clockwise round Highs and anticlockwise round Lows)
Iceland Civil Protection Department
- Updates on activity and risks within Iceland
http://www.almannavarnir.is/displayer.asp?cat_id=413
Iceland Review
- The local perspective
http://icelandreview.com
This post is a follow-up to http://johnalexanderstevenson.blogspot.com/2010/04/fire-and-ice-again-baby.html
Thursday, 15 April 2010
Fire and Ice again, baby!
Here are some of my thoughts about the eruption.
Why is this eruption different to previous?
- Both eruptions from Eyjafjallajokull volcano
- Previous eruption finished now (March 20 to 7 April), erupted onto ice free region on flank of volcano
- Current eruption (began midnight Tuesday) is bigger and from ice-filled main crater. This means that:
Firstly -
> Eruption is melting ice. Meltwater is flash-heated by magma to generate steam explosions (jargon: phreatomagmatic explosions)
> Phreatomagmatic fragmentation means that finer ash is generated, which can be carried further from volcano
> Meltwater escapes from glacier causing floods and destroying farms and roads (hence evacuations and road closures)
Secondly -
> This eruption is larger and more powerful than previous eruption. (Erupting 2 km long fissure)
> This means that ash being produced more quickly. Height of plume depends on eruption rate - faster eruption gives higher plume.
- Therefore we have more magma, erupting faster, and being broken up in steam explosions from interaction with meltwater. These all lead to bigger plume.
Has this kind of thing happened before?
- Yes. Grimsvotn 2004 eruption caused redirection of North Atlantic flights and even come KLM flights cancelled.
- Eruptions from Iceland frequently send ash across the Atlantic. Ash from Askja 1875 formed visible layer in Scandinavia. Ash from Katla 1755 and Hekla 1845 was reported falling in Shetland.
- Bigger eruptions have produced at least 7 ash layers that can be identified in peat bogs in Scotland in the last ~6000 years.
What about the weather?
- Where the ash ends up depends on wind directions. Currently a high pressure over North Atlantic is directing it towards UK.
- It takes a couple of days to arrive (eruption began Tuesday night, main ash expected this afternoon).
- Met Office have computer models developed to predict movement of nuclear fallout that they can use to predict where it will go.
- If the wind changes direction then the ash will move away.
Why divert the planes?
- The ash gets into jet engines, melts, then resolidifies and clogs them up. This has stopped engines on a number of planes e.g. Mt Redoubt, Alaska in 1989.
- The amounts of ash required to present a danger are very small (less than 1 mg per cubic metre)
How can the Icelanders fly round and take film?
- They are using a propeller plane. The ash is most harmful to jet engines.
- They can see the plume and stay upwind of it.
How long will it last?
- Hard to say. Grimsvotn 2004 lasted 4 days, with most ash generated in first 36 hours.
- Many eruptions in Iceland last a couple of weeks, like the previous phase here or the Vatnajokull eruption in 1996.
- Last recorded eruption of Eyjafjallajokull lasted over a year (1821-1823) but can't say if all was this intense. Possible to have pulses with periods of lots of ash separated by gaps with little being produced.
- Effect on air traffic will depend strongly on weather patterns too. If the wind shifts north, then the ash will move north with it.
- Even if the eruption stops now, it will take some time (1-2 days?) for ash plume to clear.
Could things get worse?
- They could, but it is hard to say how likely that is. There will be much more ash generated if there is an eruption of magma of silicic or intermediate composition.
- Basaltic eruptions, like the eruption that just ended, produce fire fountains and lava flows, but not much fine ash (less than 4%). Silicic or intermediate magmas tend to produce explosive eruptions, like Pinatubo or Mount St Helens, which make pumice and lots of fine ash (30-50%).
- These larger eruptions, termed sub-plinian or plinian, disperse ash widely. There have been 200 of these in Iceland in the last 10.000 years.
- This fine ash is much more likely to spread across the Atlantic. Silicic ash is produced in only 15% of Icelandic eruptions, but makes up 90% of the tephra layers found in Europe.
- Eyjafjallajokull is a 'central volcano' which has a long-lived magma chamber from which it has produced silicic and intermediate eruptions in the past. There are at least two ash layers in Iceland from sub-plinian/plinian eruptions in Eyjafjallajokull in the last ~10,000 years.
- The danger remains that an eruption of the neighbouring volcano Katla could be triggered. This happened during each of the only 3 historic eruptions of Eyjafjallajokull. Katla has produced numerous plinian silicic eruptions with tephras identified over northern Europe.
