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"