About me:
- Postdoctoral researcher in Physical Volcanology at Manchester University
- Did PhD with Open University and Lancaster University on "Subglacial Rhyolite Eruptions in Iceland"
Why is this eruption different to previous?
- Both eruptions from Eyjafjallajokull volcano
- Previous eruption finished now (March 20 to 7 April), erupted onto ice free region on flank of volcano
- Current eruption (began midnight Tuesday) is bigger and from ice-filled main crater. This means that:
Firstly -
> Eruption is melting ice. Meltwater is flash-heated by magma to generate steam explosions (jargon: phreatomagmatic explosions)
> Phreatomagmatic fragmentation means that finer ash is generated, which can be carried further from volcano
> Meltwater escapes from glacier causing floods and destroying farms and roads (hence evacuations and road closures)
Secondly -
> This eruption is larger and more powerful than previous eruption. (Erupting 2 km long fissure)
> This means that ash being produced more quickly. Height of plume depends on eruption rate - faster eruption gives higher plume.
- Therefore we have more magma, erupting faster, and being broken up in steam explosions from interaction with meltwater. These all lead to bigger plume.
Has this kind of thing happened before?
- Yes. Grimsvotn 2004 eruption caused redirection of North Atlantic flights and even come KLM flights cancelled.
- Eruptions from Iceland frequently send ash across the Atlantic. Ash from Askja 1875 formed visible layer in Scandinavia. Ash from Katla 1755 and Hekla 1845 was reported falling in Shetland.
- Bigger eruptions have produced at least 7 ash layers that can be identified in peat bogs in Scotland in the last ~6000 years.
What about the weather?
- Where the ash ends up depends on wind directions. Currently a high pressure over North Atlantic is directing it towards UK.
- It takes a couple of days to arrive (eruption began Tuesday night, main ash expected this afternoon).
- Met Office have computer models developed to predict movement of nuclear fallout that they can use to predict where it will go.
- If the wind changes direction then the ash will move away.
Why divert the planes?
- The ash gets into jet engines, melts, then resolidifies and clogs them up. This has stopped engines on a number of planes e.g. Mt Redoubt, Alaska in 1989.
- The amounts of ash required to present a danger are very small (less than 1 mg per cubic metre)
How can the Icelanders fly round and take film?
- They are using a propeller plane. The ash is most harmful to jet engines.
- They can see the plume and stay upwind of it.
How long will it last?
- Hard to say. Grimsvotn 2004 lasted 4 days, with most ash generated in first 36 hours.
- Many eruptions in Iceland last a couple of weeks, like the previous phase here or the Vatnajokull eruption in 1996.
- Last recorded eruption of Eyjafjallajokull lasted over a year (1821-1823) but can't say if all was this intense. Possible to have pulses with periods of lots of ash separated by gaps with little being produced.
- Effect on air traffic will depend strongly on weather patterns too. If the wind shifts north, then the ash will move north with it.
- Even if the eruption stops now, it will take some time (1-2 days?) for ash plume to clear.
Could things get worse?
- They could, but it is hard to say how likely that is. There will be much more ash generated if there is an eruption of magma of silicic or intermediate composition.
- Basaltic eruptions, like the eruption that just ended, produce fire fountains and lava flows, but not much fine ash (less than 4%). Silicic or intermediate magmas tend to produce explosive eruptions, like Pinatubo or Mount St Helens, which make pumice and lots of fine ash (30-50%).
- These larger eruptions, termed sub-plinian or plinian, disperse ash widely. There have been 200 of these in Iceland in the last 10.000 years.
- This fine ash is much more likely to spread across the Atlantic. Silicic ash is produced in only 15% of Icelandic eruptions, but makes up 90% of the tephra layers found in Europe.
- Eyjafjallajokull is a 'central volcano' which has a long-lived magma chamber from which it has produced silicic and intermediate eruptions in the past. There are at least two ash layers in Iceland from sub-plinian/plinian eruptions in Eyjafjallajokull in the last ~10,000 years.
- The danger remains that an eruption of the neighbouring volcano Katla could be triggered. This happened during each of the only 3 historic eruptions of Eyjafjallajokull. Katla has produced numerous plinian silicic eruptions with tephras identified over northern Europe.
About me:
- Postdoctoral researcher in Physical Volcanology at Manchester University
- Did PhD with Open University and Lancaster University on "Subglacial Rhyolite Eruptions in Iceland"
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